SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY (SPECT)- QUANTITATIVE ASPECTS AND STUDIES IN CANINE PULMONARY PERFUSION

Abstract

We have evaluated the quantitative aspects of a whole-body SPECT system which consists of 2 large-field-of-view scintillation cameras mounted in a rotatable gantry and interfaced to a minicomputer. Data are continuously collected through a 360 degree rotation and result in 32 contiguous transverse images which can be reorganized into 16 frontal and 16 sagittal images. Pulmonary perfusion studies were performed in dogs to compare the information from SPECT with routine gamma camera images. Five plastic spheres ranging from 2 to 6 cm in diameter were placed in a 22 cm diameter cylinder with technetium-99m distributed in the spheres and cylinder in varying concentration ratios. A semi-automatic region of interest program was used to evaluate the multiple slices from the SPECT data, and the volumes were calculated by computing the total number of voxels within each region of interest. The SPECT measured volumes correlated very well with the actual volumes. To evaluate the ability of SPECT to determine radionuclide concentrations in an object, elliptical and cylindrical phantoms were uniformly filled with technetium-99m in concentrations from 0.05 to 1.5 μCi/ml. Using attenuation corrected data, the SPECT concentrations correlated very well with the actual concentrations over the entire range tested. We also evaluated the concentration ratios of the spheres to the cylinder using attenuation corrected SPECT images. The concentration ratios were derived from the measured SPECT image contrast by correcting for attenuation, scattered photons and image degradation resulting from finite system spatial resolution. Using this procedure, the SPECT measured concentration ratios correlated well with the actual concentration ratios. Perfusion defects from normal anatomic structures, as well as perfusion abnormalities secondary to occlusion of a bronchus or pulmonary artery are better defined on the SPECT images than the gamma camera images. Thus, SPECT gives additional information concerning pulmonary perfusion.