Basics and clinical application of nonradioactive xenon-enhanced

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Nonradioactive xenon can be used as a contrast medium for the evaluation of pulmonary ventilation because the CT number of the lung increases proportional to the alveolar xenon gas concentration. In this study, a new scan and reconstruction technique was proposed for detailed mapping of pulmonary ventilation with sequentially acquired xenon-enhanced CT.Scans to measure xenon concentration were performed before xenon inhalation, at the end of 2-min inhalation of 20-percent xenon, then, 1 min after switching the gas to room air. The scans were performed by synchronizing with respiration to obtain the images in the same respiration phase. Digital image processing with nonlinear geometrical warping technique was performed to correct the small mismatch of the images. The kinetics of xenon in the lung was analyzed using principles of indicator dilution theory to create a map of ventilation rate constant. After informed written consent was obtained, xenon-enhanced CT using the above-mentioned technique was applied to healthy volunteers and volunteers with pulmonary emphysema. The averaged ventilation rate constant in the patients with pulmonary emphysema was significantly lower than that in the healthy volunteers. The area with low ventilation rate constant was well correlated with the area of emphysema on CT image. Thus the results suggest that this technique is useful for detailed mapping of impaired ventilation.