Differences in regional wash-in and wash-out time constants for xenon-CT ventilation studies |
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Authors: | Chon Deokiee Simon Brett A Beck Kenneth C Shikata Hidenori Saba Osama I Won Chulho Hoffman Eric A |
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Affiliation: | Departments of Radiology and Biomedical Engineering, University of Iowa College of Medicine, 200 Hawkins Drive, Iowa City, IA 52242, USA. |
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Abstract: | Xenon-enhanced computed tomography (Xe-CT) has been used to measure regional ventilation by determining the wash-in (WI) and wash-out (WO) rates of stable Xe. We tested the common assumption that WI and WO rates are equal by measuring WO-WI in different anatomic lung regions of six anesthetized, supine sheep scanned using multi-detector-row computed tomography (MDCT). We further investigated the effect of tidal volume, image gating (end-expiratory EE versus end-inspiratory EI), local perfusion, and inspired Xe concentration on this phenomenon. RESULTS: WO time constant was greater than WI in all lung regions, with the greatest differences observed in dependent base regions. WO-WI time constant difference was greater during EE imaging, smaller tidal volumes, and with higher Xe concentrations. Regional perfusion did not correlate with WI-WO. We conclude that Xe-WI rate can be significantly different from the WO rate, and the data suggest that this effect may be due to a combination of anatomic and fluid mechanical factors such as Rayleigh-Taylor instabilities set up at interfaces between two gases of different densities. |
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