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  Indian J Med Microbiol
 

Figure 5: There are several types of MRI that provide qualitative visualizations of metrics that correlate with aspects of tissue microstructure. Illustrated here are simplified diagrams color-coded as in [Figure 4] of the results from two studies using different advanced MRI techniques. (a). The first study used a high gradient version of diffusion MRI to calculate and visualize rough approximations of average axon diameter (upper panel) and axon density (lower panel).[23] Illustrated here are the results from a young (age 27 years) healthy female. Larger diameter axons (upper panel, orange and red) were clustered in the mid and posterior regions of the CC, and areas of lower diameter axons (upper panel, blue and green) had higher axon density (lower panel, orange and red) as predicted by microscopy. As noted by the authors, the model they utilized is known to inflate axon diameters considerably, so results should be considered qualitative rather than quantitative. (b). The second study, which used high-resolution T1 relaxation time MRI to estimate average myelinated axon diameter, reported a generally similar pattern of results.[7] Illustrated here are the average results from a group (n = 16) of young (mean age 29.2) healthy individuals (11 males, 5 females). Larger diameter axons (as indicated by higher T1 values, orange and red) were clustered in the posterior midbody and the inferior splenium and smaller diameter axons (as indicated by lower T1 values, blue and green) in the more anterior CC regions and the anterior midbody. Both studies replicated the average regional differences reported in microscopy-based studies. These rough visualizations greatly facilitate an understanding of how microscopic anatomy varies across the CC. CC: Corpus callosum, MRI: Magnetic resonance image

Figure 5: There are several types of MRI that provide qualitative visualizations of metrics that correlate with aspects of tissue microstructure. Illustrated here are simplified diagrams color-coded as in [Figure 4] of the results from two studies using different advanced MRI techniques. (a). The first study used a high gradient version of diffusion MRI to calculate and visualize rough approximations of average axon diameter (upper panel) and axon density (lower panel).<sup>[23]</sup> Illustrated here are the results from a young (age 27 years) healthy female. Larger diameter axons (upper panel, orange and red) were clustered in the mid and posterior regions of the CC, and areas of lower diameter axons (upper panel, blue and green) had higher axon density (lower panel, orange and red) as predicted by microscopy. As noted by the authors, the model they utilized is known to inflate axon diameters considerably, so results should be considered qualitative rather than quantitative. (b). The second study, which used high-resolution T1 relaxation time MRI to estimate average myelinated axon diameter, reported a generally similar pattern of results.<sup>[7]</sup> Illustrated here are the average results from a group (<i>n</i> = 16) of young (mean age 29.2) healthy individuals (11 males, 5 females). Larger diameter axons (as indicated by higher T1 values, orange and red) were clustered in the posterior midbody and the inferior splenium and smaller diameter axons (as indicated by lower T1 values, blue and green) in the more anterior CC regions and the anterior midbody. Both studies replicated the average regional differences reported in microscopy-based studies. These rough visualizations greatly facilitate an understanding of how microscopic anatomy varies across the CC. CC: Corpus callosum, MRI: Magnetic resonance image