Optimal scanning time window for 18F-FP-(+)-DTBZ (18F-AV-133) summed uptake measurements

(18)F-9-fluoropropyl-(+)-dihydrotetrabenazine ((18)F-AV-133) is a novel positron emission tomography tracer for imaging the vesicular monoamine transporter II in dopaminergic neuron degeneration, which might be indicative for Parkinson's disease (PD) and other parkinsonism. Studies were performed to optimize the imaging time window for calculating standardized uptake value ratio (SUVR) with correlation to distribution volume ratio (DVR) and in differentiating PD from normal controls (NCs).

Methods: Thirteen (18)F-AV-133 positron emission tomography studies were conducted on four NCs (age, 62.3±4.9 years) and nine PD patients (age, 60.8±6.0 years) with Hoehn and Yahr stages 2 to 3. Dynamic images were acquired within 180 min (0-30, 50-140 and 160-180 min) and were rearranged into 14 of 10-min scans. The contralateral striatum was defined as the opposite striatum to the predominantly affected limbs. Volumes of interest (VOIs) of bilateral putamen, caudate nuclei and occipital cortex (OC; as the reference region) were delineated from individual magnetic resonance imaging. SUVRs of striatum to OC were computed from 14 dynamic image sets. The DVRs were computed from Logan graphic analysis by using OC as the input. The performance of SUVR was evaluated based on the correlation of SUVR at each time window to DVR, as well as the Cohen effect size (group mean SUVR difference between PD and NC/standard deviation).

Results: (18)F-AV-133 uptake decreased in PD subjects at bilateral striatum especially at contralateral side with posterior putamen predominant as compared with NC. Consistent higher correlations of SUVRs to DVR for all VOIs were observed at later time window and reached to its maximal value of 0.9917 at 90-100 min. The group mean SUVR differences between NC and PD subjects increased and reached relatively stable values after 90 min. The effect sizes for all VOIs were stable across different time window and with the largest value around 90~120 min.

Conclusion: The scanning time of 90-100 min for (18)F-AV-133 is considered as the optimal time window for summed uptake measurements in terms of SUVRs' correlation to DVRs, differential power, stability and clinical feasibility across and between NC and PD patients.