Reconstruction of rapidly acquired Germanium-68 transmission scans for cardiac PET attenuation correction

Background: Transmission (TX) scan time by use of radionuclide sources for cardiac positron emission tomography prolong imaging and increase the likelihood of patient motion artifacts. A reconstruction algorithm combining ordered-subsets expectation maximization with a Bayesian prior was developed and applied to rapid Germanium-68 (Ge-68) TX scans. Methods and Results: A cardiac phantom with Fluorine-18 (Fl-18) was used to determine a minimal count threshold for Ge-68 TX scanning. Images were acquired over a count range from 2.5 × 10⁶ to 8 × 10⁷ and for a high-count scan of 1.6 × 10⁹ counts to study reconstruction parameters and to determine the minimum TX count threshold. The method was compared against clinical 4-minute TX scans in ten Rubidium-82 (Rb-82) rest/stress myocardial perfusion studies (body mass index, 30 ± 4 kg/m²). The minimal count threshold was 20 × 10⁶, and the mean scan time for the Rb-82 studies was 70.5 ± 3.4 seconds. More than 90% of the segmental scores computed from images acquired via rapid TX scans differed by less than 5% from those obtained with 4-minute TX scans. The mean differences in perfusion scores between the rapid and 4-minute TX scans were 0.46% (95% confidence interval, -1.84% to 0.93%) at rest and 0.39% (95% confidence interval, -1.84% to 1.07%) at stress, demonstrating equivalency of the rapid and 4-minute scans. Conclusions: Ordered-subsets expectation maximization with a Bayesian prior accurately and efficiently reconstructs rapidly acquired Ge-68 TX scans for Rb-82 myocardial perfusion positron emission tomography studies.