[Comparison of SPECT images with four kinds of 99mTc collimators]

Performance of SPECT imaging systems which use a rotating gamma camera, are affected by characteristics of the detector-collimator assembly, the data acquisition method, and the filter used in image reconstruction. The purpose of this study is to examine image qualities of SPECT with different types of low energy collimators. The SPECT imaging system in this study is a rotating gamma camera ZLC-7500 (Siemens) and a data processing unit Scintipac-700 (Shimadzu). The four types of collimators compared are UHR (ultra high resolution), HR (high resolution), AP (general all purpose), and HS (high sensitivity), with 0.27, 0.66, 1.00, and 2.06 relative sensitivity, respectively. In the case of the same collimator, the spatial resolutions measured in the slice plane showed a slight difference in the FWHM values (mean values of UHR, HR, AP, and HS were 11.3 mm, 13.6 mm, 15.8 mm, and 20.4 mm, respectively.) between the center and the circumference of the field of view, in the radial direction, but a large difference in the tangential direction, with lower FWHM values (values of UHR, HR, AP, and HS were 8.4 mm, 8.7 mm, 9.3 mm, and 10.8 mm at 12 cm from the center, respectively.). In comparison of SPECT images with the four types of collimators, except for the HS collimator, image qualities of UHR, HR, and AP collimators showed only a slight difference. From the pont of view of sensitivity and spatial resolution of the collimator, it is expected that the AP collimator would be suitable for SPeCT imaging with 99mTc.