Intravoxel incoherent motion of postmortem in-situ human brains: Insights and forensic implications.

Intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) distinguishes different diffusion processes based on varying molecular velocities. While IVIM is used in-vivo, postmortem studies are lacking, although they could provide valuable insights and validate in-vivo results. In this study, postmortem in-situ brain MRI scans of 13 deceased subjects were performed by applying a diffusion-weighted single-shot-echo-planar imaging sequence with 16 b-values (0-2500 s/mm2). The IVIM parameters perfusion fraction (f), diffusion (D), pseudo-diffusion (D*) and kurtosis (K) were determined in segmented white matter, cerebral cortex and deep gray matter. D was additionally corrected for temperature. All parameters were correlated with forehead and core temperature, postmortem interval (PMI), age at death and brain edema presence. Furthermore, differences of IVIM parameters between cases of fatal intoxication and other causes of deaths were analyzed. Postmortem f, D and D* were lower than in-vivo, while f in deep gray matter and K in all regions were higher. f did not level to 0 %. Forehead and core temperatures and PMI revealed statistically significant correlations with D. K correlated significantly with forehead temperature in deep gray matter, core temperature in cerebral cortex and PMI in white and deep gray matter. A significant difference was found in D* when comparing fatal intoxication cases with those with other causes of death. In conclusion, postmortem IVIM parameters differ from in-vivo values and are influenced by temperature and PMI. In the future, D* might enable noninvasive detection of intoxication as the cause of death.