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Session: Cardiac Diagnostics
Session starts: Friday 25 January, 10:30
Presentation starts: 10:30
Room: Lecture room 559

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Giovanna Russo (Eindhoven University of Technology)
I.H.F. Herold ()
H.C. van Assen ()
H.H.M. Korsten ()
Massimo Mischi ()

Abstract:
Blood volume (BV) assessment provides valuable information on the circulatory system functionality. Nowadays, BV measurements are performed by employment of indicator dilution techniques, such as thermodilution [1]. Although considered as the gold standard, thermodilution is a very invasive procedure due to the need for central catheterization. Recently, Dynamic Contrast-Enhanced Ultrasound (DCE-US) has been proposed as an alternative minimally-invasive approach for BV assessment [2]. This method measures the BV by using a single peripheral injection of a small bolus of Ultrasound Contrast Agent (UCA) detected by an ultrasound scanner. By measuring the acoustic backscatter, two indicator dilution curves (IDCs) can be derived from two different sites in the circulatory system. IDC analysis permits deriving the mean transit time (MTT) that the injected bolus takes to cover the distance between the two measurements sites. Assessment of the BV between these sites is therefore obtained by multiplying the MTT by the blood flow. The system is validated in-vitro for a wide range of flows and volumes, comparing the proposed method with standard thermodilution. The in vitro system consisted of a flow generator, an electromagnetic flowmeter to measure and adjust the generated flow, heating devices to keep a constant temperature (37 oC), two thermistors for thermodilution, a tube network simulating the BVs, and a pressure stabilizer. A small bolus of UCA diluted in cold saline (1-mg SonoVue® in 20 mL saline at 4 °C) was injected into the system. The cold UCA passage through a first and a second region of interest (ROI) was measured simultaneously with an ultrasound transducer and two thermistors (RADI wires). The measurements were performed for different flows and volumes. BVs were estimated by using two different approaches. In the first one, the IDCs were processed and fitted separately with dedicated models to estimate the MTT of the cold saline and the UCA bolus between the two ROIs. In the second one, the BV was quantified by estimation and analysis of the dilution impulse response between the two ROIs. A linear relation between BVs estimated by the two techniques (thermodilution and DCE-US) was observed with a correlation coefficient of 0.95. The most significant differences between the two techniques were observed in the case of high volume and low flow, possibly due to a different transport kinetics between UCAs and heat. Given the good correlation between BVs estimated with DCE-US and thermodilution, DCE-US seems a valid minimally invasive alternative to thermodilution for BV measurements. REFERENCES [1] H. J. C. Swan, et al., N. Engl. J. Med., vol. 283, pp. 251-256 (1970). [2] M.Mischi, et al, IEEE Trans UFFC, 51(9), 1137-1141 (2004).