Isolated REM sleep behavior disorder (iRBD) is a precursor to Parkinsonism. Neuromelanin-sensitive MRI can identify neurodegenerative alterations in the substantia nigra pars compacta (SNc) in parkinsonism. Using completely automated segmentation, researchers investigated SNc neuromelanin alterations in iRBD patients.
They scanned at 3 Tesla 47 iRBD patients, 134 early Parkinson’s disease (PD) patients, and 55 healthy volunteers (HVs). Convolutional neural networks were used to automatically define SNc areas of interest. The SNc volumes, volumes adjusted for total intracranial volume, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were all calculated. Adjusting for age and gender, a one-way general linear models (GLM) analysis of covariance (ANCOVA) was performed.
All SNc readings were substantially different across the three groups (except SNR in iRBD). iRBD changes were intermediate between PD and HVs. Using a completely automated SNc segmentation approach and neuromelanin-sensitive imaging, iRBD patients had lower levels of neurodegenerative alterations in the SNc than PD patients.