Objectives: One possible cause for Parkinson’s disease (PD) is increased iron accumulation in the substantia nigra pars compacta (SNpc) which may lead to neurotoxic consequences such as oxidative damage and cell death. In this work, we apply, a standardized SNpc mask based on neuromelanin-sensitive (NM) MR images from healthy subjects, to elucidate region-specific iron deposition after PD onset. 

Methods: Thirty-nine PD patients were recruited from the movement disorder outpatient clinic as well as 33 age and gender matched healthy controls. All subjects were scanned on a 3T GE scanner. Both 3D multi-echo GRE sequence and whole brain anatomical images were acquired. R2 * values were calculated using a mono-exponential fit to the signal decay. The overlap probability between the whole SNpc volume defined by the NM sensitive and R2 * hyperintense SN were used to evaluate the iron deposition. Diagnostic performance of R2 * values in the SNpc overlap volume and the SNpc overlap percentage was performed using a receiver operating characteristics (ROC) analysis. 

Results: The SNpc overlap volume corresponds to similar regions in SNpc showing reduced NM-sensitive contrast, and presumably NM depletion specifically in the lateral ventral tier. Significant R2 * increases were seen in PD in the SNpc overlap volume (p=0.03). The SNpc overlap percentage was significantly increased in PD patients compared to controls (p<0.001). The SNpc overlap volume R2 * (r=0.420; p=0.008) was positively correlated with disease duration in PD patients. ROC analysis of R2 * in the SNpc overlap volume and the SNpc overlap percentage in PD and controls found an area under the curve (AUC) of 0.661 (P=0.021), and 0.927 (P<0.001), respectively. 

Conclusion: We found an excellent diagnostic accuracy for the SNpc overlap percentage in PD. This SNpc overlap percentage applied here may represent a promising tool to investigate the nigral PD biology in vivo.