Longitudinal assessment of automated gray-white matter ratio for outcome prediction after cardiac arrest.

BACKGROUND: The gray-white matter ratio (GWR) on head CT is a well-established marker of hypoxic-ischemic brain injury after cardiac arrest, but its prognostic performance may vary with the timing of imaging. We aimed (i) to evaluate the prognostic value of GWR across serial CT scans within the same comatose patients, and (ii) to determine whether the longitudinal changes of GWR provide additional prognostic information beyond single time-point measurements. METHODS: We prospectively recruited 123 comatose patients with cardiac arrest admitted to three intensive care units. All patients underwent serial non-contrast head CT at three predefined time windows (< 24 h, 24-96 h, and 96-168 h after cardiac arrest). GWR values were automatically calculated using an atlas-based approach. Neurological outcome at 3 months was assessed with the Cerebral Performance Category score (CPC) and dichotomized into good (CPC 1-2) or poor (CPC 3-5). GWR values and their progression were compared between outcome groups. Prognostic accuracy of GWR at each time window was assessed using receiver operating characteristic (ROC) analysis. RESULTS: GWR was consistently lower in patients with poor outcomes compared to those with good outcomes across all time windows (for all p < 0.001). In poor-outcome patients, GWR declined after the first 24 h, whereas it was stable in good-outcome patients. The prognostic performance of GWR improved with later imaging, with an AUC of 0.72 (95% CI 0.62-0.81) at < 24 h, 0.78 (95% CI 0.69-0.86) at 24-96 h, and 0.81 (95% CI 0.72-0.88) at 96-168 h after cardiac arrest. Incorporating longitudinal changes in GWR slightly improved prediction, with the AUC increasing from 0.81 to 0.83 at 96-168 h. CONCLUSIONS: Automated GWR is a useful predictor of outcome after cardiac arrest, with higher accuracy on delayed CT (> 24 h). The different GWR progression trajectories between patients with poor and good outcomes suggest that longitudinal CT assessments may provide additional prognostic information.