Publications by authors named "Ivana Galinovic"

52 Publications

Preserved structural connectivity mediates the clinical effect of thrombolysis in patients with anterior-circulation stroke.

Nat Commun 2021 May 10;12(1):2590. Epub 2021 May 10.

Klinik und Poliklinik für Neurologie, Kopf- und Neurozentrum, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

Thrombolysis with recombinant tissue plasminogen activator in acute ischemic stroke aims to restore compromised blood flow and prevent further neuronal damage. Despite the proven clinical efficacy of this treatment, little is known about the short-term effects of systemic thrombolysis on structural brain connectivity. In this secondary analysis of the WAKE-UP trial, we used MRI-derived measures of infarct size and estimated structural network disruption to establish that thrombolysis is associated not only with less infarct growth, but also with reduced loss of large-scale connectivity between grey-matter areas after stroke. In a causal mediation analysis, infarct growth mediated a non-significant 8.3% (CI [-8.0, 32.6]%) of the clinical effect of thrombolysis on functional outcome. The proportion mediated jointly through infarct growth and change of structural connectivity, especially in the border zone around the infarct core, however, was as high as 33.4% (CI [8.8, 77.4]%). Preservation of structural connectivity is thus an important determinant of treatment success and favourable functional outcome in addition to lesion volume. It might, in the future, serve as an imaging endpoint in clinical trials or as a target for therapeutic interventions.
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http://dx.doi.org/10.1038/s41467-021-22786-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8110812PMC
May 2021

Magnetic resonance imaging-based changes in vascular morphology and cerebral perfusion in subacute ischemic stroke.

J Cereb Blood Flow Metab 2021 Apr 17:271678X211010071. Epub 2021 Apr 17.

Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Center for Stroke Research Berlin, Berlin, Germany.

MRI-based vessel size imaging (VSI) allows for assessment of cerebral microvasculature and perfusion. This exploratory analysis of vessel size (VS) and density (Q; both assessed via VSI) in the subacute phase of ischemic stroke involved sixty-two patients from the BAPTISe cohort ('Biomarkers And Perfusion--Training-Induced changes after Stroke') nested within a randomized controlled trial (intervention: 4-week training relaxation). Relative VS, Q, cerebral blood volume (rCBV) and -flow (rCBF) were calculated for: ischemic lesion, perilesional tissue, and region corresponding to ischemic lesion on the contralateral side (mirrored lesion). Linear mixed-models detected significantly increased rVS and decreased rQ within the ischemic lesion compared to the mirrored lesion (coefficient[standard error]: 0.2[0.08] p = 0.03 and -1.0[0.3] p = 0.02, respectively); lesion rCBF and rCBV were also significantly reduced. Mixed-models did not identify time-to-MRI, nor training as modifying factors in terms of rVS or rQ up to two months post-stroke. Larger lesion VS was associated with larger lesion volumes (β 34, 95%CI 6.2-62; p = 0.02) and higher baseline NIHSS (β 3.0, 95%CI 0.49-5.3;p = 0.02), but was not predictive of six-month outcome. In summary, VSI can assess the cerebral microvasculature and tissue perfusion in the subacute phases of ischemic stroke, and may carry relevant prognostic value in terms of lesion volume and stroke severity.
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http://dx.doi.org/10.1177/0271678X211010071DOI Listing
April 2021

BRAVE-NET: Fully Automated Arterial Brain Vessel Segmentation in Patients With Cerebrovascular Disease.

Front Artif Intell 2020 25;3:552258. Epub 2020 Sep 25.

CLAIM - Charité Lab for Artificial Intelligence in Medicine, Charité Universitätsmedizin Berlin, Berlin, Germany.

Arterial brain vessel assessment is crucial for the diagnostic process in patients with cerebrovascular disease. Non-invasive neuroimaging techniques, such as time-of-flight (TOF) magnetic resonance angiography (MRA) imaging are applied in the clinical routine to depict arteries. They are, however, only visually assessed. Fully automated vessel segmentation integrated into the clinical routine could facilitate the time-critical diagnosis of vessel abnormalities and might facilitate the identification of valuable biomarkers for cerebrovascular events. In the present work, we developed and validated a new deep learning model for vessel segmentation, coined BRAVE-NET, on a large aggregated dataset of patients with cerebrovascular diseases. BRAVE-NET is a multiscale 3-D convolutional neural network (CNN) model developed on a dataset of 264 patients from three different studies enrolling patients with cerebrovascular diseases. A context path, dually capturing high- and low-resolution volumes, and deep supervision were implemented. The BRAVE-NET model was compared to a baseline Unet model and variants with only context paths and deep supervision, respectively. The models were developed and validated using high-quality manual labels as ground truth. Next to precision and recall, the performance was assessed quantitatively by Dice coefficient (DSC); average Hausdorff distance (AVD); 95-percentile Hausdorff distance (95HD); and via visual qualitative rating. The BRAVE-NET performance surpassed the other models for arterial brain vessel segmentation with a DSC = 0.931, AVD = 0.165, and 95HD = 29.153. The BRAVE-NET model was also the most resistant toward false labelings as revealed by the visual analysis. The performance improvement is primarily attributed to the integration of the multiscaling context path into the 3-D Unet and to a lesser extent to the deep supervision architectural component. We present a new state-of-the-art of arterial brain vessel segmentation tailored to cerebrovascular pathology. We provide an extensive experimental validation of the model using a large aggregated dataset encompassing a large variability of cerebrovascular disease and an external set of healthy volunteers. The framework provides the technological foundation for improving the clinical workflow and can serve as a biomarker extraction tool in cerebrovascular diseases.
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http://dx.doi.org/10.3389/frai.2020.552258DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7861225PMC
September 2020

Synthesizing anonymized and labeled TOF-MRA patches for brain vessel segmentation using generative adversarial networks.

Comput Biol Med 2021 Apr 15;131:104254. Epub 2021 Feb 15.

CLAIM - Charité Lab for AI in Medicine, Charité Universitätsmedizin Berlin, Germany.

Anonymization and data sharing are crucial for privacy protection and acquisition of large datasets for medical image analysis. This is a big challenge, especially for neuroimaging. Here, the brain's unique structure allows for re-identification and thus requires non-conventional anonymization. Generative adversarial networks (GANs) have the potential to provide anonymous images while preserving predictive properties. Analyzing brain vessel segmentation, we trained 3 GANs on time-of-flight (TOF) magnetic resonance angiography (MRA) patches for image-label generation: 1) Deep convolutional GAN, 2) Wasserstein-GAN with gradient penalty (WGAN-GP) and 3) WGAN-GP with spectral normalization (WGAN-GP-SN). The generated image-labels from each GAN were used to train a U-net for segmentation and tested on real data. Moreover, we applied our synthetic patches using transfer learning on a second dataset. For an increasing number of up to 15 patients we evaluated the model performance on real data with and without pre-training. The performance for all models was assessed by the Dice Similarity Coefficient (DSC) and the 95th percentile of the Hausdorff Distance (95HD). Comparing the 3 GANs, the U-net trained on synthetic data generated by the WGAN-GP-SN showed the highest performance to predict vessels (DSC/95HD 0.85/30.00) benchmarked by the U-net trained on real data (0.89/26.57). The transfer learning approach showed superior performance for the same GAN compared to no pre-training, especially for one patient only (0.91/24.66 vs. 0.84/27.36). In this work, synthetic image-label pairs retained generalizable information and showed good performance for vessel segmentation. Besides, we showed that synthetic patches can be used in a transfer learning approach with independent data. This paves the way to overcome the challenges of scarce data and anonymization in medical imaging.
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http://dx.doi.org/10.1016/j.compbiomed.2021.104254DOI Listing
April 2021

Extent of FLAIR Hyperintense Vessels May Modify Treatment Effect of Thrombolysis: A Analysis of the WAKE-UP Trial.

Front Neurol 2020 4;11:623881. Epub 2021 Feb 4.

Center for Stroke Research Berlin, Charité-Universitätsmedizin Berlin, Berlin, Germany.

Fluid-attenuated inversion recovery (FLAIR) hyperintense vessels (FHVs) on MRI are a radiological marker of vessel occlusion and indirect sign of collateral circulation. However, the clinical relevance is uncertain. We explored whether the extent of FHVs is associated with outcome and how FHVs modify treatment effect of thrombolysis in a subgroup of patients with confirmed unilateral vessel occlusion from the randomized controlled WAKE-UP trial. One hundred sixty-five patients were analyzed. Two blinded raters independently assessed the presence and extent of FHVs (defined as the number of slices with visible FHV multiplied by FLAIR slice thickness). Patients were then separated into two groups to distinguish between few and extensive FHVs (dichotomization at the median <30 or ≥30). Here, 85% of all patients ( = 140) and 95% of middle cerebral artery (MCA) occlusion patients ( = 127) showed FHVs at baseline. Between MCA occlusion patients with few and extensive FHVs, no differences were identified in relative lesion growth ( = 0.971) and short-term [follow-up National Institutes of Health Stroke Scale (NIHSS) score; = 0.342] or long-term functional recovery [modified Rankin Scale (mRS) <2 at 90 days poststroke; = 0.607]. In linear regression analysis, baseline extent of FHV (defined as a continuous variable) was highly associated with volume of hypoperfused tissue (β = 2.161; 95% CI 0.96-3.36; = 0.001). In multivariable regression analysis adjusted for treatment group, stroke severity, lesion volume, occlusion site, and recanalization, FHV did not modify functional recovery. However, in patients with few FHVs, the odds for good functional outcome (mRS) were increased in recombinant tissue plasminogen activator (rtPA) patients compared to those who received placebo [odds ratio (OR) = 5.3; 95% CI 1.2-24.0], whereas no apparent benefit was observed in patients with extensive FHVs (OR = 1.1; 95% CI 0.3-3.8), -value for interaction was 0.11. While the extent of FHVs on baseline did not alter the evolution of stroke in terms of lesion progression or functional recovery, it may modify treatment effect and should therefore be considered relevant additional information in those patients who are eligible for intravenous thrombolysis. Main trial (WAKE-UP): ClinicalTrials.gov, NCT01525290; and EudraCT, 2011-005906-32. Registered February 2, 2012.
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http://dx.doi.org/10.3389/fneur.2020.623881DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7890254PMC
February 2021

On the usage of average Hausdorff distance for segmentation performance assessment: hidden error when used for ranking.

Eur Radiol Exp 2021 Jan 21;5(1). Epub 2021 Jan 21.

CLAIM - Charité Lab for Artificial Intelligence in Medicine, Charité Universitätsmedizin Berlin, Berlin, Germany.

Average Hausdorff distance is a widely used performance measure to calculate the distance between two point sets. In medical image segmentation, it is used to compare ground truth images with segmentations allowing their ranking. We identified, however, ranking errors of average Hausdorff distance making it less suitable for applications in segmentation performance assessment. To mitigate this error, we present a modified calculation of this performance measure that we have coined "balanced average Hausdorff distance". To simulate segmentations for ranking, we manually created non-overlapping segmentation errors common in magnetic resonance angiography cerebral vessel segmentation as our use-case. Adding the created errors consecutively and randomly to the ground truth, we created sets of simulated segmentations with increasing number of errors. Each set of simulated segmentations was ranked using both performance measures. We calculated the Kendall rank correlation coefficient between the segmentation ranking and the number of errors in each simulated segmentation. The rankings produced by balanced average Hausdorff distance had a significantly higher median correlation (1.00) than those by average Hausdorff distance (0.89). In 200 total rankings, the former misranked 52 whilst the latter misranked 179 segmentations. Balanced average Hausdorff distance is more suitable for rankings and quality assessment of segmentations than average Hausdorff distance.
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http://dx.doi.org/10.1186/s41747-020-00200-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7817746PMC
January 2021

Safety and efficacy of intravenous thrombolysis in stroke patients on prior antiplatelet therapy in the WAKE-UP trial.

Neurol Res Pract 2020 20;2:40. Epub 2020 Nov 20.

Klinik und Poliklinik für Neurologie, Kopf- und Neurozentrum, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany.

Background: One quarter to one third of patients eligible for systemic thrombolysis are on antiplatelet therapy at presentation. In this study, we aimed to assess the safety and efficacy of intravenous thrombolysis in stroke patients on prescribed antiplatelet therapy in the WAKE-UP trial.

Methods: WAKE-UP was a multicenter, randomized, double-blind, placebo-controlled clinical trial to study the efficacy and safety of MRI-guided intravenous thrombolysis with alteplase in patients with an acute stroke of unknown onset time. The medication history of all patients randomized in the WAKE-UP trial was documented. The primary safety outcome was any sign of hemorrhagic transformation on follow-up MRI. The primary efficacy outcome was favorable functional outcome defined by a score of 0-1 on the modified Rankin scale at 90 days after stroke, adjusted for age and baseline stroke severity. Logistic regression models were fitted to study the association of prior antiplatelet treatment with outcome and treatment effect of intravenous alteplase.

Results: Of 503 randomized patients, 164 (32.6%) were on antiplatelet treatment. Patients on antiplatelet treatment were older (70.3 vs. 62.8 years,  <  0.001), and more frequently had a history of hypertension, atrial fibrillation, diabetes, hypercholesterolemia, and previous stroke or transient ischaemic attack. Rates of symptomatic intracranial hemorrhage and hemorrhagic transformation on follow-up imaging did not differ between patients with and without antiplatelet treatment. Patients on prior antiplatelet treatment were less likely to achieve a favorable outcome (37.3% vs. 52.6%,  = 0.014), but there was no interaction of prior antiplatelet treatment with intravenous alteplase concerning favorable outcome ( = 0.355). Intravenous alteplase was associated with higher rates of favorable outcome in patients on prior antiplatelet treatment with an adjusted odds ratio of 2.106 (95% CI 1.047-4.236).

Conclusions: Treatment benefit of intravenous alteplase and rates of post-treatment hemorrhagic transformation were not modified by prior antiplatelet intake among MRI-selected patients with unknown onset stroke. Worse functional outcome in patients on antiplatelets may result from a higher load of cardiovascular co-morbidities in these patients.
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http://dx.doi.org/10.1186/s42466-020-00087-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7678217PMC
November 2020

Clinical Characteristics and Outcome of Patients With Hemorrhagic Transformation After Intravenous Thrombolysis in the WAKE-UP Trial.

Front Neurol 2020 28;11:957. Epub 2020 Aug 28.

Klinik und Poliklinik für Neurologie, Kopf- und Neurozentrum, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

Hemorrhagic transformation (HT) is an important complication of intravenous thrombolysis with alteplase. HT can show a wide range from petechiae to parenchymal hematoma with mass effect with varying clinical impact. We studied clinical and imaging characteristics of patients with HT and evaluated whether different types of HT are associated with functional outcome. We performed a analysis of WAKE-UP, a multicenter, randomized, placebo-controlled trial of MRI-guided intravenous alteplase in unknown onset stroke. HT was assessed on follow-up MRI or CT and diagnosed as hemorrhagic infarction type 1 and type 2 (HI1 and HI2, combined as HI), and parenchymal hemorrhage type 1 and type 2 (PH1 and PH2, combined as PH). Severity of stroke symptoms was assessed using the National Institutes of Health Stroke Scale (NIHSS) at baseline. Stroke lesion volume was measured on baseline diffusion weighted imaging (DWI). Primary endpoint was a favorable outcome defined as a modified Rankin Scale score 0-1 at 90 days. Of 483 patients included in the analysis, 95 (19.7%) showed HI and 21 (4.4%) had PH. Multiple logistic regression analysis identified treatment with alteplase (OR, 2.08 [95% CI, 1.28-3.40]), baseline NIHSS score (OR, 1.11 [95% CI, 1.05-1.17]), DWI lesion volume (OR, 1.03 [95% CI, 1.01-1.05]), baseline glucose levels (OR, 1.01 [95% CI, 1.00-1.01]) and atrial fibrillation (OR, 3.02 [95% CI, 1.57-5.80]) as predictors of any HT. The same parameters predicted HI. Predictors of PH were baseline NIHSS score (OR, 1.11 [95% CI, 1.01-1.22]) and as a trend treatment with alteplase (OR, 2.40 [95% CI, 0.93-6.96]). PH was associated with lower odds of favorable outcome (OR 0.25, 95% [CI 0.05-0.86]), while HI was not. Our results indicate that HI is associated with stroke severity, cardiovascular risk factors and thrombolysis. PH is a rare complication, more frequent in severe stroke and with thrombolysis. In contrast to HI, PH is associated with worse functional outcome. The impact of HT after MRI-guided intravenous alteplase for unknown onset stroke on clinical outcome is similar as in the trials of stroke thrombolysis within a known early time-window.
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http://dx.doi.org/10.3389/fneur.2020.00957DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7483750PMC
August 2020

The Effect of Scan Length on the Assessment of BOLD Delay in Ischemic Stroke.

Front Neurol 2020 5;11:381. Epub 2020 May 5.

Center for Stroke Research, Charité - Universitätsmedizin Berlin, Berlin, Germany.

To evaluate the impact of resting-state functional MRI scan length on the diagnostic accuracy, image quality and lesion volume estimation of BOLD delay maps used for brain perfusion assessment in acute ischemic stroke. Sixty-three acute ischemic stroke patients received a 340 s resting-state functional MRI within 24 h of stroke symptom onset. BOLD delay maps were calculated from the full scan and four shortened versions (68 s, 136 s, 204 s, 272 s). The BOLD delay lesions on these maps were compared in terms of spatial overlap and volumetric agreement with the lesions derived from the full scans and with time-to-maximum (Tmax) lesions derived from DSC-MRI in a subset of patients (n = 10). In addition, the interpretability and quality of these maps were compared across different scan lengths using mixed models. Shortened BOLD delay scans showed a small volumetric bias (ranging from 0.05 to 5.3 mL; between a 0.13% volumetric underestimation and a 7.7% overestimation relative to the mean of the volumes, depending on scan length) compared to the full scan. Decreased scan length was associated with decreased spatial overlap with both the BOLD delay lesions derived from the full scans and with Tmax lesions. Only the two shortest scan lengths (68 and 136 s) were associated with substantially decreased interpretability, decreased structure clarity, and increased noisiness of BOLD delay maps. BOLD delay maps derived from resting-state fMRI scans lasting 272 and 204 s provide sufficient diagnostic quality and adequate assessment of perfusion lesion volumes. Such shortened scans may be helpful in situations where quick clinical decisions need to be made.
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http://dx.doi.org/10.3389/fneur.2020.00381DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7214917PMC
May 2020

Opening the black box of artificial intelligence for clinical decision support: A study predicting stroke outcome.

PLoS One 2020 6;15(4):e0231166. Epub 2020 Apr 6.

Charité Lab for Artificial Intelligence in Medicine-CLAIM, Charité - Universitätsmedizin Berlin, Berlin, Germany.

State-of-the-art machine learning (ML) artificial intelligence methods are increasingly leveraged in clinical predictive modeling to provide clinical decision support systems to physicians. Modern ML approaches such as artificial neural networks (ANNs) and tree boosting often perform better than more traditional methods like logistic regression. On the other hand, these modern methods yield a limited understanding of the resulting predictions. However, in the medical domain, understanding of applied models is essential, in particular, when informing clinical decision support. Thus, in recent years, interpretability methods for modern ML methods have emerged to potentially allow explainable predictions paired with high performance. To our knowledge, we present in this work the first explainability comparison of two modern ML methods, tree boosting and multilayer perceptrons (MLPs), to traditional logistic regression methods using a stroke outcome prediction paradigm. Here, we used clinical features to predict a dichotomized 90 days post-stroke modified Rankin Scale (mRS) score. For interpretability, we evaluated clinical features' importance with regard to predictions using deep Taylor decomposition for MLP, Shapley values for tree boosting and model coefficients for logistic regression. With regard to performance as measured by Area under the Curve (AUC) values on the test dataset, all models performed comparably: Logistic regression AUCs were 0.83, 0.83, 0.81 for three different regularization schemes; tree boosting AUC was 0.81; MLP AUC was 0.83. Importantly, the interpretability analysis demonstrated consistent results across models by rating age and stroke severity consecutively amongst the most important predictive features. For less important features, some differences were observed between the methods. Our analysis suggests that modern machine learning methods can provide explainability which is compatible with domain knowledge interpretation and traditional method rankings. Future work should focus on replication of these findings in other datasets and further testing of different explainability methods.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0231166PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7135268PMC
July 2020

The Association Between Recanalization, Collateral Flow, and Reperfusion in Acute Stroke Patients: A Dynamic Susceptibility Contrast MRI Study.

Front Neurol 2019 25;10:1147. Epub 2019 Oct 25.

Center for Stroke Research Berlin, Charité-Universitätsmedizin Berlin, Berlin, Germany.

Collateral circulation in ischemic stroke patients plays an important role in infarct evolution und assessing patients' eligibility for endovascular treatment. By means of dynamic susceptibility contrast MRI, we aimed to investigate the effects of reperfusion, recanalization, and collateral flow on clinical and imaging outcomes after stroke. Retrospective analysis of 184 patients enrolled into the prospective observational 1000Plus study (clinicaltrials.org NCT00715533). Inclusion criteria were vessel occlusion on baseline MR-angiography, imaging within 24 h after stroke onset and follow-up perfusion imaging. Baseline Higashida score using subtracted dynamic MR perfusion source images was used to quantify collateral flow. The influence of these variables, and their interaction with vessel recanalization, on clinical and imaging outcomes was assessed using robust linear regression. Ninety-eight patients (53.3%) showed vessel recanalization. Higashida score ( = 0.002), and recanalization ( = 0.0004) were independently associated with reperfusion. However, we found no evidence that the association between Higashida score and reperfusion relied on recanalization status ( = 0.2). NIHSS on admission ( < 0.0001) and recanalization ( = 0.001) were independently associated with long-term outcome at 3 months, however, Higashida score ( = 0.228) was not. Higashida score and recanalization were independently associated with reperfusion, but the association between recanalization and reperfusion was similar regardless of collateral flow quality. Recanalization was associated with long-term outcome. DSC-based measures of collateral flow were not associated with long-term outcome, possibly due to the complex dynamic nature of collateral recruitment, timing of imaging and the employed post-processing.
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http://dx.doi.org/10.3389/fneur.2019.01147DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6823193PMC
October 2019

Quantitative Signal Intensity in Fluid-Attenuated Inversion Recovery and Treatment Effect in the WAKE-UP Trial.

Stroke 2020 01 30;51(1):209-215. Epub 2019 Oct 30.

From the Klinik und Poliklinik für Neurologie, Kopf- und Neurozentrum (B.C., A.N., C.G., G.T.), University Medical Center Hamburg-Eppendorf, Germany.

Background and Purpose- Relative signal intensity of acute ischemic stroke lesions in fluid-attenuated inversion recovery (fluid-attenuated inversion recovery relative signal intensity [FLAIR-rSI]) magnetic resonance imaging is associated with time elapsed since stroke onset with higher intensities signifying longer time intervals. In the randomized controlled WAKE-UP trial (Efficacy and Safety of MRI-Based Thrombolysis in Wake-Up Stroke Trial), intravenous alteplase was effective in patients with unknown onset stroke selected by visual assessment of diffusion weighted imaging fluid-attenuated inversion recovery mismatch, that is, in those with no marked fluid-attenuated inversion recovery hyperintensity in the region of the acute diffusion weighted imaging lesion. In this post hoc analysis, we investigated whether quantitatively measured FLAIR-rSI modifies treatment effect of intravenous alteplase. Methods- FLAIR-rSI of stroke lesions was measured relative to signal intensity in a mirrored region in the contralesional hemisphere. The relationship between FLAIR-rSI and treatment effect on functional outcome assessed by the modified Rankin Scale (mRS) after 90 days was analyzed by binary logistic regression using different end points, that is, favorable outcome defined as mRS score of 0 to 1, independent outcome defined as mRS score of 0 to 2, ordinal analysis of mRS scores (shift analysis). All models were adjusted for National Institutes of Health Stroke Scale at symptom onset and stroke lesion volume. Results- FLAIR-rSI was successfully quantified in stroke lesions in 433 patients (86% of 503 patients included in WAKE-UP). Mean FLAIR-rSI was 1.06 (SD, 0.09). Interaction of FLAIR-rSI and treatment effect was not significant for mRS score of 0 to 1 (=0.169) and shift analysis (=0.086) but reached significance for mRS score of 0 to 2 (=0.004). We observed a smooth continuing trend of decreasing treatment effects in relation to clinical end points with increasing FLAIR-rSI. Conclusions- In patients in whom no marked parenchymal fluid-attenuated inversion recovery hyperintensity was detected by visual judgement in the WAKE-UP trial, higher FLAIR-rSI of diffusion weighted imaging lesions was associated with decreased treatment effects of intravenous thrombolysis. This parallels the known association of treatment effect and elapsing time of stroke onset.
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http://dx.doi.org/10.1161/STROKEAHA.119.027390DOI Listing
January 2020

Analysis of Outcome of Intravenous Thrombolysis in Infarcts of Infratentorial Localization in the WAKE-UP Trial.

Front Neurol 2019 11;10:983. Epub 2019 Sep 11.

Klinik und Poliklinik für Neurologie, Kopf- und Neurozentrum, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

In WAKE-UP (Efficacy and Safety of MRI-based Thrombolysis in Wake-Up Stroke), patients with an acute stroke of unknown onset time were randomized to treatment with intravenous alteplase or placebo, guided by MRI. In this exploratory secondary analysis we compared clinical and imaging data, as well as treatment effects and safety of intravenous thrombolysis between patients with infra- vs. supratentorial stroke. Forty-eight out of 503 randomized patients (9.5%) presented with a stroke involving the cerebellum or brainstem. Patients with infratentorial stroke were younger compared to patients with supratentorial stroke (mean age 60 vs. 66 years), more frequently male (85 vs. 62%), and less severely affected (median NIHSS 4.5 vs. 6.0). There was no heterogeneity for treatment effect between supratentorial (OR 1.67 95% CI 1.11-2.51) and infratentorial (OR 1.31 95% CI 0.41-4.22) sub-groups (test for interaction = 0.70). In patients with infratentorial stroke, favorable outcome [a score of 0-1 on the modified Rankin scale (mRS) at 90 days] was observed in 12/22 patients (54.5%) in the alteplase group and in 13/25 patients (52.0%) in the placebo group ( = 0.59). The primary safety endpoint (death or mRS 4-6 at day 90) occurred in three patients of the alteplase group (13.6%) and three patients in the placebo group (12.0%); = 0.74. WAKE-UP was underpowered for demonstrating treatment effect in subgroup analyses however, based on our current results, there is no evidence to recommend withholding MRI-guided thrombolysis in patients with unknown onset stroke of infratentorial localization.
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http://dx.doi.org/10.3389/fneur.2019.00983DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6749039PMC
September 2019

High-resolution diffusion-weighted imaging identifies ischemic lesions in a majority of transient ischemic attack patients.

Ann Neurol 2019 09 31;86(3):452-457. Epub 2019 Jul 31.

Center for Stroke Research Berlin, Charité Universitätsmedizin Berlin, Berlin, Germany.

Transient ischemic attack (TIA) is defined as focal neurological deficit caused by ischemia resolving within 24 hours. In a secondary analysis of a large monocentric cohort of 446 TIA patients, we explored the frequency and determinants of diffusion-weighted imaging (DWI) lesions on high-resolution magnetic resonance imaging. Overall, 240 (54%) of all TIA patients presented with DWI lesions. These patients had higher National Institute of Health Stroke Scale and ABCD2 scores and presented more frequently with vessel occlusion and perfusion deficits, but had similar functional outcome at 3 months. Taken together, high-resolution DWI provides evidence of ischemic brain injury in the majority of TIA patients. ANN NEUROL 2019;86:452-457.
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http://dx.doi.org/10.1002/ana.25551DOI Listing
September 2019

Clinical Characteristics and Outcome of Patients with Lacunar Infarcts and Concurrent Embolic Ischemic Lesions.

Clin Neuroradiol 2020 Sep 3;30(3):511-516. Epub 2019 Jun 3.

Klinik und Poliklinik für Neurologie, Kopf- und Neurozentrum, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246, Hamburg, Germany.

Purpose: Lacunar infarcts are thought to result from occlusion of small penetrating arteries due to microatheroma and lipohyalinosis, pathognomonic for cerebral small vessel disease (CSVD). Concurrent embolic ischemic lesions indicate a different stroke mechanism. The purpose of this study was to examine the clinical characteristics and outcome of patients with lacunar infarcts and concurrent embolic infarcts on diffusion-weighted imaging (DWI).

Methods: All patients screened for the WAKE-UP trial (ClinicalTrials.gov number, NCT01525290) were reviewed for acute lacunar infarcts and concurrent embolic lesions on baseline DWI. Clinical characteristics and outcome were compared between lacunar infarct patients with and without concurrent embolic lesions.

Results: Of 244 patients with an acute lacunar infarct, 20 (8.2%) had concurrent acute embolic infarcts. Compared to patients with a lacunar infarct only, patients with concurrent embolic infarcts were older (mean age 69 years vs. 63 years; p = 0.031), more severely affected (median National Institutes of Health Stroke Scale [NIHSS] score 5 vs. 4; p = 0.046), and-among those randomized-had worse functional outcome at 90 days (median modified Rankin Scale [mRS] 3 vs. 1; p = 0.011).

Conclusion: Approximately 8% of lacunar infarct patients show concurrent embolic lesions suggesting a stroke etiology other than CSVD. These patients are more severely affected and have a worse functional outcome illustrating the need for a thorough diagnostic work-up of possible embolic sources even in patients with an imaging-defined diagnosis of lacunar infarcts.
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http://dx.doi.org/10.1007/s00062-019-00800-5DOI Listing
September 2020

Functional Outcome of Intravenous Thrombolysis in Patients With Lacunar Infarcts in the WAKE-UP Trial.

JAMA Neurol 2019 06;76(6):641-649

Klinik und Poliklinik für Neurologie, Kopf- und Neurozentrum, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

Importance: The rationale for intravenous thrombolysis in patients with lacunar infarcts is debated, since it is hypothesized that the microvascular occlusion underlying lacunar infarcts might not be susceptible to pharmacological reperfusion treatment.

Objective: To study the efficacy and safety of intravenous thrombolysis among patients with lacunar infarcts.

Design, Setting, And Participants: This exploratory secondary post hoc analysis of the WAKE-UP trial included patients who were screened and enrolled between September 2012 and June 2017 (with final follow-up in September 2017). The WAKE-UP trial was a multicenter, double-blind, placebo-controlled randomized clinical trial to study the efficacy and safety of intravenous thrombolysis with alteplase in patients with an acute stroke of unknown onset time, guided by magnetic resonance imaging. All 503 patients randomized in the WAKE-UP trial were reviewed for lacunar infarcts. Diagnosis of lacunar infarcts was based on magnetic resonance imaging and made by consensus of 2 independent investigators blinded to clinical information.

Main Outcomes And Measures: The primary efficacy variable was favorable outcome defined by a score of 0 to 1 on the modified Rankin Scale at 90 days after stroke, adjusted for age and severity of symptoms.

Results: Of the 503 patients randomized in the WAKE-UP trial, 108 patients (including 74 men [68.5%]) had imaging-defined lacunar infarcts, whereas 395 patients (including 251 men [63.5%]) had nonlacunar infarcts. Patients with lacunar infarcts were younger than patients with nonlacunar infarcts (mean age [SD], 63 [12] years vs 66 [12] years; P = .003). Of patients with lacunar infarcts, 55 (50.9%) were assigned to treatment with alteplase and 53 (49.1%) to receive placebo. Treatment with alteplase was associated with higher odds of favorable outcome, with no heterogeneity of treatment outcome between lacunar and nonlacunar stroke subtypes. In patients with lacunar strokes, a favorable outcome was observed in 31 of 53 patients (59%) in the alteplase group compared with 24 of 52 patients (46%) in the placebo group (adjusted odds ratio [aOR], 1.67 [95% CI, 0.77-3.64]). There was 1 death and 1 symptomatic intracranial hemorrhage according to Safe Implementation of Thrombolysis in Stroke-Monitoring Study criteria in the alteplase group, while no death and no symptomatic intracranial hemorrhage occurred in the placebo group. The distribution of the modified Rankin Scale scores 90 days after stroke also showed a nonsignificant shift toward better outcomes in patients with lacunar infarcts treated with alteplase, with an adjusted common odds ratio of 1.94 (95% CI, 0.95-3.93).

Conclusions And Relevance: While the WAKE-UP trial was not powered to demonstrate the efficacy of treatment in subgroups of patients, the results indicate that the association of intravenous alteplase with functional outcome does not differ in patients with imaging-defined lacunar infarcts compared with those experiencing other stroke subtypes.
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http://dx.doi.org/10.1001/jamaneurol.2019.0351DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6563546PMC
June 2019

Homogeneous application of imaging criteria in a multicenter trial supported by investigator training: A report from the WAKE-UP study.

Eur J Radiol 2018 Jul 15;104:115-119. Epub 2018 May 15.

Center for Stroke Research Berlin (CSB), Charité-Universitätsmedizin Berlin, Hindenburgdamm 30, 12200 Berlin, Germany.

Background And Purpose: WAKE-UP is a randomized, placebo-controlled trial of thrombolysis in stroke with unknown time of symptom onset using magnetic resonance imaging criteria to determine patients' eligibility. As it is a multicenter trial, homogeneous interpretation of criteria is an important contributor to the trial's success. We describe the investigator image training as well as results of the quality control done by the central image reading board (CIRB).

Methods: Investigators at local centers were given an imaging manual and passed a software-based image training prior to being allowed to judge images in the trial. Throughout the trial, the CIRB gave feedback to recruiting centers in cases of disagreement regarding a patient's randomization. We evaluated the investigators performance in the image training and analyzed results of this quality control from the first 1069 screened patients. Additionally, we obtained feedback from investigators regarding their experiences with the trial.

Results: Four-hundred-and-sixty physicians from eight European countries took part in the image training, of whom 436 (95%) successfully completed it. In the trial, agreement rates between the local investigators and members of the CIRB were high for the presence of an acute ischemic lesion (94%, κ = 0.87) as well as for the judgment of infarct extent (93%, κ = 0.87). Agreement for the criterion of DWI-FLAIR mismatch was 74%, κ = 0.60. The majority of investigators reported that the DWI-FLAIR mismatch was the hardest imaging criterion to evaluate. Ninety-one percent of investigators who responded to our survey stated that the image training specifically increased their confidence when assessing the DWI-FLAIR mismatch.

Conclusions: Despite its multicenter design, the WAKE-UP study has demonstrated a high level of homogeneity amongst raters in interpreting the various imaging criteria for patient randomization, including the novel criterion of DWI-FLAIR mismatch. Systematic image training increased the confidence of investigators in applying imaging criteria.
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http://dx.doi.org/10.1016/j.ejrad.2018.05.011DOI Listing
July 2018

MRI-Guided Thrombolysis for Stroke with Unknown Time of Onset.

N Engl J Med 2018 08 16;379(7):611-622. Epub 2018 May 16.

From Klinik und Poliklinik für Neurologie, Kopf- und Neurozentrum, Universitätsklinikum Hamburg-Eppendorf (G.T., B. Cheng, S.G., A.G., C.G.), the Department of Diagnostic and Interventional Neuroradiology, University Medical Center Hamburg-Eppendorf (J.F.), and ZytoService Deutschland (E.S.), Hamburg, Universitätsklinik für Neurologie, Medizinische Universität Graz, Graz (F.F.), Centrum für Schlaganfallforschung Berlin (I.G., K.G.H., K.V., M. Ebinger, M. Endres, J.B.F.) and Klinik und Hochschulambulanz für Neurologie (K.G.H., L.N., M. Endres), Charité-Universitätsmedizin Berlin, and Neurologie der Rehaklinik Medical Park Humboldtmühle (M. Ebinger), Berlin, Mediri (J. Gregori, M.G.), the Department of Neurology, Medical Faculty Mannheim, University of Heidelberg (M.H.), and Neurologische Klinik, Universitätsklinikum Heidelberg (P. Ringleb), Heidelberg, Fraunhofer MEVIS and University of Bremen, Bremen (M.G.), and Institut für Neuroradiologie, Universitätsklinikum Schleswig-Holstein, Campus Lübeck, Lübeck (A.K.) - all in Germany; the Department of Neurology, Aarhus University Hospital, Aarhus (C.Z.S., G.A.), the Department of Neurology, Bispebjerg Hospital, Copenhagen University Hospital, Copenhagen (J.M.), and Department of Neurology, Stroke Unit, Aalborg University Hospital, Aalborg (B.M.) - all in Denmark; Hospices Civils de Lyon, Service de Biostatistique (F.B., P. Roy), the Neuroradiology Department, Neurological Hospital, University Lyon (Y.B.), and the Department of Stroke Medicine, Université Claude Bernard Lyon 1, and Hospices Civils de Lyon (T.-H.C., N.N.), Lyon, and Université Lyon 1 and Centre National de la Recherche Scientifique, UMR 5558, Laboratoire de Biométrie et Biologie Evolutive, Equipe Biostatistique-Santé, Villeurbanne (F.B., P. Roy) - all in France; the Institute of Neuroscience and Psychology (B. Cheripelli, K.W.M.) and the Robertson Centre for Biostatistics (I.F.), University of Glasgow, Glasgow, United Kingdom (I.F.); Fundació Salut Empordà Hospital, Figueres (J. Guibernau), Stroke Unit, Department of Neurosciences, Hospital Universitari Germans Trias i Pujol, Barcelona (N.P.O.), and the Department of Radiology (J.P., S.P.) and the Stroke Unit (J.S.), Hospital Universitari Doctor Josep Trueta, Institut d'Investigació Biomèdica de Girona, Girona - all in Spain; the Department of Neurology, St. Antonius Hospital, Nieuwegein, and University Medical Center Utrecht, Utrecht (W.S.) - both in the Netherlands; the Department of Imaging and Pathology, University of Leuven (S.S.), the Department of Neurology, University Hospitals Leuven (A.W., R.L.), KU Leuven-University of Leuven, Department of Neurosciences, Experimental Neurology (A.W., R.L.), and the VIB-KU Leuven Center for Brain and Disease Research, Laboratory of Neurobiology (A.W., R.L.), Leuven, Belgium; and Florey Institute of Neuroscience and Mental Health, Heidelberg, VIC, Australia (V.T.).

Background: Under current guidelines, intravenous thrombolysis is used to treat acute stroke only if it can be ascertained that the time since the onset of symptoms was less than 4.5 hours. We sought to determine whether patients with stroke with an unknown time of onset and features suggesting recent cerebral infarction on magnetic resonance imaging (MRI) would benefit from thrombolysis with the use of intravenous alteplase.

Methods: In a multicenter trial, we randomly assigned patients who had an unknown time of onset of stroke to receive either intravenous alteplase or placebo. All the patients had an ischemic lesion that was visible on MRI diffusion-weighted imaging but no parenchymal hyperintensity on fluid-attenuated inversion recovery (FLAIR), which indicated that the stroke had occurred approximately within the previous 4.5 hours. We excluded patients for whom thrombectomy was planned. The primary end point was favorable outcome, as defined by a score of 0 or 1 on the modified Rankin scale of neurologic disability (which ranges from 0 [no symptoms] to 6 [death]) at 90 days. A secondary outcome was the likelihood that alteplase would lead to lower ordinal scores on the modified Rankin scale than would placebo (shift analysis).

Results: The trial was stopped early owing to cessation of funding after the enrollment of 503 of an anticipated 800 patients. Of these patients, 254 were randomly assigned to receive alteplase and 249 to receive placebo. A favorable outcome at 90 days was reported in 131 of 246 patients (53.3%) in the alteplase group and in 102 of 244 patients (41.8%) in the placebo group (adjusted odds ratio, 1.61; 95% confidence interval [CI], 1.09 to 2.36; P=0.02). The median score on the modified Rankin scale at 90 days was 1 in the alteplase group and 2 in the placebo group (adjusted common odds ratio, 1.62; 95% CI, 1.17 to 2.23; P=0.003). There were 10 deaths (4.1%) in the alteplase group and 3 (1.2%) in the placebo group (odds ratio, 3.38; 95% CI, 0.92 to 12.52; P=0.07). The rate of symptomatic intracranial hemorrhage was 2.0% in the alteplase group and 0.4% in the placebo group (odds ratio, 4.95; 95% CI, 0.57 to 42.87; P=0.15).

Conclusions: In patients with acute stroke with an unknown time of onset, intravenous alteplase guided by a mismatch between diffusion-weighted imaging and FLAIR in the region of ischemia resulted in a significantly better functional outcome and numerically more intracranial hemorrhages than placebo at 90 days. (Funded by the European Union Seventh Framework Program; WAKE-UP ClinicalTrials.gov number, NCT01525290; and EudraCT number, 2011-005906-32 .).
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http://dx.doi.org/10.1056/NEJMoa1804355DOI Listing
August 2018

The ratio between cerebral blood flow and Tmax predicts the quality of collaterals in acute ischemic stroke.

PLoS One 2018 30;13(1):e0190811. Epub 2018 Jan 30.

Center for Stroke Research Berlin (CSB), Charité-Universitätsmedizin Berlin, Berlin, Germany.

Background: In acute ischemic stroke the status of collateral circulation is a critical factor in determining outcome. We propose a less invasive alternative to digital subtraction angiography for evaluating collaterals based on dynamic-susceptibility contrast magnetic resonance imaging.

Methods: Perfusion maps of Tmax and cerebral blood flow (CBF) were created for 35 patients with baseline occlusion of a major cerebral artery. Volumes of hypoperfusion were defined as having a Tmax delay of > 4 seconds (Tmax4s) and > 6 seconds (Tmax6s) and a CBF drop below 80% of healthy, contralateral tissue. For each patient a ratio between the volume of the CBF and the Tmax based perfusion deficit was calculated. Associations with collateral status and radiological outcome were assessed with the Mann-Whitney-U test, uni- and multivariable logistic regression analyses as well as area under the receiver-operator-characteristic (ROC) curve.

Results: The CBF/Tmax volume ratios were significantly associated with bad collateral status in crude logistic regression analysis as well as with adjustment for NIHSS at admission and baseline infarct volume (OR = 2.5 95% CI[1.2-5.4] p = 0.020 for CBF/Tmax 4s volume ratio and OR = 1.6 95% CI[1.0-2.6] p = 0.031 for CBF/Tmax6s volume ratio). Moreover, the ratios were significantly correlated to final infarct size (Spearman's rho = 0.711 and 0.619, respectively for the CBF/Tmax4s volume ratio and CBF/Tmax6s volume ration, all p<0.001). The ratios also had a high area under the ROC curve of 0.93 95%CI[0.86-1.00]) and 0.90 95%CI[0.80-1.00]respectively for predicting poor radiological outcome.

Conclusions: In the setting of acute ischemic stroke the CBF/Tmax volume ratio can be used to differentiate between good and insufficient collateral circulation without the need for invasive procedures like conventional angiography.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0190811PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5790218PMC
February 2018

The characteristics of transcranial color-coded duplex sonography in children with cerebral arteriovenous malformation presenting with headache.

Childs Nerv Syst 2018 02 16;34(2):199-203. Epub 2017 Dec 16.

Department of Neuropediatrics, Children's Hospital Zagreb, Klaiceva 16, 10000, Zagreb, Croatia.

Purpose: Cerebral arteriovenous malformations (AVM) are uncommon lesions. They are most often presented in childhood as intracranial hemorrhage. The aim of this report is to present the use of transcranial color-coded duplex sonography (TCCS) in detection of AVMs in children suffering headache.

Methods: This report describes five pediatric patients with headache and cerebral AVM which were initially discovered by TCCS. Diagnosis was confirmed by magnetic resonance imaging and digital subtraction angiography.

Results: In all patients, TCCS showed saccular enlargement of the vessels with a multicolored pattern corresponding to the different directions of blood flow. Spectral analysis showed significantly high flow systolic and diastolic velocities and low resistance index.

Conclusions: In this report, we describe TCCS as a valuable non-invasive, harmless, low-cost, widely available method for the detection and follow-up of hemodynamic changes of AVMs in children with headache, before and after treatment.
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http://dx.doi.org/10.1007/s00381-017-3692-7DOI Listing
February 2018

Impact of pre-admission oral anticoagulation on ischaemic stroke volume, lesion pattern, and frequency of intracranial arterial occlusion in patients with atrial fibrillation.

Europace 2018 11;20(11):1758-1765

Center for Stroke Research Berlin, Charité-Universitätsmedizin Berlin, Charitéplatz 1, Berlin, Germany.

Aims: Therapeutic oral anticoagulation on hospital admission reduces morbidity and mortality after acute ischaemic stroke in patients with atrial fibrillation (AF). The underlying mechanism is not fully understood. In order to assess the impact of INR-level on admission on stroke volume, lesion pattern and the frequency of intracranial arterial occlusion, we analysed serial MRI measurements in AF patients suffering acute ischaemic stroke.

Methods And Results: This subgroup analysis of the prospective '1000Plus' study included patients with acute ischaemic stroke and known AF or a first episode of AF in hospital. All patients underwent serial brain magnetic resonance imaging. Stroke patients were categorized as follows: Group1, phenprocoumon intake, international normalized ratio (INR) ≥1.7 on admission, no thrombolysis; Group2, INR < 1.7 on admission, thrombolysis; and Group3, INR < 1.7, no thrombolysis. In 98 AF patients {77 ± 9 years, 60% male; median National Institute of Health Stroke Scale [NIHSS] score on admission 5 (interquartile range [IQR] 2-8)} with known AF before admission, territorial infarction was less often found in Group 1 (n = 20) compared with Group 2 + 3 (20% vs. 47%, P = 0.022). Arterial occlusion rate on admission differed among groups (30%, 75%, and 35%, respectively, P = 0.004) but not between Group 1 vs. Group 2 + 3 (30% vs. 45%, P = 0.31). Median FLAIR volume on Days 5-7 was lower in Group1 compared with Group 2 (n = 20) [3.2 cm3 (IQR 1.1-11.3) vs. 18.6 cm3 (IQR 8.2-49.4); P = 0.009] but not compared with Group 2 + 3 [7.8 cm3 (IQR 1.6-25.9); P = 0.23]. An INR ≥ 1.7 on admission was not associated with smaller stroke volume in multivariable regression analysis. Adding 57 patients with a first AF episode during the in-hospital stay, similar results were observed in 155 AF patients.

Conclusion: In this AF cohort, an INR ≥ 1.7 at stroke onset affects lesion pattern but does not affect significantly lower stroke volume and the frequency of arterial occlusion on admission.
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http://dx.doi.org/10.1093/europace/eux333DOI Listing
November 2018

Clinical characteristics of unknown symptom onset stroke patients with and without diffusion-weighted imaging and fluid-attenuated inversion recovery mismatch.

Int J Stroke 2018 01 20;13(1):66-73. Epub 2017 Apr 20.

1 Klinik und Poliklinik für Neurologie, Kopf- und Neurozentrum, Universitätsklinikum Hamburg-Eppendorf, Hamburg, Germany.

Background Diffusion-weighted imaging (DWI) and fluid-attenuated inversion recovery (FLAIR) mismatch was suggested to identify stroke patients with unknown time of symptom onset likely to be within the time window for thrombolysis. Aims We aimed to study clinical characteristics associated with DWI-FLAIR mismatch in patients with unknown onset stroke. Methods We analyzed baseline MRI and clinical data from patients with acute ischemic stroke proven by DWI from WAKE-UP, an investigator-initiated, randomized, placebo-controlled trial of MRI-based thrombolysis in stroke patients with unknown time of symptom onset. Clinical characteristics were compared between patients with and without DWI-FLAIR mismatch. Results Of 699 patients included, 418 (59.8%) presented with DWI-FLAIR mismatch. A shorter delay between last seen well and symptom recognition (p = 0.0063), a shorter delay between symptom recognition and arrival at hospital (p = 0.0025), and history of atrial fibrillation (p = 0.19) were predictors of DWI-FLAIR mismatch in multivariate analysis. All other characteristics were comparable between groups. Conclusions There are only minor differences in measured clinical characteristics between unknown symptom onset stroke patients with and without DWI-FLAIR mismatch. DWI-FLAIR mismatch as an indicator of stroke onset within 4.5 h shows no relevant association with commonly collected clinical characteristics of stroke patients. Clinical Trial Registration URL: http://www.clinicaltrials.gov . Unique identifier: NCT01525290; URL: https://www.clinicaltrialsregister.eu . Unique identifier: 2011-005906-32.
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http://dx.doi.org/10.1177/1747493017706245DOI Listing
January 2018

Stroke With Unknown Time of Symptom Onset: Baseline Clinical and Magnetic Resonance Imaging Data of the First Thousand Patients in WAKE-UP (Efficacy and Safety of MRI-Based Thrombolysis in Wake-Up Stroke: A Randomized, Doubleblind, Placebo-Controlled Trial).

Stroke 2017 03 7;48(3):770-773. Epub 2017 Feb 7.

From the Klinik und Poliklinik für Neurologie, Kopf- und Neurozentrum (G.T., B.C., C.G.) and Klinik und Poliklinik für Neuroradiologische Diagnostik und Intervention, Diagnostikzentrum (J.F.), Universitätsklinikum Hamburg-Eppendorf, Germany; Service de Biostatistique, Hospices Civils de Lyon, France (F.B., P.R.); Université Lyon 1, Villeurbanne, France (F.B., P.R.); CNRS, UMR 5558, Laboratoire de Biométrie et Biologie Evolutive, Equipe Biostatistique-Santé, Villeurbanne, France (F.B., P.R.); Centrum für Schlaganfallforschung Berlin (CSB) (J.B.F., I.G., M. Ebinger, M. Endres) and Klinik und Hochschulambulanz für Neurologie (M. Ebinger, M. Endres), Charité-Universitätsmedizin Berlin, Germany; Department of Neurology, Aarhus University Hospital, Denmark (C.Z.S.); Department of Neurology, Hospices Civils de Lyon, France (N.N., T.-H.C.); Department of Radiology, Institut de Diagnostic per la Image (IDI), Hospital Dr Josep Trueta, Institut d'Investgació Biomèdica de Girona (IDIBGI), Spain (S.P., J.P.); Department of Neurosciences, Experimental Neurology, KU Leuven-University of Leuven, VIB Center for Brain & Disease Research, and Department of Neurology, University Hospitals Leuven, Belgium (R.L.); Institute of Neuroscience and Psychology (K.W.M.) and Robertson Centre for Biostatistics (I.F.), University of Glasgow, United Kingdom; and Florey Institute of Neuroscience and Mental Health, Heidelberg, Victoria, Australia (V.T.).

Background And Purpose: We describe clinical and magnetic resonance imaging (MRI) characteristics of stroke patients with unknown time of symptom onset potentially eligible for thrombolysis from a large prospective cohort.

Methods: We analyzed baseline data from WAKE-UP (Efficacy and Safety of MRI-Based Thrombolysis in Wake-Up Stroke: A Randomized, Doubleblind, Placebo-Controlled Trial), an investigator-initiated, randomized, placebo-controlled trial of MRI-based thrombolysis in stroke patients with unknown time of symptom onset. MRI judgment included assessment of the mismatch between visibility of the acute ischemic lesion on diffusion-weighted imaging and fluid-attenuated inversion recovery.

Results: Of 1005 patients included, diffusion-weighted imaging and fluid-attenuated inversion recovery mismatch was present in 479 patients (48.0%). Patients with daytime-unwitnessed stroke (n=138, 13.7%) had a shorter delay between symptom recognition and hospital arrival (1.5 versus 1.8 hours; =0.002), a higher National Institutes of Stroke Scale score on admission (8 versus 6; <0.001), and more often aphasia (72.5% versus 34.0%; <0.001) when compared with stroke patients waking up from nighttime sleep. Frequency of diffusion-weighted imaging and fluid-attenuated inversion recovery mismatch was comparable between both groups (43.7% versus 48.7%; =0.30).

Conclusions: Almost half of the patients with unknown time of symptom onset stroke otherwise eligible for thrombolysis had MRI findings making them likely to be within a time window for safe and effective thrombolysis. Patients with daytime onset unwitnessed stroke differ from wake-up stroke patients with regards to clinical characteristics but are comparable in terms of MRI characteristics of lesion age.

Clinical Trial Registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01525290. URL: https://www.clinicaltrialsregister.eu. Unique identifier: 2011-005906-32.
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http://dx.doi.org/10.1161/STROKEAHA.116.015233DOI Listing
March 2017

Clinical-Radiological Parameters Improve the Prediction of the Thrombolysis Time Window by Both MRI Signal Intensities and DWI-FLAIR Mismatch.

Cerebrovasc Dis 2016 18;42(1-2):57-65. Epub 2016 Mar 18.

Max-Planck-Institute for Neurological Research, Cologne, Germany.

Background: With regard to acute stroke, patients with unknown time from stroke onset are not eligible for thrombolysis. Quantitative diffusion weighted imaging (DWI) and fluid attenuated inversion recovery (FLAIR) MRI relative signal intensity (rSI) biomarkers have been introduced to predict eligibility for thrombolysis, but have shown heterogeneous results in the past. In the present work, we investigated whether the inclusion of easily obtainable clinical-radiological parameters would improve the prediction of the thrombolysis time window by rSIs and compared their performance to the visual DWI-FLAIR mismatch.

Methods: In a retrospective study, patients from 2 centers with proven stroke with onset <12 h were included. The DWI lesion was segmented and overlaid on ADC and FLAIR images. rSI mean and SD, were calculated as follows: (mean ROI value/mean value of the unaffected hemisphere). Additionally, the visual DWI-FLAIR mismatch was evaluated. Prediction of the thrombolysis time window was evaluated by the area-under-the-curve (AUC) derived from receiver operating characteristic (ROC) curve analysis. Factors such as the association of age, National Institutes of Health Stroke Scale, MRI field strength, lesion size, vessel occlusion and Wahlund-Score with rSI were investigated and the models were adjusted and stratified accordingly.

Results: In 82 patients, the unadjusted rSI measures DWI-mean and -SD showed the highest AUCs (AUC 0.86-0.87). Adjustment for clinical-radiological covariates significantly improved the performance of FLAIR-mean (0.91) and DWI-SD (0.91). The best prediction results based on the AUC were found for the final stratified and adjusted models of DWI-SD (0.94) and FLAIR-mean (0.96) and a multivariable DWI-FLAIR model (0.95). The adjusted visual DWI-FLAIR mismatch did not perform in a significantly worse manner (0.89). ADC-rSIs showed fair performance in all models.

Conclusions: Quantitative DWI and FLAIR MRI biomarkers as well as the visual DWI-FLAIR mismatch provide excellent prediction of eligibility for thrombolysis in acute stroke, when easily obtainable clinical-radiological parameters are included in the prediction models.
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http://dx.doi.org/10.1159/000444887DOI Listing
November 2017

Spot Sign in Acute Intracerebral Hemorrhage in Dynamic T1-Weighted Magnetic Resonance Imaging.

Stroke 2016 Feb 29;47(2):417-23. Epub 2015 Dec 29.

From the Department of Neurology, Charité - Universitätsmedizin Berlin, Berlin, Germany (K.A.S., A.R., C.H.N.); International Graduate Program Medical Neurosciences, Berlin, Germany (A.S.); and Center for Stroke Research Berlin (CSB), Berlin, Germany (I.G., T.K., K.V., J.B.F.).

Background And Purpose: In computed tomographic imaging of acute intracerebral hemorrhage spot sign on computed tomographic angiography has been established as a marker for hematoma expansion and poor clinical outcome. Although, magnetic resonance imaging (MRI) can accurately visualize acute intracerebral hemorrhage, a corresponding MRI marker is lacking to date.

Methods: We prospectively examined 50 consecutive patients with acute intracerebral hemorrhage within 24 hours of symptom onset. The MRI protocol consisted of a standard stroke protocol and dynamic contrast-enhanced T1-weighted imaging with a time resolution of 7.07 s/batch. Stroke scores were assessed at admission and at time of discharge. Volume measurements of hematoma size and spot sign were performed with MRIcron.

Results: Contrast extravasation within sites of the hemorrhage (MRI spot sign) was seen in 46% of the patients. Patients with an MRI spot sign had a significantly shorter time to imaging than those without (P<0.001). The clinical outcome measured by the modified Rankin Scale was significantly worse in patients with spot sign compared with those without (P≤0.001). Hematoma expansion was observed in the spot sign group compared with the nonspot sign group, although the differences were not significant.

Conclusions: Spot sign can be detected using MRI on postcontrast T1-weighted and dynamic T1-weighted images. It is associated with worse clinical outcome. The time course of contrast extravasation in dynamic T1 images indicates that these spots represent ongoing bleeding.
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http://dx.doi.org/10.1161/STROKEAHA.115.011570DOI Listing
February 2016

Subtracted Dynamic MR Perfusion Source Images (sMRP-SI) provide Collateral Blood Flow Assessment in MCA Occlusions and Predict Tissue Fate.

Eur Radiol 2016 May 27;26(5):1396-403. Epub 2015 Jul 27.

Academic Neuroradiology, Center for Stroke Research (CSB), Charité-Universitätsmedizin, Campus Benjamin Franklin, Hindenburgdamm 30, 12200, Berlin, Germany.

Objectives: Collateral blood flow is accepted as a predictive factor of tissue fate in ischemic stroke. Thus, we aimed to evaluate a new method derived from MR perfusion source images to assess collateral flow in patients with ICA/MCA occlusions.

Methods: A total of 132 patients of the prospective 1000+ study were examined. MR perfusion source images were assessed according to Δimg_n = img_n + 1 - img_n - 1 using the five-grade Higashida collateral flow rating system. Higashida scores were correlated to mismatch (MM) volume, mismatch ratio, day 6 FLAIR lesion volumes and day 90 mRS.

Results: Patients with Higashida scores 3 and 4 had significantly lower admission NIHSS, smaller FLAIR day 6 lesion volumes (p < 0.001) and higher rates of better long-term outcome (mRS 0-2, p = 0.002). There was a linear trend for the association of Higashida grade 1 (p = 0.002) and 2 (p = 0.001) with unfavourable outcome (day 90 mRS 3-6), but no significant association was found for MM volume, MM ratio and day 90 mRS. Inter-rater agreement was 0.58 (95% CI 0.43-0.73) on day 1, 0.70 (95% CI 0.58-0.81) on day 2.

Conclusion: sMRP-SI Higashida score offers a non-invasive collateral vessel and tissue perfusion assessment of ischemic tissue. The predictive value of Higashida rating proved superior to MM with regard to day 90 mRS.

Key Points: • Assessment of collateral flow using subtracted dynamic MR perfusion source imaging (sMRP-SI). • sMRP-SI offers additional information about morphological characteristics of ischemic brain tissue. • sMRP-SI collateral flow assessment proves superior to mismatch volume. • Better collateral flow was significantly associated with better outcome (day 90 mRS).
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http://dx.doi.org/10.1007/s00330-015-3927-5DOI Listing
May 2016

Relative FLAIR Signal Intensities over Time in Acute Ischemic Stroke: Comparison of Two Methods.

J Neuroimaging 2015 Nov-Dec;25(6):964-8. Epub 2015 Feb 16.

Center for Stroke Research Berlin (CSB), Charité Universitätsmedizin Berlin, Germany.

Background And Purpose: Visibility of lesions on fluid attenuated inversion recovery (FLAIR) images appears indicative of the time window in acute ischemic stroke. We compared two published methods for calculation of relative FLAIR signal intensities (rSI) regarding their association with time from symptom onset in a longitudinal fashion.

Methods: We prospectively included patients receiving serial MRI examinations between 4.5 and 35 hours from symptom onset. FLAIR rSI was determined using two methods: a whole regions-of-interest (ROI) method and a hotspot method, selecting only a single area of visually highest signal. Signal intensity (rSI) was calculated relative to the contralateral side for each time point.

Results: We included 21 patients with 3-6 MRI examinations on the first 2 days after stroke onset. FLAIR rSI determined with both methods shows a linear association with time from onset, although the hotspot results showed higher variability. Both methods with their previously published thresholds are reliable for identifying patients outside the 4.5 hours time window.

Conclusion: Both methods show a similar performance, and might be a suitable help for the visual assessment of FLAIR lesion visibility.
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http://dx.doi.org/10.1111/jon.12224DOI Listing
December 2016

DWI intensity values predict FLAIR lesions in acute ischemic stroke.

PLoS One 2014 21;9(3):e92295. Epub 2014 Mar 21.

Center for Stroke Research Berlin (CSB), Charité-Universitätsmedizin, Berlin, Germany; Department of Neurology, Charité-Universtitätsmedizin, Berlin, Germany.

Background And Purpose: In acute stroke, the DWI-FLAIR mismatch allows for the allocation of patients to the thrombolysis window (<4.5 hours). FLAIR-lesions, however, may be challenging to assess. In comparison, DWI may be a useful bio-marker owing to high lesion contrast. We investigated the performance of a relative DWI signal intensity (rSI) threshold to predict the presence of FLAIR-lesions in acute stroke and analyzed its association with time-from-stroke-onset.

Methods: In a retrospective, dual-center MR-imaging study we included patients with acute stroke and time-from-stroke-onset ≤12 hours (group A: n = 49, 1.5T; group B: n = 48, 3T). DW- and FLAIR-images were coregistered. The largest lesion extent in DWI defined the slice for further analysis. FLAIR-lesions were identified by 3 raters, delineated as regions-of-interest (ROIs) and copied on the DW-images. Circular ROIs were placed within the DWI-lesion and labeled according to the FLAIR-pattern (FLAIR+ or FLAIR-). ROI-values were normalized to the unaffected hemisphere. Adjusted and nonadjusted receiver-operating-characteristics (ROC) curve analysis on patient level was performed to analyze the ability of a DWI- and ADC-rSI threshold to predict the presence of FLAIR-lesions. Spearman correlation and adjusted linear regression analysis was performed to assess the relationship between DWI-intensity and time-from-stroke-onset.

Results: DWI-rSI performed well in predicting lesions in FLAIR-imaging (mean area under the curve (AUC): group A: 0.84; group B: 0.85). An optimal mean DWI-rSI threshold was identified (A: 162%; B: 161%). ADC-maps performed worse (mean AUC: A: 0.58; B: 0.77). Adjusted regression models confirmed the superior performance of DWI-rSI. Correlation coefficents and linear regression showed a good association with time-from-stroke-onset for DWI-rSI, but not for ADC-rSI.

Conclusion: An easily assessable DWI-rSI threshold identifies the presence of lesions in FLAIR-imaging with good accuracy and is associated with time-from-stroke-onset in acute stroke. This finding underlines the potential of a DWI-rSI threshold as a marker of lesion age.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0092295PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3962388PMC
January 2015

Difficulty of MRI based identification of lesion age by acute infra-tentorial ischemic stroke.

PLoS One 2014 20;9(3):e92868. Epub 2014 Mar 20.

Center for Stroke Research Berlin, Charité-Universitätsmedizin Berlin, Berlin, Germany.

Background: Systemic thrombolysis in acute ischemic stroke is restricted to the 4.5 h time window. Many patients are excluded from this treatment because symptom onset is unknown. Magnetic resonance imaging (MRI) studies have shown that stroke patients presenting with acute supra-tentorial diffusion-weighted imaging (DWI) lesions that do not have matching lesions on fluid attenuated inversion recovery (FLAIR) are likely to be within a 4.5 hour time window. This study examines the DWI-FLAIR mismatch in infra-tentorial stroke.

Methods: This was a retrospectively conducted substudy of the "1000+" study; a prospective, single-center observational study (http://clinicaltrials.gov; NCT00715533). Fifty-six patients with infra-tentorial stroke confirmed by MRI and known symptom onset who underwent the scan within 24 h after symptom onset were analysed. Two neurologists blinded to clinical information separately rated the DWI lesion visibility on FLAIR. Lesion volume, relative signal intensities of DWI and relative apparent diffusion coefficient values were determined.

Results: Regarding baseline characteristics our study population had a median age of 66 years, a median time from symptom onset to MRI of 616.5 minutes, a median NIHSS of 3 and a median DWI lesion volume of 0.26 ml. A negative FLAIR allocated patients to a time window under 4.5 h correctly with a sensitivity of 55% and a specificity of 61%, a positive predictive value of 44% and a negative predictive value of 71%. FLAIR positivity decreased with age (p = 0.018), and showed no significant correlation to lesion volume (p = 0.145).

Conclusions: In our study the DWI-FLAIR-Mismatch does not help to reliably identify patients within 4.5 h of symptom onset in acute ischemic infra-tentorial stroke. Thus therapeutical decisions based on the DWI-FLAIR mismatch estimation of time from onset cannot be recommended in patients with infra-tentorial stroke.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0092868PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3961416PMC
November 2014