Practical benefit of [¹²³I]FP-CIT SPET in the demonstration of the dopaminergic deficit in Parkinson's disease

Abstract

Loss of striatal dopamine (DA) transporters in Parkinson's disease (PD) has been accurately assessed in vivo by single-photon emission tomography (SPET) studies using [¹²³I]β-CIT. However, these studies have also shown that adequate imaging of the striatal DA transporter content can be performed only 20–30 h following the injection of [¹²³I]β-CIT, which is not convenient for routine out-patient evaluations. Recently, a new ligand,N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)tropane (FP-CIT), became available for in vivo imaging of the DA transporter. The faster kinetics of [¹²³I]FP-CIT have been shown to allow adequate acquisition as early as 3 h following injection. In the present study, loss of striatal DA transporters in five non-medicated PD patients was assessed on two consecutive SPET scans, one with [¹²³I]β-CIT (24 h following injection) and one with [¹²³I]FP-CIT (3 h following injection). The ratios of specific to non-specific [¹²³I]FP-CIT uptake in the caudate nucleus and putamen were consistently 2.5-fold lower than those of [¹²³I]β-CIT. However, when the uptake ratio of both ligands in these brain regions of patients was expressed as a percentage of the uptake ratio found in healthy controls, both the decrease and the variation of the data were similar. It is concluded on the basis of these findings that [¹²³I]FP-CIT seems as good as [¹²³I]β-CIT for the assessment of the dopaminergic deficit in PD. The faster kinetics of [¹²³I]FP-CIT are a clear advantage.