Ventilation/perfusion ratios and simultaneous dual-radionuclide single-photon emission tomography with krypton-81m and technetium-99m macroaggregated albumin

The purpose of this study was to develop a functional image of pulmonary ventilation/perfusion (VA/Q) ratios based on data acquired with simultaneous dual-radionuclide SPET and to assess VA/Q unevenness through the VA/Q histogram in patients with various pulmonary diseases. Dual-radionuclide SPET was performed with technetium-99m MAA and krypton-81m, with the patient in the supine position. After correction for linear cross-talk, the total acquisition counts of both radionuclides were equalized. The VA/Q ratio, which was calculated in each pixel by dividing the 81mKr count by the 99mTc-MAA count, was expressed as a VA/Q image. A histogram of the pixel number plotted against the VA/Q ratios was then produced and its centre of weight and standard deviation (SD) determined. Ten healthy volunteers and 46 patients [seven with pulmonary vascular disease, nine with pulmonary emphysema, 18 with bronchogenic carcinoma and 12 with miscellaneous diseases] participated in this study. In normal volunteers, VA/Q ratios were generally even, but were slightly lower in dorsal regions. Patients with PVD had lobar and/or segmental areas with a high VA/Q ratio. Low VA/Q areas extended widely in patients with PE. Bronchogenic carcinoma exceeding 3 cm in diameter was detected as a very low VA/Q area. The SD of VA/Q ratios had a significant positive correlation both with A-aDO2(r=0.64, P <0.001) and with cigarette smoking history (r=0.72, P <0.001). It is concluded that the VA/Q ratio image produced with simultaneous dual-radionuclide SPET using 99mTc-MAA and 81mKr is a unique and simple method for demonstrating the three-dimensional distribution of VA/Q ratios. The unevenness of VA/Q distribution can be assessed through the SD of the VA/Q histogram. (orig.)