Validation of a Novel MRI Biomarker of Infarct Severity to Predict Functional Outcome after Endovascular Thrombectomy

Background: Endovascular thrombectomy (EVT) dramatically improves clinical outcomes, but the final infarct volume (FIV) on MRI only accounts for a minority of the treatment effect. An imaging biomarker that more strongly correlates with post-EVT functional outcome would be helpful for clinical prognosis and serve as a surrogate outcome measure in trials of EVT-adjuvant therapies. Here, we aimed to validate a novel MRI-based metric, infarct density, which leverages post-EVT apparent diffusion coefficient (ADC) as a marker of infarct severity. Methods: A retrospective cohort was derived from a single-center prospective EVT registry. Consecutive anterior circulation EVT patients were included from 2018-2019 who achieved successful reperfusion (mTICI ≥2b). MRI was performed 12-48 hours post-EVT and processed via RAPID to quantify FIV using the ADC <620 threshold. Lesion volume was also collected using ADC <470 threshold, and infarct density was calculated as: (volume <470/volume <620)x100%. Good outcome was defined as ≤2 on the 90-day modified Rankin Scale. Multivariable logistic regression models quantified the association between clinical/imaging variables and outcome. ROC analysis quantified model classification performance. Results: Of 319 EVT patients, 272 met inclusion criteria. The mean age was 69 ±13 years, 41% were female, and 62% achieved a good outcome. After adjusting for clinical and radiographic factors, FIV (aOR 0.99 per 1mL; 95%CI: 0.98-1.00; p=0.03) and infarct density (aOR 0.95 per 1%; 95%CI: 0.94-0.97; p<0.001) were both independently inversely associated with good outcome. The final model incorporating both FIV and infarct density achieved excellent classification performance (AUC 0.87; 95%CI: 0.83-0.91). Removing infarct density from the model diminished its performance (AUC 0.83; 95%CI: 0.78-0.88; p=0.01). Conclusion: ADC-based infarct density after EVT is independently associated with long‐term outcome and provides greater prognostic information than FIV alone. Post-EVT infarct density may be useful in clinical care and as a surrogate outcome measure in trials of EVT-adjuvant therapies.