Study of Gallium-67 Imaging Using the Triple Energy Window (TEW) Method

Abstract

Three photopeaks are generally used to obtain tumor images with gallium-67. However, in this situation, images are affected by scattered photons from high energy fractions. Therefore, we applied the triple energy window(TEW) method to correct for scattered gamma-ray and improve the quality of images. A low-energy general-purpose(LEGP) collimator was used in consideration of the total balance of resolution and sensitivity of the collimator, and photopeaks of 93 keV and 185 keV were measured. With the low-energy collimator, the influence of compton scatter, which penetrates collimators of higher energy than Ga-67, was strong. Therefore, the distance from the source to the collimator needed to be 3 meters or more when the photopeak was set using the LEGP collimator. Background count was decreased by the correction of compton scatter. FWHM and contrast improved 4.8 mm and 14.8%, respectively, and clearer images could be obtained using the LEGP collimator with scatter correction than with the usual MEGP collimator without scatter correction. However, the anatomical localization of the lesion became less clear because the background count was decreased, especially in SPECT. Addition of the TCT image clarified the anatomical localization of the lesion.