Time-resolved ADC analysis differentiates stable vs. progressive brain injury in post-cardiac arrest patients.

Aims: To investigate whether serial MRI-based apparent diffusion coefficient (ADC) analysis can evaluate the time-dependent trajectories of Hypoxic Ischemic Brain Injury (HIBI) and predict outcomes in out-of-hospital cardiac arrest (OHCA) survivors.

Methods: This retrospective cohort study included adult comatose OHCA survivors who underwent brain MRI within 6 h (ultra-early) and at 72-96 h (subacute) post-return of spontaneous circulation (ROSC). Quantitative voxel-based ADC metrics were extracted across thresholds from 200 to 1200 ×10^-6 mm²/s. ADC-R(x) was defined as the cumulative volume of voxels with ADC ≤ x. The primary outcome was poor outcome (CPC 3-5) at 6 months. Serum neuron-specific enolase (NSE) levels were measured serially and correlated with ADC values.

Results: Among 122 patients, 61 had poor outcomes. Subacute MRI showed stronger group separation and higher prognostic accuracy than ultra-early MRI, with the area under the curve peaking at 0.91 for ADC-R(400) and sensitivity improving by +0.53 at ADC-R(420). Patients with good outcomes demonstrated a rightward shift in ADC distributions and increased mid-to-high range ADC values, suggesting partial diffusion normalisation. Conversely, poor outcome patients showed progressive accumulation of low-ADC voxels (280-600 × 10^-6 mm²/s), indicating irreversible injury. ADC-R(x) correlated strongly with NSE in the poor outcome group at 6 h (ρ = 0.65), with overall cohort correlation improving by 72-96 h (ρ = 0.50).

Conclusion: Serial ADC analysis reveals dynamic and diverging HIBI patterns in OHCA survivors. Subacute MRI more accurately reflects progressive HIBI and improves prognostic performance, supporting its use in neuroprognostication beyond 72 h post-ROSC.