Comparison of different methods to evaluate and quantify defects of dopamine transporters using 123I FP-CIT

Objectives: Several studies have demonstrated the capability of 123I-FPCIT SPECT for studying dopamine transporters in patients with movement disorders. Different techniques have been suggested for semi-quantitative measurement of 123I-FPCIT uptake, based on specific to non specific ratio at equilibrium. Aim of this study was to compare the results of different methods of evaluation. Methods: We performed 123I-FPCIT SPECT scan in 12 patients with Parkinson's disease (PD) and in 3 patients with essential tremor (ET). Images were analysed using 3 different methods: a) visual analysis (0=normal; 0.5=near normal, minimal abnormalities; 1=mild reduced uptake at one or both putamen; 2=severely reduced uptake at both putamen; 3=reduced uptake at caudate and putamen); b) large rectangular ROIs (including entire striatum); c) small irregular ROIs (manually drawn; different for putamen and caudate nucleus). All evaluations were carried out by 3 different operators. Results: Visual analysis and large rectangular ROIs showed the higher reproducibility, while small irregular ROIs were found more affected by operator-dependency. Visual analysis resulted very effective in distinguishing between PD and ET (given 1-3 scores as PD we had 15/15 correct diagnosis); large rectangular ROIs failed in several cases (using a 50% value as cut-off point we had 7/12 correct diagnosis of PE and 3/3 correct diagnosis of ET); small ROIs did not allow to identify a cut-off value enabling to effectively distinguish PD and ET. Conclusions: Reliability and reproducibility of a technique to evaluate 123I-FPCIT SPECT is crucial for its application in routine clinical studies. Our data indicate visual analysis as the more effective method, while the use of approaches based on ROIs, although enabling a semi-quantitative evaluation of defects, were not successful for differential diagnosis. Large ROIs approach was limited by the fact that many PD patients showed a normal uptake at caudate nuclei that increased overall values for ratio. Small ROIs technique was significantly operator dependent, probably due to the small dimensions of analysed structures