Partial volume compensation for gated cardiac imaging

Objectives In cardiac imaging, partial volume effects (PVEs) due to limited spatial resolution and heart beating greatly reduce quantitative accuracy. We have previously proposed a partial volume compensation (PVC) method that compensates for both effects. In this work we evaluated the method using dog studies

Methods Gated myocardial perfusion PET using ten isochronal frames and contrast-enhanced gated cardiac CT were performed on 5 dogs. Binary volume-of-interest (VOI) maps of the left ventricle myocardium (LV) and blood pool (BP) were defined in gated CT images and then registered with corresponding PET frames. Our cardiac PVC method was applied to PET data at both end-diastolic (ED) and end-systolic (ES) phases using corresponding VOI maps. For comparison, PVC was also applied to time-averaged PET images using VOI maps defined from time-averaged CT images.

Results Similar to simulation studies, PVEs caused ~24% underestimation of LV activity with 3-4% due to heart beating. PVC increased contrast between ischemic and non-ischemic regions. The ratio between total LV activity estimates with and without PVC were 1.322±0.075, 1.376±0.076, and 1.297±0.052 for averaged, ED, and ES images, respectively. A Student t-test indicated no significant differences between the activity estimates for the averaged images and ED or ES images (P=0.21 and P=0.48, respectively). However, the difference was significant between the ED and ES phase images (P=0.04). The differences in BP activity estimates were not statistically significant.

Conclusions PVC at each cardiac phase greatly reduced PVEs, but there was no statistically significant difference between PVC on a single phase and averaged images. Those results indicate that, when gated data is not available, PVC using averaged images can still provide a substantial improvement in accuracy of myocardial activity estimates.