Impact of penalizing factor in a block-sequential regularized expectation maximization reconstruction algorithm for 18F-fluorocholine PET-CT regarding image quality and interpretation

BackgroundRecently, the block-sequential regularized expectation maximization (BSREM) reconstruction algorithm was commercially introduced (Q.Clear, GE Healthcare, Milwaukee, WI, USA). However, the combination of noise-penalizing factor (), acquisition time, and administered activity for optimal image quality has not been established for F-18-fluorocholine (FCH). The aim was to compare image quality and diagnostic performance of different reconstruction protocols for patients with prostate cancer being examined with F-18-FCH on a silicon photomultiplier-based PET-CT. Thirteen patients were included, injected with 4MBq/kg, and images were acquired after 1h. Images were reconstructed with frame durations of 1.0, 1.5, and 2.0min using of 150, 200, 300, 400, 500, and 550. An ordered subset expectation maximization (OSEM) reconstruction with a frame duration of 2.0min was used for comparison. Images were quantitatively analyzed regarding standardized uptake values (SUV) in metastatic lymph nodes, local background, and muscle to obtain contrast-to-noise ratios (CNR) as well as the noise level in muscle. Images were analyzed regarding image quality and number of metastatic lymph nodes by two nuclear medicine physicians.ResultsThe highest median CNR was found for BSREM with a of 300 and a frame duration of 2.0min. The OSEM reconstruction had the lowest median CNR. Both the noise level and lesion SUVmax decreased with increasing . For a frame duration of 1.5min, the median quality score was highest for 400-500, and for a frame duration of 2.0min the score was highest for 300-500. There was no statistically significant difference in the number of suspected lymph node metastases between the different image series for one of the physicians, and for the other physician the number of lymph nodes differed only for one combination of image series.ConclusionsTo achieve acceptable image quality at 4MBq/kg F-18-FCH, we propose using a of 400-550 with a frame duration of 1.5min. The lower should be used if a high CNR is desired and the higher if a low noise level is important.