Clinical evaluation of whole-body oncologic PET with time-of-flight and point-spread function for the hybrid PET/MR system

Purpose: Hybrid positron emission tomography/magnetic resonance (PET/MR) imaging is a new multimodality imaging technology that can provide structural and functional information simultaneously. The aim of this study was to investigate the effects of the time-of-flight (TOF) and point-spread function (PSF) on small lesions observed in PET/MR images from clinical patient image sets. Materials and methods: This study evaluated 54 small lesions in 14 patients who had undergone F-18-fluorodeoxyglucose (FDG) PET/MR. Lesions up to 30 mm in diameter were included. The PET data were reconstructed with a baseline ordered-subsets expectation-maximization (OSEM) algorithm, OSEM + PSF, OSEM + TOF and OSEM + TOF + PSF. PET image quality and small lesions were visually evaluated and scored by a 3-point scale. A quantitative analysis was then performed using the mean and maximum standardized uptake value (SUV) of the small lesions (SUVmean and SUVmax). The lesions were divided into two groups according to the long-axis diameter and the location respectively and evaluated with each reconstruction algorithm. We also evaluated the background signal by analyzing the SUVliver. Results: OSEM + TOF + PSF provided the highest value and OSEM + TOF or PSF showed a higher value than OSEM for the visual assessment and quantitative analysis. The combination of TOF and PSF increased the SUVmean by 26.6% and the SUVmax by 30.0%. The SUV(liver)was not influenced by PSF or TOF. For the OSEM + TOF + PSF model, the change in SUVmean and SUVmax for lesions < 10 mm in diameter was 31.9% and 35.8%, and 24.5% and 27.6% for lesions 10-30 mm in diameter, respectively. The abdominal lesions obtained the higher SUV than those of chest on the images with TOF and/or PSF. Conclusion: Application of TOF and PSF significantly increased the SUV of small lesions in hybrid PET/MR images, potentially improving small lesion detectability.