Introduction: The major mechanism of morbidity of delayed cerebral ischemia after subarachnoid hemorrhage (SAH) is considered to be severe vasospasm. Quantitative MRA (QMRA) provides direct measurements of vessel-specific volumetric blood flow and may permit a clinically relevant assessment of the risk of ischemia secondary to cerebral vasospasm.
Purpose: To evaluate the utility of QMRA as an alternative imaging technique for the assessment of cerebral vasospasm after SAH.
Methods: QMRA volumetric flow rates of the anterior cerebral artery (ACA), middle cerebral artery (MCA), and posterior cerebral artery (PCA) were compared with vessel diameters on catheter-based angiography. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of QMRA for detecting cerebral vasospasm was determined by receiver-operating characteristic curves. Spearman correlation coefficients were calculated for QMRA flow versus angiographic vessel diameter.
Results: Sixty-six vessels (10 patients) were evaluated with QMRA and catheter-based angiography. The median percent QMRA flow of all vessels with angiographic vasospasm (55.0%, IQR 34.3-71.6%) was significantly lower than the median percent QMRA flow of vessels without vasospasm (91.4%, IQR 81.4-100.4%) (p < 0.001). Angiographic vasospasm reduced QMRA-assessed flow by 23 ± 5 (p = 0.018), 95 ± 12 (p = 0.042), and 16 ± 4 mL/min (p = 0.153) in the ACA, MCA, and PCA, respectively, compared to vessels without angiographic vasospasm. The sensitivity, specificity, PPV, and NPV of QMRA for the discrimination of cerebral vasospasm was 84%, 72%, 84%, and 72%, respectively, for angiographic vasospasm >25% and 91%, 60%, 87%, and 69%, respectively, for angiographic vasospasm >50%. The Spearman correlation indicated a significant association between QMRA flows and vessel diameters (rs = 0.71, p < 0.001).
Conclusion: Reduction in QMRA flow correlates with angiographic vessel narrowing and may be useful as a non-invasive imaging modality for the detection of cerebral vasospasm after SAH.
Keywords: Cerebral vasospasm; delayed cerebral ischemia; non-invasive optimal vessel analysis; quantitative MRA; subarachnoid hemorrhage.