[Assessment of pulmonary ventilation/perfusion ratio by dual radionuclides SPECT using 81mKr gas and 99mTc-MAA].

The accuracy and clinical availability of pulmonary ventilation/perfusion (V/Q) ratio images by 81mKr gas and 99mTc-MAA dual radionuclides SPECT was assessed in 10 normal volunteers and 31 patients with pulmonary diseases. After equalizing the total acquisition counts of both radionuclides, the ratio of 81mKr/99mTc count was calculated in each pixel and expressed as the functional map of V/Q. Then, the histogram of pixel numbers against V/Q ratio was drawn and the center of weight (CW) and standard deviation (SD) of the distribution were determined. The reproducibility of this method was excellent. In normal volunteers, CW was 1.07 and the SD was 0.25. The V/Q was lower in dorsal than in the ventral portion. SD was large and lobar or segmental high V/Q areas were clearly noted in the patients with pulmonary vascular diseases. In pulmonary emphysema, large low V/Q areas coexisted with patchy high V/Q areas. CW was small and SD was large in this group. There was a significant positive correlation between SD and PA-aO2. The author believes that the pulmonary ventilation/perfusion (V/Q) ratio images by dual radionuclides SPECT is a useful diagnostic procedure. Further, SD determined by this examination is thought to be a good parameter of uneven distribution of pulmonary ventilation and perfusion.