Impact of clinical factors on reproducibility of dopamine transporter imaging: A 99mTc-TRODAT SPECT study with sufficient size

Objective

Reproducible measurement of dopamine transporter (DAT) availability is crucial for research investigating group differences or within-subject changes. However, existing DAT imaging test-retest studies are limited by short between-session intervals, restricted participant representativeness, and small sample sizes.

Methods

Fifty-seven healthy subjects (27 female, 30 male) underwent two 99mTc-TRODAT SPECT scans to assess DAT availability, with between-session intervals ranging from 18 to 129 days. We calculated intraclass correlation coefficient (ICC) for reliability, and within-subject coefficient of variation (WSCV) and absolute variability (absVAR) for repeatability. The influence of outliers, between-session intervals, participant characteristics, and sample size on these metrics was evaluated.

Results

The ICC values ranged from 0.73 to 0.80 with good precision (± 0.11). The values of WSCV (%) and coefficient of variation (COV) (%) ranged from 5.7 % to 7.9 % and 12.8 % to 15.2 %, respectively. Reporting both WSCV and COV values is crucial for interpreting ICC values and their applications. Exclusion of six outliers slightly improved reliability but not statistically significant. Longer between-session intervals (using a 42-day cutoff) did not significantly reduce ICC values. Similarly, age, sex, and body mass index did not significantly impact reliability or repeatability. Importantly, small sample sizes were found to potentially overestimate ICC values.

Conclusion

This study demonstrates the robust reproducibility of 99mTc-TRODAT SPECT for measuring DAT availability, supporting its use in clinical research and addressing limitations of previous reproducibility studies of DAT imaging. These findings emphasize the importance of reporting appropriate repeatability and reliability indices and employing adequate sample sizes in future test-retest studies.