Phantom study and clinical application of total-body ¹⁸F-FDG PET/CT imaging: How to use small voxel imaging better?

Background: Conventional PET/CT imaging reconstruction is typically performed using voxel size of 3.0-4.0 mm in three axes. It is hypothesized that a smaller voxel sizes could improve the accuracy of small lesion detection. This study aims to explore the advantages and conditions of small voxel imaging on clinical application. Methods: Both NEMA IQ phantom and 30 patients with an injected dose of 3.7 MBq/kg were scanned using a total-body PET/CT (uEXPLORER). Images were reconstructed using matrices of 192 x 192, 512 x 512, and 1024 x 1024 with scanning duration of 3 min, 5 min, 8 min, and 10 min, respectively. Results: In the phantom study, the contrast recovery coefficient reached the maximum in matrix group of 512 x 512, and background variability increased as voxel size decreased. In the clinical study, SUVmax, SD, and TLR increased, while SNR decreased as the voxel size decreased. When the scanning duration increased, SNR increased, while SUVmax, SD, and TLR decreased. The SUVmean was more reluctant to the changes in imaging matrix and scanning duration. The mean subjective scores for all 512 x 512 groups and 1024 x 1024 groups (scanning duration >= 8 min) were over three points. One false-positive lesion was found in groups of 512 x 512 with scanning duration of 3 min, 1024 x 1024 with 3 min and 5 min, respectively. Meanwhile, the false-negative lesions found in group of 192 x 192 with duration of 3 min and 5 min, 512 x 512 with 3 min and 1024 x 1024 with 3 min and 5 min were 5, 4, 1, 4, and 1, respectively. The reconstruction time and storage space occupation were significantly increased as the imaging matrix increased. Conclusions: PET/CT imaging with smaller voxel can improve SUVmax and TLR of lesions, which is advantageous for the diagnosis of small or hypometabolic lesions if with sufficient counts. With an F-18-FDG injection dose of 3.7 MBq/kg, uEXPLORER PET/CT imaging using matrix of 512 x 512 with 5 min or 1024 x 1024 with 8 min can meet the image requirements for clinical use.