Ischemic Stroke: Collateral Blood Vessels Detected by Arterial Spin Labeling MRI Correlates With Good Neurological Outcome Interview with:
Jalal B. Andre M.D., D.A.B.R.®

Drector of neurological MRI and
MRI safety officer at Harborview Medical Center
University of Washington What is the background for this study?

Response: Acute ischemic stroke (AIS) patients with good collaterals have better clinical outcomes. AIS is characterized by an ischemic penumbra, a region of salvageable brain tissue, that surrounds a core of irreversible ischemic infarct. The penumbra is tenuously perfused by collateral blood vessels which, if extensive enough, can maintain penumbral perfusion, improving the odds that a larger volume of brain tissue will survive. Standard, first-line methods for evaluating collaterals in the acute setting include CT angiography, MR angiography, and (less commonly) digital subtraction angiography. Arterial spin labeling (ASL) is an emerging MRI technique that assesses cerebral perfusion. Its advantages include relatively short scan time (4-6 minutes), lack of ionizing radiation, and independence from an exogenous contrast agent (contraindicated in patients with impaired renal function or documented sensitivity). Collaterals can be identified within ASL images as foci of curvilinear hyperintensity bordering regions of hypoperfusion. We sought to explore a novel relationship between the presence of ASL collaterals (ASLc) and neurological outcome in acute ischemic stroke patients. What are the main findings?

Response: Thirty-eight patients met the study inclusion criteria. In 25 of 38 patients (66%), collaterals were detected using ASL, which was significantly associated with both a good outcome (mRS 0-2 at discharge, p = 0.02) and a one-point decrease in mRS at discharge (6.4, 95% CI, 1.7-23.4, p <0.01). In a multivariable ordinal logistic regression model, controlling for stroke severity (admission NIHSS), premorbid mRS, atrial fibrillation, and stroke parent artery status (< 50% stenosis vs. > 50% stenosis vs. occluded), there was a strong association between the presence of ASL collaterals and a one point decrease in the mRS at discharge (odds ratio 5.1, 95% CI, 1.2 – 22.1, p = 0.03). What should readers take away from your report?

Response: Following acute ischemic stroke, the presence of ASL collaterals (ASLc) predicts better neurological outcome at hospital discharge. After adjusting for potential confounders, patients with ASLc were 5 times more likely to have a one-point decrease in mRS at hospital discharge compared to those without ASLc. Patients with ASLc were also more likely to have a good neurologic outcome (mRS 0-2) compared to those without ASLc. ASL has not historically been used to visualize collaterals, although a pilot study demonstrated a strong agreement with digital subtraction angiography in predicting the presence and intensity of collateral blood flow (identified as ATA) in patients with Moyamoya disease. A subsequent study identified ATA in 12/17 ischemic stroke patients, but did not attempt to correlate their presence with outcome. Our results extend this research to demonstrate that collaterals on ASL also correlate with improved neurologic outcome at hospital discharge, which can provide relevant clinical information for a subset of patients unable to tolerate intravenous contrast. What recommendations do you have for future research as a result of this study?

Response: ASL may eventually provide a safer standard of care for acute AIS imaging and is underutilized for acute stroke, largely due to lack of familiarity with the technique. If ASL can provide useful information about penumbral and collateral status in a single acquisition, its utility in acute stroke would be even more apparent. In light of our results, additional prospective study is warranted to further explore the complex relationships between ASLc, penumbra, collaterals identified with other modalities, effectiveness of AIS interventions in the setting of ASLc, and long-term functional outcome. Is there anything else you would like to add?

Response: ASL has several advantages over traditional imaging techniques for detecting collaterals: it provides quantitative cerebral blood flow (CBF) evaluation, has minimal sensitivity to blood brain barrier disruption, requires no exogenous contrast agent or radiation exposure, lends itself to serial measurements, and poses little/no risk to the patient. Furthermore, ASL is commercially available on all major MRI vendor platforms and its reproducibility has been demonstrated in multi-center studies.  We have no relevant disclosures. Thank you for your contribution to the community


Association of Collateral Blood Vessels Detected by Arterial Spin Labeling Magnetic Resonance Imaging With Neurological Outcome After Ischemic Stroke
JAMA Neurol. 2017 Feb 13. doi: 10.1001/jamaneurol.2016.4491. [Epub ahead of print]

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

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