Optimal acquisition time window for quantification of dopamine transporter availability with [¹⁸F]FE-PE2I in controls and PD patients

Objectives [¹⁸F]FE-PE2I is a novel PET radioligand for imaging of the dopamine transporter (DAT). Noninvasive methods for DAT quantification using [¹⁸F]FE-PE2I rely on dynamic acquisitions, but a simplified protocol is preferable in a clinical setting. The aim of the study was to identify an optimal acquisition time window for simplified DAT quantification using [¹⁸F]FE-PE2I in control subjects (CS) and Parkinson’s disease (PD) patients.

Methods 10 CS and 10 PD patients were examined with [¹⁸F]FE-PE2I (HRRT, 93 min). ROIs for caudate (CAU), putamen (PUT), ventral striatum (VS), substantia nigra (SN) and cerebellum (CER) were drawn on co-registered MRI. Binding potentials (BP_ND) were obtained using wavelet-aided parametric imaging (WAPI), and specific binding ratios (SBR) were calculated using several time intervals, with CER as reference region. The time window that resulted in the highest correlation between BP_ND and SBR was used to create a mean image on which new SBR values were calculated. Effect sizes of SBR and BP_ND were calculated to assess differences between CS and PD patients.

Results The SBR values that correlated best to BP_ND were obtained for the time window between 16.5 and 42 min. A significant correlation between BP_ND and SBR was observed for CS (R² =0.96) and PD patients (R²= 0.98). In the striatum, SBR values underestimated BP_ND by 18%±2% in CS and by 11%±4% in PD patients. In the SN, SBR overestimated BP_ND by 5% in CS and by 11% in PD patients. Similar effect sizes for BP_ND and SBR were found in CAU (both 0.6), PUT (1.7 and 1.5), VS (both 0.7), and SN (0.5 and 0.4).

Conclusions The optimal acquisition time window for simplified DAT quantification using [¹⁸F]FE-PE2I is between 16.5 and 42 min. Despite underestimation of BP_ND in high density regions, the SBR can be viewed as a valid quantification method for DAT using [¹⁸F]FE-PE2I, since it provides similar differentiation as BP_ND between CS and PD patients.

Research Support Swedish Foundation for Strategic Research