To promote therapeutic treatment trials in Parkinson’s disease (PD), reliable and precise imaging biomarkers of dopaminergic cell neurodegeneration are required. Neurodegeneration in the substantia nigra pars compacta has been detected using neuromelanin-sensitive MRI methods (SNpc). For a study, researchers determined the changes in neuromelanin signaling in the SNpc over time in people with PD. They grouped 140 patients with PD and 64 healthy volunteers into two cohorts in this prospective, longitudinal, observational case-control research. Cohort I consisted of 99 early patients with PD (disease duration: 1.5 +1.0 years) and 41 healthy volunteers who were scanned at baseline (V1), followed by 79 patients with PD and 32 healthy volunteers after 2.0+ 0.2 years of follow-up (V2). At V1, 30 patients with PD were rescanned after 2.4 0.5 years of follow-up. Cohort II included 41 advancing patients with PD patients (disease duration, 9.3+ 3.7 years) and 23 healthy volunteers. Three-dimensional T1-weighted and neuromelanin-sensitive imaging were used to scan the subjects at 3 T MRI. To determine SN volumes, volumes adjusted by total intracranial volume, signal-to-noise ratio, and contrast-to-noise ratio, regions of interest were manually identified.

The findings revealed (1) a significant reduction in volume and volume corrected by total intracranial volume between visits, which was greater in progressing PD than nonsignificant changes in healthy volunteers; (2) no significant effects of visit for signal intensity (signal-to-noise ratio); and (3) a significant interaction in volume between group and visit; (4) Female patients had a higher volume corrected by total intracranial volume at baseline, as well as a higher decrease in volume and increase in the contrast-to-noise ratio in progressing patients with PD than male patients; and (5) correlations between neuromelanin SN changes and disease severity and duration.

Researchers found a gradual and quantifiable decline in neuromelanin-based SN signal and volume in people with Parkinson’s disease, which might allow for a non-invasive evaluation of SN loss and serve as a target biomarker for disease-modifying therapy.