Impact of TOF on Brain PET With Short-Lived (11)C-Labeled Tracers Among Suspected Patients With AD/PD: Using Hybrid PET/MRI

OBJECTIVE: To explore the impact of the time-of-flight (TOF) reconstruction on brain PET with short-lived (11)C-labeled tracers in PET magnetic resonance (PET/MR) brain images among suspected patients with Alzheimer's and Parkinson's disease (AD/PD). METHODS: Patients who underwent (11)C-2-ß-carbomethoxy-3-b-(4-fluorophenyl) tropane ((11)C-CFT) and 2-(4-N-[(11)C] methylaminophenyl)-6-hydroxybenzothiazole ((11)C-PiB) PET/MRI were retrospectively included in the study. Each PET LIST mode data were reconstructed with and without the TOF reconstruction algorithm. Standard uptake values (SUVs) of Caudate Nucleus (CN), Putamen (PU), and Whole-brain (WB) were measured. TOF and non-TOF SUVs were assessed by using paired t-test. Standard formulas were applied to measure contrast, signal-to-noise ratio (SNR), and percentage relative average difference of SUVs (%RAD-SUVs). RESULTS: Total 75 patients were included with the median age (years) and body mass index (BMI-kg/m(2)) of 60.2 ± 10.9 years and 23.9 ± 3.7 kg/m(2) in (11)C-CFT (n = 41) and 62.2 ± 6.8 years and 24.7 ± 2.9 kg/m(2) in (11)C-PiB (n = 34), respectively. Higher average SUVs and positive %RAD-SUVs were observed in CN and PU in TOF compared with non-TOF reconstructions for the two (11)C-labeled radiotracers. Differences of SUV(mean) were significant (p < 0.05) in CN and PU for both (11)C-labeled radiotracers. SUV(max) was enhanced significantly in CN and PU for (11)C-CFT and CN for (11)C-PiB, but not in PU. Significant contrast enhancement was observed in PU for both (11)C-labeled radiotracers, whereas SNR gain was significant in PU, only for (11)C-PiB in TOF reconstruction. CONCLUSION: Time-of-flight leads to a better signal vs. noise trade-off than non-TOF in (11)C-labeled tracers between CN and PU, improving the SUVs, contrast, and SNR, which were valuable for reducing injected radiation dose. Improved timing resolution aided the rapid decay rate of short-lived (11)C-labeled tracers, and it shortened the scan time, increasing the patient comfort, and reducing the motion artifact among patients with AD/PD. However, one should adopt the combined TOF algorithm with caution for the quantitative analysis because it has different effects on the SUV(max), contrast, and SNR of different brain regions.