Combined Striatal Binding and Cerebral Influx Analysis of Dynamic ^sup 11^C-Raclopride PET Improves Early Differentiation Between Multiple-System Atrophy and Parkinson Disease

Striatal dopamine D^sub 2^ receptor (D2R) PET has been proposed to differentiate between Parkinson disease (PD) and multiple-system atrophy with predominant parkinsonism (MSA-P). However, considerable overlap in striatal D^sub 2^ binding may exist between PD and MSA-P. It has been shown that imaging of neuronal activity, as determined by metabolism or perfusion, can also help distinguish PD from MSA-P. We investigated whether the differential diagnostic value of ^sup 11^C-raclopride PET could be improved by dynamic scan analysis combining D2R binding and regional tracer influx. Methods: ^sup 11^C-raclopride PET was performed in 9 MSA-P patients (mean age ± SD, 56.2 ± 10.2 y; disease duration, 2.9 ± 0.8 y; median Hoehn-Yahr score, 3), 10 PD patients (mean age ± SD, 65.7 ± 8.1 y; disease duration, 3.3 ± 1.5 y; median Hoehn-Yahr score, 1.5), and 10 healthy controls (mean age ± SD, 61.6 ± 6.5 y). Diagnosis was obtained after prolonged follow-up (MSA-P, 5.5 ± 2.0 y; PD, 6.0 ± 2.3 y) using validated clinical criteria. Spatially normalized parametric images of binding potential (BP) and local influx ratio (R^sub 1^ = K^sub 1^/K'^sub 1^) of ^sup 11^C-raclopride were obtained using a voxelwise reference tissue model with occipital cortex as reference region. Stepwise forward discriminant analysis with cross-validation, with and without the inclusion of regional R^sub 1^ values, was performed using a predefined volume-of-interest template. Results: Using conventional BP values, we correctly classified 65.5% (all values given with cross-validation) of 29 cases only. The combination of BP and R^sub 1^ information increased discrimination accuracy to 79.3%. When healthy controls were not included and patients only were considered, BP information alone discriminated PD and MSA-P in 84.2% of cases, but the combination with R^sub 1^ data increased accuracy to 100%. Conclusion: Discriminant analysis using combined striatal D2R BP and cerebral influx ratio information of a single dynamic ^sup 11^C-raclopride PET scan distinguishes MSA-P and PD patients with high accuracy and is superior to conventional methods of striatal D2R binding analysis. [PUBLICATION ABSTRACT]