Adam de Havenon, MD

Nael K, Khan R, Choudhary G, Meshksar A, Villablanca P, Tay J, et al. Six-Minute Magnetic Resonance Imaging Protocol for Evaluation of Acute Ischemic Stroke: Pushing the Boundaries. Stroke. 2014

    Noncontrast head CT is the sole imaging modality needed to triage patients for the only evidence-based treatment of acute ischemic stroke therapy – IV tPA. After a series of negative trials last year, the utility of endovascular thrombectomy is questionable, along with the utility of angiography or perfusion imaging in the acute phase of ischemic stroke. However, there are good reasons to get a CT angiogram, the most compelling being to rule out basilar artery occlusion, which will always be an endovascular emergency, but also to enroll patients in trials for new treatment options. Currently the majority of stroke centers rely on CT angiogram and CT perfusion for this imaging niche, but there are limitations to CT, the most important being the lack of diffusion-weighted imaging (DWI), but also the significant dose of ionizing radiation and contrast dye. MRI provides the entire package, but conventional DWI, MRA, FLAIR, and GRE take up to 20 minutes for even an abbreviated scan. 

    Kambiz Nael et al. describe a 6 minute acute stroke MRI protocol, that utilizes newer sequences with rapid scan times and only mild image quality degradation. The authors use this protocol on 62 patients with ischemic stroke in the last 24 hours and NIHSS ≥ 3, and then repeated it on 22 of those patients. The protocol includes a DWI, an echo-planar imaging (EPI) FLAIR, EPI-GRE, contrast-enhanced MRA neck and brain, and DSC perfusion. The EPI sequences had good correlation with conventional FLAIR and GRE; and there was excellent interobserver agreement for the scans, the vast majority of which were diagnostic.

    From an imaging perspective, the protocol is a success and it is remarkable that we can reduce the scan time for so many different sequences to only 6 minutes. It should be noted, however, that the excellent signal-to-noise ratio the authors achieve requires a 3 tesla magnet and multi-coil technology. Many comprehensive stroke centers lack this degree of imaging sophistication.

    MRI research should continue to investigate ways to reduce scan time and improve image quality, but the question is if there is a role for such innovation in acute stroke. Many stroke neurologists feel there is, even in the administration of IV tPA, but at present the data is not compelling. Ultimately, though, we may find ourselves using MRI for all acute stroke patients if widespread technology permits such rapid scan times with preserved image quality. Future research will determine the role for this 6 minute MRI, and, invariably, the 5 minute one as well.