Magnetic Resonance Imaging versus Noncontrast Computed Tomography for Selecting Patients with Acute Ischemic Stroke of Large Vessel Occlusion for Endovascular Thrombectomy: A Systematic Review and Meta-Analysis

BACKGROUND: Neuroimaging in the acute phases after the onset of the stroke symptoms is necessary to determine large vessel occlusion presence as well as the extent of the ischemic insult before deeming eligibility for endovascular thrombectomy (EVT).

PURPOSE: To evaluate the clinical outcomes in acute ischemic stroke patients selected for EVT based on initial imaging; non-contrast computed tomography (NCCT) compared to those selected using magnetic resonance imaging (MRI).

DATA SOURCES: PubMed, Embase, Scopus, and Web of Science were searched from inception to August, 2024.

STUDY SELECTION: We included observational studies comparing functional independence (mRS 0-2), successful reperfusion (TICI 2b-3), symptomatic intracerebral hemorrhage (sICH) or mortality in patients selected for EVT using NCCT±CT angiography versus MRI ±MR angiography. We excluded studies that used perfusion imaging in their patient selection for EVT.

DATA ANALYSIS: Data were pooled using random-effects model, and heterogeneity was assessed using I² statistics. A subgroup analysis was performed to determine the effect of treatment window (<6h vs >6h from last known well). The quality of eligible studies was assessed by using Newcastle Ottawa Scale.

DATA SYNTHESIS: Seven studies (n=3,940 patients) met the inclusion criteria. Two studies had low risk of bias and others had some concerns. Patients with MRI selection showed better chances of functional independence (Odds ratio (OR), 1.85 [95% CI, 1.28-2.67]; p<0.01, I²=45%), lower rates of sICH (OR 0.59, 95% CI 0.39–0.89; p=0.01, I2=0%), reduced 90 days mortality (OR 0.63, 95% CI 0.51–0.78; p<0.01, I²=0%) and no difference in successful reperfusion (OR 0.99, 95% CI 0.62–1.58; p=0.95, I²=0%) compared to NCCT in patients treated within 6 hours of stroke onset. There were no significant differences in any endpoints between MRI and NCCT for patients treated beyond 6 hours.

LIMITATIONS: Our meta-analysis comprised only observational studies, with different populations and imaging protocols limiting the strength of the conclusions.

CONCLUSIONS: Within the crucial <6-hour window, MRI's superior patient selection justifies its use despite longer acquisition times. Beyond 6 hours, the focus should shift to rapid EVT access rather than imaging modality choice, as the benefits of MRI diminish.

ABBREVIATIONS: EVT = Endovascular Thrombectomy; IVT = Intravenous Thrombolysis; AIS-LVO = Acute Ischemic Stroke-Large Vessel Occlusion