Microstructural abnormalities of substantia nigra in Parkinson's disease: A neuromelanin sensitive MRI atlas based study

Abstract

Microstructural changes associated with degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNc) in Parkinson's disease (PD) have been studied using Diffusion Tensor Imaging (DTI). However, these studies show inconsistent results, mainly due to methodological variations in delineation of SNc. To mitigate this, our work aims to construct a probabilistic atlas of SNc based on a 3D Neuromelanin Sensitive MRI (NMS‐MRI) sequence and demonstrate its applicability to investigate microstructural changes on a large dataset of PD. Using manual segmentation and deformable registration we created a novel SNc atlas in the MNI space using NMS‐MRI sequences of 27 healthy controls (HC). We first quantitatively evaluated this atlas and then employed it to investigate the micro‐structural abnormalities in SNc using diffusion MRI from 133 patients with PD and 99 HCs. Our results demonstrated significant increase in diffusivity with no changes in anisotropy. In addition, we also observed an asymmetry of the diffusion metrics with a higher diffusivity and lower anisotropy in the left SNc than the right. Finally, a multivariate classifier based on SNc diffusion features could delineate patients with PD with an average accuracy of 71.7%. Overall, from this work we establish a normative baseline for the SNc region of interest using NMS‐MRI while the application on PD data emphasizes on the contribution of diffusivity measures rather than anisotropy of white matter in PD.

Longitudinal Changes in Neuromelanin MRI Signal in Parkinson's Disease: A Progression Marker

“…Automated methods may improve the reproducibility of segmentation techniques. 74 , 75 , 76 , 77 Manual segmentation has the advantage of allowing careful quality control of images and removal of areas containing artifacts from measurements. Experienced raters can achieve good reproducibility of measurements, as it was in our case, in line with those reported in previous studies.…”

“…First, we used manual segmentation to delineate the SN. Automated methods may improve the reproducibility of segmentation techniques 74‐77 . Manual segmentation has the advantage of allowing careful quality control of images and removal of areas containing artifacts from measurements.…”

Neuroimaging Advances in Parkinson's Disease and Atypical Parkinsonian Syndromes

“…Combined analysis of diffusion parameters and apparent transverse relaxation rates was found to be superior in differentiating PD vs. MSA-P (sensitivity 97%, specificity 100%, positive predictive value [PPV] 100%, negative predictive value [NPV] 93%), and PD vs. MSA-P/PSP group (sensitivity 86%, specificity 87%, PPV 88%, NPV 84%) ( 61 ). In SNpc (delineated using a probabilistic atlas based on neuromelanin sensitive imaging), asymmetric alterations predominantly in the diffusion metrices rather than anisotropy were observed ( 62 ).…”

Deciphering the Network Effects of Deep Brain Stimulation in Parkinson's Disease

“…Measures of WM microstructure, particularly AD and RD, and their alterations in localized brain regions have previously shed light on important processes of PD pathology [57][58][59], due to their ability to depict even small variations in structural connectivity [60,61]. The finding that AD and RD are related to the qUPDRS-III substantiated that both the integrity of the axons and the level of myelination within the targeted network influence the outcome of STN-DBS.…”