Reproducibility of ^99mTc-TRODAT-1 SPECT measurement of dopamine transporters in Parkinson's disease

Functional brain imaging targeting the presynaptic dopamine nerve terminal of the nigrostriatal system has been used for monitoring disease progression and evaluating therapeutic effectiveness in patients with Parkinson's disease (PD). ^99mTc-TRODAT-1 binds with high selectivity to the dopamine transporters in the striatum and can be imaged with SPECT 4 h after injection. We studied the test and retest reproducibility of ^99mTc-TRODAT-1 SPECT measures in patients with PD to assess the reliability of ^99mTc-TRODAT-1 for longitudinal evaluation of the nigrostriatal dopaminergic function. Methods: Each of 20 patients with PD underwent 2 ^99mTc-TRODAT-1 SPECT scans at an interval of 2-3 wk. Patients were imaged 4 h after injection of 925 MBq ^99mTc-TRODAT-1. Two imaging outcome measures were evaluated: the ratio of specific-striatal-to-nonspecific uptake and the striatal asymmetry index. For both measures, the test/retest variability was calculated. Reproducibility of the 2 outcome measures was evaluated in terms of intraclass correlation coefficient (ICC) and 95% limits of agreement. Results: The mean ratio of specific-striatal-to-nonspecific uptake showed excellent test/retest reproducibility with a mean variability of 10.20%, an ICC of 0.95 (95% confidence interval = 0.88-0.98), and 95% limits of agreement, ranging from -0.19 to 0.19. The striatal asymmetry index had larger test/retest variability (60.41%), a slightly smaller ICC of 0.86 (95% confidence interval = 0.65-0.95), and a wider range of 95% limits of agreement (-16.09 to 15.19). In addition, there was a significant negative correlation between the mean ratio of specific-striatal-to-nonspecific uptake and the motor subscore of the Unified Parkinson's Disease Rating Scale in both test and retest conditions. Conclusion: Our data indicate that the imaging outcome expressed by the mean ratio of specific-striatal-to-nonspecific uptake has an excellent test/retest reproducibility and correlates with disease severity. These findings suggest that ^99mTc-TRODAT-1 SPECT imaging is useful and feasible for measuring disease progression in PD.