THE RELATIVE CONTRIBUTIONS OF SCATTER AND ATTENUATION CORRECTIONS TOWARD IMPROVED BRAIN SPECT QUANTIFICATION

Mounting evidence indicates that scatter and attenuation are major con founds to objective diagnosis of brain disease by quantitative SPECT. There is considerable debate, however, as to the relative importance o f scatter correction (SC) and attenuation correction (AC), and how the y should be implemented. The efficacy of SC and AC for Tc-99m brain SP ECT was evaluated using a two-compartment fully tissue-equivalent anth ropomorphic head phantom. Four correction schemes were implemented: un iform broad-beam AC, non-uniform broad-beam AC, uniform SC + AC, and n on-uniform SC + AC. SC was based on non-stationary deconvolution scatt er subtraction, modified to incorporate a priori knowledge of either t he head contour (uniform SC) or transmission map (non-uniform SC). The quantitative accuracy of the correction schemes was evaluated in term s of contrast recovery, relative quantification (cortical:cerebellar a ctivity), uniformity ((coefficient of variation of 230 macro-voxels)x1 00%), and bias (relative to a calibration scan). Our results were: uni form broad-beam (mu = 0.12 cm(-1)) AC (the most popular correction): 7 1% contrast recovery, 112% relative quantification, 7.0% uniformity, 23% bias. Non-uniform broad-beam (soft tissue mu = 0.12 cm(-1)) AC: 73 %, 114%, 6.0%, +21%, respectively. Uniform SC + AC: 90%, 99%, 4.9%, +1 2%, respectively. Non-uniform SC + AC: 93%, 101%, 4.0%, +10%, respecti vely. SC and AC achieved the best quantification; however, non-uniform corrections produce only small improvements over their uniform counte rparts. SC + AC was found to be superior to AC; this advantage is dist inct and consistent across all four quantification indices.