MRI before intraarterial therapy in ischemic stroke: feasibility, impact, and safety

Clinical Imaging of the Penumbra in Ischemic Stroke: From the Concept to the Era of Mechanical Thrombectomy

The ischemic penumbra is defined as the severely hypoperfused, functionally impaired, at-risk but not yet infarcted tissue that will be progressively recruited into the infarct core. Early reperfusion aims to save the ischemic penumbra by preventing infarct core expansion and is the mainstay of acute ischemic stroke therapy. Intravenous thrombolysis and mechanical thrombectomy for selected patients with large vessel occlusion has been shown to improve functional outcome. Given the varying speed of infarct core progression among individuals, a therapeutic window tailored to each patient has recently been proposed. Recent studies have demonstrated that reperfusion therapies are beneficial in patients with a persistent ischemic penumbra, beyond conventional time windows. As a result, mapping the penumbra has become crucial in emergency settings for guiding personalized therapy. The penumbra was first characterized as an area with a reduced cerebral blood flow, increased oxygen extraction fraction and preserved cerebral metabolic rate of oxygen using positron emission tomography (PET) with radiolabeled O₂. Because this imaging method is not feasible in an acute clinical setting, the magnetic resonance imaging (MRI) mismatch between perfusion-weighted imaging and diffusion-weighted imaging, as well as computed tomography perfusion have been proposed as surrogate markers to identify the penumbra in acute ischemic stroke patients. Transversal studies comparing PET and MRI or using longitudinal assessment of a limited sample of patients have been used to define perfusion thresholds. However, in the era of mechanical thrombectomy, these thresholds are debatable. Using various MRI methods, the original penumbra definition has recently gained a significant interest. The aim of this review is to provide an overview of the evolution of the ischemic penumbra imaging methods, including their respective strengths and limitations, as well as to map the current intellectual structure of the field using bibliometric analysis and explore future directions.

Current approaches and advances in the imaging of stroke

A stroke occurs when the blood flow to the brain is suddenly interrupted, depriving brain cells of oxygen and glucose and leading to further cell death. Neuroimaging techniques, such as computed tomography and magnetic resonance imaging, have greatly improved our ability to visualise brain structures and are routinely used to diagnose the affected vascular region of a stroke patient's brain and to inform decisions about clinical care. Currently, these multimodal imaging techniques are the backbone of the clinical management of stroke patients and have immensely improved our ability to visualise brain structures. Here, we review recent developments in the field of neuroimaging and discuss how different imaging techniques are used in the diagnosis, prognosis and treatment of stroke.

Summary: Stroke imaging has undergone seismic shifts in the past decade. Although magnetic resonance imaging (MRI) is superior to computed tomography in providing vital information, further research on MRI is still required to bring its full potential into clinical practice.

Acute imaging for evidence-based treatment of ischemic stroke

PURPOSE OF REVIEW

Until recently, intravenous thrombolysis and mechanical thrombectomy for acute stroke treatment relied on reported information on the known time of symptom onset and was limited to treatment within a narrow time window. New trials have provided evidence for imaging-based effective reperfusion treatment in an extended time window and unknown-onset stroke. This review summarizes evidence from recent clinical trials and suggests a simple algorithm for the choice of imaging modalities to guide evidence-based reperfusion treatment of acute stroke.

RECENT FINDINGS

Two trials have provided evidence for benefit of mechanical thombectomy in patients with stroke from large vessel occlusion up to 24 h after symptom onset or with unknown symptom onset who have a small infarct core but large perfusion lesion or severe clinical deficit (DAWN, DEFUSE-3). An MRI-based trial has demonstrated the benefit of intravenous thrombolysis with alteplase in patients with unknown onset stroke who present with MRI findings of DWI-FLAIR mismatch (WAKE-UP). Another trial demonstrated benefit of intravenous alteplase in an extended or unknown time-window in patients with penumbral pattern on MRI or CT perfusion (EXTEND).

SUMMARY

In stroke patients with unknown symptom onset or known symptom onset up to 24 h, advanced imaging with MRI or with CT perfusion can guide effective acute reperfusion treatment with mechanical thrombectomy and intravenous alteplase.

Multimodal MRI-Based Triage for Acute Stroke Therapy: Challenges and Progress

Revascularization therapies have been established as the treatment mainstay for acute ischemic stroke. However, a substantial number of patients are either ineligible for revascularization therapy, or the treatment fails or is futile. At present, non-contrast computed tomography is the first-line neuroimaging modality for patients with acute stroke. The use of magnetic resonance imaging (MRI) to predict the response to early revascularization therapy and to identify patients for delayed treatment is desirable. MRI could provide information on stroke pathophysiologies, including the ischemic core, perfusion, collaterals, clot, and blood–brain barrier status. During the past 20 years, there have been significant advances in neuroimaging as well as in revascularization strategies for treating patients with acute ischemic stroke. In this review, we discuss the role of MRI and post-processing, including machine-learning techniques, and recent advances in MRI-based triage for revascularization therapies in acute ischemic stroke.

Magnetic Resonance Imaging Selection for Endovascular Stroke Therapy

Background and Purpose—

The GOLIATH trial (General or Local Anesthesia in Intra-Arterial Therapy) compared infarct growth and outcome in patients undergoing endovascular therapy under either general anesthesia or conscious sedation. Magnetic resonance imaging was performed before and after the procedure to study infarct growth. In this post hoc analysis of GOLIATH, we aimed to characterize the workflow of patients undergoing magnetic resonance imaging selection before endovascular therapy.

Methods—

We randomized 128 patients with anterior circulation large vessel occlusion stroke within 6 hours of onset to either general anesthesia or conscious sedation (1:1 allocation). We studied workflow time intervals to examine whether magnetic resonance imaging conferred a time delay in treatment when compared with computed tomography-based studies that emphasized rapid workflow.

Results—

Of 128 patients enrolled between March 2015 and February 2017, 65 were randomized to general anesthesia. Baseline demographic and clinical variables were balanced between the treatment arms. The median interval from scan to groin puncture was 56.5 minutes (interquartile range, 44.5–73.5) for all patients. The median interval from admission to groin puncture was 68 minutes (interquartile range, 54.5–87 minutes). Comparable intervals in recent randomized data were 51 minutes (interquartile range, 39–68) for scan to groin puncture in the ESCAPE trial (Endovascular Treatment for Small Core and Anterior Circulation Proximal Occlusion With Emphasis on Minimizing CT to Recanalization Times) and 90 minutes (interquartile range, 69–120 minutes) for door to groin puncture in the SWIFT-PRIME study (Solitaire With the Intention for Thrombectomy as Primary Endovascular Treatment).

Conclusions—

Workflow in GOLIATH demonstrates that magnetic resonance imaging selection for endovascular therapy can be accomplished rapidly and within a similar time frame as computed tomography-based selection.

Clinical Trial Registration—

URL: https://www.clinicaltrials.gov . Unique identifier: NCT02317237.

Anesthetic strategy during endovascular therapy: General anesthesia or conscious sedation? (GOLIATH - General or Local Anesthesia in Intra Arterial Therapy) A single-center randomized trial

RATIONALE

Endovascular therapy after acute ischemic stroke due to large vessel occlusion is now standard of care. There is equipoise as to what kind of anesthesia patients should receive during the procedure. Observational studies suggest that general anesthesia is associated with worse outcomes compared to conscious sedation. However, the findings may have been biased. Randomized clinical trials are needed to determine whether the choice of anesthesia may influence outcome.

AIM AND HYPOTHESIS

The objective of GOLIATH (General or Local Anestesia in Intra Arterial Therapy) is to examine whether the choice of anesthetic regime during endovascular therapy for acute ischemic stroke influence patient outcome. Our hypothesis is that that conscious sedation is associated with less infarct growth and better functional outcome.

METHODS

GOLIATH is an investigator-initiated, single-center, randomized study. Patients with acute ischemic stroke, scheduled for endovascular therapy, are randomized to receive either general anesthesia or conscious sedation.

STUDY OUTCOMES

The primary outcome measure is infarct growth after 48-72 h (determined by serial diffusion-weighted magnetic resonance imaging). Secondary outcomes include 90-day modified Rankin Scale score, time parameters, blood pressure variables, use of vasopressors, procedural and anesthetic complications, success of revascularization, radiation dose, and amount of contrast media.

DISCUSSION

Choice of anesthesia may influence outcome in acute ischemic stroke patients undergoing endovascular therapy. The results from this study may guide future decisions regarding the optimal anesthetic regime for endovascular therapy. In addition, this study may provide preliminary data for a multicenter randomized trial.

Imaging biomarkers in acute ischemic stroke trials: a systematic review

BACKGROUND AND PURPOSE

Imaging biomarkers are increasingly used to provide a better understanding of the pathophysiology of acute ischemic stroke. However, this approach of routinely using imaging biomarkers to inform treatment decisions has yet to be translated into successful randomized trials. The aim of this study was to systematically review the use of imaging biomarkers in randomized controlled trials in patients with acute ischemic stroke, exploring the purposes for which the imaging biomarkers were used.

MATERIALS AND METHODS

We performed a systematic review of imaging biomarkers used in randomized controlled trials of acute ischemic stroke, in which a therapeutic intervention was trialed within 48 hours of symptom onset. Data bases searched included MEDLINE, EMBASE, strokecenter.org, and the Virtual International Stroke Trials Archive (1995-2014).

RESULTS

Eighty-four studies met the criteria, of which 49 used imaging to select patients; 31, for subgroup analysis; and 49, as an outcome measure. Imaging biomarkers were broadly used for 8 purposes. There was marked heterogeneity in the definitions and uses of imaging biomarkers and significant publication bias among post hoc analyses.

CONCLUSIONS

Imaging biomarkers offer the opportunity to refine the trial cohort by minimizing participant variation, to decrease sample size, and to personalize treatment approaches for those who stand to benefit most. However, within imaging modalities, there has been little consistency between stroke trials. Greater effort to prospectively use consistent imaging biomarkers should help improve the development of novel treatment strategies in acute stroke and improve comparison between studies.

MRI-guided selection of patients for treatment of acute ischemic stroke

PURPOSE OF REVIEW

To summarize what is known about the use of MRI in acute stroke treatment (predominantly thrombolysis), to examine the assumptions and theories behind the interpretation of magnetic resonance images of acute ischemic stroke and how they are used to select patients for therapies, and to suggest directions for future research.

RECENT FINDINGS

Recent studies have been contradictory about the usefulness of MRI in selecting patients for treatment. New MRI models for selecting patients have emerged that focus not only on the ischemic penumbra but also on the infarct core. Fixed time-window selection parameters are being replaced by timing-based individualized MRI stroke features. New ways to interpret traditional MRI stroke sequences are emerging.

SUMMARY

Although the efficacy of acute stroke treatment is time dependent, the use of fixed time windows cannot account for individual differences in infarct evolution, which could potentially be detected with MRI. Although MRI shows promise for identifying patients who should be treated, as well as excluding patients who should not be treated, definitive evidence is still lacking. Future research should focus on validating the use of MRI to select patients for intravenous therapies in extended time windows.