Evaluating the effect of incremental dose reduction on perfusion defect detection employing hybrid cardiac perfusion SPECT slices
Accruing enough patient studies with an acceptable gold standard diagnosis to evaluate reconstruction strategies is costly and cumbersome. We recently improved and streamlined a method developed earlier for inserting cardiac perfusion defects into SPECT slices of hearts deemed normal by experienced physicians. In this study we employed our improved methodology to study the effect of incremental dose reduction on perfusion defect detection. All patients included in this study were under IRB approval with written consent. Imaging consisted of list-mode acquisitions during stress Tc-99m sestamibi perfusion SPECT on a BrightView SPECT/CT (Philips, Cleveland, OH) employing the standard clinical protocol. Patient body and respiratory motion tracking were performed to correct SPECT slices during reconstruction. A method was developed to randomly select fractions of list-mode events for inclusion in decreased dose acquisitions spanning the total acquisition time. The original data were then reconstructed with a combination of respiratory and rigid-body motion compensation and perfusion defects inserted to reflect a 50% reduction in wall counts. The same defects were subsequently inserted into the lower dose acquisitions. Finally, the hybrid projections were reconstructed with and without respiratory motion compensation and evaluated using polar map quantitation comparing the percentage reduction of the counts in the lower dose defects with that in the original hybrid acquisitions. Also, success was assumed when the polar map software flagged the inserted defect as a region with disease according to the ASNC guidelines. In our preliminary evaluation, we were able to reduce the dose to 25% of the original counts and obtain similar decreases in defect counts while still been flagged as diseased. However, other distractors (noise, respiratory motion when not corrected) now clearly influence the accuracy in location and size of the defects. Therefore, other processing methods not yet clinically available should be explored, especially for dose reduction below 50% of that used in standard acquisition protocols.