Magnetic resonance imaging in acute ischemic stroke treatment

Reliability of fast magnetic resonance imaging for acute ischemic stroke patients using a 1.5-T scanner

OBJECTIVES

To determine whether fast scanned MRI using a 1.5-T scanner is a reliable method for the detection and characterization of acute ischemic stroke in comparison with conventional MRI.

METHODS

From May 2015 to June 2016, 862 patients (FLAIR, n = 482; GRE, n = 380; MRA, n = 190) were prospectively enrolled in the study, with informed consent and under institutional review board approval. The patients underwent both fast (EPI-FLAIR, ETL-FLAIR, TR-FLAIR, EPI-GRE, parallel-GRE, fast CE-MRA) and conventional MRI (FLAIR, GRE, time-of-flight MRA, fast CE-MRA). Two neuroradiologists independently assessed agreements in acute and chronic ischemic hyperintensity, hyperintense vessels (FLAIR), microbleeds, susceptibility vessel signs, hemorrhagic transformation (GRE), stenosis (MRA), and image quality (all MRI), between fast and conventional MRI. Agreements between fast and conventional MRI were evaluated by generalized estimating equations. Z-scores were used for comparisons of the percentage agreement among fast FLAIR sequences and fast GRE sequences and between conventional and fast MRA.

RESULTS

Agreements of more than 80% were achieved between fast and conventional MRI (ETL-FLAIR, 96%; TR-FLAIR, 97%; EPI-GRE, 96%; parallel-GRE, 98%; fast CE-MRA, 86%). ETL- and TR-FLAIR were significantly superior to EPI-FLAIR in the detection of acute ischemic hyperintensity and hyperintense vessels, while parallel-GRE was significantly superior to EPI-GRE in the detection of susceptibility vessel sign (p value < 0.05 for all). There were no significant differences in the other scores and image qualities (p value > 0.05).

CONCLUSIONS

Fast MRI at 1.5 T is a reliable method for the detection and characterization of acute ischemic stroke in comparison with conventional MRI.

KEY POINTS

• Fast MRI at 1.5 T may achieve a high intermethod reliability in the detection and characterization of acute ischemic stroke with a reduction in scan time in comparison with conventional MRI.

Development and validation of a penumbra-based predictive model for thrombolysis outcome in acute ischemic stroke patients

The use of thrombolysis in acute ischemic stroke is restricted to a small proportion of patients because of the rigid 4·5-h window. With advanced imaging-based patient selection strategy, rescuing penumbra is critical to improving clinical outcomes. In this study, we included 155 acute ischemic stroke patients (84 patients in training dataset, age from 43 to 80, 59 males; 71 patients in validation dataset, age from 36 to 80, 45 males) who underwent MR scan within the first 9-h after onset, from 7 independent centers. Based on the mismatch concept, penumbra and core area were identified and quantitatively analyzed. Moreover, predictive models were developed and validated to provide an approach for identifying patients who may benefit from thrombolytic therapy. Predictive models were constructed, and corresponding areas under the curve (AUC) were calculated to explore their performances in predicting clinical outcomes. Additionally, the models were validated using an independent dataset both on Day-7 and Day-90. Significant correlations were detected between the mismatch ratio and clinical assessments in both the training and validation datasets. Treatment option, baseline systolic blood pressure, National Institutes of Health Stroke Scale score, mismatch ratio, and three regional radiological parameters were selected as biomarkers in the combined model to predict clinical outcomes of acute ischemic stroke patients. With the external validation, this predictive model reached AUCs of 0·863 as short-term validation and 0·778 as long-term validation. This model has the potential to provide quantitative biomarkers that aid patient selection for thrombolysis either within or beyond the current time window.

Neuroprotective measures throughout the TAVI pathway

Aortic stenosis (AS) is the most common clinical valvular heart disorder that warrants active treatment. Symptomatic and severe AS is associated with increased morbidity and mortality if left untouched. Transcatheter aortic valve implantation (TAVI) is an innovative therapeutic modality approved initially for patients with prohibitive surgical risk and subsequently became a mainstream practice and the preferred treatment modality for many patients with severe AS at high and moderate surgical risk. Consistently global TAVI volumes have increased and indications continue to widen toward younger and lower-risk patients. However, periprocedural stroke is one of the most feared complications of TAVI, and when clinically evident, it is often associated with significant increase in mortality, physical disability, social isolation and financial costs. Furthermore, even when clinically overt stroke is not evident following TAVI, highly sensitive imaging modalities have demonstrated new post-procedural ischemic lesions in most patients. Although little is known about the long-term clinical significance of these lesions, there are strong signals showing they might be related with reduced subsequent neurocognitive function. This review provides a comprehensive contemporary insight of the definitions, incidence and temporal trends of stroke in TAVI patients, as well as the mechanisms, etiologies and risk factors for such neurological events. Furthermore, an integrated approach of neuroprotective measures targeted to reduce the incidence of stroke during each phase of the periprocedural TAVI pathway is suggested with a special focus on the role of embolic protective devices.

Susceptibility Vessel Sign in the ASTER Trial: Higher Recanalization Rate and More Favourable Clinical Outcome after First Line Stent Retriever Compared to Contact Aspiration

Background and Purpose

In the Aspiration vs. Stent Retriever for Successful Revascularization (ASTER) trial, which evaluated contact aspiration (CA) versus stent retriever (SR) use as first-line technique, the impact of the susceptibility vessel sign (SVS) on magnetic resonance imaging (MRI) was studied to determine its influence on trial results.

Methods

We included patients having undergone CA or SR for M1 or M2 occlusions, who were screened by MRI with T2^* gradient recalled echo. Occlusions were classified as SVS (+) or SVS (–) in each randomization arm. Modified thrombolysis in cerebral infarction (mTICI) 2b, 2c, or 3 revascularization rates were recorded and clinical outcomes assessed by the overall distribution of modified Rankin scale (mRS) at 90 days.

Results

Among the 202 patients included, 143 patients were SVS (+) (70.8%; 95% confidence interval [CI], 64.5% to 77.1%). Overall, there was no difference in angiographic and clinical outcomes according to SVS status. However, compared to SR, CA achieved a lower mTICI 2c/3 rate in SVS (+) patients (risk ratio [RR] for CA vs. SR, 0.60; 95% CI, 0.51 to 0.71) but not in SVS (–) (RR, 1.11; 95% CI, 0.69 to 1.77; P for interaction=0.018). A significant heterogeneity in favor of superiority of first-line SR strategy in SVS (+) patients was also found regarding the overall mRS distribution (common odds ratio for CA vs. SR, 0.40 vs. 1.32; 95% CI, 0.21 to 0.74 in SVS (+) vs. 95% CI, 0.51 to 3.35 in SVS (–); P for interaction=0.038).

Conclusions

As a first line strategy, SR achieved higher recanalization rates and a more favourable clinical outcome at 3 months compared to CA when MRI shows SVS within the thrombus.

Diffusion-weighted imaging detects early brain injury after hypothermic circulatory arrest in pigs

OBJECTIVES

Cerebral injury is a complication of surgery with deep hypothermic circulatory arrest (DHCA). This study aimed to evaluate diffusion-weighted imaging (DWI) for the early detection of brain injury after DHCA in an animal model.

METHODS

Twelve healthy, adult, male miniature pigs were randomly divided into the DHCA (to receive DHCA; n = 6) and the control (sham surgery under anaesthesia; n = 6) groups. All animals received DWI, T1-weighted imaging (T1WI) and T2WI the day before surgery, 7 h postoperatively and 24 h postoperatively. Histopathological evaluation of the brain tissues was performed in the DHCA group using the Fluoro-Jade C staining to detect neuronal degeneration, the Nissl staining to show neuronal morphology and the TUNEL assay for apoptosis. The Cohen's kappa coefficient was used to compare the results of DWI with those of the histopathological evaluation.

RESULTS

All animals survived surgery. In the control group, no new focal brain lesions were detected by postoperative DWI, T1WI or T2WI. In the DHCA group, new focal brain lesions were detected as early as 7 h postoperatively by DWI but not T1WI or T2WI. All three imaging sequences revealed abnormalities 24 h after surgery. In sections from areas showing abnormalities on DWI, the Fluoro-Jade C staining detected neuronal degeneration, the Nissl staining showed morphological abnormalities and the TUNEL assay demonstrated apoptotic cells. The Cohen's kappa statistics showed agreement between DWI findings and the results of all 3 histopathological examinations (TUNEL: kappa = 0.553; Nissl: kappa = 0.652; Fluoro-Jade C: kappa = 0.778; all P < 0.001).

CONCLUSIONS

DWI is superior to T1WI or T2WI for the early detection of neurological lesions after DHCA in pigs.

Lateral Medullary Infarction with or without Extra-Lateral Medullary Lesions: What Is the Difference?

BACKGROUND

Lateral medullary infarction (LMI) is not an uncommon disease. Although lesions are usually restricted to the lateral medullary area, some patients have additional infarcts in other parts of the brain. The clinical features and prognosis of isolated LMI (pure LMI, LMIpr) have been investigated. However, it remains unclear whether clinical characteristics, prognosis and factors associated with prognosis differ between patients with LMIpr and those with additional lesions (LMI plus, LMIpl).

METHODS

Patients with LMI identified by MRI were enrolled. The demographic and clinical characteristics, in-hospital outcome (intensive care unit [ICU] admission, pneumonia and modified Rankin scale [mRS] at discharge), and long-term residual symptoms (vertigo/dizziness, sensory disturbances, dysphagia) and outcomes (occurrence of stroke, acute coronary syndrome [ACS], death, and mRS at follow-up) were compared between LMIpr and LMIpl patients. Factors associated with poor functional outcome (mRS 2-6) at the follow-up were analyzed.

RESULTS

Among 248 LMI patients, 161 (64.9%) had LMIpr and 87 (35.1%) had LMIpl. During admission, patients with LMIpl more frequently experienced ICU care, pneumonia and had a higher discharge mRS (3 vs. 2; p < 0.001) than LMIpr patients. The occurrence of stroke, ACS, frequency of death and functional outcome was not different during follow-up. However, residual neurologic symptoms such as dizziness (p = 0.002), dysphagia (p = 0.04) and sensory symptoms (p < 0.001) were more frequent in LMIpr than in LMIpl patients. In LMIpr patients, the rostral location of LMI was associated with poor functional outcome (p = 0.041), whereas in LMIpl patients, the presence of medial posterior-inferior cerebellar artery lesion was associated with good functional outcome (p = 0.030).

CONCLUSION

Although the short-term outcome is poorer in LMIpl than LMIpr patients, long-term residual symptoms are more common in LMIpr patients. The location of the LMI and extra-medullary lesion affects the long-term functional outcome of LMIpr and LMIpl patients respectively.

Remote Diffusion-Weighted Imaging Lesions in Intracerebral Hemorrhage: Characteristics, Mechanisms, Outcomes, and Therapeutic Implications

Spontaneous intracerebral hemorrhage (ICH) is one of the most fatal form of stroke, with high mortality and disability rate. Small diffusion-weighed imaging lesions are not rare to see in regions remote from the hematoma after ICH and have been generally considered as related with poor outcome. In this review, we described the characteristics of remote ischemic lesions, discussed the possible mechanisms and clinical outcomes of these lesions, and evaluated the potential therapeutic implications.

Deep into the Brain: Artificial Intelligence in Stroke Imaging

Artificial intelligence (AI), a computer system aiming to mimic human intelligence, is gaining increasing interest and is being incorporated into many fields, including medicine. Stroke medicine is one such area of application of AI, for improving the accuracy of diagnosis and the quality of patient care. For stroke management, adequate analysis of stroke imaging is crucial. Recently, AI techniques have been applied to decipher the data from stroke imaging and have demonstrated some promising results. In the very near future, such AI techniques may play a pivotal role in determining the therapeutic methods and predicting the prognosis for stroke patients in an individualized manner. In this review, we offer a glimpse at the use of AI in stroke imaging, specifically focusing on its technical principles, clinical application, and future perspectives.

Patterns of Acute Ischemic Strokes After Carotid Endarterectomy and Therapeutic Implications

AIM

Acute ischemic strokes following surgical treatment of carotid stenosis lead to substantial disability and mortality, and vascular mechanisms underlying their development are not fully elucidated. The goal of this study was to analyze the topographic patterns of acute ischemic stroke following carotid endarterectomy (CEA) on diffusion-weighted and perfusion-weighted magnetic resonance imaging (MRI).

MATERIAL AND METHODS

Data were retrospectively collected from consecutive patients who underwent CEA and developed postoperative acute ischemic stroke. Based on the MRI data sets, the lesion patterns of acute stoke were characterized. Morphology of the circle of Willis, the 3-D time-of-flight (3D-TOF) of the cerebral arteries, and status of the carotid circulation were also analyzed in order to determine the vascular mechanisms involved in stroke development.

RESULTS

Between January 2008 and May 2015, 821 patients were treated surgically for a symptomatic or asymptomatic carotid stenosis at the University Hospital of Nice. Nineteen (2.3%) patients had an acute ischemic stroke after surgery. Among them, 11 (57.9%) patients had a territorial infarction and 8 (42.1%) patients had an internal watershed infarction, cortical watershed infarction, or mixed border zone infarction. According to imaging data sets, embolic mechanism of stroke was reported for 12 (63.2%) patients, hemodynamic mechanism for 2 (10.5%) patients, and mixed mechanism for 5 (26.3%) patients. An asymmetry on 3D-TOF was observed in 60% and 50% of patients with hemodynamic and mixed stroke and in 25% of patients with embolic stroke. The latter 2 patients with embolic stroke underwent successful mechanical thrombectomy using stent-retriever devices.

CONCLUSION

In this cohort, embolic mechanism leading to postoperative stroke was more frequently observed than hemodynamic mechanism. Immediate characterization of the cerebral lesion by postoperative brain MRI is of utmost importance because it may rapidly identify patients eligible for treatments such as mechanical thrombectomy.

Association between nocturnal blood pressure variation and wake-up ischemic stroke

Ischemic stroke during nocturnal sleep, known as wake-up stroke (WUS), has been reported to have more severe symptoms and worse outcomes than non-WUS. However, studies on risk factors for WUS are scarce and the association between nocturnal blood pressure (BP) and WUS is unclear. In this study, we used ambulatory blood pressure monitoring (ABPM) to examine the association between WUS and variation in nocturnal BP. A total of 369 patients with ischemic stroke within one week were consecutively enrolled. ABPM was applied 1-2weeks after the ictus because of possible reactive increments of BP; antihypertensive medications were delayed until ABPM. Patients were classified into two groups: WUS and non-WUS. Clinical characteristics, including ABPM parameters, were compared. Sixty-seven (18%) patients had WUS. In univariate analysis, patients with WUS had more severe stroke symptoms than patients with non-WUS. There were no differences in clinical characteristics. In addition, ABPM parameters, including nocturnal BP dipping and morning BP surge, were not associated with occurrence of WUS. Patients with WUS had more severe stroke symptoms and worse outcomes than those with non-WUS. Variation in nocturnal BP may not associated with the occurrence of WUS.

Total mismatch of diffusion-weighted imaging and susceptibility-weighted imaging in patients with acute cerebral ischemia

BACKGROUND AND PURPOSE

Multiple hypointense vessels (MHV) on susceptibility-weighted imaging (SWI) is associated with an increased oxygen demand in acute cerebral ischemia. Occasionally, some patients exhibit extensive MHV on SWI despite of negative diffusion-weighted imaging (DWI), which is a phenomenon called total mismatch DWI-SWI. We analyzed the clinical characteristics and imaging findings in patients with the total DWI-SWI mismatch.

MATERIALS AND METHODS

We selected patients with total DWI-SWI mismatch who underwent MRI within 12hours from onset. To evaluate the degree of collateral flow, we graded vessels on post-contrast time-of-flight MR angiography as 3 groups. Perfusion lesion volume was measured using threshold of>6seconds of mean transit time on perfusion-weighted imaging.

RESULTS

Total DWI-SWI mismatch was found in 10 (2.7%) out of 370 patients. Four out of 10 patients were excluded due to lack of data on perfusion studies. Hence 6 patients were finally selected in the study. Two patients with internal carotid artery dissection were treated with emergent stenting, one patient with intravenous thrombolysis and mechanical thrombectomy, and two patients with drug-induced hypertension. All of the enrolled patients exhibited extensive MHV on SWI and good collateral flows. The mean perfusion lesion volume was 72.6±15.3ml (range 0-325.0ml). Clinical outcome was favorable in all of the patients (mRS at 3 months, 0).

CONCLUSIONS

Our results demonstrate that total mismatch of DWI-SWI is associated with good collateral flow and may be a predictor of good response to treatment in patients with acute cerebral ischemia.

Unclear-onset stroke: Daytime-unwitnessed stroke vs. wake-up stroke

BACKGROUND AND PURPOSE

The onset of wake-up stroke and daytime-unwitnessed stroke is unclear. Though the clinical importance is similar by both being excluded from reperfusion therapy, the characteristics of daytime-unwitnessed stroke are less known than that of wake-up stroke. Here, we compared the characteristics between daytime-unwitnessed stroke and wake-up stroke.

METHODS

Unclear-onset (i.e., last-known normal time ≠ first-found abnormal time) stroke patients admitted within 24 h of recognition of stroke between February 2011 and October 2013 were reviewed. Demographics and clinical and imaging variables were compared between patients with daytime-unwitnessed stroke and those with wake-up stroke.

RESULTS

Among the 762 ischemic stroke patients, 276 (36.2%) had unclear-onset stroke (104 daytime-unwitnessed stroke and 172 wake-up stroke). Compared to wake-up stroke, daytime-unwitnessed stroke patients had a higher prevalence of cardioembolic stroke and more frequently presented altered mental status (p < 0.001) and/or aphasia (p < 0.001) with more severe neurological deficit (p < 0.001). However, the time from symptom recognition to hospital arrival was shorter (p < 0.001), and diffusion-weighted image-fluid-attenuated inversion recovery image mismatch (p = 0.02) and perfusion-diffusion mismatch (p = 0.001) were also more frequently observed in daytime-unwitnessed stroke. Finally, the proportion of patients eligible for thrombolysis (p < 0.001) was higher in daytime-unwitnessed stroke patients.

CONCLUSIONS

Clinical and imaging characteristics of daytime-unwitnessed stroke significantly differ from those of wake-up stroke. Daytime-unwitnessed stroke patients are more likely to receive reperfusion therapy, as they arrive at the hospital earlier after symptom recognition, compared to wake-up stroke patients.

Patient Selection and Clinical Efficacy of Urgent Superficial Temporal Artery-Middle Cerebral Artery Bypass in Acute Ischemic Stroke Using Advanced Magnetic Resonance Imaging Techniques

BACKGROUND: Selected patients with acute ischemic stroke might benefit from superficial temporal artery-middle cerebral artery (STA-MCA) bypass, but the indications for urgent STA-MCA bypass are unknown.

OBJECTIVE: To report our experiences of urgent STA-MCA bypass in patients requiring urgent reperfusion who were ineligible for other reperfusion therapies, using advanced magnetic resonance imaging (MRI) techniques.

METHODS: The inclusion criteria for urgent STA-MCA bypass were as follows: acute infarct volume &lt;70 mL with a ratio of perfusion/diffusion lesion volume ≥1.2, and a regional cerebral blood volume ratio &gt;0.85. From January 2013 to October 2015, 21 urgent STA-MCA bypass surgeries were performed. The control group included 19 patients who did not undergo bypass surgery mainly due to refusal of surgery or the decision of the neurologist. Clinical and radiological data were compared between the surgery and control group.

RESULTS: The median age of the control group (70 years, interquartile range [IQR] 58-76) was higher than that of the surgery group (62 years, IQR 49-66), but the median preoperative diffusion and perfusion lesion volumes of the surgery group (13.8 mL, IQR 7.5-26.0 and 120.9 mL, IQR 84.9-176.0, respectively) were higher than those of the control group (5.6 mL, IQR 2.1-9.1 and 69.7 mL, IQR 23.9-125.3, respectively). Sixteen (76.2%) patients in the surgery group and 2 (10.5%) patients in the control group had favorable outcomes (P &lt; .001). Logistic regression analysis identified bypass surgery as the strongest predictive factor.

CONCLUSION: STA-MCA bypass can be used as a therapeutic tool for acute ischemic stroke. Advanced MRI techniques are helpful for selecting patients and for decision making.

Role of Perfusion-Weighted Imaging in a Diffusion-Weighted-Imaging-Negative Transient Ischemic Attack

BACKGROUND AND PURPOSE

The absence of acute ischemic lesions in diffusion-weighted imaging (DWI) in transient ischemic attack (TIA) patients makes it difficult to diagnose the true vascular etiologies. Among patients with DWI-negative TIA, we investigated whether the presence of a perfusion-weighted imaging (PWI) abnormality implied a true vascular event by identifying new acute ischemic lesions in follow-up magnetic resonance imaging (MRI) in areas corresponding to the initial PWI abnormality.

METHODS

The included patients underwent DWI and PWI within 72 hours of TIA and also follow-up DWI at 3 days after the initial MRI. These patients had visited the emergency room between July 2009 and May 2015. Patients who demonstrated initial DWI lesions were excluded. The initial PWI abnormalities in the corresponding vascular territory were visually classified into three patterns: no abnormality, focal abnormality, and territorial abnormality.

RESULTS

No DWI lesions were evident in initial MRI in 345 of the 443 TIA patients. Follow-up DWI was applied to 87 of these 345 DWI-negative TIA patients. Initial PWI abnormalities were significantly associated with follow-up DWI abnormalities: 8 of 43 patients with no PWI abnormalities (18.6%) had new ischemic lesions, whereas 13 of 16 patients with focal perfusion abnormalities (81.2%) had new ischemic lesions in the areas of initial PWI abnormalities [odds ratio (OR)=15.1, 95% confidence interval (CI)=3.6-62.9], and 14 of 28 patients with territorial perfusion abnormalities (50%) had new lesions (OR=3.7, 95% CI=1.2-11.5).

CONCLUSIONS

PWI is useful in defining whether or not the transient neurological symptoms in DWI-negative TIA are true vascular events, and will help to improve the understanding of the pathomechanism of TIA.

Prognostic Value of Diffusion-Weighted Imaging (DWI) Apparent Diffusion Coefficient (ADC) in Patients with Hyperacute Cerebral Infarction Receiving rt-PA Intravenous Thrombolytic Therapy

BACKGROUND The aim of this study was to investigate the potential value of apparent diffusion coefficient (ADC) of diffusion-weighted imaging (DWI) in the prognosis of patients with hyperacute cerebral infarction (HCI) receiving intravenous thrombolytic therapy with recombinant tissue plasminogen activator (rt-PA). MATERIAL AND METHODS From June 2012 to June 2015, 58 cases of HCI (<6 h) undergoing rt-PA intravenous thrombolytic therapy (thrombolysis group) and 70 cases of HCI (<6 h) undergoing conventional antiplatelet and anticoagulant therapy (control group) in the same period were collected. DWI was conducted on all the subjects, and ADC maps were generated with Functool software to quantify ADC value. The clinical outcomes of HCI patients were observed for 3 months, and prognostic factors were analyzed. RESULTS Before thrombolysis treatment, the lesion area presented high signal intensity on DWI map and low signal intensity on ADC map, and gradually weakened signal intensity on DWI map and gradually enhanced signal intensity on ADC map were observed after thrombolysis. The ADC values of the thrombolysis group were significantly higher than those of the control group after treatment (24 h, 7 d, 30 d, and 90 d) (all P<0.05), and the ADC and rADC values in the thrombolysis group gradually increased over time (all P<0.05). Multiple logistic regression analysis showed that baseline National Institutes of Health Stroke Scale (NIHSS) score, baseline rADC value, and stroke history were the independent factors for the prognosis of HIC patients with thrombolysis (all P<0.05). CONCLUSIONS The values of ADC and rADC may provide guidance in the prognosis of HCI patients receiving rt-PA, and the baseline rADC value is the protective factor for the prognosis of HCI patients receiving rt-PA.

Hyperdense middle cerebral artery sign as the only radiological manifestation of hyperacute ischemic stroke in computed tomography

OBJECTIVES

The main aim of the study was to find the effect of hyperdense middle cerebral artery sign (HMCAS), as the only admission computed tomography (CT) manifestation of ischemic stroke involving middle cerebral artery (MCA) region, on the extent of stroke measured by Alberta Stroke Program Early CT score (ASPECTS) in the follow-up CT. The secondary aim was to determine the correlation between length of hyperdense MCA segment on admission CT and ASPECTS in follow-up CT.

METHODS

The group analyzed consisted of 118 patients with ischemic MCA region stroke, with no early signs of brain tissue ischemia on admission CT, but infarcts confirmed in follow-up CT, with extent evaluated using ASPECTS. For the subgroups: 66 patients with HMCAS present and 52 with HMCAS absent, median ASPECTS values were compared. In the subgroup with HMCAS present, length of hyperdense segment was measured and correlation with ASPECTS was determined.

RESULTS

The median ASPECTS 6 (min. 0, max. 9) in the subgroup with HMCAS present was significantly lower, compared to the score 8.5 (min. 0, max. 9) in the subgroup with HMCAS absent. Moderate correlation between the length of hyperdense segment and ASPECTS was found (R=-0.45).

CONCLUSION

In patients with ischemic stroke involving MCA region and no early signs of brain tissue ischemia on the admission CT, HMCAS is associated with significantly lower ASPECTS in the follow-up CT. There is moderate correlation between the length of hyperdense MCA segment and ASPECTS.

A spatiotemporal theory for MRI T2 relaxation time and apparent diffusion coefficient in the brain during acute ischaemia: Application and validation in a rat acute stroke model

The objective of this study is to present a mathematical model which can describe the spatiotemporal progression of cerebral ischaemia and predict magnetic resonance observables including the apparent diffusion coefficient (ADC) of water and transverse relaxation time T2 This is motivated by the sensitivity of the ADC to the location of cerebral ischaemia and T2 to its time-course, and that it has thus far proven challenging to relate observations of changes in these MR parameters to stroke timing, which is of considerable importance in making treatment choices in clinics. Our mathematical model, called the cytotoxic oedema/dissociation (CED) model, is based on the transit of water from the extra- to the intra-cellular environment (cytotoxic oedema) and concomitant degradation of supramacromolecular and macromolecular structures (such as microtubules and the cytoskeleton). It explains experimental observations of ADC and T2, as well as identifying the rate of spread of effects of ischaemia through a tissue as a dominant system parameter. The model brings the direct extraction of the timing of ischaemic stroke from quantitative MRI closer to reality, as well as providing insight on ischaemia pathology by imaging in general. We anticipate that this may improve patient access to thrombolytic treatment as a future application.

Brain microbleeds: Epidemiology and clinical implications

INTRODUCTION

Brain microbleeds (BMB) are haemosiderin deposits contained within macrophages, which are displayed as hypointense images in some T2-weighted magnetic resonance imaging sequences. There are still many questions to be answered about the pathophysiology and clinical relevance of BMB.

DEVELOPMENT

We conducted a literature review of the main epidemiological, clinical, and anatomical pathology studies of BMB performed in the general population, in patients at risk of or already suffering from a vascular disease, and in patients with cognitive impairment. We analysed the prevalence of BMB, risk factors, and potential pathophysiological mechanisms and clinical implications.

CONCLUSIONS

The prevalence of BMB is highly variable (3%-27% in the general population, 6%-80% in patients with vascular risk factors or vascular disease, and 16%-45% in patients with cognitive impairment). BMB are associated with ageing, Alzheimer disease (AD), and in particular haemorrhagic or ischaemic cerebrovascular disease. The pathological substrate of BMB is either lipohyalinosis (subcortical BMB) or cerebral amyloid angiopathy (lobar BMB). BMB exacerbate cognitive impairment, possibly through cortical-subcortical and intracortical disconnection, and increase the risk of death, mostly due to vascular causes. BMB also increase the risk of cerebral haemorrhage, particularly in patients with multiple lobar BMB (probable erebral amyloid angiopathy). Therefore, anticoagulant treatment may be contraindicated in these patients. In patients with lower risk of bleeding, the new oral anticoagulants and the combination of clinical and magnetic resonance imaging follow-up could be helpful in the decision-making process.

Rapid and Sensitive Differentiating Ischemic and Hemorrhagic Strokes by Dried Blood Spot Based Direct Injection Mass Spectrometry Metabolomics Analysis

Cerebral infarction (CI) and intracerebral hemorrhage are lethal cerebrovascular diseases, sometimes sharing similar clinical manifestations but with distinct therapeutic strategies. Delayed treatment usually resulted in poor prognosis. A timely diagnosis report is highly warranted especially in emergency. One hundred twenty-nine CI patients, 73 intracerebral hemorrhage (ICH) patients, and 98 controls were enrolled in this study. A direct injection mass spectrometry metabolomics approach was adopted using dried blood spot samples. This targeted metabolomics analysis focused on absolute quantitation of 23 amino acids, 26 carnitine/carnitine esters, and 22 calculated ratios parameters. Compared to the normal control group, CI and ICH showed distinct metabolite changes, respectively. For stroke differentiation, Tyr, C5-OH/C0, Cit, Asn, Pro, Val, Arg/Orn, Leu, and Val/Phe were elevated in the CI group. On the contrary, C5:1, Phe/Tyr, (C0 + C2 + C3 + C16 + C18:1)/Cit, and Met/Leu were of lower levels in the CI group. Using regression model based on some of the above-mentioned parameters, 79.07% of stroke patients from a new set could be definitely confirmed. This study proved the targeted metabolomics analysis was a promising tool for rapid and timely stroke differentiation.

Usefulness of voxel-based lesion mapping for predicting motor recovery in subjects with basal ganglia hemorrhage: A preliminary study with 2 case reports

It is important to estimate motor recovery in the early phase after stroke. Many studies have demonstrated that both diffusion tensor tractography (DTT) and motor-evoked potentials (MEP) are valuable predictors of motor recovery, but these modalities do not directly reflect the status of the injured gray matter. We report on 2 subjects with basal ganglia hemorrhage who showed similar DTT and MEP findings, but had markedly different clinical outcomes. Specifically, Subject 1 showed no improvement in motor function, whereas Subject 2 exhibited substantial improvement 7 weeks after onset. To determine if differences in gray matter might lend insight into these different outcomes, we analyzed gray matter lesions of the 2 subjects using a novel voxel-based lesion mapping method. The lesion of Subject 1 mainly included the putamen, thalamus, and Heschl's gyri, indicating extension of the hemorrhage in the posterior direction. In contrast, the lesion of Subject 2 mainly included the putamen, insula, and pallidum, indicating that the hemorrhage extended anterior laterally. These differential findings suggest that voxel-based gray matter lesion mapping may help to predict differential motor recovery in subjects with basal ganglia hemorrhage with similar DTT and MEP findings.

Effect of color visualization and display hardware on the visual assessment of pseudocolor medical images

PURPOSE

Even though the use of color in the interpretation of medical images has increased significantly in recent years, the ad hoc manner in which color is handled and the lack of standard approaches have been associated with suboptimal and inconsistent diagnostic decisions with a negative impact on patient treatment and prognosis. The purpose of this study is to determine if the choice of color scale and display device hardware affects the visual assessment of patterns that have the characteristics of functional medical images.

METHODS

Perfusion magnetic resonance imaging (MRI) was the basis for designing and performing experiments. Synthetic images resembling brain dynamic-contrast enhanced MRI consisting of scaled mixtures of white, lumpy, and clustered backgrounds were used to assess the performance of a rainbow ("jet"), a heated black-body ("hot"), and a gray ("gray") color scale with display devices of different quality on the detection of small changes in color intensity. The authors used a two-alternative, forced-choice design where readers were presented with 600 pairs of images. Each pair consisted of two images of the same pattern flipped along the vertical axis with a small difference in intensity. Readers were asked to select the image with the highest intensity. Three differences in intensity were tested on four display devices: a medical-grade three-million-pixel display, a consumer-grade monitor, a tablet device, and a phone.

RESULTS

The estimates of percent correct show that jet outperformed hot and gray in the high and low range of the color scales for all devices with a maximum difference in performance of 18% (confidence intervals: 6%, 30%). Performance with hot was different for high and low intensity, comparable to jet for the high range, and worse than gray for lower intensity values. Similar performance was seen between devices using jet and hot, while gray performance was better for handheld devices. Time of performance was shorter with jet.

CONCLUSIONS

Our findings demonstrate that the choice of color scale and display hardware affects the visual comparative analysis of pseudocolor images. Follow-up studies in clinical settings are being considered to confirm the results with patient images.

Wake-up stroke: Dawn of a new era

Wake-up stroke or stroke with unclear onset of symptoms is known to occur in one-fourth of ischemic stroke patients. These patients are not considered for thrombolytic therapy based on time designation of their symptom onset as per the current guidelines. Observational studies have investigated the pathophysiology and suggested actual onset of symptoms to be approximate to the awakening time for these patients. Use of advanced imaging modalities in these patients tends to identify favorable patient profiles for thrombolysis. Results of the ongoing trials will likely beckon a seminal juncture in stroke therapy and deliver critical modifications in the current treatment guidelines for thrombolysis in this substantial, yet neglected, group of stroke patients. In this article, we have reviewed the predisposing factors, preferred imaging modalities and various ongoing thrombolytic and endovascular trials to date for patients with unclear time of symptom onset or who wake up with stroke symptoms.

Readout-segmented echo-planar imaging in diffusion-weighted imaging of the kidney: comparison with single-shot echo-planar imaging in image quality

OBJECTIVE

The purpose of this study was to compare the image quality of readout-segmented echo-planar imaging (RS-EPI) and that of standard single-shot echo-planar imaging (SS-EPI) in the kidney in a rat model.

MATERIALS AND METHODS

Twelve Wistar rats undergoing MRI examinations were imaged with two diffusion-weighted (DW) imaging protocols: a standard SS-EPI and a new RS-EPI protocol, both with a 1.0 × 1.0 × 3.0 mm voxel. The two groups of diffusion-weighted images were independently scored on geometric distortion, image blurring, signal dropout, and the overall image quality by two radiologists. Signal-to-noise ratio (SNR) and apparent diffusion coefficient (ADC) were measured on both sequences. Inter-rater agreement (IRA) was evaluated by Fleiss kappa (κ) and inter-class correlation coefficient (ICC) statistics. Comparisons of image qualities were made by Wilcoxon signed-rank test and paired-sample t test.

RESULTS

Both RS-EPI and SS-EPI had good IRAs in scoring image qualities (κ = 0.607-0.833) and measuring renal ADCs (ICC = 0.828-0.945). Compared to SS-EPI, RS-EPI produced less geometric distortion (median score 1.5 versus 2.5, p < 0.0001), less image blurring (1.75 versus 2.0, p = 0.0003), less signal dropout (1.0 versus 3.0, p = 0.0001), and a lower score in overall image artifacts (4.25 versus 7.25; p < 0.0001). RS-EPI had higher SNR of renal DW images than SS-EPI (p < 0.001). The intra-variability of ADCs in cortex, outer medulla, and inner medulla ranged from 9.6% to 11.1% (Pearson correlation coefficient ρ = 0.675-0.729; p < 0.001) between the two protocols.

CONCLUSION

We showed that for DWI of the kidney at 1.0 × 1.0 × 3.0 mm(3) voxel sizes, the new protocol provided better image quality than standard SS-EPI protocol.

Silent new ischemic lesions after index stroke and the risk of future clinical recurrent stroke

OBJECTIVE

To test whether a silent new ischemic lesion (SNIL) on MRI after stroke predicted future recurrent ischemic stroke or vascular events.

METHODS

In this prospective study, we analyzed data from patients presenting with acute ischemic stroke who underwent MRI <24 hours and 5 and 30 days after symptom onset. The presence of a SNIL at 5 (5D-SNIL) and 30 (30D-SNIL) days was determined on diffusion-weighted and fluid-attenuated inversion recovery images. Patients were contacted every 3-6 months to identify recurrent clinical events. The log-rank test and Cox proportional hazard model were used to estimate the hazard ratio of recurrent ischemic stroke and composites of recurrent ischemic stroke, transient ischemic attack, acute coronary syndrome, and vascular death.

RESULTS

The 5D- and 30D-SNILs were found in 24.4% (66/270) and 7.4% (19/256) of patients. During the 5-year follow-up, clinical events were observed in 42 patients (15.6%). The 5D- and 30D-SNIL independently predicted recurrent ischemic stroke (hazard ratio [95% confidence interval] 2.9 [1.3-6.4] and 9.6 [4.1-22.1], respectively) and composite vascular events (2.4 [1.3-4.5] and 6.1 [3.1-12.4], respectively).

CONCLUSIONS

Patients with a SNIL within the first few weeks after index stroke have an increased risk of recurrent ischemic stroke or vascular events. The presence of a SNIL on MRI could serve as a surrogate endpoint for clinical recurrence in secondary prevention clinical trials.

Lesion Location-Based Prediction of Visual Field Improvement after Cerebral Infarction

Background

Although the prognosis of ischemic stroke is highly dependent on the lesion location, it has rarely been quantitatively utilized. We investigated the usefulness of regional extent of ischemic lesion (rEIL) predicting the improvement of visual field defect (VFD) in patients with posterior cerebral artery infarction.

Methods

The rEILs were measured in each individual cortex after transforming the lesions to a standard atlas. Significant improvement of VFD was tentatively defined as 20% improvement at 3 months after stroke. The performances of clinical and imaging variables predicting significant improvement were measured by support vector machine. The maximum performance of variables predicting the significant improvement was compared between subgroups of variables (clinical, baseline severity and lesion volume) and the effect of adding rEIL to those subgroups of variables was evaluated.

Results

A total of 35 patients were enrolled in this study. Left PCA infarct, MR-time from onset, rEILs in the lingual, calcarine, and cuneus cortices were good prognostic indicators of hemi-VFD (performance for predicting the significant improvement: 72.8±11.8%, 66.1±11.2%, respectively). A combination of the rEILs of each cortical subregions demonstrated a better predictive performance for hemi-VFD (83.8±9.5%) compared to a combination of clinical variables (72.8±11.8; p<0.001), baseline severity (63.0±11.9%; p<0.001), or lesion volume (62.6±12.7%; p<0.001). Adding a rEIL to other variables improved the prognostic prediction for hemi-VFD (74.4±11.6% to 91.3±7.7%; p<0.001).

Conclusions

An estimation of rEIL provides useful information regarding the ischemic lesion location. rEIL accurately predicts the significant improvement of VFD and enhances the prediction power when combined with other variables.

The Capillary Index Score before thrombectomy: an angiographic correlate of favorable outcome

BACKGROUND AND PURPOSE

The angiography based Capillary Index Score (CIS) has recently emerged as a potential surrogate marker of cerebral perfusion before intra-arterial thrombolysis. We assessed the prevalence of a favorable CIS (f-CIS) and its relationship with clinical outcome in patients treated by mechanical thrombectomy (MT).

METHODS

Data from consecutive patients treated by MT from acute middle cerebral artery (MCA) occlusion were retrospectively analyzed. CIS was calculated from a pre-intervention cerebral angiogram. Association with favorable clinical outcome (modified Rankin Scale score ≤2) at 3 months was assessed in multivariate analysis.

RESULTS

146 patients were included in the study. f-CIS was observed in 106/146 (72%) patients with an acceptable inter-rater agreement (κ=0.73, p<0.001). It was associated with a lower pretreatment National Institutes of Health Stroke Scale (NIHSS) score (p=0.014), an isolated M1/M2 occlusion without internal carotid occlusion (p=0.042), and an Alberta Stroke Program Early CT Score (ASPECTS) >4 (p=0.004). In binary regression, a favorable outcome was independently associated with f-CIS (OR (-95% CI, +95% CI)=3.8 (1.3 to 10.9), p=0.013), as well as NIHSS (p=0.007), ASPECTS (p=0.005), isolated M1/M2 occlusion (p=0.013), and age (p=0.032). The positive predictive value of f-CIS for a favorable outcome was 67%.

CONCLUSIONS

f-CIS was strongly associated with a favorable outcome after MT of acute MCA occlusion. As an easy surrogate marker of cerebral perfusion, it may be a useful-albeit not sufficient-diagnostic test to select patients just before an MT or to manage them after recanalization.

Distance to Thrombus in Acute Middle Cerebral Artery Occlusion Predicts Target Mismatch and Ischemic Penumbra

BACKGROUND AND PURPOSE

In patients with occlusion of the middle cerebral artery (MCA) treated by intravenous thrombolysis (IVT), the distance to thrombus (DT) has been proposed as a predictor of outcome. The purpose of the present study was to investigate how DT relates to dynamic susceptibility contrast perfusion metrics.

METHODS

Retrospective analysis was undertaken of patients who were diagnosed with acute MCA occlusion by magnetic resonance imaging and treated with IVT. Volumes of time-to-maximum (Tmax) perfusion deficits and diffusion-weighted imaging (DWI) lesions, diffusion-perfusion mismatch volumes, and the presence of target mismatch were determined. Correlations between the above stoke measures and DT were then calculated.

RESULTS

Fifty-five patients were included. DT showed significant inverse correlations with Tmax greater than 4, 6, 8, and 10 seconds, respectively, and mismatch volumes. Using the DT group median (14 mm) as a separator, significant intergroup differences were observed for Tmax greater than 4, 6, and 8 seconds, respectively, and for mismatch volumes. Grouping DT into quartiles showed significant intergroup differences regarding mismatch volumes and Tmax values greater than 4 and 6 seconds. Binary logistic regression identified DT (odds ratio [OR] = .89; 95% confidence interval [CI], .81-.99) and DWI lesion volumes (OR = .92; 95% CI, .86-.97) as independent predictors of target mismatch. A low DT predicted target mismatch with an area under the curve of .69.

CONCLUSIONS

DT correlates inversely with Tmax perfusion deficits and mismatch volumes and acts as an independent predictor of target mismatch.

Choosing a Hyperacute Stroke Imaging Protocol for Proper Patient Selection and Time Efficient Endovascular Treatment: Lessons from Recent Trials

Recently, several prospective randomized control trials regarding endovascular treatment for patients with intracranial large artery occlusions causing acute ischemic stroke have been successfully reported. Effort to minimize time delays to endovascular treatment, patient selection and the use of retrievable stent were important factors for the success of these trials. The inclusion and exclusion criteria for each of these trials did include differences in imaging protocols. In this review, we focus on the importance of baseline non-invasive angiography prior to deciding endovascular treatment. Then imaging protocols are described for each trial according to measurement of infarct volume and collateral grading.

Imaging of cerebrovascular disorders: precision medicine and the collaterome

Imaging of stroke and neurovascular disorders has profoundly enhanced clinical practice and related research during the last 40 years since the introduction of computed tomography (CT) and magnetic resonance imaging (MRI) enabled mapping of the brain. We highlight recent advances in neurovascular imaging. We describe how the convergence of readily available data and new clinical trial paradigms will recast our methods for studying the neurovascular patient. The application of a precision medicine approach to the collaterome, a comprehensive synthesis of neurovascular pathophysiology, will entail novel methods for clinical trial randomization, collection of routine and clinical trial imaging results, data archiving, and analysis.

Neuroprotective effects of SMADs in a rat model of cerebral ischemia/reperfusion

Previous studies have shown that up-regulation of transforming growth factor β1 results in neuroprotective effects. However, the role of the transforming growth factor β1 downstream molecule, SMAD2/3, following ischemia/reperfusion remains unclear. Here, we investigated the neuroprotective effects of SMAD2/3 by analyzing the relationships between SMAD2/3 expression and cell apoptosis and inflammation in the brain of a rat model of cerebral ischemia/reperfusion. Levels of SMAD2/3 mRNA were up-regulated in the ischemic penumbra 6 hours after cerebral ischemia/reperfusion, reached a peak after 72 hours and were then decreased at 7 days. Phosphorylated SMAD2/3 protein levels at the aforementioned time points were consistent with the mRNA levels. Over-expression of SMAD3 in the brains of the ischemia/reperfusion model rats via delivery of an adeno-associated virus containing the SMAD3 gene could reduce tumor necrosis factor-α and interleukin-1β mRNA levels, down-regulate expression of the pro-apoptotic gene, capase-3, and up-regulate expression of the anti-apoptotic protein, Bcl-2. The SMAD3 protein level was negatively correlated with cell apoptosis. These findings indicate that SMAD3 exhibits neuroprotective effects on the brain after ischemia/reperfusion through anti-inflammatory and anti-apoptotic pathways.