4th Dutch Bio-Medical Engineering Conference 2013
24-25 January 2013, Egmond aan Zee, The Netherlands

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16:00   Poster session II
R.J. Doll, Jan Buitenweg, Hil Meijer, Peter Veltink
Abstract: Nociceptive thresholds show dynamic changes during noxious events such as disease, clinical intervention or experimental perturbations. Estimation of thresholds is relevant for early de-tection of nociceptive related diseases (e.g. hyperalgesia). However, these thresholds are mo-mentary recordings and therefore do not reveal dynamic behavior. In addition, different stimulus parameters result in different thresholds [1]. Simultaneous estimation of multiple psychophysical thresholds, each with different stimulus parameters, might provide more in-formation about the momentary state of the nociceptive system. Tracking of multiple thresh-olds before, during and after a noxious event can reveal dynamics in the nociceptive system. This information of nociceptive dynamics might be relevant for early detection of nociceptive diseases (e.g. post-operative chronic pain). In a previous study, we showed the feasibility of tracking a threshold over time [2]. However, no information is available on how many thresholds can be simultaneously tracked without losing significant information about the dynamics within the nociceptive system. This study aims to compare bias, precision and bandwidth of tracked thresholds. Monte Carlo simulations were performed to compare bias, precision and bandwidth of thresh-old estimates while varying the number of simultaneous tracked thresholds (1-7). An adaptive random staircase procedure was used as stimulus selection procedure while logistic regression was used to obtain threshold estimates. We found that the bias was similar in all simulations. Moreover, precision and bandwidth lowered with more simultaneous tracked thresholds. Three different numbers of simultaneous tracked thresholds were compared in a human sub-ject study. A cold pressor was applied as nociceptive conditioning stimulus. Electrocutaneous stimulation was used for nociceptive detection threshold tracking before, during and after the conditioning stimulus. With the obtained results, we are able to make a trade-off between es-timation precision and bandwidth and the number of simultaneous tracked thresholds. With the findings of this study, we are able to perform experiments where multiple thresholds can be tracked in healthy subjects leading to better characterization of the nociceptive system. Eventually, simultaneously tracking multiple nociceptive thresholds might be useful in clinical environments (e.g. pre-operative detection of post-operative chronic pain development). REFERENCES [1] E.M. van der Heide, J.R. Buitenweg, E. Marani, W.L.C. Rutten, “Single pulse and train modulation of cutaneous electrical stimulation: a comparison of methods,” J Clin Neuro-physiol, vol. 26, pp. 54-60, Feb 2009 [2] R.J. Doll, H.G.E. Meijer, J.R. Buitenweg, P.H. Veltink, “Tracking of nociceptive thresholds using adaptive psychophysical methods,” To be submitted
Stefan Sandker, Hendrik Buikema, Jan Grandjean
Abstract: Introduction Over the last two decades, the radial artery (RA) has become a routinely used graft for coronary artery bypass graft surgery (CABG). A potential disadvantage of the RA is its higher susceptibility to vasospasm compared to other arterial grafts [1]. This tendency to spasm, occurring in 5 to 10% of the patients, has been correlated to a significant proportion of early RA graft failures [1, 2]. It is generally accepted that the adventitia provides structural support to the vessel. Although, in the last decade, several studies have indicated that the adventitia also has an active role in vasomotor tone [3]. In this study we investigated the effects of adventitial dissection of the RA for reducing vasospasm. Methods Following harvesting, adventitial dissection was carried out as longitudinal dissection of total adventitia and all bundles of circumferential collagen fibers on the ventral side of the RA using coronary scissors. Surplus radial artery segments (n=35) with and without adventitial dissection and internal mammary artery segments (IMA; n=11) of patients undergoing CABG were collected and pairwise assessment of vasoreactivity to potassium chloride (KCl), U46619 and acetylcholine was performed in organ bath experiments. Results Full curve and maximal vasoconstriction to potassium chloride (p=0.015 and p=0.001) and U46619 (p=0.048 and p=0.001) was significantly reduced for adventitial dissected RA compared to non-adventitial dissected RA. Furthermore, vasoconstriction responses of the IMA were significantly less compared to (non) adventitial dissected RA (p<0.05). Endothelium-dependent relaxation to acetylcholine of adventitial dissected RA was significantly increased (p=0.006) compared to non-adventitial dissected RA. Maximal vasorelaxation to acetylcholine was 33.1±4.6% for adventitial dissected RA compared to 20.9±3.5% for non-adventitial dissected RA (p=0.018). Conclusion The adventitial dissected RA is less susceptible to vasoconstriction and more prone to vasorelaxation ex vivo. Therefore, we recommend to perform adventitial dissection of the RA graft to reduce vasospasm for arterial revascularization in CABG. Previously, our research group has demonstrated that the use of adventitial dissected RA as Y-graft is an effective treatment for patients undergoing off-pump CABG [4]. REFERENCES [1] Kobayashi J. Radial artery as a graft for coronary artery bypass grafting. Circ J 2009; 73: 1178-1183. [2] Attaran S, John L, El-Gamel A. Clinical and potential use of pharmacological agents to reduce radial artery spasm in coronary artery surgery. Ann Thorac Surg 2008; 85: 1483-1489. [3] Auger FA, D'Orleans-Juste P, Germain L. Adventitia contribution to vascular contraction: hints provided by tissue-engineered substitutes. Cardiovasc Res 2007; 75: 669-678. [4] Halbersma WB, Arrigoni SC, Mecozzi G, Grandjean JG et al. Four-year outcome of OPCAB no-touch with total arterial Y-graft: making the best treatment a daily practice. Ann Thorac Surg 2009; 88: 796-801.
Marinette van der Graaf, Geert Wanten
Abstract: INTRODUCTION: Patients with severe chronic intestinal failure depend on parenteral nutrition, often administered at home as home parenteral nutrition (HPN) [1]. These patients are at risk for developing steatosis, and their hepatic iron and manganese content may increase. The aim of this study was to non-invasively determine hepatic lipid content by MRS in patients receiving HPN, taking into account the possibility of altered relaxation behavior as result of increased hepatic manganese or iron content. SUBJECTS AND METHODS: 13 patients (5M/8F) with a mean age of 46 yrs (range 20-64 yrs), who have been on HPN for 8.2 yrs (range 2-36 yrs). MRS was performed on a clinical 3T MR system (Siemens Magnetom Tim Trio). Proton MR spectra were acquired from a volume of 30x30x30mm3 positioned in the center of a liver lobe avoiding large vessel structures using STEAM without water suppression (TR=3s). Six averages were obtained during 15-sec breath holding for different echo times (TE=20,30,40,50msec; each TE was measured twice). Post-processing consisted of time-domain fitting of the water signal at 4.7 ppm and the methylene lipid signal at 1.3 ppm using AMARES [2]. To correct for T2 relaxation the ratio (lipid intensity (L)/water intensity (W)) was plotted as function of echo time and an exponential function {L/W=(L/W)0•exp(TE*K) with K=(1/T2W-1/T2L)}was fitted to the data to obtain the value for TE=0 msec. From this ratio the hepatic lipid content was calculated by the formula (100x(L/W)0)/(1+(L/W)0). RESULTS: Five patients showed an increased hepatic lipid content (>5%) with an average value of 12.8±3.5% (mean±SD), while the other eight had normal liver fat concentration (1.1±0.6%). K-values were obtained in the range between 0.0148 and 0.0330 msec-1 (0.0216±0.0056 msec-1). The lowest value agrees very well with a reference K-value of 0.0147 msec-1 calculated from literature values for T2W and T2L of 34 and 68 msec, respectively [3]. The other patients showed higher K-values, caused by increased T2 relaxation behavior probably due to elevated hepatic iron or manganese content. CONCLUSION: Our results show that hepatic lipid content of HPN patients can be non-invasively determined by MRS. However, for these patients possible increased T2-relaxation behavior has to be taken into account to obtain reliable values. REFERENCES: [1] Wanten GJ and Calder PC, 2007, Am J Clin Nutr. 85:1171-1184; [2] http://sermn02.uab.es/mrui/; [3] de Bazelaire CM, et al., 2004, Radiology 230:652–659.
Stefan Been, Michelle Agenant, Wim Koomen, Herke Jan Noordmans
Abstract: During transurethral resection of bladder tumours (TURBT) a scope is placed through the urethra, inside the bladder to biopt or resect a lesion. During this procedure the sight of the bladder wall can be impeded by bleeding from that lesion, cloudy urine caused by an infection or blue light during photodynamic diagnosis (PDD). To overcome this problem we built a real-time bladder registration and navigation system, where virtual arrows placed over the endoscope imaging lead the clinician to the primarily marked points of interest. A special tracking device (floil) was developed to make sure that the endoscope could always be seen by the stereo tracking camera, despite interference of the head of the surgeon, legs of the patient and 180º rotation of the endoscope. To assess the accuracy in marking and retrieve previously marked lesions, lab experiments were performed on two developed phantoms: First a rigid box phantom to determine the technical accuracies of the system. It appeared that lesions could be marked with an accuracy of 2-4 mm and could be retrieved in 94% of the cases. Second, a flexible balloon phantom to get an idea about the inaccuracies encountered in a real bladder with its deformaties. The largest shifts occurred, as expected, when lesions were marked at one volume and retrieved at a much bigger or smaller volumes. However, thanks to the field of view of the endoscope, in 70% of the cases the lesions were on the endoscopic video screen after navigation. The next step is the clinical evaluation of this newly developed system, of which inclusion of patients has been started. We hope that this concept of bladder navigation will lead to better reproducibility of cystoscopy. Therefore, lesion should better be recognized resulting in less recurrence and less residual tumours after TURBT. This improves the quality of life and increases the cost effectiveness of the procedure.
Chunman Fan, Filip Jelinek, Dimitra Dodou, Paul Breedveld
Abstract: In the last decade, with a minimal access approach, experimental surgical procedures are carried out through natural openings in the human body by following 3D anatomical pathways (such as NOTES: Natural Orifice Transluminal Endoscopic Surgery). In this type of surgery, the instrument manipulation is limited because the incision point reduces the instrument’s Degrees of Freedom (DOFs) and the anatomical pathway restricts the instrument’s motion. The ideal surgical instruments for pathway surgery should thus have full manoeuvrability to approach a target which locates either along the pathway or at the end of the pathway. Surgical instruments with a manoeuvrable tip, in which the tip may be consist of single or multiple steering segments, are under development. However, few knowledge is known about manual control skills for steerable surgical instruments, and it is unclear which control method is more intuitive for a dexterous performance. We developed a simulator device, called the Endo-PathController, to investigate manual control skills for steerable MIS instruments. The Endo-PathController consists of a mechanism that mimics the shaft and handle of a steerable surgical instrument with standard dimensions, and is electronically connected to a laptop computer by a USB data acquisition unit LabJack-U3 (LabJack Corporation, U.S.). Endo-PathController measures manual control motions in 5DOFs: 2DOFs rotation at the instrument incision point (left/right ±90°; up/down 0-60°), 2DOFs rotation at the instrument steering unit (up/down and left/right, ±40°) and 1DOF shaft translation along its axis (0-100mm). Endo-PathController has the standard surgical instrument dimension, and can accommodate various control methods (such as, thumb control or wrist control). A custom designed software was employed for simulating the tip steering and evaluating the control skills. A pilot-test of Endo-PathController in order to investigate two control methods (thumb control and wrist control) for tip orientation in a computer animated tasks will be carried out. The participants will be asked to guide the Endo-PathController towards a target locating at the end of an animated curved tunnel without any collision. The participants are divided into two groups with opposite control-method usage sequence. The assessment of performance will be evaluated by means of the recorded task execution time, motion trajectories and mental load test results (TLX: the NASA Task Load Index) .
Marjolein van der Krogt, Bart Koopman, Vivian Weerdesteyn, Roel Wirix-Speetjens, Søren Tørholm, Robert Sitnik, Thomas Feilkas, Nico Verdonschot
Abstract: The burden of musculoskeletal diseases and prosthetic revision operations is huge and increasing rapidly with the aging population. For patients that require a major surgical intervention, procedures are unsafe, uncertain in outcome and have a high complication rate. The goal of the European project TLEMsafe is to create a software-based pre-operative surgical navigation system that helps the surgeon to predict the functional outcome of his/her patient after severe musculoskeletal surgery. TLEMsafe is dedicated to generating semi-automated 3-D image-analyzing tools to simulate the musculoskeletal system. The patient-specific parameters are fed into models with which the patient-specific functional outcome can be predicted. The surgeon can identify within the model what the changes will be (e.g. due to the removal of a muscle in a tumor patient) and the functional effect of this intervention can be calculated. Once the surgeon is satisfied with the operative plan, it is fed into a computer navigation system. During the first 24 months of the project, functional measurements were performed and MRI scans were made of ten healthy subjects and of two pilot patients. These scans are currently analyzed and software is developed to extract personalized parameters from the images. Cadaver experiments were performed in which muscle attachment points and muscle volumes were measured to enable validation of MRI-based personification of musculoskeletal models. Currently, we are measuring tumor and hip revision patients in order to create their personalized models and to predict functional outcome. By measuring their actual functional outcome we will be able to validate our predictions. Furthermore, a virtual pre-planning toolbox is generated, which allows the surgeon to operate on the virtual patient; the output is coupled to the Brainlab computer navigation system. Finally, special output software is developed to quantify functional outcome in a way that is surgically and clinically relevant. In conclusion, we have made considerable progress in patient-specific modeling; we have generated a surgeon friendly virtual pre-planner; and a way to quantify the outcome of the calculations in a clinically relevant manner. Next steps are to focus on the validity of personalized musculoskeletal models and to assess the pre- and post-operative functionality of patients and their adaptive capacity during the recovery period after severe musculoskeletal surgery. Acknowledgement: The TLEMsafe Project (http://www.tlemsafe.eu/) is financially supported under the Seventh Framework Programme (FP7) of the European Commission.
Joris Jaspers, Matthijs Wassink, Stefan Been
Abstract: Surgery is a labour intensive, physically intensive and mostly non-ergonomic process. For an average (MIS) procedure at least five staff members (e.g Surgeon, assistant, scrub-nurse, circulation nurse, anaesthetist (assistant)) are present in the OR, often even more, increasing the OR-costs. Most of the medical technological innovations for the Operating Theatre/Room (OR) are investigator or surgeon driven. Hardly any of the innovations are initiated by other members of the OR-staff. Therefore we did an inventory, asking OR-staff members their opinion about demanding, non-ergonomic, non-optimal and time-consuming tasks and device-related problems they encounter. Furthermore we asked them their ideas how they would improve these devices or tasks. Beside a long list of minor problems or problems which cannot be improved by medical technology, a few problems were mentioned often and/or might be solved by medical technological solutions: • Instrument baskets are not complete or instruments are not functional (e.g. not sharp) • Instrument baskets are over-complete, being time-consuming sorting them out on the instrument table and visa-versa • Wires, tubes and lines are all over the place, are difficult to differentiate, and makes it hard to move, or to reposition trolleys. • Depending on the procedure, additional (often heavy but vulnerable) equipment, like endoscopy trolleys, C-arm, Microscopes or Robots have to be moved in towards the OR-table and positioned accurately. This is a hard to perform, non-ergonomic and time consuming task. This last problem was mentioned by the majority of the OR-staff members and could in our opinion be improved by introducing technology. Existing products to overcome these problems do not provide an add-on or save solution, therefore together with students, OR-staff members and designers of our department we developed concepts. By introducing force-controlled, power-assisting solutions (e-bike technology), it might be able to lower the forces needed to manipulate heavy equipment and to improve the accurate positioning of these devices. Involving OR-staff members in technological innovations might improve OR-procedures, improve the efficiency and time, and in addition the costs of the OR.
Joris Jaspers, Jesse Bosma, Arto Boeken Kruger
Abstract: Performing complex tasks like endoscopic suturing or static tasks like camera holding or organ retracting in Minimally Invasive Surgery (MIS) is very demanding, cumbersome and labour intensive, due to a disturbed hand-eye co-ordination, indirect way of observing, non-ergonomic instruments with limited degrees of freedom and a lack of easy to use assisting devices. Robotic tele-manipulators and camera systems enhance surgical dexterity and control. This allows the surgeon to operate in an ergonomically favourable position with more intuitive manipulation of the instruments and the camera. Robotic systems, however, are very bulky, expensive, do not provide ergonomic benefits for the rest of the team and did not really proof the benefits for patient outcome. In our view robotic systems are only beneficial for manipulation beyond the capabilities of the human hand or for standard repetitive tasks. Because human hands are capable of performing complex tasks in MIS and are very intuitive to control, the aim of our project was to develop simple, mechanical, economic and easy to use alternatives for robotic systems for MIS. The Minimally Invasive Manipulator (MIM) is designed as a purely mechanical device, for intuitive manual control of surgical instruments in 7 DoFs. When manipulating the handle of the MIM, the instrument tip should follow the handle movements, without any scaling or mirroring effect. Our third prototype is evolved into a slender but stiff device, roughly equal to that of a conventional endoscopic instrument and therefore provide force feedback. First phantom experience indicates that the system functions properly and that complex manipulations like endoscopic suturing are feasible in an ergonomically way, without introducing to much force to the tissue. The last generation of our camera and retractor positioning device is designed as a simple construction that aims at user friendly operation of the device. This includes easy one-handed operation of the device and a slender design that minimizes the interference with other instruments in the sterile field. The positioning system actually fixates all degrees of freedom of the trocar and the instrument going through it simultaneously, in a drag ‘n drop manner. First experiments with the system showed its feasibility and demonstrated the system is intuitive and easy to use. A combination of the MIMs and the positioning system can be a cost effective, ergonomically and intuitive alternative for robotic systems. In addition to complete safety, they are completely manual controlled ad provide (limited) force feedback. It will offer surgeons the capability to perform complex MIS, and will provide a more labour-efficient way of performing Minimally Invasive Surgery.
Development of an EMF probe based on fiber-optic communication
Daniel de Jong, R.A.M. Canters, J. van der Zee, Gerard van Rhoon
Abstract: Background: In hyperthermia treatment of cancer, phased-array applicators are used to heat the tumor to 40..44 degC. Nowadays advanced algorithms are used to calculate applicator settings resulting in best predicted heating of tumor tissue [1]. However, the advanced strategies will become less effective if they are not properly transferred into the clinic. Practical issues, such as mutual radiation impedance in phased arrays are influenced by patient movement, which changes the electromagnetic field (EM field). Also, impedance matching networks used in dipole antenna systems, may change in time due to heating and vary between antennas. Therefore, current standards. i.e. measuring S11-parameters at the feed points of the antennas are not always reliable indicators of the applied EM field during treatment. Methods: In order to control the EM field in annular phased-arrays, the complex field will be measured at fixed points in between the antennas and subsequently matched to the modeled (optimized) EM field. To this end, a sensor is built based on a vertical-cavity surface-emitting laser (VCSEL). This type of laser is commonly used in fiber-optic communication and can be used to measure EM fields with time domain info. To overcome measurement threshold, the EMF probe (VCSEL) is forward biased by power generated by a single-junction (silicon) solar cell, which is illuminated by an external laser diode transmitting the light along an optical fiber. The EMF probe responds to the applied EM field by emitting coherent light down a second fiber which is detected by optical receivers adjacent to the powering laser. Results: First tests in the 77-100 MHz range have shown promising results. The sensor offers high spatial resolution and measures both phase and amplitude in EM fields from 1000 down to 1 V/m. Because of its full optical operation, small size and limited use of metal material, perturbation of the EM field is expected to be small. The prototype sensor is used to measure the EM field inside a hyperthermia applicator (-60) for model validation. Results with respect to phase information showed good agreement with modeled data. Amplitude measurements could not be compared so far, because the forward bias changed during the measurement due to fiber bending. A second prototype is in development in which fiber bending should give no problems. Conclusion: The optical powered sensor is a good low cost solution for measuring complex EM fields in aqueous media. References: 1. RAM Canters, MM Paulides, MF Franckena, J van der Zee, GC van Rhoon, ”Implementation of treatment planning in the routine clinical procedure of regional hyperthermia treatment of cervical cancer: An overview and the Rotterdam experience”, Int. J. Hyperthermia, Vol. 28, pp. 570-581, (2012) - This work is supported by the Dutch Cancer Society, Grant EMCR2009􀀀4448 -
Vera Lagerburg, Bertjan Arends
Abstract: Introduction: The use of medical equipment is subject to regulations, among which the most important ones are the medical devices law [1] and the medical devices directive [2]. In this case study the regulations that apply to a customized medical device will be addressed. On the initiative of our hospital a chair is being developed for the paediatrics department, to offer patients comfort and distraction during the administration of cytostatic drugs. This chair has a child friendly design and incorporates various electronic devices, such as a gaming computer. The chair is especially designed and produced for our hospital and is developed in collaboration with several companies and organisations. Regulation: The first question to be addressed is which regulations apply to this chair. Therefore it must be determined if this chair is a medical device. Article 1a of the medical devices law states the definition of a medical device [1]. Because the chair is custom designed for the paediatric oncology department to give comfort to the patient and thereby alleviate their treatment, this chair is a medical device and therefore should fulfil all the requirements of the medical device regulations. The second question that has to be answered is whether this device needs CE marking. Article 7 of the medical devices directive [2] states that all medical devices being placed on the market, should have CE marking, except custom-made devices and devices intended for clinical investigation. Because only one single copy will be made, and the chair will not be marketed, it is not required to have a CE marking. The chair is not used for research, so conformation to the requirements for research purposes is not necessary either. The directive states that ‘custom-made’ devices are intended for the sole use of a particular patient, which is not the case for this chair. This means that the chair does not have to meet the regulations regarding the medical devices directive, although it is a medical device. Practical approach: Still the hospital must ensure the safe use of the chair [3]. We decided to use the IMDD (Investigational Medical Device Dossier) as a checklist to cover the most essential safety aspects of the chair. The IMDD is used by the CCMO (Central Committee on Research inv. Human Subjects) and is written for non-CE-marked medical devices intended for clinical investigation. Not all the parts of the IMDD will apply to single copies, but certain parts are without doubt relevant, such as instructions for use and a risk analysis. The manufacturer has to fill in the IMDD. Based on this a clinical physicist will decide whether the chair can be safely used at the hospital. Subsequently, the medical technology department will perform some acceptance checks, among which an electrical safety test. Preliminary conclusion: This case illustrates that, under certain conditions, it may be possible to safely use non CE-marked equipment. The product safety of the equipment is the responsibility of the hospital and may be checked in a structured way using the IMDD.
Zhanqi Zhao, Sabine Krueger-Ziolek, Knut Möller
Abstract: Respiratory system consists of series of interacting functions, including ventilation, perfusion, gas exchange and controlling of breathing muscles. Pulmonary function diagnosis is important to identify the severity of pulmonary impairment. However, information of regional ventilation distribution is missing from traditional pulmonary function diagnosis, such as spirometry, body plethysmography or diffusion test. Electrical impedance tomography (EIT) is a non-invasive functional imaging technique that is capable of tracing regional gas volume changes [1]. Previous studies showed that valuable information was gained by combining spirometry with EIT [2, 3]. Body plethysmography provides information that cannot be obtained with spirometry, e.g. lung residual volume and airway resistance. In the current study, we present a measurement system that combines body plethysmography and EIT. This study was supported by the body plethysmograph manufacturer Ganshorn (Niederlauer, Germany) and the EIT manufacturer Dräger (Lübeck, Germany). The system is under construction. EIT electrode cables are permanently mounted in the body plethysmograph through the bottom of the body box and conducted along the box pillar. The connection of the EIT device and the electrode cables is achieved with an adaptor. Calibration process of the body box and measurement procedure remain unchanged. Interactions between EIT and body plethysmography are still not clear and should be examined in further studies. The new measurement system combining body plethysmography and EIT delivers information on both global and regional ventilation distribution. Further clinical studies are warrant to evaluate the contribution of the system in prognosis and diagnosis of respiratory status.
Christian Knöbel, Knut Möller
Abstract: For adapting mechanical ventilation to the physiological conditions of the patient’s lung and to avoid damage of lung tissue due to inappropriate ventilator settings, it is necessary to use intelligent and adaptive therapy regimes [1]. These regimes are based on individualised mathematical models representing the patient’s respiratory mechanics. In order to test these algorithms directly with a ventilator machine, active or passive lung simulators are used. As passive lung simulators are not capable of modelling dynamic lung behaviour and diseases, an active lung simulator, based on a cylinder-piston-system has been developed [2], [3]. To achieve high dynamics and low friction, an electromagnetic linear motor is used. In order to keep friction at a minimum level and to create an airtight seal between cylinder and piston, two roll membranes are employed that move with the piston over the whole travel length. They are stabilized using air pressure that is higher than the atmospheric and the maximum ventilation pressure. This reduces the risk of membrane jamming and ensures avoiding air leakages that would influence the ventilator machine. While “ventilating” the simulator, the volume of the artificial lung can be changed by a con-trolled movement of the piston inside the cylinder. Physiological properties of lung mechanics (i.e. compliance) can be modelled by varying the piston velocity. The necessary piston movement is calculated employing a mathematical patient model and a real-time controller. As the dynamics of one cylinder-piston-system is only able to simulate simple respiratory mechanics, several bigger and smaller modules can be combined for modelling more complex structures. Bigger modules can then be used to simulate low-frequent changes in residual vol-ume, whereas smaller modules can simulate high-frequent influences like coughing, sneezing or heart beats.
Thu Nguyen, Jörn Kretschmer, Knut Möller
Abstract: Modern approaches to respiratory therapy based on computer modeling ought to keep up with the latest technologies. In the era of tablet PCs and smartphones, lung diagnoses and therapy optimization could be brought to patients right at their bedside. To this end, previously presented simulations of patient physiology [1] were redesigned to run on mobile devices. In order to run the application on an Android operating system, the previously developed MATLAB code must be rewritten in Java. The Java codes are then converted to a special bytecode run by Dalvik Virtual Machine provided by Android. Development tools and integrated environment required are: Android software development kit (SDK), Eclipse IDE and Android Development Tools (ADT) plugin. With ADT plugin being installed for Eclipse, Android applications are easily built and debugged using Android SDK tools. Moreover, the layout for user interface (UI) elements defined via XML is fully supported on Android. A Graphical User Interface (GUI) was designed so that one can choose any combination of a ventilation mode (Volume Control, Pressure Control, SIMV or BiPAP), a combination of submodels describing lung mechanics, gas exchange and cardiovascular dynamics. Moreover, simulation can be adapted to individual patients by selecting lung diseases (chronic obstructive pulmonary disease or adult respiratory distress syndrome), as well as enter parameters for those selections. Outputs of interest such as airway pressure or flow can be reviewed after running the simulation thanks to an android library called androidplot. Volume controlled, pressure controlled, SIMV and BiPAP ventilation applied on a 1st order respiratory mechanics [1] model have been successfully developed. Initial tests show that mobile devices can easily be implemented in today’s medical decision support. The presented software is constantly improved and extended to further implement additional ventilation modes and patient models. Simulation is run with Euler integration, Ordinary Differential Equation (ODE) solver applying Runge Kutta method with either fixed step-size or step-size control. Other solver algorithms can be added in the future. REFERENCES [1] Kretschmer J, Wahl A, Möller K, “Dynamics generated models for medical decision support systems”, Comput Biol Med., 41(10):899-907, October 2011. [2] Nguyen T, Zhao Z, Kretschmer J, Möller K, “Simulation model for patient ventilator interaction with focus on changing disease states”, 6th International Conference on Bioinformatics and Biomedical Engineering (iCBBE), Shanghai, China, 2012
Axel Riedlinger, Jörn Kretschmer, Knut Möller
Abstract: Patient-specific mathematical models effectively predict physiological processes. They might be exploited to support therapeutic decision making directly at the bedside. In mechanically ventilated patients, the oxygenation status of the patient should at all times be sufficient. Gas exchange models are able to describe concentrations and distribution of both oxygen (O2) and carbon dioxide (CO2) inside the lung and the blood circuit. To represent a specific patient, model parameters need to be adapted to his individual behavior via measurements from the patient monitoring. Models of gas exchange with different complexity and therefore with different accuracy are described in the literature [1, 2]. The more complex the model, the higher the number of model parameters that have to be adapted to mimic a specific patient. Selecting suboptimal initial values often leads to model parameters deviating far from their correct values. In models with numerous parameters, fitting results may strongly depend on the chosen initial values because of the high number of possible parameter combinations. Thus, parameter identification of complex models with numerous parameters is potentially not robust. Erroneous model parameters would lead to a model that does not represent the patient status adequately leading to an unfavorable therapy recommendation. A hierarchical model structure may support robust identification of model parameters and allow flexible simulations of patient’s reactions to therapeutic decisions [3]. We have built a hierarchically structured family of gas exchange models, where the simplest gas exchange model acts on the assumption of a single lung compartment plus a shunt describing an area of the lung that is perfused but not ventilated. This model can be exploited to estimate the shunt parameter using a minimal set of information. This allows the reduction of the amount of parameters to be identified in the more complex models where different ventilation and perfusion rates (V/Q mismatch) are implemented [4]. Applying such a hierarchical parameter identification approach therefore simplifies model adaptation, making it more robust. First results of parameter identification of complex gas exchange models are promising. Further verification by means of patient data is necessary to prove this finding.
Arjo Loeve, Jenny Dankelman, Paddy French
Abstract: INTRODUCTION Optical Coherence Tomography (OCT) is increasingly being applied in small-diameter instruments, like catheters, bone drills, and steerable needles. For such applications, rotational scanning is usually most feasible and/or desired, making coupling of the light from the stationary OCT light source into a rotating part a common design issue. Coupling light between rotating optical parts is especially challenging due to the very strict demands on tolerances and alignments. We developed two optical couplings for high-speed (2000 rpm) rotational OCT that are applicable in instruments with diameters below 1 mm. The goal of the current research is to evaluate the designed optical couplings in terms of durability and feasibility. METHODS Two optical couplings (the “Steady Coupling” concept and the “Wagging Tail” concept) were built, and compared. The Steady Coupling concept consists of a stationary probe, tightly aligned with a rotating instrument tip, on a 0.2 mm thick bearing, with light being coupled between the stationary and the rotary part by two collimating GRIN lenses. The Wagging Tail concept is a design in which coupling is completely avoided and in which an optical fibre (with 0.25 mm GRIN lens at its tip) is deformed by the rotations of the instrument tip to make a conical scanning motion. Both concepts were tested on their weakest points. For the Steady Coupling concept, wear of the bearing was investigated. For the Wagging Tail concept, it was investigated whether the high-speed deformation cycles would create excessive heat or damage the optical fibre, which would cause deterioration of the light transmission. The wear of the bronze bearing and the damage to the optical fibre were tested simultaneously using a dedicated setup. RESULTS In the Wagging Tail concept the fibre still showed about 100 % efficiency after 350.000 rotations at 2000 rpm for a bending radius of 40 mm, a much sharper bend than in the prototype, and no noticeable heating or significant wear after rotating about 10 minutes. The bearing wear in the Steady Coupling concept was severe; after the tests, it appeared that the bearing had turned into powder and jammed the mechanism. CONCLUSION The simplicity, optical efficiency, and durability of the Wagging Tail concept clearly make this concept the optical coupling of choice for instruments where this mechanism can be applied. Drill tests on animal bone will have to shed light on the durability of the imaging lens in the tip of the drill. If the concept endures all tests, high-speed rotational OCT scanning can be embodied into many small diameter medical instruments. This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organisation for Scientific Research (NOW), and which is partly funded by the Ministry of Economic Affairs, Agriculture and Innovation. Project 7505
Jyotirmoy Banerjee, Adriaan Moelker, Wiro Niessen, Theo van Walsum
Abstract: Visual tasks such as detection, localization, categorization, and recognition are important subjects of study in medical image analysis. These tasks are often difficult due to apparent within-class inhomogeneity. Invariant image descriptors extract information from images which is invariant to the variability introduced due to the image formation process. One class of such descriptors is texture patterns. Texture has received considerable attention [1] with application in areas of medical imaging [2]. The local binary patterns [LBP], introduced by Ojala et al. [3], are an efficient method for texture description in 2D. One of the important aspects of this texture descriptor is its rotational invariance. The aim of our work is to extend the conventional LBP and its rotational invariant property mentioned in [3], to a 3D paradigm. Our method is capable of rotationally invariant description of landmarks or regions in 3D using LBP. The LBP in 3D requires a spherical sampling, which is represented in a spherical harmonics framework [4]. The framework helps in obtaining rotation invariant representation. Further, the region information is collected to a set of histograms that are invariant to rotation. The similarity between any two regions can be computed using the Chi-square distance measure [5] between the corresponding set of histograms. Concluding, we presented a method for rotationally invariant 3D LBP, using spherical harmonic decomposition. We applied the method on vessel-like phantom data and a clinical dataset, with encouraging results. More in-depth analysis and integration of complementary measures is part of future work.
Gert Weijers, Han Thijssen, Chris de Korte
Abstract: The aim of this study was to test the hypothesis that the Computer Aided UltraSound (CAUS) method developed by the authors [1-4] for the estimation of UltaSound Tissue Characteristics (UTC) parameters on transcutaneous (Transc) ultrasound (US) images can predict the liver fat content with similar accuracy and precision as with intraoperative (Intraop) US. A large animal study in post partum dairy cows (N=151) was performed to test these hypotheses. Five Transc B-Mode US liver image were acquired before surgery. During abomasal displacement surgery five Intraop US B-Mode liver images and a liver biopsy was taken. In liver tissue samples, triacylglycerol (TAG) content was measured by biochemical analysis. Firstly the equipment preset, which was kept fixed during whole study time, was carefully calibrated. For the echo level calibration a TMP was used, and all UTC parameters were expressed relatively to those of the phantom. Prior to UTC parameters estimation several pre-processing steps were performed: Back-Scan Conversion (BSC); Look Up Table (LUT) correction; superficial tissue layers (Fat layer) attenuation correction and Automatic Gain Correction (AGC) were performed. Also several post-processing steps were incorporated like: Automatic segmentation and residual attenuation correction were performed. Stepwise multiple linear regression analysis on a training set (N=76) was performed. In all cases the Residual Attenuation coefficient (ResAtt, R=0.81) was the only selected parameter. The results were tested on the residual cows (test set N=75) to predict the TAG content in the liver. Receiver Operating Characteristics (ROC) analysis then was applied to estimate the Area Under the Curve (AUC) and the sensitivity and specificity of the CAUS method. Equivalent high predictive values for AUC (95%), sensitivity(87%) and specificity (83%) for Intraop and Transc applications were found. Consequently, it can be concluded, applied Fat layer attenuation correction to Transc US images was performed adequately.
H.H. Rachmat, Dennis Janssen, W.J. Zevenbergen, Bart Verkerke, R.L. Diercks, Nico Verdonschot
Abstract: Computational models of the human knee need information on the attachment sites of the knee ligaments, which play an important role in the knee kinematics studies. These attachment sites usually are determined based on MRI scans, guided by anatomical atlas. It is, however, unknown how accurate one is able to determine the actual insertion and origo, which may have a substantial effect on the predicted knee kinematics. In this study, we therefore evaluated the intra- and inter- observer variability when determining the knee ligaments attachment site positions on MRI scans. These MRI measurements were compared with actual physical measurements on the cadaver knee. A right knee of a 66 years old male donor was scanned in 3T MRI scan (pixel size of 0.5x0.5mm, slice thickness 0.5mm). The MRI measurements were performed by five observers, with various backgrounds (senior and junior scientific researcher, orthopaedic surgeon, orthopaedic resident), using image processing software (Mimics 14). Prior to the measurements, the observers received a short introduction to the software and were given an anatomical atlas as a guide. The observers were free to choose in which plane they measured the ligament attachment sites (sagital-coronal-transversal). We evaluated the difference in location and size of the area of the ligament attachment sites. One observer repeated the measurements 3 times, with a one week interval. We furthermore investigated the differences relative to the physical measurements, which were performed on the same cadaver, using 3Space Fastrak (Polhemus). The largest intra- and inter-observer differences were 4.3 mm (ACL origin) and 17.3 mm (superficial MCL insertion), respectively. Relative to the physical measurement, the maximum intra- and inter-observer differences were 32.6 mm (superficial MCL insertion) and 22.4 mm (deep MCL insertion), respectively. The largest area was measured for the ACL origin (73± 46mm2), while the smallest area was found for the MCL origin (13.8± 9mm2). This study demonstrates the difficulty of clearly identifying knee ligament attachments based on MRI data, which can have serious implications for computational models of the human knee.
Pieter Oomen, Kenneth Meijer, Paul Willems, Maarten Drost
Abstract: Introduction Muscle architecture is a main determinant of muscle function. Architecture of a muscle can be described as the arrangement of muscle fibers within a muscle relative to the axis of force generation [1]. In addition, pennation angle, physiological cross sectional area (PCSA) and tension per unit of PCSA can determine muscle force. Previous literature only provides these muscle parameters post-mortem [2, 3]. Recent advances in imaging techniques gave the opportunity to study these parameters in-vivo [4]. Diffusion Tensor Imaging (DTI) is a promising non-invasive method to determine muscle fiber trajectories in-vivo. In this study we will focus on PCSA only. Therefore, the purpose of this study is to calculate PCSA of the m. rectus femoris from DT images. Method In this study one healthy adult male (age: 24 years, weight: 80kg, height: 1.89m) participated. A Philips 3.0 Tesla scanner was used to obtain T1 and DT images. The upper leg was measured within 3 stacks with a 20 mm overlap. The following imaging parameters were used: FOV 400 mm × 400 mm; Voxel size T1: 0.83 mm × 0.83 mm × 4 mm; Voxel size DTI: 3.1 mm × 3.1 mm × 4 mm. Segmentation of both right and left m. rectus femoris (RF) volumes were done using Research Volumetool v1.3.0 [5]. Intra-rater reproducibility was assessed by segmenting left and right RF twice. RF volumes were imported in vISTe [6], and fiber trajectories were tracked within the muscle volume. Trajectories were imported in a custom developed program in Matlab and finally PCSA was calculated. Results & Discussion The volumes of the RF (right: 339 ml; left: 346 ml) were found to have excellent ICC: 0.997. Importing these volumes in the DTItool gave promising results in visualising fiber trajectories of the muscle. A PCSA of 27.5 cm2 for the right RF and 26.2 cm2 for the left RF were calculated from the custom build Matlab program. However, validation is required to demonstrate the reliability of this computational approach of calculating PCSA. Relative to fixed cadaveric measurements from literature these volumes and PCSAs are much larger (volume: 54.5 ml - 104.7 ml and PCSA 8.9 cm2 - 15.2 cm2) [2, 3]. This discrepancy is most likely due to a different target population in the cadaveric studies. The mean age in these studies was 83 years which could induce atrophy of the muscles; the mean height was 1.68m which can result in considerably smaller muscles than our test subject. However, a cadaver study by Klein Horstman et al [7] found RF PCSA of 28.9 cm2 (volume 225.5ml) within a 105 kg male specimen. Conclusion DTI is a relative new technique to measure skeletal muscle architecture in-vivo [4]. This study showed possibilities in calculating PCSA of the RF from DT images. More research is needed to validate these outcomes and the application in other skeletal muscles. References 1. Lieber, R.L., Skeletal muscle structure, function, and plasticity : the physiological basis of rehabilitation. 3rd ed. 2010, Philadelphia, Pa., [etc.]: Wolters Kluwer/Lippincott Williams & Wilkins. VIII, 304, [8] p. pl. 2. Ward, S.R., et al., Are current measurements of lower extremity muscle architecture accurate? Clin Orthop Relat Res, 2009. 467(4): p. 1074-82. 3. Wickiewicz, T.L., et al., Muscle architecture of the human lower limb. Clin Orthop Relat Res, 1983(179): p. 275-83. 4. Galban, C.J., et al., Diffusive sensitivity to muscle architecture: a magnetic resonance diffusion tensor imaging study of the human calf. Miyatani, M., 2004. 93(3): p. 253-62. 5. Bol, G.H., et al., Simultaneous multi-modality ROI delineation in clinical practice. Ravichandiran, K., 2009. 96(2): p. 133-40. 6. Department of Biomedical Engineering. vIST/e. 2012; Available from: http://bmia.bmt.tue.nl/software/VISTE/. 7. Klein Horsman, M.D., et al., Morphological muscle and joint parameters for musculoskeletal modelling of the lower extremity. Clin Biomech (Bristol, Avon), 2008. 22(2): p. 239-47.
Harm Nieuwstadt, Ali Akyildiz, Lambert Speelman, Jolanda Wentzel, Ton van der Steen, Frank Gijsen
Abstract: Biomechanical models are used extensively to study risk factors, such as peak stresses, for vulnerable atherosclerotic plaque rupture [1, 2]. Typically, 3D patient-specific arterial models are reconstructed by interpolating between cross sectional contour data which have a certain axial sampling, or image, resolution. The influence of the axial sampling resolution on computed stresses, as well as the comparison of 3D with 2D simulations, is quantified in this study. A set of histological data of four atherosclerotic human coronary arteries was used which were reconstructed in 3D with a high sampling (HS) and low sampling (LS) axial resolution, and 4 slices were treated separately for 2D simulations. Stresses were calculated using finite element analysis (FEA). High stresses were found in thin cap regions and regions of thin vessel walls, low stresses were found inside the necrotic cores and media and adventitia layers. Axial sampling resolution was found to have a minor effect on general stress distributions, peak plaque/cap stress locations and the relationship between peak cap stress and minimum cap thickness. Axial sampling resolution did have a profound influence on the error in computed magnitude of peak plaque/cap stresses (±15.5% for HS vs. LS geometries and ±24.0% for HS vs. 2D geometries for cap stresses). The findings of this study show that 2D models suffice to obtain general stress distributions, but that 3D models are needed when accurate computation of peak stress magnitudes is required. This research was supported by the Center for Translational Molecular Medicine and the Netherlands Heart Foundation (PARISk). REFERENCES [1] U. Sadat, Z. Teng and J.H. Gillard, “Biomechanical structural stresses of atherosclerotic plaques”, Expert Rev. Cardiovasc. Ther. 8(10), pp. 1469–1481, (2010). [2] A.C. Akyildiz, L. Speelman, H. van Brummelen, M. A. Gutiérrez, R. Virmani, A. van der Lugt, A.F.W. van der Steen, J.J. Wentzel, F.J. Gijsen, “Effects of intima stiffness and plaque morphology on peak cap stress”, BioMedical Engineering OnLine, 10:25, (2011).
Leah Winkel, Harald Groen, Bibi van Thiel, Ton van der Steen, Jolanda Wentzel, Marion de Jong, Kim van der Heiden
Abstract: Atherosclerosis is a lipid driven inflammatory disease of the larger arteries leading to clinical complications such as myocardial infarction or cerebrovascular events. Atherosclerotic plaques are found at specific locations in the arterial tree i.e. near bends and bifurcations, where shear stress is low. Two types of atherosclerotic plaques can develop; vulnerable and stable plaques. Vulnerable plaques have a high risk of rupture, causing acute clinical events. Therefore, the need for non-invasive molecular imaging to distinguish stable from vulnerable atherosclerotic plaques is evident. We have a mouse model in which we can generate both a stable and a vulnerable plaque by placing a tapering cast, which alters shear stress profiles, around the carotid artery of ApoE-/- mice on a high fat diet1. We use this model to test whether we can distinguish vulnerable from stable plaques with non-invasive imaging techniques. In this study, we tested the feasibility of a folate-based radiopharmaceutical; EC0800 (Endocyte Inc.), visualised with high-resolution animal SPECT/CT. This folate tracer binds folate receptors, expressed by activated macrophages. Macrophages play an important role in atherosclerosis and are differentially activated between stable and vulnerable plaques. We intravenously injected our mice with EC0800, radiolabelled to 111Indium via DOTA-benzyl-ethylenediamine-(γ), 24 hours before SPECT/CT imaging. The cast-induced vulnerable and stable plaques showed 111In-EC0800 uptake with a higher uptake in the vulnerable plaque, suggesting EC0800 could function as a vulnerable plaque marker. However, upon histological examination of the plaques we found that the vulnerable plaque was considerably larger in size. We, therefore, determined tracer uptake for plaque volume. Surprisingly, this shows a relatively higher uptake of 111In-EC0800 in stable plaques. We are currently further investigating this. This study could provide a new method to non-invasively distinguish between vulnerable and stable plaques.
Mathijs Peters, Jan Nijs, Bastiaan Kietselaer, Frans van de Vosse, Richard Lopata
Abstract: The elastic behavior of the ascending aorta has been extensively studied in vitro [1]. Non-invasive in vivo characterization of elastic behavior of the aortic aneurysmal wall may provide substantial improvement in adequate patient selection and preoperative workup. The goal of this study is to investigate and estimate the mechanical properties of ascending thoracic aortic aneurysms (ATAAs) using an in vivo ultrasound technique and validate the results with in vitro mechanical testing on resected aortic specimens. However, before testing on human data, the proposed method was validated experimentally using porcine tissue. Porcine aortas (n = 3) were mounted in an experimental setup in which the vessels were pressurized from 0 to 130 mmHg in incremental steps of 10 mmHg. Raw ultrasound data were obtained at a single cross-section with a MyLab 70 (Esaote Europe, NL) with a linear array transducer. Data were processed using in-house developed 2D displacement estimation and tracking software [2]. The physiological circumferential strain range and Young’s modulus (E) were estimated. To examine the influence of longitudinal pre-stretch (LP), all measurements were performed for two previously reported values, LP = 1.1 and 1.3 [3, 4]. For validation of the US method, rectangular samples of the porcine tissue were tested in a bi-axial tensile testing device (CellScale, Canada). The samples (15 mm x 15 mm) were tested for circumferential strains of 0.1 to 0.5, for LP = 1.1 and 1.3. To investigate temperature dependency, all experiments were conducted at both room (21ºC) and body temperature (37ºC). In an ongoing in vivo study, biplane data were obtained in five patients with an ATAA using an iE33 with an X7-2t transesophageal probe (Philips, USA). Two-dimensional speckle tracking was performed on these data to estimate the mechanical behavior. Next, resected samples were stored in phosphate-buffered saline solution at -80ºC awaiting tensile testing. In the ultrasound experiment, the estimated physiological strain range was 0.21 ± 0.02 (end diastole) to 0.27 ± 0.01 (end systole) at LP = 1.1. For LP = 1.3, the strain was 0.25 ± 0.01 (end diastole) to 0.30 ± 0.02 (end systole). For the US-data, Eu = 224 ± 20 kPa (LP = 10%) and Eu = 258 ± 12 kPa (LP = 30%). The corresponding tensile test data revealed Et = 289 ± 82 kPa (LP = 10%) and Et = 296 ± 45 kPa (LP = 30%). The large variation was caused by one aorta that seemed considerably stiffer during the tensile test (348 – 383 kPa), whereas the other data were in good agreement (Eu = 201 – 257 kPa vs. Et = 234 – 276 kPa). Although different results were observed at both temperatures, no conclusions could be drawn. The in vivo ultrasound results revealed peak circumferential strains of 5 – 10% in the aortic root. However, the speckle tracking technique needs further improvement and revealed drift in the direction of the aortic wall. Tensile testing on human samples will be performed in the near future for validation of the US results. Other future work includes the assessment of local variability of Young’s modulus and strain and comparison with tensile test data.
Geert Claassen, Roy van Pelt, Andrea Fuster, Anna Vilanova
Abstract: Cardiovascular diseases (CVDs) are the number one cause of death worldwide[1]. It is important to investigate these diseases in order to find better diagnostic techniques. Blood-flow data provides important information for the analysis of cardiovascular diseases, since the bloodstream influences vessel walls, and vice versa. Anomalies in the blood flow can therefore be a result or cause of CVDs. Blood-flow measurements can reveal patterns and anomalies, and can be used to gain a better understanding of the cardiovascular physiology and pathology. Visual inspection of blood-flow data potentially provides newfound insight in the flow characteristics. However, visual analysis is challenging because of the abundance and complexity of information. New visualization methods showing clearly the anomalous flow areas are needed. This often involves simplification of the velocity fields by means of feature extraction. The goal of this research is to compare and cross-validate points and patterns in 4D (3D cine) PC-MRI blood-flow data. PC-MRI blood-flow data consists of 3D vector fields for several time points within one heart cycle. The data of each time point is combined data from measurements during several heart cycles. We investigate three methods to obtain patterns in the blood-flow field. The winding number method was adapted to make it applicable to vector fields[2,3], and to extract critical points within the blood flow. Furthermore, we have inspected the λ2 criterion by Jeong and Hussein[4] for the detection of vortices. For flow-pattern recognition, a method proposed by Heiberg et al.[5] is examined. Although these methods provide intrinsically different results, they can be compared because they all indicate the presence of patterns in the blood-flow field. The robustness of the winding number algorithm and the λ2 criterion are investigated on several artificial data sets under increasing noise levels. The winding number is able to extract saddle points in images with a signal to noise ratio (SNR) of 4 or larger. The λ2 criterion is able to extract vortices in images with a SNR of 8 or larger. This difference is largely due to the fact that the winding number uses more information from the local environment. In future work, robustness experiments regarding the pattern matching method will be performed. We expect the pattern matching method to be more robust than the winding number and λ2 criterion approaches, because no derivatives are used, and more information from the local environment is incorporated. Furthermore, an advantage of the pattern matching method is that it can detect multiple patterns. Initial experiments on artificial data sets show promising results. This will be further investigated using measured blood-flow velocity data.
Frank Gijsen, Hans Schuurbiers, Alina van der Giessen, Anton van der Steen, Jolanda Wentzel
Abstract: Background: Heterogeneity in plaque composition in human coronary artery bifurcations is associated with blood flow induced shear stress. To compute shear stress distribution in human coronary arteries, we need 3D lumen data. We investigated two new procedures to generate 3D lumen data and combined the 3D reconstructions with computational fluid dynamics to study the relationship between shear stress and wall thickness in vivo. Methods: We imaged 10 patients with multislice computer tomography (MSCT) and intravascular ultrasound (IVUS). The 3D reconstruction of the main branch was based on the fusion of MSCT and IVUS [1]. The proximal part of side branch was reconstructed using IVUS data or MSCT data, resulting in two different reconstructions of the bifurcation region. The distal part of the side branch was based on MSCT data alone. The reconstructed lumen was combined with CFD to determine the shear stress [2]. Low and high shear stress regions were defined and shear stress patterns in the bifurcation regions were related to wall thickness values from derived IVUS. Results: The geometrical features of the bifurcation region for the two reconstruction procedures did not reveal appreciable differences. The shear stress maps however, showed differences between the reconstruction procedures: both the low and high shear stress regions in the bifurcation only showed an overlap of approximately 75%. The average wall thickness in the low and the high shear stress regions was not different for the two reconstruction procedures. The relationship between shear stress and wall thickness was not influenced by the reconstruction procedure. An inverse relationship between shear stress and wall thickness, which one might expect in these mildly diseased bifurcations, was observed in 3 out of 10 bifurcations. Conclusion: Reconstruction of the side branch with MSCT data alone is an adequate technique to study shear stress and wall thickness in the bifurcation region. The reconstruction procedure can be applied to further investigate the effect of shear stress on the progression atherosclerosis in coronary bifurcations. REFERENCES [1] Van der Giessen et al., Int.J. Cardiovasc Imaging, vol.26(7), pp. 78196, (2010). [2] Gijsen et al., Journal of Biomechannics, vol. 40(11), pp. 2349-57, (2007).
Sanne Roeles, Frans Steenbrink, Josien van den Noort, Jaap Harlaar
Abstract: Gait retraining with real-time visual feedback on well chosen gait parameters may have potential to treat pathological gait patterns [1]. Especially the Knee Adduction Moment (KAM) is a relevant target parameter in patients with Knee Osteoarthritis (KO). In this study we evaluate the feasibility of real-time visual feedback. Four types of feedback on both a kinematic and a kinetic gait parameter were used on healthy subjects to modify their gait pattern. It was hypothesized that visual feedback of both kinematic and kinetic parameters is an effective technique for gait pattern modification. Subsequently possible effect size differences between different types of visual feedback were investigated. Healthy subjects (8 males; age 28±7.6y) walked on the GRAIL (Gait Real-time Analysis Interactive Lab; dual-belt instrumented treadmill, motion-capture system and virtual reality (Motek Medical B.V.)). Compared to a baseline recording subjects were asked to increase internal hip rotation or decrease knee adduction moment based on four types of visual feedback, i.e. bar, polar plot, color changes, graph. With visual feedback hip rotation increased (P=0.001; baseline: 3.03±7.27°, bar: 9.23±9.64°, polar plot: 12±13°, color: 10±13°, graph: 10±13°) and knee adduction moment decreased (P<0.001; baseline: 0.4±0.1 Nm/kg, bar: 0.2±0.2 Nm/kg, polar plot: 0.2±0.1 Nm/kg, color: 0.2±0.2 Nm/kg, graph: 0.2±0.1 Nm/kg) compared to baseline levels. The amount of change in the gait parameters was not significantly influenced by the type of visual feedback. Real-time visual feedback can be used to modify subject specific gait parameters in healthy controls and can potentially be used for gait retraining in patients. Our findings demonstrate the potential of these techniques for conservative treatment of KO patients by active and dynamic KAM reduction, potentially postponing knee replacement. The effect-size of the modified gait pattern was not influenced by the type of feedback, suggesting that the type of visual feedback is not of primary concern. REFERENCES [1] Wheeler, J., et al. (2011). Real-time knee adduction moment feedback for gait retraining through visual and tactile displays. Journal of Biomechanical Engineering 133, 1-4.
Octavio Martinez Manzanera, Marit Sanders, Jan Willem Elting, Natasha Maurits
Abstract: Tremor is an ubiquitous, often disabling neurological disorder with varying etiologies. Some tremors, such as enhanced physiological tremor, essential tremor and psychogenic tremor, can be difficult to distinguish and therefore hard to diagnose. Moreover tremors might only occur during specific postures, movements or periods during the day, hampering tremor diagnosis by a physician on the basis of clinical symptoms alone. Long-term tremor recordings during daily life can help detecting more tremor occurrences and facilitating more extensive analyses. Here a method is presented to automatically detect tremor in long-term accelerometer recordings based on auto-regressive (AR) modeling [1], with the specific aim to distinguish psychogenic tremor from other tremors.
Fokke van Meulen, Jasper Reenalda, Peter Veltink
Abstract: Stroke often results in impaired balance which is a major cause of locomotor disability and may decrease the performance of many activities of daily living. Patients who suffered a stroke are trained to recover adequate control over their movements with the objective to optimize their daily-life functional performance. Continuous daily-life monitoring of balance control of stroke survivors in an ambulatory setting, is essential for optimal guidance of rehabilitation therapy by medical professionals and coaching of the patient. Schepers et al. [1] developed instrumented force shoes (IFS) for the ambulatory assessment of the ground reaction force and the estimation of the position of centre of mass. They demonstrated the evaluation of dynamic balance control in stroke patients. However, for the assessment of body balance, foot placement (i.e. relative foot position), is a crucial variable. The IFS does not provide information about relative foot positions. In order to estimate the relative foot position, the Xsens (Enschede, the Netherlands) MVN Biomech measurement system will be used [2], which contains 17 inertial magnetic measurement units. Position information of all sensors will be estimated with Xsens’ software, MVN studio Pro. The purpose of this study is to demonstrate in stroke patients, the relation between qualitative parameters of body balance [3], while measuring in a simulated ambulatory setting using on-body measurement systems, and the results of a generally accepted clinical balance assessment. A total of twenty stroke subjects will be included in a clinical study which is approved by the local medical ethical committee. Subjects will perform tasks in a simulated ambulatory setting; daily-life tasks: sitting, moving an object over a table, rising up, walking to another room, opening a door and returning an item from the other room. During the experiment, movements will be evaluated using the IFS and MVN Biomech system and afterwards qualitative parameters will be calculated and compared with the results of the clinical balance assessment (e.g. Berg Balance Scale [4]). Although the IFS and the MVN Biomech system need to be redesigned to make them applicable for measurements during daily-life, it is expected that the combination of both systems allows to assess qualitative parameters of balance control in stroke patients in an ambulatory setting.
Stijn Luca, Peter Karsmakers, Kris Cuppens, Tom Croonenborghs, Anouk Van de Vel, Berten Ceulemans, Lieven Lagae, Sabine Van Huffel, Bart Vanrumste
Abstract: Nocturnal home monitoring of epileptic children is often not feasible due to the cumbersome manner of seizure detection with the standard method of video/EEG-monitoring. We propose a method for hypermotor seizure detection based on accelerometers attached to the extremities. Hypermotor seizures often involve violent movements with the arms or legs, which increases the need for an alarm system as the patient can injure himself during the seizure. In the literature, classification models are commonly estimated in a supervised manner. Such models are estimated using annotated examples. This annotation of data requires expert (human) interaction and results therefore in a substantial cost in the estimation process of the seizure detection model. In this work we propose the use of an unsupervised approach for estimating seizure detection models. This method does not require any annotation of data while obtaining state-of-the-art classification scores that are comparable to those of a model estimated in a supervised manner. The proposed methodology is based on extreme value statistics (EVT). The EVT approach starts from a model of normal behaviour. This model is estimated using a multivariate kernel density estimation. Based on this estimation extreme value statistics are used to model rare events. These rare events are situated in the tails of the model. Generally however the approach also models rare events lying between multiple modes in case of a multimodal dataset. Finally, the model of rare events can be used to judge new incoming data to be rare or not. In this work epilepsy seizure detection is based on data, recorded during the night using accelerometers attached to each limb of a patient. After segmenting the acquired acceleration signals in movement events, features are extracted for further processing. The fact that the dataset is heavily unbalanced (roughly only 3% of the data is coming from seizures) allows to use all data to estimate a model of normal behavior. The small portion of seizure-related data will only have a minor effect on the parameters of this model. Signals and/or features are determined such that extremities with respect to this model of normal movements can be considered as seizure related movements. As a consequence, a person-dependent epileptic seizure detector can be estimated with little human interaction. The EVT-methodology is applicable on a broad range of datasets and was able in our example to detect all hypermotor seizures in five of the seven patients with a satisfying sensitivity and positive predictive value.
Lamia Elloumi, Qiwen Zhang, Bert-Jan van Beijnum, Hermie Hermens
Abstract: Currently, we witness the growth of ICT-mediated solutions for chronic diseases management, especially to assist and support patients in lifestyle changes in order to improve their health condition. Being physically active is one the recommended lifestyle changes for patients with chronic diseases. The challenge within those ICT-mediated solutions for physical activity support is to allow patients to manage themselves their physical activity level (PAL) and provide them with the needed social support. One of those solutions available is the use of Virtual Community (VC). Current VCs provide a part of social support needed by patients, mostly informational and emotional support, but not appraisal (feedback) and instrumental support. Our current work is focusing on the providing patients enrolled in the VC the instrumental support. To achieve our goal, we developed a VC for physical activity support. The VC allows its members to interact within a Social Networking Portal. We used a sensor system (a triaxial accelerometer and a smartphone) coupled with it to record the PAL of the VC’s members. Monitoring the physical activity of the VC’s members in term of energy expenditure is how instrumental support will be provided. They are able to see their current physical activity level, to share it within their community and to comment on the results. The platform provides members some communication means that allows them to provide feedback and emotional support to their peers. The VC is based on two modules: a personal and a group module. Activity performance metrics within those modules were suggested in [1] used to enhance the understand of the PAL and, the collaboration and communication between VC’s members. The personal level module the members can understand their PAL with some extended metric, decide to share it within the VC and get system feedback. The group level module defines a group metric for the VC and computes the contribution of each member to a group goal. In addition, members can view each member contribution to the fulfilment of the group goal, can view the PAL of the members, if shared, can comment on what other members shared or the group goal, and give other feedback on the results. A preliminary evaluation of the implemented VC was done with 2 groups of 5 healthy subjects each for two days. It was conducted to test the performance of the VC, and to test the PAL support modules, for both personal and group levels. No errors or anomalies that have impact on the stability or the functionality were detected. First results suggest that the group dynamics depend on a person who takes the role of leader spontaneously; if the “leader” is active and encouraging the other members, they get also active. Also feedbacks and encouragements of the administrator had the same effect. Since the evaluation was conducted only for two days, these results are not conclusive: a longer period evaluation is needed to confirm it. More improvements are needed to be done in the personal and the group module to provide more extended services to members; improvement of the instrumental support. Next steps will be also about the provision of the appraisal support/ feedback in the VC. REFERENCES [1] L. Elloumi, B.J. van Beijnum, and H. Hermens, “Towards Physical Activity Support Community”, 6th International Symposium on Medical Information and Communication Technology, 26 - 29 March 2012, la Jolla, California, USA, (2012).
Dirk Weenk, Alien Stevens, Bart Koning, Bert-Jan van Beijnum, Hermie Hermens, Peter Veltink
Abstract: Soft-tissue artifacts cause inaccurate estimates of body segment orientations. The inertial sensor (or optical marker) is orientating (or displacing) with respect to the bone it has to measure, due to muscle and skin movement [1]. In this pilot study 11 inertial and magnetic sensors (MTw, Xsens Technologies) were placed on the rectus femoris, vastus medialis and vastus lateralis (upper leg). One sensor was positioned on the tendon plate behind the quadriceps (iliotibial tract, as used in Xsens MVN [1]) and used as reference sensor. Walking, active and passive knee extensions and muscle contractions without flexion/extension were recorded using one subject. The orientation of each sensor with respect to the reference sensor was calculated. During walking, relative orientations of up to 28.6º were measured (22.4±3.6º). During muscle contractions without flexion/extension the largest relative orientations were measured on the rectus femoris (up to 11.1º) [2]. This pilot showed that the ambulatory measurement of deformation of the upper leg is feasible; however, improving the measurement technology is required. We therefore have designed a new inertial and magnetic sensor system containing smaller sensors, based on the design of an instrumented glove for the assessment of hand kinematics [3]. This new sensor system will then be used to investigate soft-tissue artifacts more accurately; in particular we will focus on in-use estimation and elimination of these artifacts.
Dirk Weenk, Michiel van der Coelen, Arno Geessink, Frank van der Hoek, Bart Verstoep, Henk Kortier, Fokke van Meulen, Bert-Jan van Beijnum, Peter Veltink
Abstract: The recording of human movement is used for biomedical applications like physical therapy and sports training. Over the last few years inertial sensors have been proven to be a useful ambulatory alternative to traditional optical systems. An example of a successful application is the instrumented shoe, which contains two 6D force/moment sensors beneath the heel and the forefoot and two inertial sensors rigidly attached to the force/moment sensors [1]. These shoes can be used for ambulatory assessment of walking kinetics and kinematics. The relative position of the feet is currently not measured directly but estimated from double integration of feet accelerations. However, this method immediately leads to large position errors (drift) when the estimated inertial accelerations are inaccurate. In this study we investigated the ambulatory estimation of the relative positions of the feet using ultrasound transducers. On one shoe we mounted a 400PT120 Air Ultrasonic Ceramic Transducer (13 mm diameter, 10 mm height, 85º beam angle) sending a 40 kHz pulse to a similar transducer on the other shoe. Using the time of flight, the distance is estimated. Under static conditions a mean error of 5.7 ±0.8 mm was obtained over a range of 5 till 75 cm [2]. From this pilot study we concluded that the distance between the feet can be estimated ambulatory using small and low-cost ultrasound transducers. Future research includes the use of multiple transducers on each foot for a distance measure during different daily-life activities. Also the relative positions of the feet will be investigated by fusing the distance estimates with inertial sensor data.
Adrian Cooke, Maarten Bonnema, Bart Koopman
Abstract: The goal of this study is to use the Augmented Reality Tool Kit (ARToolKit[1]) video tracking system with Inertial Measurement Units (IMU) to measure the roll angle on a bicycle. The research forms part of the Slimme Ondersteunde FIEts (SOFIE, intelligent assisted bicycles) project (http://mobilitylabtwente.nl/sofie) at the University of Twente. The SOFIE project is investigating how to make bicycles safer for elderly people and bicycle instrumentation is an important part of the research plan. The Inertial Measurement Unit (IMU) systems are being used extensively in experimental research on human subjects. Over the last few years the accuracy of these systems have increased but they still suffer from problems of drift and magnetic interference. This presentation wishes to compare the accuracy of a modern Inertial Measurement Unit with a video processing marker tracker system using ARToolKit and a standard USB Webcam. The AR Tracker system is traditionally used for Augmented Reality applications such as gaming and education. It has been shown that for certain applications IMU's are a viable system to use for kinematic research [2]. For the roll angle calculation on a bicycle, IMU's alone do not give enough resolution. These two systems are compared to the Visualeyez VZ-4000 optical tracker system, which is assumed to be the golden standard. A sensor fusion algorithm is then developed to use the AR Tracker and IMU information to improve the accuracy of the roll angle measurements on a bicycle. Results of experiments designed to compare the accuracy and usability of the systems will be discussed. This will give an analysis of the difference between the AR Markers and IMU to the Visualeyez. Additionally preliminary results of the sensor fusion algorithm (using the IMU and AR Markers) will be given.
Lode Vuegen, Peter Karsmakers, Hugo Van Hamme, Bart Vanrumste
Abstract: In 2060 the total EU’s population will rise only by 2% while the number of over 65 year olds will increase by 85%. This causes significant budgetary implications on today’s care system. To cope with these facts transferring elderly to expensive nursing and retirement homes should be delayed as long as possible. A possible solution is automatic home observation where a) acute (e.g. fall detection) and gradual events (e.g. change of sleep rhythm) can be detected and b) person specific reports with information related to clinical and care status can be generated. During the last decade many modalities have been examined in order to achieve these objectives. However, the usage of low-cost compact ultrasonic sensors in the intended application has to our knowledge not yet been investigated. In this work, it is explored if domestic events can be recognized based on ultrasonic signals. This is done by recording events with a 40kHz ultrasound receiver which can be tuned in the frequency range between 28-44kHz. Next, the recorded signals will be shifted towards the audio spectrum with a bandwidth of 10kHz. This makes the captured signals audible for the human hearing and easy to record with standard audio hardware. To get an idea of the potential that ultrasonic signals might have for classifying domestic events, Gaussian Mixture Models based on Mel-Frequency Cepstral Coefficients were used. The latter are a classical method for speaker recognition [1] which seems to be related to the problem at hand. In total 14 different events (including coughing, shuffling, running water, watching television, opening and closing doors, speech) were recorded multiple times in a simulated setup, both when the receiver was tuned to the 25-35kHz band and to the 35-45kHz band. The capturing distance between receiver and source (event) varies between 0.1m and 1m. Promising results were obtained in this configuration. An average accuracy of 98.4% and 91,0% with a standard deviation of 3 and 5 was reached, respectively when the receiver was tuned into the 25-35kHz and 35-45kHz band. As a result, this preliminary study indicates that ultrasound contains useful information related to domestic events. In future research this result is studied in more detail and on real-life data.
Jan-Willem van 't Klooster, Bert-Jan van Beijnum, Hermie Hermens
Abstract: This article presents lessons learned from a longitudinal pilot study in which 6 elderly clients in a nursing home used a personalized care system to increase self-management. The aging population is an omnipresent problem in western countries. For economical and demographical reasons, it becomes necessary to put nursing home clients more into a self-mana-gement position, using ICT to support them in their daily life and only call for professional aid in case of necessity. Clearly, electronic care services can contribute to this desire but in general they are expensive, they are not well integrated and not well tailored to specific needs [1]. Hence we currently integrate and personalize care services by means of development and testing of a middleware care services platform, integrating services from multiple vendors. Based on stakeholder discussions and interviews, we included remote monitoring of vital signs, medication guidance and dispense, and social services related to communication and activity management. The high-level architecture of the care platform is presented in Fig. 1. It is used as follows: caregivers set personalized care plans relevant to the elderly’s personal situation in the tailoring interface. E.g.; measure blood pressure daily, and if the values exceed a set limit, warn a nurse. The personalised service plans are submitted to the Integration tier. They are stored and executed by orchestrating all necessary plan parts. If the execution of a plan needs external service building blocks (such as sensors), they are available through a set of Adapters. It is not always the case that a plan outcome is known in full at design time. For example, if a plan defines that an alert should only be sent if a measurement value exceeds a limit, this should be reasoned at runtime. Hence, a reasoning component judges actual activity within the system. The Telecare system finally provides the application services defined in the service plan to the end user. At the top, Fig. 1 shows a possible set of combined devices integrated by the platform. 4 Caregivers and 6 clients (82 ± 12 yr.) in nursing homes received training instruction and then used the system for 3 months. Clients had to perform self-measurements, which shifted work-load from caregivers to clients themselves. Appreciation of this by some clients was that this eliminated waiting time and resulted in better overview. However, other clients had learning problems operating the devices without assistance. For social services, memorizing clients on activities in a personalized way is now possible. Interaction through the telecare system alongside face-to-face contact was not only used between client and family, but also between clients and nurses. General acceptance as per the CSCQ [2] is shown in Table 1. Interestingly, employees are more satisfied because of them better being able to operate, understand and judge the new system.
Marjolein van der Krogt, Lianne Kraan, Tessa Hoekstra, Jaap Harlaar
Abstract: GRAIL (Gait Real-time Analysis Interactive Lab, Motek Medical BV) is a newly developed tool for real-time gait analysis and gait training. It combines an instrumented dual-belt treadmill with a Virtual Reality (VR) environment (180o semi-cylindrical screen) and 3D motion capture. GRAIL allows for direct interaction with the subject, for instance to adjust the belt speed to the subject’s self-chosen walking speed. Previous studies have indicated that fixed-speed treadmill mode and lack of visual flow are potential causes for differences in gait parameters between overground and treadmill walking. The aim of this study was to investigate whether walking on the GRAIL in a self-paced mode with VR is similar to overground walking in terms of spatiotemporal and kinematic parameters. Ten typically developing children (age 8-15y, 7 male, 3 female) walked at their own preferred walking speed, both on the GRAIL and overground in a conventional gait lab, within the same session. Spatiotemporal parameters and 3D kinematics (Optotrak, Northern Digital Inc) were compared, as quantified by 17 key gait parameters and the Gillette Gait Index (GGI) [1]. Walking speed and cadence did not differ significantly between GRAIL and overground walking, while step width was somewhat higher on the GRAIL (0.10m vs 0.07m, p<0.05). Kinematic patterns were very similar, and most parameters did not differ significantly between GRAIL and overground walking. However, some significant differences were found: on the GRAIL, peak ankle dorsiflexion in swing was smaller, the hip was slightly more abducted in swing (right leg only), and more exorotated in stance (left leg only). All mean differences were in the order of 1-3 degrees. GGI scores were significantly higher on the GRAIL (right 53.2, left 31.1 versus 15.7 for both left and right overground). In conclusion, GRAIL and overground walking were very similar, but differences were found in step width and some kinematic parameters. Most differences were small, and likely not clinically significant. These findings indicate that GRAIL walking may be used instead of overground walking, but further study is needed. In ongoing analyses, we are investigating the individual effects of VR and self-paced treadmill mode on gait parameters, as well as the effects on kinetics. Furthermore, to evaluate the applicability for clinical gait analysis, we are studying GRAIL versus overground walking in children with cerebral palsy.
Monique Tabak, Harm op den Akker, Hermie Hermens
Abstract: Background: The promotion of physical activity in daily life is an important aspect in the treatment of COPD patients [1]. We developed a telemedicine application – the Activity Coach – that aims to increase activity levels and to balance activities over the day. Activity levels are measured using a triaxial accelerometer, and time-related feedback text messages are provided on a smartphone. The objective of this study was to investigate how COPD patients responded to the feedback messages on a short-term notice. Intervention: Fifteen patients with COPD participated. Patients used the Activity Coach with a minimum of 4 days per week, for four consecutive weeks. During the intervention, patients received feedback text messages every two hours with advice on how to improve their activity level, based on their measured activity levels. There were three types of feedback messages: encouraging messages (e.g. “go for a walk”), discouraging messages (e.g. “sit down for a while”) and neutral messages (e.g. “keep up the good work!”). Methods: Daily activity was assessed by accelerometry and expressed as amount of activity in counts per minute [2]. To investigate the response to the feedback messages, we compared the amount of activity 30 min before the feedback message was seen by the patient with a time interval (10, 20 and 30 min) after the message was seen by the patient. The magnitude of the response is expressed as the percentage of change. Results: In total, 1394 feedback messages were provided to the patients, of which 35% encouraging, 51% neutral, and 14% discouraging messages. On a group level, the amount of activity significantly decreased after a discouraging message was seen: a decrease of 23% after 10 min, 25% after 20 min, and 29% after 30 min (all p<0.001). After an encouraging message, the amount of activity significantly increased with 16% (p=0.010) after 10 min. There was no significant increase after 20 and 30 min (resp. p=0.051 and p=0.087). Conclusions: COPD patients significantly change their activity level on a short-term notice in response to time-related feedback messages provided on a smartphone. Ambulant feedback messages might therefore be a valuable component of telemedicine interventions that aim to improve activity behaviour of COPD patients.
Simone Boerema, Hermie Hermens
Abstract: INTRODUCTION Accelerometry-based activity sensors are nowadays widely deployed in ambulatory monitoring of physical activity. Field experiments are characterized by very little control over usage of the sensor [1]. A quick and reliable calibration procedure is required [2], focused on determining the relation between the accelerometer output and physical activity across a range of activity levels. The purpose of this study was to design an easy spot-check to monitor the validity and reliability of activity sensors. METHOD Four sensors were securely fastened to a mechanical oscillator (Vibration Exciter, type 4809, Brüel & Kjær) and moved at various frequencies (6.67Hz; 13.45Hz; 19.88Hz) within the range of human physical activity. For each of the three sensor axes, the sensors were simultaneously moved for five minutes per defined frequency. The acceleration of each movement was expressed by its RMS value (RMSinput). Raw sensor output (sample frequency 200 Hz) was converted to IMA counts per minute (cpm, in [ms-2]), according to Bouten et al. (1997) [3]. Linear regression analysis was used to examine the relationship between the RMS and IMA. Factors taken into account were the four sensors and the three axes. The device tested in this study was the ProMove2 (Inertia Technology), containing the 3D MEMS inertial sensor (type: LIS3LV02DL, ST Microsystems). RESULT The RMS output of the sensors was within 6% of the RMSinput at each frequency, indicating a high accuracy of the sensors. There were no significant differences between the sensors in IMA values at 6.67Hz and 13.45Hz. Differences found in IMA values at all frequencies and all the different axes, were not significant when added to the regression model. The resulting regression model is: IMA*10-3 [ms-2] = 783*RMS [ms-2] (R2=0.980), indicating that only RMSinput is significant for the output of the sensors. The tested intensity levels are, compared to normal living, in the range of low intensity activities (e.g. reading a book ±200cpm, compared to ±320cpm at 6.67Hz in the experiment) to moderate intensity activities (e.g. shopping ±1800cpm, compared to ±1740cpm at 19.88Hz). DISCUSSION AND CONCLUSION The developed method provides an easy to perform procedure to test an individual activity sensor as well as to determine the inter-variability of a set of sensors. This is especially useful when multiple sensors are used in field experiments.
Simone Boerema, Mark Brul, Charles Willems, Hermie Hermens
Abstract: INTRODUCTION: With an increasing prevalence of dementia in the Netherlands from 235.000 in 2008 (1 per 70 inhabitants) up to an estimated 500.000 in 2050 (1 per 34 inhabitants), assisting technologies are needed to support care delivery in the home environment. Remote activity monitoring systems show the potential to support caregivers in providing home care to elderly with dementia by facilitating objective information on the activities of daily living (ADL) of these elderly. The challenge is however to design a system that complies with the needs of the contemplated users of the system: the informal and professional caregivers. The goal of this study is to elicit users’ needs and translate these into a functional description of a remote activity monitoring system. METHODS: A user centred approach is deployed to involve caregivers in the design process, by applying scenario based analysis supported with mock-ups. In three iterating workshops we involved 8 informal and 5 professional caregivers. The workshops respectively focused on: Eliciting global users’ needs, Defining a first set of requirements in a scenario analysis, and Evaluating mock-ups of user interfaces. RESULTS: Informal caregivers expressed the need for remote activity monitoring system as a reassuring tool, providing peace-of-mind, whereas professional caregivers expressed the need for objective information to support decision making in their profession of providing care. Both expressed the need for simple representations of the monitored information. The participants defined nine general ADL that they would like to monitor remotely: 1) mobility, 2) use of household equipment, 3) medication intake, 4) deterioration of health, 4) social involvement, 5) personal care, 6) daily structure, 7) sleeping, 8) eating and 9) drinking. Based on these needs both Functional Requirements (e.g. quality of sleep) and Non Functional Requirements were formulated (e.g. security/privacy, unobtrusiveness for the demented person, cope with unpredictable behaviour, and validity of information). DISCUSSION: Functional requirements were defined qualitatively on a high abstract level (e.g. quality of sleep). Participants had difficulty quantifying the measures and defining the needed representation of the information (e.g. quality of sleep can be represented by measures like: sleep duration, number of night walks, or duration of wake ups). CONCLUSION: We presented a first list of user needs, based on a functional description of an activity monitoring system in the setting of dementia at home. This list should be further specified in succeeding user centred design iterations to design easy interpretable monitoring information that represents the complex concept of human ADL.
Mike van Diest, Claudine Lamoth, Jan Stegenga, Klaas Postema, Bart Verkerke
Abstract: Background. Fall injuries are responsible for significant disability, physical dysfunction and loss of independence among elderly. A major risk factor for falls in the elderly population is poor postural control. Fall incidence can be reduced through balance training programs[1,2]. Therapy adherence however is low, particularly when prevention is the goal[3]. To increase motivation for balance training and make a training more accessible we aim to develop a balance training game system, a so-called exergame (=exercise and game), for the home situation thereby quantifying balance ability of elderly during training activities. However, current (clinical) quantifications of postural control are not applicable during activities[4, 5]. Therefore the aim of the present study was to develop parameters based on motion caption that can be used to quantify balance ability during exergaming among young and elderly. Methods. 9 elderly and 6 young adults performed a 1-minute weight shifting exergame task in the frontal plane under 16 different conditions in 5 task domains in a CAREN lab (Computer Assisted Rehabilitation Environment, Motek Medical BV). The task domains included: higher sway amplitude, faster sway, faster object dodging, lifting one leg, higher dodge difficulty. Position of trunk, pelvis and lower limbs as well as ground reaction forces were recorded using a motion capture system (VICON V8) and force plates (Bertec FP4060-08) respectively. Task and age effects of sway amplitude, movement regularity (Harmonicity ratio and peak power spectrum), root mean square (RMS) values and Sample Entropy (SE) of the trunk motion were calculated. Results. Trunk sway and RMS values were higher for young adults then for elderly, for all task conditions. Harmonicity ratio, movement frequency and sample entropy were also higher in young adults, indicating a faster and smoother movement then that of elderly. Several task effects were found which need further analysis. Conclusions and further work. Preliminary data analysis showed several interesting condition and age effects. In combination with force plate data the selected parameters can be used to quantify balance during an exergame. Keywords: exergames, postural control, balance parameters, healthy aging
Surahyo Sumarsono, Bart Verkerke, J. C. Wortmann
Abstract: Increased use of Information and Communication Technology (ICT) and reengineered care processes that provide integration among patients, health care providers, research centres and vendors will be key drivers for pervasive health care services in aging societies. The important factor is the continuously increasing life expectancy that is leading to aging societies with consequences for a new model of health care services, particularly in rehabilitation process. Telerehabilitation (TR) is the implementation of ICT for supporting rehabilitation services [1]. TR provides a practical solution by minimizing the barrier of distance in the delivery of comprehensive rehabilitation services. The rehabilitation process typically requires continuous and frequent monitoring of the patient’s status. TR services will be mostly in a low intensity and in a long period of time. One of the challenges facing TR services is the relative lack of use of sensor-based measures within rehabilitation. Within the project ExerGaming (exercise with serious gaming) a training system will be developed for ageing societies to train their balance [2]. TR will be used to support ExerGaming and it shall enable all medical devices involved to be semantically integrated, makes interoperable platforms to access, communicate and store the rehabilitation status. However, semantic interoperability is difficult to obtain. To date, much of the research on medical device interoperability claims that interoperability can be obtained through standardization [3]. This research argues that standardization alone is unlikely to achieve the goals of interoperability. A methodical design process is the methodology used in this research. It utilizes a cyclical model of design, prototyping, and evaluation of outcomes in order to develop constructs, models or methods. Through methodical design, an existing conceptual model from the ExerGaming case study will be explored to develop a set of interoperability requirements for the TR system. These requirements will be used to develop a framework and demonstrate proof-of-concept implementations. REFERENCES [1] J. M. Winters, “Telerehabilitation research: emerging opportunities.,” Annual review of biomedical engineering, vol. 4, pp. 287–320, Jan. 2002. [2] C. Lamoth, “Exergaming for Balance Training of Elderly,” 2012. [Online]. Available: http://www.imdi-sprint.nl/files/Presentatie Claudine Lamoth.pdf. [3] K. Lesh, S. Weininger, J. M. Goldman, B. Wilson, and G. Himes, “Medical Device Interoperability-Assessing the Environment,” in 2007 Joint Workshop on High Confidence Medical Devices, Software, and Systems and Medical Device Plug-and-Play Interoperability (HCMDSS-MDPnP 2007), 2007, pp. 3–12.
Marc Mertens, Glen Debard, Bert Bonroy, Els Devriendt, Koen Milisen, Jos Tournoy, Jesse Davis, Tom Croonenborghs, Bart Vanrumste
Abstract: Due to the ageing population, more elderly people will depend on the support of others. In order to improve the quality of care and life and to keep the cost of health care sustainable, new ways to allow the elderly to live independently in their own home environment need to be considered. The aim of our research is to develop and evaluate a system that can automatically detect the activities of daily living (ADL) of older persons living alone at home. This automatic detection is based on measurements with contactless sensors that are installed in the home environment of the older person. The results can be used to assess the self reliance of the person monitored. In this research we deploy sensors that can measure the consumption of public utilities (electricity, water and gas), movement sensors and video cameras. This abstract describes the results of the first step towards recognition of ADL using electricity sensoring at one central point at the electricity cabinet. By identifying which electrical appliance is being turned on or off, we can deduce the ADL the person is performing with a certain probability. Recently there has been interest in the automatic classification of electrical appliances [1], mainly in the field of energy management. We try to improve results by using extended features describing the electrical current signal and by applying machine learning techniques. We divide the appliances into four categories, based on their electrical architecture: lighting (e.g., fluorescent, incandescent, halogen), motored appliances (e.g., hairdryers, mixers) heating (e.g., halogen heaters) and electronics appliances (e.g., TV sets, radios, computers) The features we use to discriminate between appliance classes include power, phase shift with respect to mains voltage, harmonics, correlation with a pure sine wave, etc. We measured the electrical current profile of several commonly used appliances (e.g., microwaves, hairdryers, lighting) which can be linked to an ADL (e.g., cooking, eating). Measurement specifications were 5kS/s sampling speed and 12 bit resolution. Our training set consists of 106 measurements covering 16 appliances. Using the simple J48 tree classifier in the machine learning toolkit Weka, we correctly classified 95 out of 106 instances. This test is a good first step in appliance discrimination towards detecting performed ADL, especially when it will be combined later on with information such as position and posture information. The next step in our research is working with combined signals. When several appliances are powered simultaneous, we need to first decompose the electrical current signal into the discrete current profiles.
Jonathan Dikken, Bert-Jan van Beijnum, Hermie Hermens
Abstract: COPD is a preventable and treatable chronic pulmonary disease which leads to a non-fully reversible airflow limitation. Because of their bad physical condition, COPD patients are inactive and become socially isolated, resulting in an even worse physical condition. To overcome this downward spiral, patients can be enrolled in a rehabilitation program. This consists of group sessions for about 12 weeks, 2 or 3 times a week, at the physiotherapist to perform physical activities, both aerobic exercise as resistance training. After the rehabilitation program, patients need to maintain their physical condition themselves. Often patients are not compliant to the training advice, resulting in a bad physical condition, more COPD related health issues and reenrolment to the rehabilitation program. To improve the compliance to the training advice patients need to be motivated. For that purpose the Integrated Training System (ITS) for COPD patients has been developed. The ITS supports the improvement and maintenance of the physical condition safely, at home and using a virtual group environment. Safety is ensured by preventing oxygen desaturations in the blood. The heart rate and oxygen saturation level is measured for the safety and effectiveness of the exercise. With these parameters, the resistance of the home trainer is set based on an individually tailored control system. The ITS will be used at home. This limits barriers for patients to come to a training session. A virtual group environment is used to enable the motivation of patients. In the virtual group environment, patients are motivated by the system and by each other. The four components of the ITS are the home trainer, the virtual exercise environment, the controller and the web portal. The home trainer is an ergo bike which has a digital computer interface. The virtual exercise environment is a computer game in which a patient can cycle together with other patients. The controller collects data from the home trainer component, analyses it and sets the resistance level on the home trainer to ensure a safe and efficient training and sends the physiological data and exercise data to the web portal. On the web portal this data is shown. Technical evaluation of the ITS prototype shows a accurate heart rate and cadence measurement, a moderate measurement of the power and a poor oxygen saturation level measurement. The control systems of the prototype for performance, safety and training together work as expected. This explorative research is promising in improving and maintaining the physical condition of COPD patients. A solid base is expounded, but improvements and further research need to be done.
Jan de Jong, Martijn Wessels, Arno Stienen, Herman van der Kooij
Abstract: DESIGN OF A TRANSCRANICAL MAGNETIC STIMULTION ROBOT Jan J. de Jong*, Martijn Wessels, Arno H.A. Stienen, and Herman van der Kooij *University of Twente, Drienerlolaan 5, 7522 NB, Enschede The Netherlands e-mail: j.j.dejong@utwente.nl Web page: http://www.utwente.nl/ctw/bw/ ABSTRACT Transcranial Magnetic Stimulation (TMS) is a non-invasive method to modify behaviour of neurons in the brain. TMS is applied by running large currents through a coil close to the scalp. For consistent results it is required to maintain the coil position within millimetres of the targeted location, but natural head sway and practitioner fatigue may hinder this. Serial robots are currently used to assist the application of TMS. However, their low stiffness limits the performance and their high moving mass limits the operating speeds for safety reasons. Since 6-DOF parallel manipulators combine high stiffness with low moving mass, they have potential for safe, fast and accurate positioning required for TMS during activities. Features of the TMS robot design: 1. The TMS coil applies the TMS therapy. 2. A spring connects the coil to the robotic manipulator to ensure a soft interaction between the coil and the head. 3. The 6-DOF parallel manipulator holds the spring and the TMS coil and is actuated to follow the head during head sway. 4. A positioning frame positions the robotic manipulator at the proper height and angle to adjust for different tasks and subjects. 5. A neuronavigation and a visual tracking system is used to track the motion of the head and link the it to a fMRI image. 6. While different base stations on which the subject is situated can be implemented, the TMS robot is designed to be used with a subject walking on a treadmill wearing a robotic exoskeleton (such as the LOPES) or sitting on a chair. In this poster presentation, the TMS robot is elaborated, and a functioning prototype of the manipulator is presented.
Aki Kunikoshi, Helene Clogenson, Jenny Dankelman
Abstract: Purpose: Endovascular catheter interventions require special instruments and manual dexterity when patient’s anatomy is to be accessed via a small incision. Large number of catheters exist and new steerable catheters are under development. To evaluate the differences between those catheters on their manipulation properties as well as to evaluate interventional manipulation skills of residents, an objective measurement method is desired. Various methods to evaluate interventional manipulation skills of residents have been developed. Most of them require human raters or are only based on elapsed time to accomplish certain tasks. We propose an objective approach to evaluate interventional manipulation skills. Methods: To determine whether certain catheter/resident is better than another, we developed the Activity Feature Vector (AFV) method and analysed the distribution of AFVs in a feature space using pattern recognition techniques. An AFV is defined as a six dimensional vector extracted from one catheter manipulation task. Each dimension represents total time for the task of waiting, catheter rotation, catheter advancement, catheter retraction, guidewire advancement and guidewire retraction respectively. We implemented an application that is able to extract AFVs automatically from the videos of catheter manipulation. Extracted AFVs were submitted to principal component analysis (PCA) and the 1st to 3rd principal components were used to perform linear discriminant analysis (LDA). Performance of the proposed method was evaluated using a leave-one-out cross-validation. Result: The results demonstrated that our proposed method is able to predict the used catheter more than 70% correctly. In addition, our proposed method showed the possibility of a combination of AFV and LDA to classify residents based on their skills. REFERENCES [1] J. Dankelman, C. A. Grimbergen and H. G. Stassen, Engineering for Patient Safety: Issues in Minimally Invasive Procedures, CRC Press, 2004. [2] M. K. Chmarra, S. Klein, J. C. F. de Winter, F. W. Jansen and J. Dankelman, “Objective classification of residents based on their psychomotor laparoscopic skills”, Surg. Endosc., Vol. 24, pp. 10311039, (2010).
S. Dobbenga, J. Hassing, K. Thomson, S.P. Pellegrini, N. Tolou
Abstract: As technology improves, more medical devices are designed for implantation in the body, for example hearing aids, pacemakers and deep brain stimulators. When a battery is used as power supply for an implantable device, a surgery is needed every time the battery needs to be replaced. Patients will suffer multiple surgeries for battery replacement during their lives, depending on the battery life span of the implanted medical device. Combining these implantable medical devices with an energy harvester offers the possibility to create a lifelong power supply for implantable devices, and therefore save the surgeries for battery changing. The goal of this research is to investigate the potential of the energy harvester as power supply for implantable medical devices in terms of saved surgeries. The research was done on combining the energy harvester with the pacemaker, which is the most commonly implanted device. The data acquisition was performed using a research of the Central Bureau of Statistics of the Netherlands, which was on the amount of pacemaker surgeries in the Netherlands. The amount of pacemaker surgeries divided in age groups was shown for the year 2009, also a distinction was made in gender, and time of hospitalization (one-day for battery changing and long-term for first surgery). The average life expectations of men and women in the Netherlands and the battery lifespan are used for calculating the amount of battery changing surgeries these patients will suffer during a lifetime. It was shown that using an energy harvester as power supply for pacemakers could save up to an average of 3 surgeries per patient per lifetime and about 1600 pacemaker surgeries per annum in the Netherlands. This may result in saving more that 25m€ per annum in the Netherlands alone. This research encourages further development of the use of energy harvesters in medical devices.