Comprehensive Evaluation of the effects of Time-of-flight Technique on Regional Brain PET using Hybrid PET/MRI

Abstract

Background The purpose of this study was to evaluate the effects of time-of-flight (TOF) reconstruction on regional brain positron emission tomography (PET) obtained from hybrid PET/magnetic resonance imaging (PET/MRI). Patients (n = 34) who underwent 18F-FDG PET/MRI brain imaging were retrospectively included in this study. The PET list mode data were reconstructed with and without a TOF reconstruction algorithm. Regional brain volumes of interest (VOIs, 18 regions) were segmented and their standardized uptake values (SUVs) were measured. Standard formulas were applied to measure contrast, signal to noise ratio (SNR), and percentage relative average difference of SUVs (%RAD-SUVs). The results were compared using paired t-tests. Results In all the VOIs, the SUVmax was significantly higher with TOF reconstruction than without it. The %RAD-SUVmax was greater than 3% for all VOIs in TOF compared to non-TOF reconstructions, and was largest in the caudate nuclei. The SUVmean values in 14/18 VOIs were significantly higher with TOF reconstruction, although the %RAD-SUVmean values were comparably smaller than the %RAD-SUVmax. The highest %RAD-SUVmean between TOF and non-TOF reconstruction was again in the caudate nuclei. Contrast and SNR were higher with TOF reconstruction in 12/17 and 9/17 VOIs, respectively. Although the differences were small, they almost showed statistical significance (p < 0.05). In the caudate nuclei, the percentage difference in SNR was nearly 50%. However, in the PA, SN, CoC, WM and CM, contrast was higher with non-TOF reconstruction, and SNR was higher in regions adjoining occipital lobe and nucleus accumbens. Conclusions With the TOF-technique, the SUVmax in the segmented VOIs was higher compared with non-TOF reconstruction, unlike SUVmean, which showed varying differences across the different VOIs according to the use of TOF and non-TOF reconstruction. The temporal lobe and caudate nucleus achieved considerably higher SNR with the TOF technique, but not the other regions. Overall, we recommend that these quantitative differences among VOIs are considered when diagnosing Alzheimer’s disease and Parkinson’s disease.