Diffusion Tensor Imaging of Dystrophic Skeletal Muscle : Comparison of Two Segmentation Methods Adapted to Chemical-shift-encoded Water-fat MRI.

Abstract

To compare the influence of two different regions of interest (ROIs) on diffusion tensor metrics in dystrophic thigh muscles using acustom-made (whole muscle) ROI including and aselective ROI excluding areas of fatty replacement. Diffusion tensor imaging (DTI) and chemical-shift-encoded water-fat magnetic resonance imaging (MRI) of the thigh was conducted on a3-Tesla system in 15cases with muscular dystrophy and controls. The ROIs were chosen according to patterns of fatty replacement on co-registered axial DTI and gradient echo sequence (GRE) images. Fractional anisotropy (FA), apparent diffusion coefficient (ADC), fiber track length (FTL), and muscle fat fractions (MFF) were compared between both ROI segmentations. These comparisons, muscle-specific correlation coefficients, and the influence of ROI localization on tensor metrics were derived based on linear mixed effects regression models. In the cases ahigh correlation was observed for ADC and FA with MFF using acustom ROI. The correlation was weaker but still significant with aselective ROI method. Using the custom ROI, FTL correlated significantly with MFF in 3 out of 4muscles (r ≤ -0.51). Acorrelation was not found for the selective ROI method. Interaction analysis revealed that the association of ADC and FA with MFF was not significantly influenced by the ROI localization. For FTL the ROI localization significantly reduced the negative association with MFF. The DTI metrics and FTL of custom ROI segmentation are significantly influenced by MFF. Contrary to ADC and FA, the effect of MFF on FTL is significantly reduced when applying selective ROI segmentation, which could therefore be abetter option for MR tractography.