Improved Overall Image Quality and Lesion Detectability Enabled by High Definition 2mm Voxel Reconstruction: An Intra-individual Comparison Study in Whole Body FDG PET/CT

619 Objectives Current generation clinical PET/CT is routinely reconstructed using 4 or 3 mm voxel length volume leading to 144x144 to 288x288 matrix sizes for the standard field of view. This has not changed nearly over the last decade despite many other PET system improvements. With the availability of GPU based reconstruction systems larger reconstruction matrix with smaller voxel volumes have become clinically feasible. Therefore, we investigated if differences in overall image quality and lesion detectability can be observed by an intra-individual comparison of the system default 4x4x4 mm3 voxel volume reconstruction and a previously optimized 2x2x2 mm3 approach in a population of patients enrolled in a breast cancer therapy response assessment trial. Methods 36 list-mode acquired FDG PET/CT studies performed within a clinical response assessment in 13 patients performed using a Gemini 64 TF, Astonish PET/CT (576 mm FOV) were reconstructed using 4 mm 3i33s (144x144 matrix, 64 mm3 voxel volume) and with 2 mm isotropic voxel datasets using previously optimized 15 subsets with 3 iterations (288x288 matrix, 8 mm3 voxel volume). Overall image quality was assessed by blinded readers using a preference scale for individual blinded case assessment as well as for the blinded matched pair comparison. As the patients were enrolled within a therapy trial of metastatic recurrent disease, conventional RECIST assessment was not enabling enough insight into lesion detectability, however was performed. Using a blinded matched pair comparison, the readers were asked to review similar to a baseline follow up comparison and identify if lesions could be better identified at one or the other image set, what the reader preference is and the level of confidence. All findings were tabulated and statistical assessment performed after correction for multiple comparisons. Results Blinded, independent reads found in 85% of the cases a significant (p<.01) improvement in whole body image quality using the optimized 2mm voxel length (64 vs 8 mm3 voxel volume) reconstruction; 15% were rated equivalent and none was rated inferior. The image quality improvement was most commonly described as crisper, sharper, better delineated and better visualization of lesion heterogeneity. As a side note, if non optimized recon setting were used, all 2mm recons were rated noisier, validating that the recon parameter settings have to be optimized when major changes in voxel size and thus relative count density occur. In 2/3 of the cases (p Conclusions Smaller voxel, higher definition optimized reconstruction improves significantly overall PET image quality as well as lesion detectability. This study should encourage the utilization of smaller voxel reconstruction in today’s clinical PET systems that should lead to considerable improvement of image quality and diagnostic impact. Current generation system should increasingly support advanced reconstruction approaches similar to the vast improvements we have seen on CT in the recent years.