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Session: Medical Instruments - Surgery II
Session starts: Friday 25 January, 13:00
Presentation starts: 14:15
Room: Lecture room 557

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Ruud Verdaasdonk (VU University Medical Center)
Joost de Jong (VU University Medical Center)
Albert van der Veen (VU University Medical Center)
Keith Cover (VU University Medical Center)

Abstract:
Infections can be a serious complication after surgery. In the design of operating rooms (OR), a laminar flow of clean air is created above the field of surgery to prevent contaminations. In this study, various air flow visualization techniques have been developed and compared to optimize for high sensitivity, large field of view and practical to be applied in a live OR setting. The visualization techniques are based on contrast enhancement using either ‘analoge’ optical methods (Schlieren) or digital image processing methods enabling quantification of the images e.g. applying colour intensity projection. Small density gradients in air induced by e.g. temperature differences, will deflect light beams. By discriminating the deflected rays from background light using spatial filters or digital subtraction techniques, air flow can be visualized. An enormous contrast enhancement was obtained with a classical Schlieren (CS) setup using concave mirror and a spatial filter (knife edge). However, the field of view was limited to the size of the mirror (35 cm and 200 cm focal length). To enlarge the field of view, a background oriented Schlieren setup (BOS) was developed by placing a high contrast pattern (e.g. lines ~10/cm) in the background and subtracting images during the air flow either with a ‘analoge’ spatial filter or digitally. This proved less sensitive compared to CS. The Schlieren setup showed significant disturbance of the laminar flow of clean air above the operation table depending on the position of the operating lamp. Looking at the air flow around various instruments that are standard in the OR, air turbulence over 1 m distance was visible created by the cooling vent. When these vents are directed to the ground or into the operation field, the flow of clean air intended to prevent infections, could easily be disrupted. Schlieren techniques are useful to investigate potential sources for infection in a live operation room.