Optimization of regularization of attenuation and scatter corrected 99 mTc cardiac SPECT studies for defect detection using hybrid images

Through means of an ROC study, the authors optimize the iteration number and 3-D Gaussian post-filtering of ^{99 m}Tc cardiac emission OSEM reconstructions that implement corrections for both attenuation and scatter. Hybrid images were used for this optimization wherein perfusion defects were added artificially to clinical patient studies that were read as being normally perfused. The test conditions included 3 different iteration numbers of OSEM (1, 5 and 10), followed by 3-D Gaussian low-pass filtering at each iteration level. The level of Gaussian low-pass filtering was varied using standard deviations (σ) of 0.6, 0.75, 1 and 1.25 pixels, in addition to a case where no post-filtering was applied. Four observers read 80 images for each of the 15 test conditions being investigated, providing confidence ratings as to the presence or absence of perfusion defects. Results indicate a slowly varying trend between very little filtering and quite heavy levels of smoothing with a gentle plateau for post-filters in the range of σ=0.6 to 1 pixel. No significant improvement in detection accuracy was observed with increasing iteration number as long as the reconstructions are post-filtered with σ in the range of 0.6 to 1 pixel, suggesting that 1 complete iteration of OSEM should suffice