Combined R2* and Diffusion Tensor Imaging Changes in the Substantia Nigra in Parkinson's Disease

Abstract

Recent magnetic resonance imaging studies suggest an increased transverse relaxation rate and reduced diffusion tensor imaging fractional anisotropy values in the substantia nigra in Parkinson's disease. The transverse relaxation rate and fractional anisotropy changes may reflect different aspects of Parkinson's disease-related pathological processes (ie, tissue iron deposition and microstructure disorganization). This study investigated the combined changes of transverse relaxation rate and fractional anisotropy in the substantia nigra in Parkinson's disease. High-resolution magnetic resonance imaging (T2-weighted, T2*, and diffusion tensor imaging) were obtained from 16 Parkinson's disease patients and 16 controls. Bilateral substantia nigras were delineated manually on T2-weighted images and coregistered to transverse relaxation rate and fractional anisotropy maps. The mean transverse relaxation rate and fractional anisotropy values in each substantia nigra were then calculated and compared between Parkinson's disease subjects and controls. Logistic regression, followed by receiver operating characteristic curve analysis, was employed to investigate the sensitivity and specificity of the combined measures for differentiating Parkinson's disease subjects from controls. Compared with controls, Parkinson's disease subjects demonstrated increased transverse relaxation rate (P<.0001) and reduced fractional anisotropy (P=.0365) in the substantia nigra. There was no significant correlation between transverse relaxation rate and fractional anisotropy values. Logistic regression analyses indicated that the combined use of transverse relaxation rate and fractional anisotropy values provides excellent discrimination between Parkinson's disease subjects and controls (c-statistic=0.996) compared with transverse relaxation rate (c-statistic=0.930) or fractional anisotropy (c-statistic=0.742) alone. This study shows that the combined use of transverse relaxation rate and fractional anisotropy measures in the substantia nigra of Parkinson's disease enhances sensitivity and specificity in differentiating Parkinson's disease from controls. Further studies are warranted to evaluate the pathophysiological correlations of these magnetic resonance imaging measurements and their effectiveness in assisting in diagnosing Parkinson's disease and following its progression.