Phantom-based evaluation of yttrium-90 datasets using Biograph Vision Quadra

Abstract Purpose The image quality characteristics of a NEMA body phantom with yttrium-90 were evaluated on a total body PET/CT. The purpose of the study is to identify the optimized reconstruction setup for the imaging protocol of yttrium-90 radioembolization treatment on patients with malignant liver tumors. Methods Two NEMA IEC NU2 body phantoms were used for the study. One was filled with activity concentrations of 0.13 MBq/ml and 1.3 MBq/ml for the background and spheres respectively (ratio 1:10). The second one did not have any background concentration but had similar concentration for the spheres. Scan time was 50 minutes and the phantoms were positioned on the same bed and scanned simultaneously. The number of iterations varied from 2 up to 8 (5 subsets), the Gaussian filter from 2mm up to 6mm full-width-at-half-maximum. Images were reconstructed with a matrix of 440 x 440 and 220 x 220, with high sensitivity (HS) and ultra-high sensitivity (UHS) modes with the improved 3D scatter correction method. We simulated shorter acquisition times based on the list-mode data with 40, 30, 20, 10 and 5-minutes. The measurements included contrast recovery coefficients, signal-to-noise ratio, background variability and lung error. List mode data of a patient were rebinned in 1, 5, 10 and 20 minute time frames and evaluated. Results The recovery coefficient (RC) for the hot phantom was 0.36, 0.45, 0.53, 0.63, 0.68 and 0.84 for the spheres with diameters of 10, 13, 17, 22, 28, 37 mm respectively for UHS 2 iterations and a 220x220 matrix. The SNR was highest for 2 iterations, measured 11.7, 16.6, 17.6, 19.4, 21.9 and 27.7 and the lung error was 18%. The SNR was 19%, 20%, 24% and 31% higher for 2 iterations compared to 4 iterations for 20, 10, 5 and 1 minutes time frames respectively. Conclusions The long AFOV delivers images of Y-90 with the smallest sphere well visualized with a high RC. SNR for the patient data was maximum for 2 iterations and for 20-minutes acquisition while even 5-minutes acquisition time delivers images with no great loss of SNR (-20%). Further clinical investigation is recommended to check also the effects on post-treatment dosimetry validation.