GMM, Freesurfer, and MSNS comparison. Example images and resulting ChP segmentation for two representative subjects. As the figure shows, contrast agent enhances ChP intensity, allowing for better visualization and manual segmentation (A). We used MSC as the ground truth to compare segmentations performed on T1-weighted MRIs without contrast (Freesurfer, GMM, and MSNC). Dice coefficient (DC) was used to calculate similarity between each pair of segmentations. GMM significantly improved Freesurfer segmentation (ΔDC=0.2, p < 0.005), and had a performance close to human eye (ΔDC=0.05, p = 0.03). MSC, manual segmentations performed on cT1w MRIs; MSNC, manual segmentations performed on T1-w MRIs; GMM, Gaussian Mixture Model; DC, dice coefficient.