The infarct core is well represented by the acute diffusion lesion: sustained reversal is infrequent

Acute ischemic stroke treatment, part 1: patient selection "the 50% barrier and the capillary index score"

The current strategy for intra-arterial treatment (IAT) of acute ischemic stroke focuses on minimizing time from ictus to revascularization and maximizing revascularization. Employing this strategy has yet to lead to improved rates of successful outcomes. However, the collateral blood supply likely plays a significant role in maintaining viable brain tissue during ischemia. Based on our prior work, we believe that only approximately 50% of patients are genetically predisposed to have sufficient collaterals for a good outcome following treatment, a concept we call the 50% barrier. The Capillary Index Score (CIS) has been developed as a tool to identify patients with a sufficient collateral blood supply to maintain tissue viability prior to treatment. Patients with a favorable CIS (f CIS) may be able to achieve a good outcome with IAT beyond an arbitrary time window. The CIS is incorporated into a proposed patient treatment algorithm. For patients suffering from a large stroke without aphasia, a non-enhanced head CT should be followed by CT angiography (CTA). For patients without signs of stroke mimics or visible signs of structural changes due to large irreversible ischemia, CTA can help confirm the vascular occlusion and location. The CIS can be obtained from a diagnostic cerebral angiogram, with IAT offered to patients categorized as f CIS.

Multimodal imaging in acute ischemic stroke

OPINION STATEMENT

Recent years have seen the development of novel neuroimaging techniques whose roles in the management of acute stroke are sometimes confusing and controversial. This may be attributable in part to a focus on establishing simplified algorithms and terminology that omit consideration of the basic pathophysiology of cerebral ischemia and, consequently, of the full potential for optimizing patients' care based upon their individual imaging findings. This review begins by discussing cerebral hemodynamic physiology and of the effects of hemodynamic disturbances upon the brain. Particular attention will be paid to the hemodynamic measurements and markers of tissue injury that are provided by common clinical imaging techniques, with the goal of enabling greater confidence and flexibility in understanding the potential uses of these techniques in various clinical roles, which will be discussed in the remainder of the review.

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.

Alberta Stroke Program Early Computed Tomographic Scoring Performance in a Series of Patients Undergoing Computed Tomography and MRI

Background and Purpose—

In this study, we compare the performance of pretreatment Alberta Stroke Program Early Computed Tomographic scoring (ASPECTS) using noncontrast CT (NCCT) and MRI in a large endovascular therapy cohort.

Methods—

Prospectively enrolled patients underwent baseline NCCT and MRI and started endovascular therapy within 12 hours of stroke onset. Inclusion criteria for this analysis were evaluable pretreatment NCCT, diffusion-weighted MRI (DWI), and 90-day modified Rankin Scale scores. Two expert readers graded ischemic change on NCCT and DWI using the ASPECTS. ASPECTS scores were analyzed with the full scale or were trichotomized (0–4 versus 5–7 versus 8–10) or dichotomized (0–7 versus 8–10). Good functional outcome was defined as a 90-day modified Rankin Scale score of 0 to 2.

Results—

Seventy-four patients fulfilled our study criteria. The full-scale inter-rater agreement for CT-ASPECTS and DWI-ASPECTS was 0.579 and 0.867, respectively. DWI-ASPECTS correlated with functional outcome ( P =0.004), whereas CT-ASPECTS did not ( P =0.534). Both DWI-ASPECTS and CT-ASPECTS correlated with DWI volume. The receiver operating characteristic analysis revealed that DWI-ASPECTS outperformed both CT-ASPECTS and the time interval between symptom onset and start of the procedure for predicting good functional outcome (modified Rankin Scale score, ≤2) and DWI volume ≥70 mL.

Conclusion—

Inter-rater agreement for DWI-ASPECTS was superior to that for CT-ASPECTS. DWI-ASPECTS outperformed NCCT ASPECTS for predicting functional outcome at 90 days.

Impact of Severe Extracranial ICA Stenosis on MRI Perfusion and Diffusion Parameters in Acute Ischemic Stroke

Purpose: The aim of this study was to investigate the impact of a coexisting internal carotid artery (ICA) stenosis on lesion volumes as well as diffusion and perfusion parameters in acute ischemic stroke resulting from middle cerebral artery (MCA) occlusion.

Material and methods: Magnetic resonance imaging data of 32 patients with MCA occlusion with or without additional ICA stenosis imaged within 4.5 h of symptom onset were analyzed. Both groups consisted of 16 patients. Acute diffusion lesions were semi-automatically segmented in apparent diffusion coefficient (ADC) MRI datasets. Perfusion maps of cerebral blood volume (CBV), cerebral blood flow, mean transit time and T_max were calculated using perfusion-weighted MRI datasets. Tissue-at-risk (TAR) volumes were generated by subtracting the ADC lesion from the hypoperfusion lesion defined by T_max >6 s. Median ADC and perfusion parameter values were extracted separately for the diffusion lesion and TAR and used for statistical analysis.

Results: No significant differences were found between the groups regarding the diffusion lesion and TAR volumes. Statistical analysis of diffusion and perfusion parameters revealed CBV as the only parameter with a significant difference (p = 0.009) contributing a small effect (η² = 0.11) to the group comparison with higher CBV values for the patient group with a coexisting ICA stenosis, while no significant effects were found for the other diffusion and perfusion parameters analyzed.

Conclusion: The results of this study suggest that a coexisting ICA stenosis does not have a strong effect on tissue status or perfusion parameters in acute stroke patients except for a moderate elevation of CBV. This may reflect improved collateral circulation or ischemic preconditioning in patients with a pre-existing proximal stenosis balancing impaired perfusion from the stenosis.

Spectroscopy of reperfused tissue after stroke reveals heightened metabolism in patients with good clinical outcomes

The aim of acute stroke treatment is to reperfuse the penumbra. However, not all posttreatment reperfusion is associated with a good outcome. Recent arterial spin labeling (ASL) studies suggest that patients with hyperperfusion after treatment have a better clinical recovery. This study aimed to determine whether there was a distinctive magnetic resonance spectroscopy (MRS) metabolite profile in hyperperfused tissue after stroke reperfusion therapy. We studied 77 ischemic stroke patients 24 hours after treatment using MRS (single voxel spectroscopy, point resolved spectroscopy, echo time 30 ms), ASL, and diffusion-weighted imaging (DWI). Magnetic resonance spectroscopy voxels were placed in cortical tissue that was penumbral on baseline perfusion imaging but had reperfused at 24 hours (and did not progress to infarction). Additionally, 20 healthy age matched controls underwent MRS. In all, 24 patients had hyperperfusion; 36 had reperfused penumbra without hyperperfusion, and 17 were excluded due to no reperfusion. Hyperperfusion was significantly related to better 3-month clinical outcome compared with patients without hyperperfusion (P=0.007). Patients with hyperperfusion showed increased glutamate (P<0.001), increased N-Acetylaspartate (NAA) (P=0.038), and increased lactate (P<0.002) in reperfused tissue compared with contralateral tissue and healthy controls. Hyperperfused tissue has a characteristic metabolite signature, suggesting that it is more metabolically active and perhaps more capable of later neuroplasticity.

Predicting intracerebral hemorrhage by baseline magnetic resonance imaging in stroke patients undergoing systemic thrombolysis

Objectives

Intracerebral hemorrhage (ICH) remains a serious complication in ischemic stroke patients undergoing systemic thrombolysis. Here, we examined whether the risk of treatment-associated hemorrhage can be predicted from magnetic resonance imaging (MRI) using fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted imaging (DWI) within 3 h after symptom onset.

Methods

In this single-center observational study involving 122 ischemic stroke patients between January 2005 and December 2008, the incidence of FLAIR-positive lesions within diffusion-restricted areas was determined on baseline MRI, which was carried out prior to treatment with tissue plasminogen activator (Actilyse®) within 3 h from symptom onset. The rate of ICH was assessed by computed tomography performed within 24 h after treatment. Relationships between FLAIR-positive lesions, DWI lesion size, proportion of FLAIR/DWI-positive lesions, and occurrence of bleeding were explored.

Results

Data from 97 patients were evaluated. FLAIR-positive lesions were present in 25 patients (25.8%) and ICH occurred in 32 patients (33.0%). FLAIR-positive lesions were associated with a bleeding rate of 80.0% compared with 16.7% in FLAIR-negative patients (P < 0.001; odds ratio 20.0, positive predictive value 0.8). DWI lesion size was significantly correlated with the rate of ICH (P = 0.001). In contrast, FLAIR/DWI proportion was not associated with ICH (P = 0.788).

Conclusions

In ischemic stroke patients within 3 h from symptom onset, the existence of FLAIR-positive lesions on pretreatment MRI is significantly associated with an increased bleeding risk due to systemic thrombolysis. Therefore, considering FLAIR-positive lesions on baseline MRI might guide treatment decisions in ischemic stroke.

Impact of diffusion-weighted imaging Alberta stroke program early computed tomography score on the success of endovascular reperfusion therapy

BACKGROUND AND PURPOSE

In acute ischemic stroke patients treated by intravenous thrombolysis, a diffusion-weighted imaging (DWI) Alberta Stroke Program Early Computed Tomography Score (ASPECTS) is an independent factor of functional outcomes. Our aim was to assess the impact of pretreatment DWI-ASPECTS on outcomes after endovascular therapy, with a specific emphasis on recanalization.

METHODS

We analyzed data collected between April 2007 and March 2013 in a prospective clinical registry of acute ischemic stroke patients treated by endovascular approach. Every patient with a documented internal carotid artery or middle cerebral artery occlusion who underwent an acute DWI-MRI before treatment was eligible for this study. The primary outcome was a favorable outcome defined by modified Rankin Scale of 0 to 2 at 90 days.

RESULTS

Two hundred ten patients were included and median DWI-ASPECTS was 7 (interquartile range, 4-8). DWI-ASPECTS≥5 was the optimal threshold to predict a favorable outcome (area under the curve=0.69; sensitivity, 90%; specificity, 38%). In a multivariate analysis including confounding variables, the adjusted odds ratio for favorable outcomes associated with a DWI-ASPECTS of ≥5 was 5.06 (95% confidence interval, 1.86-13.77; P=0.002). Nonetheless, the occurrence of a complete recanalization was associated with an increased rate of favorable outcomes in patients with DWI-ASPECTS under 5 (50% versus 3%, P<0.001).

CONCLUSIONS

DWI-ASPECTS≥5 seems to be the optimal threshold to predict favorable outcomes among patients undergoing endovascular reperfusion within 6 hours. Selected patients with a DWI-ASPECTS of <5 may still benefit when a complete reperfusion is achieved.

Early diffusion-weighted imaging reversal after endovascular reperfusion is typically transient in patients imaged 3 to 6 hours after onset

BACKGROUND AND PURPOSE

The aim of this study was to assess the frequency and extent of early diffusion-weighted imaging (DWI) lesion reversal after endovascular therapy and to determine whether early reversal is sustained or transient.

METHODS

MRI with DWI perfusion imaging was performed before (DWI 1) and within 12 hours after (DWI 2) endovascular treatment; follow-up MRI was obtained on day 5. Both DWIs were coregistered to follow-up MRI. Early DWI reversal was defined as the volume of the DWI 1 lesion that was not superimposed on the DWI 2 lesion. Permanent reversal was the volume of the DWI 1 lesion not superimposed on the day 5 infarct volume. Associations between early DWI reversal and clinical outcomes in patients with and without reperfusion were assessed.

RESULTS

A total of 110 patients had technically adequate DWI before endovascular therapy (performed median [interquartile range], 4.5 [2.8-6.2] hours after onset); 60 were eligible for this study. Thirty-two percent had early DWI reversal >10 mL; 17% had sustained reversal. The median volume of permanent reversal at 5 days was 3 mL (interquartile range, 1.7-7.0). Only 2 patients (3%) had a final infarct volume that was smaller than their baseline DWI lesion. Early DWI reversal was not an independent predictor of clinical outcome and was not associated with early reperfusion.

CONCLUSIONS

Early DWI reversal occurred in about one third of patients after endovascular therapy; however, reversal was often transient and was not associated with a significant volume of tissue salvage or favorable clinical outcome.

Lesion development and reperfusion benefit in relation to vascular occlusion patterns after embolic stroke in rats

Vascular occlusion sites largely determine the pattern of cerebral tissue damage and likelihood of subsequent reperfusion after acute ischemic stroke. We aimed to elucidate relationships between flow obstruction in segments of the internal carotid artery (ICA) and middle cerebral artery (MCA), and (1) profiles of acute ischemic lesions and (2) probability of subsequent beneficial reperfusion. Embolic stroke was induced by unilateral intracarotid blood clot injection in normotensive (n=53) or spontaneously hypertensive (n=20) rats, followed within 2  hours by magnetic resonance (MR) angiography (MRA), diffusion- (DWI) and perfusion-weighted magnetic resonance imaging (MRI) (PWI). In a subset of animals (n=9), MRI was repeated after 24 and 168  hours to determine the predictive value of the occlusion pattern on benefit of reperfusion. The extent of cerebral perfusion and diffusion abnormality was related to the pattern of flow obstruction in ICA and MCA segments. Hypertensive animals displayed significantly larger cortical perfusion lesions. Acute perfusion-diffusion lesion mismatches were detected in all animals that subsequently benefitted from reperfusion. Yet, the presence of an angiography-diffusion mismatch was more specific in predicting reperfusion benefit. Combination of DWI, PWI, and MRA exclusively informs on the impact of arterial occlusion profiles after acute ischemic stroke, which may improve prognostication and subsequent treatment decisions.

Comparison of fast MRI-based individual thrombolysis therapy for patients with superacute infarction

BACKGROUND

The aim of this study is to investigate the outcomes of magnetic resonance imaging (MRI)-based individual thrombolysis therapy using recombinant tissue plasminogen activator (rt-PA) in patients with superacute infarction, comparing the outcome in 1 group of patients treated within 4.5 hours compared with 4.5- to 12-hour window treatment group.

METHODS

We studied 135 patients stratified to 2 different groups based on whether they presented with stroke symptoms within 4.5 hours (4.5-hour group, 72 patients) or between 4.5 and 12 hours (4.5- to 12-h group, 63 patients). All patients were treated with rt-PA after MRI confirmed superacute ischemic stroke (hyperintense in diffusion-weighted imaging but no hypointense change in T2-weighted image (T2WI) or fluid-attenuated inversion recovery). Clinical neurologic deficit was evaluated using the National Institutes of Health Stroke Scale on admission, at 24 hours, and 7 days later. A 90-day clinical outcome was assessed using the modified Rankin Scale (mRS).

RESULTS

There was no significant difference in the clinical outcome between the patients treated with thrombolysis within the first 4.5 hours and those treated between 4.5 and 12 hours. The 2 groups both had recanalization, mRS, and favorable outcome at 90 days (P > .05).

CONCLUSIONS

Our study suggested that fast MR-based thrombolysis using rt-PA was safe and reliable in superacute infarction within 4.5 hours and 4.5-12 hours poststroke.

How much diffusion lesion reversal occurs after treatment within three-hours of stroke onset?

In this issue of the journal, Sakamoto et al. present an analysis of diffusion lesion evolution in acute ischemic stroke patients first imaged less than three-hours from stroke onset. Although temporary lesion volume reduction was observed following reperfusion, the affected regions were generally abnormal on follow-up fluid attenuated inversion recovery imaging, indicating lack of tissue salvage. Taken in conjunction with other recent articles, it seems that temporary postreperfusion 'reversal' of diffusion lesions is quite common but usually does not translate to permanent tissue salvage. A minority of patients demonstrate permanent reversibility of a component of the acute diffusion lesion. This is dependent on early reperfusion and is more frequent when patients are treated within three-hours. Early reperfusion is clearly associated with a reduction in infarct growth through salvage of ischemic penumbra, and this probably contributes more to the favorable neurological outcomes in these patients than the relatively small volumes of diffusion reversal. It is currently unknown whether future therapeutic advances that increase the speed and success rates of reperfusion will increase the proportion of reversibility further and lead to clinically relevant salvage within the diffusion lesion. For the present, it appears that intravenous tissue plasminogen activator rarely achieves substantial permanent reversal of diffusion lesions, even when administered within three-hours.

DWI reversal is associated with small infarct volume in patients with TIA and minor stroke

BACKGROUND AND PURPOSE

More than half of patients with TIA/minor stroke have ischemic lesions on early DWI, which represent irreversibly damaged tissue. The presence and volume of DWI lesions predict early deterioration in this population. We aimed to study the rate and implications of DWI reversal in patients with TIA/minor stroke.

MATERIALS AND METHODS

Patients with TIA/minor stroke were prospectively enrolled and imaged within 24 hours of onset. Patients were followed for 3 months with repeat MR imaging either at day 30 or 90. Baseline DWI/PWI and follow-up FLAIR final infarct volumes were measured.

RESULTS

Of 418 patients included, 55.5% had DWI and 37% had PWI (time-to-peak of the impulse response ≥2 seconds' delay) lesions at baseline. The median time from symptom onset to baseline and follow-up imaging was 13.4 (interquartile range, 12.7) and 78.73 hours (interquartile range, 60.2), respectively. DWI reversal occurred in 5.7% of patients. The median DWI lesion volume was significantly smaller in those with reversal (0.26 mL, interquartile range = 0.58 mL) compared with those without (1.29 mL, interquartile range = 3.6 mL, P = .002); 72.7% of DWI reversal occurred in cortically based lesions. Concurrent tissue hypoperfusion (time-to-peak of the impulse response ≥2 seconds) was seen in 36.4% of those with DWI reversal versus 62.4% without (P = .08). DWI reversal occurred in 3.3% of patients with penumbral patterns (time-to-peak of the impulse response ≥6 seconds - DWI) > 0 and in 6.8% of those without penumbral patterns (P = .3). The severity of hypoperfusion, defined as greater prolongation of time-to-peak of the impulse response (≥2, ≥4, ≥6, ≥8 seconds), did not affect the likelihood of DWI reversal (linear trend, P = .147). No patient with DWI reversal had an mRS score of ≥2 at 90 days versus 18.2% of those without reversal (P = .02).

CONCLUSIONS

DWI reversal is uncommon in patients with TIA/minor stroke and is more likely to occur in those with smaller baseline lesions. DWI reversal should not have a significant effect on the accuracy of penumbra definition.

Translational Perspectives on Perfusion–Diffusion Mismatch in Ischemic Stroke

Magnetic resonance imaging has tremendous potential to illuminate ischemic stroke pathophysiology and guide rational treatment decisions. Clinical applications to date have been largely limited to trials. However, recent analyses of the major clinical studies have led to refinements in selection criteria and improved understanding of the potential implications for the risk vs. benefit of thrombolytic therapy. In parallel, preclinical studies have provided complementary information on the evolution of stroke that is difficult to obtain in humans due to the requirement for continuous or repeated imaging and pathological verification. We review the clinical and preclinical advances that have led to perfusion–diffusion mismatch being applied in phase 3 randomized trials and, potentially, future routine clinical practice.

A Multicenter, Randomized, Controlled Study to Investigate Extending the Time for Thrombolysis in Emergency Neurological Deficits with Intra-Arterial Therapy (EXTEND-IA)

Background and Hypothesis

Thrombolysis with tissue plasminogen activator is proven to reduce disability when given within 4.5 h of ischemic stroke onset. However, tissue plasminogen activator only succeeds in recanalizing large vessel arterial occlusion in a minority of patients. We hypothesized that anterior circulation ischemic stroke patients, selected with ‘dual target’ vessel occlusion and evidence of salvageable brain using computed tomography or magnetic resonance imaging ‘mismatch’ within 4.5 h of onset, would have improved reperfusion and early neurological improvement when treated with intra-arterial clot retrieval after intravenous tissue plasminogen activator compared with intravenous tissue plasminogen activator alone.

Study Design

EXTEND-IA is an investigator-initiated, phase II, multicenter prospective, randomized, open-label, blinded-endpoint study. Ischemic stroke patients receiving standard 0.9 mg/kg intravenous tissue plasminogen activator within 4.5 h of stroke onset who have good prestroke functional status (modified Rankin Scale <2, no upper age limit) will undergo multimodal computed tomography or magnetic resonance imaging. Patients who also meet dual target imaging criteria: vessel occlusion (internal carotid or middle cerebral artery) and mismatch (perfusion lesion: ischemic core mismatch ratio >1.2, absolute mismatch >10 ml, ischemic core volume <70 ml) will be randomized to either clot retrieval with the Solitaire FR device after full dose intravenous tissue plasminogen activator, or tissue plasminogen activator alone.

Study Outcomes

The coprimary outcome measure will be reperfusion at 24 h and favorable clinical response (reduction in National Institutes of Health Stroke Scale by ≥8 points or reaching 0–1) at day 3. Secondary outcomes include modified Rankin Scale at day 90, death, and symptomatic intracranial hemorrhage.

Perfluorocarbons enhance a T2*-based MRI technique for identifying the penumbra in a rat model of acute ischemic stroke

Accurate imaging of ischemic penumbra is crucial for improving the management of acute stroke patients. T2* magnetic resonance imaging (MRI) combined with a T2*oxygen challenge (T2*OC) is being developed to detect penumbra based on changes in blood deoxyhemoglobin. Using 100% O2, T2*OC-defined penumbra exhibits ongoing glucose metabolism and tissue recovery on reperfusion. However, potential limitations in translating this technique include a sinus artefact in human scans with delivery of 100% OC and relatively small signal changes. Here we investigate whether an oxygen-carrying perfluorocarbon (PFC) emulsion can enhance the sensitivity of the technique, enabling penumbra detection with lower levels of inspired oxygen. Stroke was induced in male Sprague-Dawley rats (n=17) with ischemic injury and perfusion deficit determined by diffusion and perfusion MRI, respectively. T2* signal change was measured in regions of interest (ROIs) located within ischemic core, T2*OC-defined penumbra and equivalent contralateral areas during 40% O2±prior PFC injection. Region of interest analyses between groups showed that PFC significantly enhanced the T2* response to 40% O2 in T2*-defined penumbra (mean increase of 10.6±2.3% compared to 5.6±1.5% with 40% O2, P<0.001). This enhancement was specific to the penumbra ROI. Perfluorocarbon emulsions therefore enhances the translational potential of the T2*OC technique for identifying penumbra in acute stroke patients.

Perfusion imaging in brain disease

Perfusion CT or MRI have been extensively developed over the last years and are accessible on most imaging machines. Perfusion CT has taken a major place in the assessment of a stroke. Its role has to be specified for the diagnosis and treatment of the vasospasm, complicating a subarachnoid hemorrhage. Perfusion MRI should be included in the assessment of any brain tumor, both at the time of the diagnosis as well as in the post-treatment monitoring. It is included in the multimodal approach required for the optimum treatment of this disease. The applications in epilepsy and the neurodegenerative diseases are in the evaluation process.

Advanced neuroimaging to guide acute stroke therapy

Traditionally non-contrast CT has been considered the first choice imaging modality for acute stroke. Acute ischemic stroke patients presenting to the hospital within 3-hours from symptom onset and without any visible hemorrhages or large lesions on CT images are considered optimum reperfusion therapy candidates. However, non-contrast CT alone has been unable to identify best reperfusion therapy candidates outside this window. New advanced imaging techniques are now being used successfully for this purpose. Non-invasive CT or MR angiography images can be obtained during initial imaging evaluation for identification and characterization of vascular lesions, including occlusions, aneurysms, and malformations. Either CT-based perfusion imaging or MRI-based diffusion and perfusion imaging performed immediately upon arrival of a patient to the hospital helps estimate the extent of fixed core and penumbra in ischemic lesions. Patients having occlusive lesions with small fixed cores and large penumbra are preferred reperfusion therapy candidates.

Negative diffusion-weighted imaging after intravenous tissue-type plasminogen activator is rare and unlikely to indicate averted infarction

BACKGROUND AND PURPOSE

Some patients treated with intravenous (IV) tissue-type plasminogen activator (tPA) have negative diffusion-weighted imaging (DWI) on follow-up imaging. Without a visible infarct, there may be uncertainty as to whether the patient was having a stroke that was averted by tPA or whether the symptoms had not been cerebrovascular in origin. We evaluated patients presenting with suspected acute stroke with a positive DWI lesion before IV tPA to determine the probability of finding a negative DWI up to 48 hours after treatment.

METHODS

We included patients from the Lesion Evolution in Stroke and Ischemia On Neuroimaging (LESION) project who had acute MRI screening with a positive DWI lesion before IV tPA treatment and had follow-up MRI up to 48 hours later. Experienced readers interpreted all acute and follow-up MRIs looking for ischemic lesions on DWI.

RESULTS

There were 231 patients who met study inclusion criteria, of which 225 patients (97.4%) had a persistent positive DWI corresponding to the acute stroke lesion on all follow-up imaging. Four patients (1.7%) had transient DWI lesion reversal with positive DWI on subsequent follow-up imaging. There were only 2 cases (0.9%) of complete DWI lesion reversal on all follow-up imaging.

CONCLUSIONS

Averted infarction after IV tPA is rare, occurring in 0.9% of patients with pretreatment positive DWI evidence of acute ischemia. For IV tPA-treated patients who have a negative DWI on follow-up imaging, a cause other than acute stroke should be explored.

Complete Early Reversal of Diffusion-Weighted Imaging Hyperintensities After Ischemic Stroke Is Mainly Limited to Small Embolic Lesions

Background and Purpose—

Case reports have demonstrated complete early reversal of hyperintensities on diffusion-weighted imaging (DWI) after clinically diagnosed stroke. We aimed to investigate systematically the rate and characteristics of reversible diffusion hyperintensities (RDHs) in the first week after stroke.

Methods—

Patients with clinical diagnosis of an acute cerebrovascular event and evidence of ischemia on DWI were included. MRI scans were performed on admission, on the following day, and 4 to 7 days after onset of symptoms with DWI and fluid-attenuated inversion recovery. Baseline and follow-up DWIs were coregistered and examined for individual RDHs. Characteristics of patients and of hyperintensities associated with early reversal were identified.

Results—

We included 153 patients with a median National Institutes of Health Stroke Scale score of 4 (interquartile range, 2–8). In 3 patients (2%), MR images normalized completely. Thirty-seven patients (24%) displayed individual RDHs. Of 611 initial DWI hyperintensities, 97 (16%) reversed. Thirteen percent of the RDHs had corresponding abnormalities on fluid-attenuated inversion recovery images at the third measurement. Median size of the RDHs was 0.029 mL (interquartile range, 0.013–0.055). RDHs were associated with a multiple infarct pattern (odds ratio, 22.1; 95% confidence interval, 4.5–109.7) and symptomatic carotid stenosis (odds ratio, 5.5; 95% confidence interval, 1.4–21.5). Fifty-nine percent of the patients with RDHs had new additional lesions on follow-up DWI. RDHs were not associated with functional improvement on the National Institutes of Health Stroke Scale score.

Conclusions—

In this population of mainly minor to moderate stroke patients, complete normalization of MR images was rare. Complete reversal of individual DWI hyperintensities was limited to very small lesions and mostly occurred in embolic stroke patients.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00715533.

Advanced imaging to extend the therapeutic time window of acute ischemic stroke

Reperfusion therapy for acute stroke has evolved from the initial use of intravenous tissue plasminogen activator (tPA) within 3 hours of symptom onset to more recent guideline-recommended use up to 4.5 hours. In addition, endovascular therapy is increasingly utilized for stroke treatment and is typically initiated up to 8 hours after onset. Recent studies demonstrate that imaging of the ischemic penumbra with diffusion/perfusion magnetic resonance imaging (MRI) can identify subgroups of patients who are likely to improve following successful reperfusion (Target Mismatch profile) and others who are at increased risk for hemorrhage and poor clinical outcomes (Malignant profile). New data indicate that stent retriever devices provide better recanalization efficacy and clinical outcomes than the previously available mechanical thrombectomy devices. Going forward, we believe that the use of penumbral imaging with validated MRI techniques, as well as the currently less well-validated computed tomography (CT) perfusion approach, will maximize benefit and reduce the risk of adverse events and poor outcomes when used both early after stroke onset and at later time points. New trials that feature diffusion/perfusion MRI or CT perfusion-based patient selection for treatment with intravenous tPA and or endovascular therapies versus nonreperfused control groups are planned or in progress. We predict that these trials will confirm the hypothesis that penumbral imaging can enhance patient selection and extend the therapeutic time window for acute ischemic stroke.

The Massachusetts General Hospital acute stroke imaging algorithm: an experience and evidence based approach

The Massachusetts General Hospital Neuroradiology Division employed an experience and evidence based approach to develop a neuroimaging algorithm to best select patients with severe ischemic strokes caused by anterior circulation occlusions (ACOs) for intravenous tissue plasminogen activator and endovascular treatment. Methods found to be of value included the National Institutes of Health Stroke Scale (NIHSS), non-contrast CT, CT angiography (CTA) and diffusion MRI. Perfusion imaging by CT and MRI were found to be unnecessary for safe and effective triage of patients with severe ACOs. An algorithm was adopted that includes: non-contrast CT to identify hemorrhage and large hypodensity followed by CTA to identify the ACO; diffusion MRI to estimate the core infarct; and NIHSS in conjunction with diffusion data to estimate the clinical penumbra.

Early diffusion-weighted imaging and perfusion-weighted imaging lesion volumes forecast final infarct size in DEFUSE 2

BACKGROUND AND PURPOSE

It is hypothesized that early diffusion-weighted imaging (DWI) lesions accurately estimate the size of the irreversibly injured core and thresholded perfusion-weighted imaging (PWI) lesions (time to maximum of tissue residue function [Tmax] >6 seconds) approximate the volume of critically hypoperfused tissue. With incomplete reperfusion, the union of baseline DWI and posttreatment PWI is hypothesized to predict infarct volume.

METHODS

This is a substudy of Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution Study 2 (DEFUSE 2); all patients with technically adequate MRI scans at 3 time points were included. Baseline DWI and early follow-up PWI lesion volumes were determined by the RAPID software program. Final infarct volumes were assessed with 5-day fluid-attenuated inversion recovery and were corrected for edema. Reperfusion was defined on the basis of the reduction in PWI lesion volume between baseline and early follow-up MRI. DWI and PWI volumes were correlated with final infarct volumes.

RESULTS

Seventy-three patients were eligible. Twenty-six patients with >90% reperfusion show a high correlation between early DWI volume and final infarct volume (r=0.95; P<0.001). Nine patients with <10% reperfusion have a high correlation between baseline PWI (Tmax >6 seconds) volume and final infarct volume (r=0.86; P=0.002). Using all 73 patients, the union of baseline DWI and early follow-up PWI is highly correlated with final infarct volume (r=0.94; P<0.001). The median absolute difference between observed and predicted final volumes is 15 mL (interquartile range, 5.5-30.2).

CONCLUSIONS

Baseline DWI and early follow-up PWI (Tmax >6 seconds) volumes provide a reasonable approximation of final infarct volume after endovascular therapy.

MRI profile and response to endovascular reperfusion after stroke (DEFUSE 2): a prospective cohort study

BACKGROUND

Whether endovascular stroke treatment improves clinical outcomes is unclear because of the paucity of data from randomised placebo-controlled trials. We aimed to establish whether MRI can be used to identify patients who are most likely to benefit from endovascular reperfusion.

METHODS

In this prospective cohort study we consecutively enrolled patients scheduled to have endovascular treatment within 12 h of onset of stroke at eight centres in the USA and one in Austria. Aided by an automated image analysis computer program, investigators interpreted a baseline MRI scan taken before treatment to establish whether the patient had an MRI profile (target mismatch) that suggested salvageable tissue was present. Reperfusion was assessed on an early follow-up MRI scan (within 12 h of the revascularisation procedure) and defined as a more than 50% reduction in the volume of the lesion from baseline on perfusion-weighted MRI. The primary outcome was favourable clinical response, defined as an improvement of 8 or more on the National Institutes of Health Stroke Scale between baseline and day 30 or a score of 0-1 at day 30. The secondary clinical endpoint was good functional outcome, defined as a modified Rankin scale score of 2 or less at day 90. Analyses were adjusted for imbalances in baseline predictors of outcome. Investigators assessing outcomes were masked to baseline data.

FINDINGS

138 patients were enrolled. 110 patients had catheter angiography and of these 104 had an MRI profile and 99 could be assessed for reperfusion. 46 of 78 (59%) patients with target mismatch and 12 of 21 (57%) patients without target mismatch had reperfusion after endovascular treatment. The adjusted odds ratio (OR) for favourable clinical response associated with reperfusion was 8·8 (95% CI 2·7-29·0) in the target mismatch group and 0·2 (0·0-1·6) in the no target mismatch group (p=0·003 for difference between ORs). Reperfusion was associated with increased good functional outcome at 90 days (OR 4·0, 95% CI 1·3-12·2) in the target mismatch group, but not in the no target mismatch group (1·9, 0·2-18·7).

INTERPRETATION

Target mismatch patients who had early reperfusion after endovascular stroke treatment had more favourable clinical outcomes. No association between reperfusion and favourable outcomes was present in patients without target mismatch. Our data suggest that a randomised controlled trial of endovascular treatment for patients with the target mismatch profile is warranted.

FUNDING

National Institute for Neurological Disorders and Stroke.

Early Ischaemic Diffusion Lesion Reduction in Patients Treated with Intravenous Tissue Plasminogen Activator: Infrequent, but Significantly Associated with Recanalization

Background and purpose

Recent studies have shown that thrombolysis could decrease or eliminate ischaemic diffusion-weighted imaging lesions. However, the features of such diffusion-weighted imaging lesion reduction are not well known.

Aims

To clarify, the frequency of and factors associated with lesion reduction were investigated.

Methods

Patients given intravenous tissue plasminogen activator therapy within three-hours of onset were prospectively enrolled. Magnetic resonance imaging including diffusion-weighted imaging and magnetic resonance angiography was performed four times: on admission, just after intravenous tissue plasminogen activator, 24 h from intravenous tissue plasminogen activator, and seven-days after intravenous tissue plasminogen activator. The diffusion-weighted imaging lesion volume was measured by manual trace using National Institutes of Health imaging software. All patients were divided into three groups according to the early diffusion-weighted imaging lesion volume change from admission to just after intravenous tissue plasminogen activator: the lesion reduction group (>20% decrease); the lesion growth group (>20% increase); and the lesion unchanged group.

Results

In total, 105 patients [56 males, median age 77 (interquartile range 70–83) years, and National Institutes of Health Stroke Scale score 16 ( 10 – 22 )] were enrolled. Early diffusion-weighted imaging lesion reduction was observed in seven (7%) patients. The decreased lesion increased subsequently. On multivariate analysis, the glucose level on admission (odds ratio 0·95, 95% confidence interval 0·91 to 0·99, P = 0·045) and early recanalization (odds ratio 15·7, 95% confidence interval 1·61 to 153, P = 0·018) were independently related to early lesion reduction.

Conclusion

Early diffusion-weighted imaging lesion reduction was observed in 7% of patients treated with intravenous tissue plasminogen activator. The decreased lesion increased subsequently. Initial glucose level and early recanalization were independently associated with early diffusion-weighted imaging lesion reduction.

Treatment of acute ischemic stroke: systemic or local?

Systemic treatment of acute ischemic stroke currently means intravenous infusion of plasminogen activator in patients with the stroke syndrome after exclusion of brain hemorrhage irrespective of whether thrombotic arterial obstruction is present or not. In contrast, local intra-arterial treatment requires digital subtraction angiography and means direct treatment of the arterial pathology with the aim of recanalization and brain tissue reperfusion. Randomized controlled trials that test these two treatment approaches are missing. This paper discusses whether the time-saving systemic treatment approach is more promising for acute ischemic stroke patients than is the time-consuming endovascular local approach.

The Desmoteplase in Acute Ischemic Stroke (DIAS) Clinical Trial Program

Background

Desmoteplase is a novel, highly fibrin-specific thrombolytic agent in phase III of clinical development. In comparison to alteplase, it has high fibrin selectivity, is associated with minimal or no neurotoxicity, and has no apparent negative effect on the blood–brain barrier. The safety and efficacy of desmoteplase is being studied in the Desmoteplase in Acute Ischemic Stroke clinical trial program. Three studies (Dose Escalation Study of Desmoteplase in Acute Ischemic Stroke, Desmoteplase in Acute Ischemic Stroke, and Desmoteplase in Acute Ischemic Stroke-2) have been completed, two large randomized, double-blind, placebo-controlled, phase III trials are ongoing at >200 sites worldwide (Desmoteplase in Acute Ischemic Stroke-3 and Desmoteplase in Acute Ischemic Stroke-4, n = 800; DIAS-3 and DIAS-4), and a randomized, double-blind, placebo-controlled, dose-escalation phase II trial is ongoing in Japan (Desmoteplase in Acute Ischemic Stroke-Japan, n = 48; DIAS-J).

Aims

The objective of DIAS-3 and DIAS-4 is to evaluate the safety and efficacy of a single IV bolus injection of 90 μg/kg desmoteplase given three- to nine-hours after onset of ischemic stroke (National Institutes of Health Stroke Scale 4–24, age 18–85 years). The objective of DIAS-J is to evaluate the safety and tolerability of desmoteplase 70 and 90 μg/kg three- to nine-hours after ischemic stroke onset in Japanese patients.

Methods

Patients are included with occlusion or high-grade stenosis (thrombolysis in myocardial infarction 0–1) in proximal cerebral arteries on magnetic resonance or computed tomography angiography but excluded with extended ischemic edema on computed tomography or diffusion-weighted imaging.

Conclusion

Desmoteplase is the only thrombolytic agent in late-stage development for acute ischemic stroke that is now tested in patients with proven stroke pathology. The results of the Desmoteplase in Acute Ischemic Stroke clinical trial program will show whether patients with major artery occlusions but not extended ischemic brain damage can be safely and effectively treated up to nine-hours after onset.

Comparison of computed tomography perfusion and magnetic resonance imaging perfusion-diffusion mismatch in ischemic stroke

BACKGROUND AND PURPOSE

Perfusion imaging has the potential to select patients most likely to respond to thrombolysis. We tested the correspondence of computed tomography perfusion (CTP)-derived mismatch with contemporaneous perfusion-diffusion magnetic resonance imaging (MRI).

METHODS

Acute ischemic stroke patients 3 to 6 hours after onset had CTP and perfusion-diffusion MRI within 1 hour, before thrombolysis. Relative cerebral blood flow (relCBF) and time to peak of the deconvolved tissue residue function (Tmax) were calculated. The diffusion lesion (diffusion-weighted imaging) was registered to the CTP slabs and manually outlined to its maximal visual extent. Volumetric accuracy of CT-relCBF infarct core (compared with diffusion-weighted imaging) was tested. To reduce false-positive low CBF regions, relCBF core was restricted to voxels within a relative time-to-peak (relTTP) >4 seconds for lesion region of interest. The MR-Tmax >6 seconds perfusion lesion was automatically segmented and registered to CTP. Receiver-operating characteristic analysis determined the optimal CT-Tmax threshold to match MR-Tmax >6 seconds. Agreement of these CT parameters with MR perfusion-diffusion mismatch in coregistered slabs was assessed (mismatch ratio >1.2, absolute mismatch >10 mL, infarct core <70 mL).

RESULTS

In analysis of 49 patients (mean onset to CT, 213 minutes; mean CT to MR, 31 minutes), constraining relCBF <31% within the automated relTTP perfusion lesion region of interest reduced the median magnitude of volumetric error (vs diffusion-weighted imaging) from 47.5 mL to 15.8 mL (P<0.001). The optimal CT-Tmax threshold to match MR-Tmax >6 seconds was 6.2 seconds (95% confidence interval, 5.6-7.3 seconds; sensitivity, 91%; specificity, 70%; area under the curve, 0.87). Using CT-Tmax >6 seconds "penumbra" and relTTP-constrained relCBF "core," CT-based and MRI-based mismatch status was concordant in 90% (kappa=0.80).

CONCLUSIONS

Quantitative CTP mismatch classification using relCBF and Tmax is similar to perfusion-diffusion MRI. The greater accessibility of CTP may facilitate generalizability of mismatch-based selection in clinical practice and trials.

Standards and pitfalls of focal ischemia models in spontaneously hypertensive rats: with a systematic review of recent articles

We reviewed the early development of various focal ischemia models in spontaneously hypertensive rats (SHR), and summarized recent reports on this topic. Among 6 focal ischemia models established in divergent substrains of SHR, distal middle cerebral artery occlusion is the most frequently used and relevant method of focal ischemia in the light of penumbra concept. We performed an online PubMed search (2001–2010), and identified 118 original articles with focal ischemia in SHR. Physiological parameters such as age, body weight, and even blood pressure were often neglected in the literature: the information regarding the physiological parameters of SHR is critical, and should be provided within the methodology section of all articles related to stroke models in SHR. Although the quality of recent studies on neuroprotective strategy is improving, the mechanisms underlying the protection should be more clearly recognized so as to facilitate the translation from animal studies to human stroke. To overcome the genetic heterogeneity in substrains of SHR, new approaches, such as a huge repository of genetic markers in rat strains and the congenic strategy, are currently in progress.

Refining the mismatch concept in acute stroke: lessons learned from PET and MRI

In ischemic stroke, positron-emission tomography (PET) established the imaging-based concept of penumbra. It defines hypoperfused, but functionally impaired, tissue with preserved viability that can be rescued by timely reperfusion. Diffusion-weighted and perfusion-weighted (PW) magnetic resonance imaging (MRI) translated the concept of penumbra to the concept of mismatch. However, the use of mismatch-based patient stratification for reperfusion therapy remains a matter of debate. The equivalence of mismatch and penumbra, as well as the validity of the classical mismatch concept is questioned for several reasons. First, methodological differences between PET and MRI lead to different definitions of the tissue at risk. Second, the mismatch concept is still poorly standardized among imaging facilities causing relevant variability in stroke research. Third, relevant conceptual issues (e.g., the choice of the adequate perfusion measure, the best quantitative approach to perfusion maps, and the required size of the mismatch) need further refinement. Fourth, the use of single thresholds does not account for the physiological heterogeneity of the penumbra and probabilistic approaches may be more promising. The implementation of this current knowledge into an optimized state-of-the-art mismatch model and its validation in clinical stroke studies remains a major challenge for future stroke research.

Current acute stroke trials and their potential impact on the therapeutic time window

Several trials in acute stroke are underway or have been completed recently. Among the latter, ECASS 3 was a milestone regarding the extension of the rigid 3-h time window out to 4.5 h for intravenous thrombolysis with recombinant tissue plasminogen activator. Several other approaches are being tested for thrombolytic therapy, among them modern imaging-based patient selection of patients and interventional approaches. Other pharmaceutical strategies include neuroprotection, and restoration, biophysical approaches, such as near infrared laser therapy, hemodynamic augmentation, and sphenopalatine ganglion stimulation. This perspective will cover the recently completed and currently recruiting acute stroke trials with respect to their potential role in expanding the therapeutic time window for acute ischemic stroke.

Perfusion/Diffusion mismatch is valid and should be used for selecting delayed interventions

The mismatch between a larger perfusion lesion and smaller diffusion lesion on magnetic resonance imaging is a validated signal of the ischemic penumbra, namely the region at risk in acute ischemic stroke that is critically hypoperfused and the target of reperfusion therapies. Clinical trials have shown strong correlations between reperfusion in mismatch patients and improved clinical outcomes. Attenuation of infarct growth is associated with reperfusion and corresponding clinical gains. Using computed tomography perfusion, the mismatch between relative cerebral blood flow or cerebral blood volume and perfusion delay is a comparable penumbral marker. Automated techniques allow rapid quantitative assessment of mismatch with thresholding to exclude benign oligemia. The penumbra is often present beyond the current 4.5-h time window, defined for the use of intravenous tPA. Treatment beyond this time point remains investigational. Although the efficacy of thrombolysis in mismatch patients requires further validation in randomized trials, there is now sufficient evidence to recommend that advanced neuroimaging of mismatch should be used for selection of delayed therapies in phase 3 trials.