Assessing mTBI-related brain changes: insights from bi-exponential and tri-exponential intravoxel incoherent motion (IVIM) MRI models.

Abstract

This pilot study investigated microstructural and perfusion changes in individuals with mTBI using both bi-exponential and tri-exponential intravoxel incoherent motion (IVIM) MRI models. Twenty patients with mTBI in the subacute phase and 20 healthy controls (HCs) underwent advanced diffusion MRI, with a subset of 11 controls participating in a test-retest reliability analysis. The tri-exponential IVIM model, which separates diffusion and perfusion into three distinct compartments, demonstrated superior sensitivity and reproducibility compared to the conventional bi-exponential model. Voxel-wise analysis revealed that mTBI subjects showed widespread alterations in IVIM parameters, including reduced apparent slow diffusion (Ds) and elevated perfusion-related fractions (Fp and Ff), particularly in frontal white matter, corpus callosum, and subcortical regions. These changes were robustly associated with lower cognitive performance, as measured by the Montreal Cognitive Assessment (MoCA), highlighting the link between microstructural integrity, perfusion, and cognitive outcomes. While IVIM parameters showed strong correlations with MoCA scores, their associations with the Glasgow Outcome Scale-Extended (GOS-E) were more modest, reflecting the complexity of brain injury recovery. This study represents the first direct comparison of bi-exponential and tri-exponential IVIM models in the context of mTBI, demonstrating their capacity to detect subtle brain alterations that remain undetected by conventional imaging and standard diffusion models. Additionally, these findings indicate that the tri-exponential IVIM approach might be a promising and reliable tool for non-invasively characterizing brain changes following mTBI, suggesting its potential utility as an imaging biomarker in brain injury research.