Abstract
This work aims to characterize fiber-tract-specific, orientation-dependent [Formula: see text] values across seven callosal segments (CC1[Formula: see text]CC7) using high-resolution diffusion tensor imaging (DTI) datasets from the Human Connectome Project. White matter (WM) voxels within each segment were identified using jointly applied thresholds of fractional anisotropy (FA) and mode of anisotropy (MO) to ensure robust selection of coherently oriented fibers. Orientation-dependent [Formula: see text] profiles were then derived from T2W images (b = 0), incorporating voxel-wise principal fiber orientations. These profiles were modeled using a cone-based framework that captures directional variations in transverse relaxation, enabling a clean separation of the magnitude of anisotropic [Formula: see text] component ([Formula: see text]) from its isotropic counterpart. Across segments, fits obtained at different b-values showed no major discrepancies aside from changes in [Formula: see text]. On average, [Formula: see text] increased from 2.4 ± 0.2 s- 1 to 3.2 ± 0.3 s- 1 with higher b-values. Additionally, [Formula: see text] showed an increasing trend from CC1 to CC7, while the cone's opening angle [Formula: see text] remained around 65°. As expected, FA also increased from CC1 to CC7 and with decreasing b-values. In conclusion, this study demonstrates that fiber-tract-specific anisotropic [Formula: see text] profiles in callosal segments can be quantified using a cone model, providing a valuable framework for reinterpreting existing clinical DTI data and guiding future studies targeting WM microstructure in both healthy and diseased populations.