Cardiac arrest (CA) survivors are often comatose and their arousal recovery is dependent on the extent of hypoxic-ischemic injury (HII). Long-term neurologic outcomes are variable, difficult to predict, and biased by withdrawal of life-sustaining therapy. Somatosensory evoked potentials (SSEP) remain the gold standard for predicting arousal potential, but is not broadly available. We hypothesized that early hi-resolution MRI may help assess arousal recovery potential as predicted by electrophysiologic outcome.

Comatose survivors of cardiac arrest admitted to an ICU between June 2015 and January 2018 who underwent SSEP and advanced diffusion imaging were retrospectively identified. Manual rating of HII volume on 3D-FLAIR sequences and semi-automated region-of-interest (ROI) tools in MIPAV to assess DWI region intensity were used to measure HII burden. Subjects with advanced imaging sequences went through a diffusion pre-processing pipeline for evaluation of diffusion kurtosis maps. Our outcome of interest was SSEP findings classified in two prognostic categories: indeterminate (bilaterally present N20s or unilateral presence of N20s) and poor prognosis (bilaterally absent N20s). We used paired t-tests to compare presence of manually rated signal abnormality as well as voxel-based unpaired t-tests of each individual DKI image (FA, MD, MK) to compare prognostic group differences.

42 consecutive CA survivors (mean age of 51.3, 31% female) were included. No significant differences were noted in baseline characteristics or clinical exam at 72 hours post-rewarming between groups. Nineteen (45%) had poor prognosis. Manual rating of FLAIR HII extent and ROI intensities did not predict SSEP status. Decreases in mean diffusivity with associated increases in mean kurtosis were found in posterior cortical white matter structures (p = 0.01).

In comatose survivors of cardiac arrest, higher B-values and kurtosis imaging may improve the ability of quantitative diffusion MRI to accurately measure the extent and critical regions for hypoxic-ischemic injury and predict arousal recovery potential.