Benefit of time-of-flight reconstruction for cardiac PET of obese patients

Objectives The benefit of time-of-flight (TOF) PET is well established for oncology studies by improving signal-to-noise and enhancing lesion detection. The benefit of TOF for cardiac PET is less certain because tracer uptake and study interpretation differ substantially from oncology PET. We investigate the impact of TOF on myocardial Rb-82 distribution and perfusion scores with a focus on the most challenging cases of obese patients.

Methods Rb-82 cardiac PET data of ten obese patients (range 110 to 191 kg, mean 137 kg) and F-18 phantom data were reconstructed with and without TOF information and with varying number of iterative updates (2 to 12 iterations, 21 subsets). Convergence and clinical relevance of differences were assessed both visually and quantitatively (automated 17-segment scoring).

Results TOF imaging provided significant improvement in image quality and convergence rate compared to non-TOF imaging. TOF reconstruction typically required 2 to 4 iterations to converge versus 8 to 12 iterations for non-TOF reconstruction, improving the signal-to-noise and accuracy of myocardial perfusion images. Even at 12 iterations (highest setting available on the scanner workstation), non-TOF images often had segmental differences in relative perfusion exceeding 10 percent compared to TOF images that were considered likely to affect clinical interpretation. Differences in summed perfusion scores ranged from 0 to 8 (mean 2.9). The locations of these artifacts related to non-TOF reconstruction depended on the patient’s anatomy and attenuation.

Conclusions TOF reconstruction has a significant clinical impact for Rb-82 cardiac PET of obese patients. When interpreting cardiac studies from non-TOF-capable PET scanners, one must ensure to reconstruct images with sufficient iterations and to account for potential residual artifacts.