Tractography of corpus callosum connections to other brain structures

A microstructural damage of corpus callosum (cc) is demonstrated by histological post-mortem study in many neurodegenerative diseases, while at present the only in-vivo investigation is provided by DTI and tractography. However, the lesional load which often accompanies these pathologies can severely limit the image registration steps necessary for reliable DTI computation. A technical study for specific cc investigation and for the enhancement of main tracts connecting cc and other brain structures is presented, analyzing 5 subjects with different lesional loads. Atlas of 116 brain structures and segmented cc, derived from high-resolution-Tl images, are coregistered onto DTI directly or by 2 passages. For 2 patients with high lesional load, the 2- steps coregistration gives best results, indeed mutual information between Tl and DTI is higher for Tl coregistered with 2 steps than directly. Volumes of entire cc, portions of cc, brain structures connected to cc are computed. Also DTI-derived indices (MD, FA) are computed for the same structures. For all the subjects, the volume of cc anterior portion was less than posterior one; for 4 subjects FA of anterior bundles were less then FA of posteriors. The parameters of fiber tracking allowed to extract bundles connecting cc to other brain structures and to compute indices of their microstructural integrity, within the limits, in terms of acquisition time, of a clinically feasible protocol.