BackgroundRecent pathological studies have suggested that thalamic degeneration may represent a site of non-dopaminergic degeneration in Parkinson's Disease (PD). Our objective was to determine if changes in the thalami could be non-invasively detected in structural MRI images obtained from subjects with Parkinson disease (PD), compared to age-matched controls.ResultsNo significant differences in volume were detected in the thalami between eighteen normal subjects and eighteen PD subjects groups. However significant (p < 0.03) shape differences were detected between the Left vs. Right thalami in PD, between the left thalami in PD and controls, and between the right thalami in PD and controls using a recently-developed, spherical harmonic-based representation.ConclusionSystematic changes in thalamic shape can be non-invasively assessed in PD in vivo. Shape changes, in addition to volume changes, may represent a new avenue to assess the progress of neurodegenerative processes. Although not directly discernable at the resolution of standard MRI, previous pathological studies would suggest that the shape changes detected in this study represent degeneration in the centre median-parafascicular (CM-Pf) complex, an area known to represent selective non-dopaminergic degeneration in PD.

In earlier work, we have shown the importance of including 3D shape characteristics when analyzing regions of interest (ROIs) in magnetic resonance imaging (MRI) data. Spherical harmonics (SPHARM) based ROI shape descriptors were proposed and shown to provide important complementary information to traditionally used simple volumetric ROI measures. In this paper we extend our SPHARM shape parameterization technique by using functions defined on concentric spherical shells. We then propose the use of a novel radial transform to obtain unique features even under independent rotations of the constituting shells. These enhanced features enable the analysis of 3D ROIs with complex topologies including those with possible disconnections (e.g. ventricles). We validate the proposed 3D shape descriptors on synthetic data and demonstrate their sensitivity to subtle shape changes in the presence of inter-subject variability. We also apply our approach to real MRI data and detect significant shape changes in the left and right thalamus in Parkinson's disease (PD) patients when compared against normal volunteers, complementing the observed volumetric changes.

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Abstract-It has been recently shown that spatial patterns of activation within regions of interest (ROIs) in functional magnetic resonance imaging (fMRI) data can be used as sensitive markers of brain activation differences. In this paper, we propose novel invariant features for characterizing such spatial activation patterns based on spherical harmonic (SPHARM) data representations. The proposed three dimensional (3-D) spatial features are novel in that; first, they provide a unique representation of any ROI's functional data; second, they simultaneously account for inherent inter-subject anatomical variability that may influence any spatial characterization; third, they are invariant to similarity transformations and hence allow for direct comparisons between ROIs without any requirement for normalization to an atlas. We present quantitative validation demonstrating our method's improved sensitivity in performing group analysis when compared to traditional spatial normalization using synthetic data at the ROI level. We also use the proposed technique along with traditional normalization approach on real fMRI data collected from PD patients and normal subjects. The proposed features provide a powerful means to sensitively detect group-wise changes in ROI-based fMRI activation patterns even in the presence of anatomical variability.Index Terms-Functional magnetic resonance imaging (fMRI), group analysis, invariant features, ROI-based activation analysis, spatial activation analysis, spherical harmonics (SPHARM).

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