Pharmacokinetic modeling of 18F-FDOPA PET in human brain for early Parkinson’s disease

INTRODUCTION: Early detection is essential for the treatment approaches of Parkinson’s disease (PD). Clinical criteria alone may not be sufficient to distinguish the early PD from other conditions. This study aimed to investigate the transfer rate constants of 6-18F-fluoro-L-dopa (18F-FDOPA) in positron emission tomography (PET) brain images as a sensitive parameter to detect early PD.
METHODS: Retrospective 18F-FDOPA PET data of five patients with early PD were collected. PET data were acquired for 90 min after an intravenous injection of 306-379 MBq 18F-FDOPA, and reconstructed into a series of 18 five minute frames. Reoriented PET images were co-registered and normalized with the PET brain template on the Statistical Parametric Mapping (SPM). The 18F-FDOPA activity concentrations were measured in the striatum, the caudate and the putamen on both sides: contralateral (as PD) and ipsilateral (as control) to the main motor symptoms. The pharmacokinetic (PK) model, based on Wahl and Nahmias, was generated using the SAAM II simulation software. The transfer rate constants across the blood brain barrier (froward, K1 and reverse, k2) and decarboxylation rate constant (k3) were estimated in these regions.
RESULTS: The activity uptakes in the contralateral striatum (0.0323 ± 0.0091%) and putamen (0.0169 ± 0.0054%) were significantly lower than control (0.0353 ± 0.0086%, 0.0199 ± 0.0054%, respectively). The K1 and k3 were significantly lower in the contralateral striatum and putamen (p<0.05). There were no significant differences in any transfer rate constants in the caudate.
DISCUSSION AND CONCLUSION: The transfer rate constants (K1 and k3) of 18F-FDOPA on the contralateral striatum and putamen were significantly lower than control. These biokinetic data could be potential indicators for quantitative detection of early PD diagnosis.