Quantification and discriminative power of ¹⁸F-FE-PE2I PET in patients with Parkinson's disease

Dopamine transporter (DAT) imaging is an important adjunct in the diagnostic workup of patients with Parkinsonism. ¹⁸F-FE-PE2I is a suitable PET radioligand for DAT quantification and imaging with good pharmacokinetics. The aim of this study was to determine a clinical optimal simplified reference tissue-based image acquisition protocol and to compare the discriminatory value and effect size for ¹⁸F-FE-PE2I to that for ¹²³I-FP-CIT scan currently used in clinical practice.

Nine patients with early Parkinson's disease (PD, 64.3 ± 6.8 years, 3M), who had previously undergone a ¹²³I-FP-CIT scan as part of their diagnostic workup, and 34 healthy volunteers (HV, 47.7 ± 16.8 years, 13M) underwent a 60-min dynamic ¹⁸F-FE-PE2I PET-MR scan on a GE Signa 3T PET-MR. Based on dynamic data and MR-based VOI delineation, BP_ND, semi-quantitative uptake ratio and SUVR_[t1-t2] images were calculated using either occipital cortex or cerebellum as reference region. For start-and-end time of the SUVR interval, three time frames [t₁-t₂] were investigated: [15-40] min, [40-60] min, and [50-60] min postinjection. Data for putamen (PUT) and caudate nucleus-putamen ratio (CPR) were compared in terms of quantification bias versus BP_ND and discriminative power.

Using occipital cortex as reference region resulted in smaller bias of SUVR with respect to BP_ND + 1 and higher correlation between SUVR and BP_ND + 1 compared with using cerebellum, irrespective of SUVR [t₁-t₂] interval. Smallest bias was observed with the [15-40]-min time window, in accordance with previous literature. The correlation between BP_ND + 1 and SUVR was slightly better for the late time windows. Discriminant analysis between PD and HV using both PUT and CPR SUVRs showed an accuracy of ≥ 90%, for both reference regions and all studied time windows. Semi-quantitative ¹²³I-FP-CIT and ¹⁸F-FE-PE2I values and relative decrease in the striatum for patients were highly correlated, with a higher effect size for ¹⁸F-FE-PE2I for PUT and CPR SUVR.

¹⁸F-FE-PE2I is a suitable radioligand for in vivo DAT imaging with high discriminative power between early PD and healthy controls. Whereas a [15-40]-min window has lowest bias with respect to BP_ND, a [50-60]-min time window at pseudoequilibrium can be advocated in terms of clinical feasibility with optimal discriminative power. The occipital cortex may be slightly preferable as reference region because of the higher time stability, stronger correlation of SUVR with BP_ND + 1, and lower bias. Moreover, the data suggest that the diagnostic accuracy of a 10-min static ¹⁸F-FE-PE2I scan is non-inferior compared with ¹²³I-FP-CIT scan used in standard clinical practice.