Echo Time Effects on tensor-valued diffusion MRI: Implications for Standardization and Microstructural Characterization

Diffusion Magnetic Resonance Imaging (dMRI) is a non-invasive technique that examines the microscopic organization of brain tissues by measuring the random motion of water molecules. Advances like b-tensor encoding have enhanced the ability to distinguish between isotropic and anisotropic diffusion, providing deeper insights into complex tissue structures. This study evaluates the impact of echo time (TE) on dMRI parameters in white matter (WM), cortical gray matter (GM), and deep gray matter (DGM). Using multiple TE values and integrating free water elimination (FWE), we identified significant tissue-specific sensitivities to TE, particularly in kurtosis metrics within DGM. While WM exhibited minimal sensitivity to TE, cortical GM and DGM showed notable variations, reflecting their intricate microstructural properties. These results emphasize the importance of standardized imaging protocols to ensure consistency and reproducibility across institutions. Additionally, TE-sensitive metrics hold potential as biomarkers for diagnosing and monitoring neurological conditions that affect GM and DGM, such as Alzheimer’s disease and stroke. Future studies should aim to disentangle the effects of TE and diffusion time to deepen our understanding and apply these findings to clinical settings. Keywords: Diffusion Magnetic Resonance Imaging, B-tensor Encoding, Microstructure, Echo Time.