I-123 DaTscan SPECT Brain Imaging in Parkinsonian Syndromes: Utility of the Putamen-to-Caudate Ratio

Computer-based analysis of Dopamine transporter imaging (DaTscan) can aid in image interpretation. In this study, we examined the distribution of putamen-to-caudate ratios (PCRs) obtained by using a clinically available semiquantification method.

Medical records of 32 patients (M:16) with a diagnosis of Parkinson's disease (PD) (n = 22) or Parkinson's plus syndromes (PPS) (n = 10) based on clinical follow-up, were retrospectively reviewed. Single photon emission tomography (SPECT) imaging was performed 4 hours after intravenous injection of 3-5 mCi [I-123]-ioflupane. Semiquantitative evaluation using DaTQUANT software was performed. Utility of PCR with a cutoff of .7 and .8 in the diagnosis of nigrostriatal degeneration was assessed. PD and PPS groups based on clinical assessment and caudate-to-background ratio (CBR) were assessed separately.

Minimum PCR for both hemispheres was .74 ± .09 (Mean ± SD, range: .58-.89), with 65.63% patients (21/32) having PCR > .7. Mean PCR in mild nigrostriatal degeneration was .77 ± .08 (range: .62-.89) and in advanced nigrostriatal degeneration was .73 ± .09 (range: .58-.89). Mean PCR in PD group was .73 ± .09 (range: .58-.89) and in PPS group was .75 ± .10 (range: .61-.88).

Although PCR can intrinsically be a useful indication of disease, this ratio obtained in our analysis by using one of the clinically available automatic semiquantitative methods has large variability and might not be a reliable numeric marker in interpretation of [I-123]ioflupane studies. This may be due to difficulty in separating caudate from putamen on SPECT images, as well as the nonuniform decreased Ioflupane uptake in both putamen and caudate.