Evolving Role of Imaging in Acute Ischemic Stroke Care

HomeStrokeVol. 55, No. 3Evolving Role of Imaging in Acute Ischemic Stroke Care Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBEvolving Role of Imaging in Acute Ischemic Stroke Care Johanna Maria Ospel and Grégoire Boulouis Johanna Maria OspelJohanna Maria Ospel Correspondence to: Johanna Maria Ospel, MD, PhD, Departments of Radiology and Clinical Neurosciences, University of Calgary, Foothills Medical Centre, 1403, 29th St. NW, Calgary, AB, T2N 2T9, Canada. Email E-mail Address: [email protected] https://orcid.org/0000-0003-0029-6764 Departments of Diagnostic Imaging and Clinical Neurosciences, University of Calgary, AB, Canada (J.M.O.). and Grégoire BoulouisGrégoire Boulouis https://orcid.org/0000-0001-8422-9205 Diagnostic and Interventional Neuroradiology, Centre d’investigation Clinique, Innovation Technologique (CIC-IT) 1415, Centre Hospitalier Régional Universitaire de Tours (CHRU) de Tours, INSERM 1253 iBrain, Tours, France. Originally published21 Dec 2023https://doi.org/10.1161/STROKEAHA.123.044264Stroke. 2024;55:765–768Other version(s) of this articleYou are viewing the most recent version of this article. Previous versions: December 21, 2023: Ahead of Print Neuroimaging is an indispensable link in patients with a neurological deficit that swiftly confirms the clinical suspicion of stroke and guides decisions for potential interventions. With the success of revascularization strategies being tightly linked to the promptness of their initiation and adequate patient selection, the insights gained with acute imaging need to be precise and then rapidly translated into patient-specific therapeutic actions.Some fundamental principles of stroke imaging from the past still hold true today.Ruling out hemorrhage: are the symptoms of the patients caused by an intracranial hemorrhage or an acute ischemic stroke (AIS)?Detecting an arterial occlusion: is there an arterial occlusion? Is it amenable to endovascular thrombectomy (EVT)?Some aspects, such as the delineation of brain areas that are viable, viable but on the verge of infarction, or already irreversibly damaged, have become less crucial over time, while others have gained importance, reflecting the changing need for patient care in the face of therapeutic innovation.GUIDING REVASCULARIZATION THERAPIES: CHANGING LANESBefore the advent of EVT and since the ECASS (European Cooperative Acute Stroke Study) trials, the principal objective of imaging was to rule out an intracranial hemorrhage and identify increased bleeding risk that might result from intravenous thrombolysis, focusing predominantly on brain parenchyma. This remained the status quo for over 3 decades, until EVT became the standard of care in 2015 and the imaging paradigm expanded to maximize the timely identification of proximal occlusions,1 hence relying increasingly on vascular imaging.2This momentum was sustained with the expansion of EVT indications to the late time window in 2018, which established the use of perfusion imaging for tissue viability assessment.3 Computed tomography or magnetic resonance perfusion to estimate the viability of brain tissue has since been used to offer EVT to late-presenting patients that meet target mismatch criteria, that is, in whom advanced imaging indicates the presence of salvageable brain tissue (tissue window versus time window; Figure).Download figureDownload PowerPointFigure. Acute stroke imaging workflows in the present and future. A, Current workflows based on North American and European guidelines, and (B) probable changes that will occur in the near and mid-term future. Changes in B are highlighted in green. Currently, the absence of substantial tissue left to salvage, that is, a low Alberta Stroke Program Early Computed Tomography Score (ASPECTS) or large infarct core on baseline non-contrast computed tomography (NCCT) or magnetic resonance imaging ([MRI]; although MRI as the primary acute stroke imaging modality is performed only in a minority of hospitals) is considered a hard exclusion criterion for endovascular treatment (EVT). However, with several recent trials having shown the benefit of EVT in patients with low ASPECTS/large core, this criterion may soon be softened. Furthermore, current guidelines recommend EVT only in patients with large vessel occlusions (intracranial carotid artery, M1 segment, and possibly M2 segment of the middle cerebral artery). However, if the ongoing medium vessel occlusion EVT trials are able to prove EVT benefit, EVT recommendations may soon be expanded to medium vessel occlusions. In these patients, advanced imaging may help with occlusion detection. Finally, for patients presenting beyond 6 h from the last known well (late time window patients), current guideline recommendations for EVT are restricted to patients meeting certain computed tomography (CT)/magnetic resonance perfusion criteria. However, the recently published MR CLEAN LATE trial (Endovascular Treatment of Acute Stroke for Late Arrivals Trial) showed that patients in the late time window can be selected based on collateral assessment on computed tomography angiography (CTA) as well, which may soon be incorporated in future guidelines. We would argue that the main purpose of perfusion imaging is now the detection of medium-sized EVT-eligible vessel occlusions. If CTP is performed and shows evidence of a penumbra on CTP, this would obviate the need for collateral assessment on CTA. However, if there is no penumbra on CTP, but there are sufficient collaterals on CTA, EVT should be pursued as per MR CLEAN LATE criteria. *Intravenous thrombolysis (IVT) can also be administered in patients beyond 4.5 h if an MRI diffusion-weighted imaging–fluid attenuation inversion recovery mismatch is present. However, because MRI is not readily available in many hospitals, the goal is to simplify late-time window IVT eligibility criteria in the future. LKW indicates last known well; and MRA, magnetic resonance angiography.As the community is still adapting to this new evidence, the MR CLEAN LATE trial (Endovascular Treatment of Acute Stroke for Late Arrivals Trial)4 and recent trials on large ischemic volumes5 suggest that advanced imaging may lose its central role even for late window or large core patients, emphasizing that with sound clinical judgment, EVT is rarely harmful in proximal occlusions.With the likely mainstreaming of EVT for medium-sized vessel occlusions, computed tomography and magnetic resonance perfusion may find a renewed role in pinpointing hypoperfused territories, allowing to better detect smaller artery occlusions. This shift suggests that while the relevance of advanced imaging is intact, its role is evolving—from a tissue-centric role to a vascular occlusion-centric role. The dawn of automated occlusion detection possibly augurs that the importance of perfusion imaging may overall decrease. Certainly, not every patient with a vessel occlusion can benefit from EVT, but many of them will.Regarding imaging for intravenous thrombolysis selection, the shift from highly selective to broader, more pragmatic treatment indications seems to progress more slowly compared with EVT. This may be related to the comparatively lower treatment effect, multiple clinical contraindications, and the severity of hemorrhagic complications that may result from intravenous thrombolysis. Hence, the primary focus in the context of imaging for intravenous thrombolysis continues to be the identification of patients who are at risk of experiencing bleeding complications. Magnetic resonance imaging is recommended to select patients in the late time window (up to 24 hours) based on a diffusion-weighted imaging/fluid attenuation inversion recovery mismatch, which has been shown to identify late-time window patients who can benefit from IV thrombolysis (Figure).6STREAMLINED AND SEAMLESS: INTEGRATED PLATFORMS FOR IMAGING AND INTERVENTIONRecent advancements in stroke understanding and means of treatment have given rise to integrated platforms that combine imaging and interventional tools for hyperacute care. These platforms offer opportunities for new imaging and workflow paradigms, most notably allowing for direct-to-angio workflows and minimizing delays between imaging and treatment. Such platforms have the potential to transform traditional workflows by providing a comprehensive environment in which diagnostics and treatments can be conducted concurrently. This may soon become the norm for acute stroke care.FUTURE FORESEEN: IMAGING GUIDED ADJUNCTIVE STROKE TREATMENT AND OUTCOME PREDICTIONEven after angiographic complete reperfusion has been achieved by endovascular means, microcirculatory impairment may still persist. The CHOICE trial (Chemical Optimization of Cerebral Embolectomy Trial)7 showed that intra-arterial alteplase following successful reperfusion after EVT can improve clinical outcomes, presumably due to improved microcirculatory reperfusion. Looking ahead, modern flat-panel imaging technologies could enable us to identify patients with impaired microcirculation who may benefit from such adjunctive post-EVT treatments right on the angio table.Another potential future application of AIS imaging is individualized outcome prediction. Infarct volume is currently the best available imaging surrogate for clinical poststroke outcomes, but it is far from perfect. As an example, only 12% of the EVT benefit can be explained by a reduction of infarct volume.8 Recent studies show that infarct pattern, morphology and tissue-specific infarct volumes are additional, important prognostic factors besides and independent from total infarct volume.9 Furthermore, artificial intelligence algorithms yield substantial potential to improve poststroke prognostication and could guide us toward more accurate, individualized treatment decisions.10 Using these additional tools may soon allow for more accurate imaging-based outcome prediction.CONCLUSIONSAIS imaging protocols have undergone major changes since EVT and intravenous thrombolysis have become the standard of care. While in the past, a major focus of imaging has been to determine tissue viability and quantify infarct core, in the coming years, the focus will most likely shift toward the detection of treatment-eligible vessel occlusions. Refined imaging-based outcome prediction and imaging-guided adjunctive EVT therapies are additional long-term goals, but none of these aims are static: AIS imaging will evolve just like AIS treatment does, in ways that we may not imagine today.ARTICLE INFORMATIONSources of FundingNone.Disclosures Dr Ospel is a consultant for Nicolab. Dr Boulouis reports no conflicts.FootnotesThe American Heart Association celebrates its 100th anniversary in 2024. This article is part of a series across the entire AHA Journal portfolio written by international thought leaders on the past, present, and future of cardiovascular and cerebrovascular research and care. To explore the full Centennial Collection, visit https://www.ahajournals.org/centennial.For Sources of Funding and Disclosures, see page 767.The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association.Correspondence to: Johanna Maria Ospel, MD, PhD, Departments of Radiology and Clinical Neurosciences, University of Calgary, Foothills Medical Centre, 1403, 29th St. NW, Calgary, AB, T2N 2T9, Canada. Email johannaospel@gmail.comREFERENCES1. Goyal M, Menon BK, van Zwam WH, Dippel DWJ, Mitchell PJ, Demchuk AM, Dávalos A, Majoie CBLM, van der Lugt A, de Miquel MA, et al; HERMES collaborators. Endovascular thrombectomy after large-vessel ischaemic stroke: a meta-analysis of individual patient data from five randomised trials.Lancet. 2016; 387:1723–1731. doi: 10.1016/S0140-6736(16)00163-XCrossrefMedlineGoogle Scholar2. Boulouis G, Siddiqui KA, Lauer A, Charidimou A, Regenhardt RW, Viswanathan A, Leslie-Mazwi TM, Rost N, Schwamm LH. 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