Late Breaking Abstracts

Abstract

Objectives: PET system with silicon photomultiplier (SiPM) has been developed and clinically available. The Biograph Vision is the third commercial SiPM-based PET/ CT system, which introduces SiPM and 3.2 mm lutetium oxyorthosilicate (LSO) crystal. We aimed to optimize reconstruction parameters for brain PET scans with the Biograph Vision. Methods: A PET scan with Hoffman brain phantom injected with [ 18 F]FDG was performed during 30 minutes. The acquired phantom data was reconstructed by ordered subset expectation maximization (OSEM) algorithm applying with time-of-flight (TOF) and point spread function (PSF) correction [OSEMþTOFþPSF]. Reconstruction by OSEM with TOF without PSF correction [OSEMþTOF] and filtered back projection (FBP) with TOF [FBPþTOF] were also performed. Iteration for OSEM was varied by 1 to 30. Post reconstruction Gaussian filter was also varied by 0, 3, 5 mm full width half maximum (FWHM) for OSEMþTOF and FBPþTOF. Subset for OSEM was fixed to 5. Image matrix and voxel sizes of reconstructed image were 440 x 440 x 159 voxels and 0.825 x 0.825 x 1.646 mm, 3 respectively. To evaluate contrast and variability, regions of interest (ROI) were manually drawn on gray matter (GM), white matter (WM) and centrum semiovale (CS). The GM/WM contrast was calculated with {(radioactivity concentration on GM)/ (radioactivity concentration on WM)-1} * 100%. The coefficient of variability (CV) was calculated with (standard deviation in CS)/ (radioactivity concentration on CS) * 100%. To test the optimized reconstruction parameters for actual brain PET scans, [ 18 F]FDG brain PET data acquired with a healthy volunteer was also reconstructed by OSEMþTOFþPSF, OSEMþTOF and FBPþTOF with the optimized parameters. Results: Higher GM/WM contrast was observed in images reconstructed by OSEMþTOFþPSF than OSEMþ TOF and FBPþTOF. The highest contrast was observed with OSEMþTOFþPSF, iteration 8. OSEMþTOF with 3 mm FWHM post filter resulted in lower CV than other algorithms. OSEMþTOFþPSF with iteration 4 and subset 5 approached the ideal condition (100% contrast and 0% CV) the best among all conditions. The brain [ 18 F]FDG images for the healthy volunteer, reconstructed with the optimized parameters, were shown in Figure. Apparently higher contrast with OSEMþTOFþPSF was observed than the other algorithms. However, unnaturally high activities on edges in the images reconstructed by OSEMþTOFþPSF, such as Gibbs artifacts, were also observed (see white arrow in Figure). Conclusion: OSEMþTOFþPSF for data acquired with the Biograph Vision can achieve much high contrast brain PET images. Further study to investigate the artifacts due to PSF correction is required for quantitative brain PET studies.