DWI Lesion Patterns Predict Outcome in Stroke Patients with Thrombolysis

Portable, low-field magnetic resonance imaging enables highly accessible and dynamic bedside evaluation of ischemic stroke

Brain imaging is essential to the clinical management of patients with ischemic stroke. Timely and accessible neuroimaging, however, can be limited in clinical stroke pathways. Here, portable magnetic resonance imaging (pMRI) acquired at very low magnetic field strength (0.064 T) is used to obtain actionable bedside neuroimaging for 50 confirmed patients with ischemic stroke. Low-field pMRI detected infarcts in 45 (90%) patients across cortical, subcortical, and cerebellar structures. Lesions as small as 4 mm were captured. Infarcts appeared as hyperintense regions on T2-weighted, fluid-attenuated inversion recovery and diffusion-weighted imaging sequences. Stroke volume measurements were consistent across pMRI sequences and between low-field pMRI and conventional high-field MRI studies. Low-field pMRI stroke volumes significantly correlated with stroke severity and functional outcome at discharge. These results validate the use of low-field pMRI to obtain clinically useful imaging of stroke, setting the stage for use in resource-limited environments.

Inter-vendor performance of deep learning in segmenting acute ischemic lesions on diffusion-weighted imaging: a multicenter study

There is little evidence on the applicability of deep learning (DL) in the segmentation of acute ischemic lesions on diffusion-weighted imaging (DWI) between magnetic resonance imaging (MRI) scanners of different manufacturers. We retrospectively included DWI data of patients with acute ischemic lesions from six centers. Dataset A (n = 2986) and B (n = 3951) included data from Siemens and GE MRI scanners, respectively. The datasets were split into the training (80%), validation (10%), and internal test (10%) sets, and six neuroradiologists created ground-truth masks. Models A and B were the proposed neural networks trained on datasets A and B. The models subsequently fine-tuned across the datasets using their validation data. Another radiologist performed the segmentation on the test sets for comparisons. The median Dice scores of models A and B were 0.858 and 0.857 for the internal tests, which were non-inferior to the radiologist’s performance, but demonstrated lower performance than the radiologist on the external tests. Fine-tuned models A and B achieved median Dice scores of 0.832 and 0.846, which were non-inferior to the radiologist's performance on the external tests. The present work shows that the inter-vendor operability of deep learning for the segmentation of ischemic lesions on DWI might be enhanced via transfer learning; thereby, their clinical applicability and generalizability could be improved.

Asymmetrical cortical vessel sign predicts prognosis after acute ischemic stroke

INTRODUCTION

To assess whether the asymmetrical cortical vessel sign (ACVS) on susceptibility-weighted imaging (SWI) could predict 90-day poor outcomes in anterior circulation acute ischemic stroke (AIS) patients treated with recombinant tissue plasminogen activator (r-tPA).

METHODS

Clinical data of consecutive patients with anterior circulation AIS treated with r-tPA were retrospectively analyzed. Clinical variables included age, sex, vascular risk factors, NIHSS score, onset to treatment time, and initial hematologic and neuroimaging findings. Follow-up was performed 90 days after onset. Poor outcome was defined as a modified Rankin scale (mRS) ≥3 at 90 days.

RESULTS

A total of 145 patients were included, 35 (24.1%) patients presented with ACVS (≥Grade 1) on SWI. Fifty-three (36.6%) patients had a poor outcome at 90 days. ACVS (≥Grade 1) occurred in 21 (39.6%) patients with poor outcome compared with 14 (15.2%) patients with favorable outcome (p = .001). Univariate analysis indicated that age, NIHSS score on admission, previous stroke, hemorrhagic transformation, severe intracranial large artery stenosis or occlusion (SILASO), and ACVS were associated with 90-day poor outcome (p < .05). Since SILASO and ACVS were highly correlated and ACVS had different grades, we used three logistic regression models. Results from the three models showed that ACVS was associated with 90-day poor outcome.

CONCLUSIONS

In r-tPA-treated patients with anterior circulation AIS, ACVS might be a helpful neuroimaging predictor for poor outcome at 90 days.

Boundary and vulnerability estimation of the internal borderzone using ischemic stroke lesion mapping

Distinction between deep and superficial middle cerebral artery (MCA) territories and their junctional vascular area (the internal borderzone or IBZ) constitutes a predictor of stroke patient outcome. However, the IBZ boundaries are not well-defined because of substantial anatomical variance. Here, we built a statistical estimate of the IBZ and tested its vulnerability to ischemia using an independent sample. First, we used delineated lesions of 122 patients suffering of chronic ischemic stroke grouped in deep, superficial and territorial topographies and statistical comparisons to generate a probabilistic estimate of the IBZ. The IBZ extended from the insular cortex to the internal capsule and the anterior part of the caudate nucleus head. The IBZ showed the highest lesion frequencies (~30% on average across IBZ voxels) in our chronic stroke patients but also in an independent sample of 87 acute patients. Additionally, the most important apparent diffusion coefficient reductions (−6%), which reflect stroke severity, were situated within our IBZ estimate. The IBZ was most severely injured in case of a territorial infarction. Then, our results are in favour of an increased IBZ vulnerability to ischemia. Moreover, our probabilistic estimates of deep, superficial and IBZ regions can help the everyday spatial classification of lesions.

The implementation of natural language processing to extract index lesions from breast magnetic resonance imaging reports

BACKGROUND

There are often multiple lesions in breast magnetic resonance imaging (MRI) reports and radiologists usually focus on describing the index lesion that is most crucial to clinicians in determining the management and prognosis of patients. Natural language processing (NLP) has been used for information extraction from mammography reports. However, few studies have investigated NLP in breast MRI data based on free-form text. The objective of the current study was to assess the validity of our NLP program to accurately extract index lesions and their corresponding imaging features from free-form text of breast MRI reports.

METHODS

This cross-sectional study examined 1633 free-form text reports of breast MRIs from 2014 to 2017. First, the NLP system was used to extract 9 features from all the lesions in the reports according to the Breast Imaging Reporting and Data System (BI-RADS) descriptors. Second, the index lesion was defined as the lesion with the largest number of imaging features. Third, we extracted the values of each imaging feature and the BI-RADS category from each index lesion. To evaluate the accuracy of our system, 478 reports were manually reviewed by two individuals. The time taken to extract data by NLP was compared with that by reviewers.

RESULTS

The NLP system extracted 889 lesions from 478 reports. The mean number of imaging features per lesion was 6.5 ± 2.1 (range: 3-9; 95% CI: 6.362-6.638). The mean number of imaging features per index lesion was 8.0 ± 1.1 (range: 5-9; 95% CI: 7.901-8.099). The NLP system demonstrated a recall of 100.0% and a precision of 99.6% for correct identification of the index lesion. The recall and precision of NLP to correctly extract the value of imaging features from the index lesions were 91.0 and 92.6%, respectively. The recall and precision for the correct identification of the BI-RADS categories were 96.6 and 94.8%, respectively. NLP generated the total results in less than 1 s, whereas the manual reviewers averaged 4.47 min and 4.56 min per report.

CONCLUSIONS

Our NLP method successfully extracted the index lesion and its corresponding information from free-form text.

Temporal evolution and spatial distribution of quantitative T2 MRI following acute ischemia reperfusion injury

Background

Determining mechanisms of secondary stroke injury related to cerebral blood flow and the severity of microvascular injury contributing to edema and blood-brain barrier breakdown will be critical for the development of adjuvant therapies for revascularization treatment.

Aim

To characterize the heterogeneity of the ischemic lesion using quantitative T2 imaging along with diffusion-weighted magnetic resonance imaging (DWI) within five hours of treatment.

Methods

Quantitative T2 magnetic resonance imaging was acquired within 5 h (baseline) and at 24 h (follow-up) of stroke treatment in 29 patients. Dynamic contrast enhanced permeability imaging was performed at baseline in a subgroup of patients. Absolute volume change and lesion percent change was determined for the quantitative T2, DWI, and absolute volume change sequences. A Gaussian process with RRELIEFF feature selection algorithm was used for prediction of relative quantitative T2 and DWI lesion growth, baseline and follow-up quantitative T2/DWI lesion ratios, and also NIHSS at 24 h and change in NIHSS from admission to 24 h.

Results

In n = 27 patients, median (interquartile range) lesion percent change was 114.8% (48.9%, 259.1%) for quantitative T2, 48.2% (−12.6%, 179.6%) for absolute volume change, and 62.7% (26.3%, 230.9%) for DWI, respectively. Our model, consisting of baseline NIHSS, CT ASPECTS, and systolic blood pressure, showed a strong correlation with quantitative T2 percent change (cross correlation R2 = 0.80). There was a strong predictive ability for quantitative T2/DWI lesion ratio at 24 h using baseline NIHSS and last seen normal to 24 h magnetic resonance imaging time (cross correlation R2 = 0.93). Baseline dynamic contrast enhanced permeability was moderately correlated to the baseline quantitative T2 values (rho = 0.38).

Conclusion

Quantitative T2 imaging provides critical information for development of therapeutic approaches that could ameliorate microvascular damage during ischemia reperfusion.

Rich-Club Organization: An Important Determinant of Functional Outcome After Acute Ischemic Stroke

Objective: To determine whether the rich-club organization, essential for information transport in the human connectome, is an important biomarker of functional outcome after acute ischemic stroke (AIS). Methods: Consecutive AIS patients (N = 344) with acute brain magnetic resonance imaging (MRI) (<48 h) were eligible for this study. Each patient underwent a clinical MRI protocol, which included diffusion weighted imaging (DWI). All DWIs were registered to a template on which rich-club regions have been defined. Using manual outlines of stroke lesions, we automatically counted the number of affected rich-club regions and assessed its effect on the National Institute of Health Stroke Scale (NIHSS) and modified Rankin Scale (mRS; obtained at 90 days post-stroke) scores through ordinal regression. Results: Of 344 patients (median age 65, inter-quartile range 54-76 years) with a median DWI lesion volume (DWIv) of 3cc, 64% were male. We established that an increase in number of rich-club regions affected by a stroke increases the odds of poor stroke outcome, measured by NIHSS (OR: 1.77, 95%CI 1.41-2.21) and mRS (OR: 1.38, 95%CI 1.11-1.73). Additionally, we demonstrated that the OR exceeds traditional markers, such as DWIv (OR_NIHSS 1.08, 95%CI 1.06-1.11; OR_mRS 1.05, 95%CI 1.03-1.07) and age (OR_NIHSS 1.03, 95%CI 1.01-1.05; OR_mRS 1.05, 95%CI 1.03-1.07). Conclusion: In this proof-of-concept study, the number of rich-club nodes affected by a stroke lesion presents a translational biomarker of stroke outcome, which can be readily assessed using standard clinical AIS imaging protocols and considered in functional outcome prediction models beyond traditional factors.

Diffusion-weighted imaging lesion growth occurs despite recanalization in acute ischemic stroke: Implications for future treatment trials

Background

A proportion of patients presenting with acute small ischemic strokes have poor functional outcomes, even following rapid recanalization treatment.

Aims

Infarct growth may occur even after successful recanalization and could represent an appropriate endpoint for future stroke therapy trials.

Methods

Magnetic resonance diffusion-weighted imaging lesion volumes were obtained at 5 h (initial posttreatment) and 24 h (follow-up) after acute stroke treatment for n = 33 in ischemic stroke patients. Sample sizes per arm (90% power, 30% effect size) for diffusion-weighted imaging lesion growth between initial and 24 h, early change in the National Institutes of Health Stroke Scale between pre- and 24 h, National Institutes of Health Stroke Scale at 24 h, and diffusion-weighted imaging lesion volume at 24 h were estimated to power a placebo-controlled stroke therapy trial.

Results

For patients with poor recanalization (modified thrombolysis in cerebral infarction <2 a; modified arterial occlusion lesion = 0–2) (n = 11), the median diffusion-weighted imaging lesion growth was 8.1 (interquartile range: 4.5, 22.4) ml and with good recanalization (modified thrombolysis in cerebral infarction =2 b or 3; modified arterial occlusion lesion = 3) (n = 22), the median diffusion-weighted imaging lesion growth was 10.0 (interquartile range: 6.0, 28.2) ml ( P = 0.749). When considering a 30% effect size, the sample size required per arm to achieve significance in an acute stroke study would be: (1) N = 49 for the diffusion-weighted imaging lesion growth between initial posttreatment and follow-up time points, (2) N = 65 for the change in the National Institutes of Health Stroke Scale between admission and 24 h, (3) N = 259 for the National Institutes of Health Stroke Scale at 24 h, and (4) N = 256 for diffusion-weighted imaging volume at 24 h.

Conclusion

Despite best efforts to recanalize the ischemic brain, early diffusion-weighted imaging lesion growth still occurs. Treatment trials in stroke should consider early diffusion-weighted imaging lesion growth as a surrogate outcome measure to significantly reduce sample sizes.

Clinical and radiological factors associated with unfavorable outcome after intravenous thrombolysis in patients with mild ischemic stroke

BACKGROUND

A significant proportion of patients with mild ischemic stroke become disabled despite receiving intravenous thrombolytic therapy. The purpose of this study was to assess the clinical and radiological factors associated with unfavorable outcomes in patients with minor ischemic stroke that received intravenous recombinant tissue plasminogen activator (rt-PA) therapy.

METHODS

We identified anterior circulation stroke patients with initial National Institutes of Health Stroke Scale (NIHSS) scores ≤5 who received intravenous thrombolysis within 4.5 h of stroke onset and had pretreatment magnetic resonance (MR)/MR angiography using our prospective stroke database. We analyzed baseline characteristics, infarction patterns on diffusion-weighted imaging (DWI), and steno-occlusive lesions on MR angiography. Unfavorable outcome was defined as a modified Rankin Scale (mRS) score ≥ 2 at 90 days. Logistic regression was used to determine independent predictors of unfavorable outcomes.

RESULTS

Among 121 patients (85 men; mean age, 63.4 ± 11.3 years) included in this study, 46 (38%) had unfavorable outcomes at 90 days and DWI lesion patterns showing infarction in the deep middle cerebral artery (MCA) territory involving the perforating artery area was observed in 47 (38.8%) patients. On multivariable analysis, unfavorable outcomes at 90 days were associated with diabetes [odds ratio (OR), 3.41; 95% confidence interval (CI), 1.06-10.9; P = 0.039), NIHSS score on admission (OR, 2.11; 95% CI, 1.35-3.30; P = 0.001), and infarction in the deep MCA territory on DWI (OR, 4.19; 95% CI, 1.63-10.8; P = 0.003). Lesions in the deep MCA territory was independently associated with early neurological deterioration (P = 0.032). The patients without deep MCA territory infarction had a higher prevalence of cardiac embolism (P = 0.009).

CONCLUSIONS

Higher NIHSS scores, diabetes, and deep MCA territory infarction may be useful for predicting unfavorable outcomes in patients with minor stroke treated with intravenous rt-PA therapy.

Cerebrovascular risk factors for patients with cerebral watershed infarction: A case-control study based on computed tomography angiography in a population from Southwest China

To determine cerebrovascular risk factors for patients with cerebral watershed infarction (CWI) from Southwest China.Patients suffering from acute ischemic stroke were categorized into internal CWI (I-CWI), external CWI (E-CWI), or non-CWI (patients without CWI) groups. Clinical data were collected and degrees of steno-occlusion of all cerebral arteries were scored. Arteries associated with the circle of Willis were also assessed. Data were compared using Pearson chi-squared tests for categorical data and 1-way analysis of variance with Bonferroni post hoc tests for continuous data, as appropriate. Multivariate binary logistic regression analysis was performed to determine independent cerebrovascular risk factors for CWI.Compared with non-CWI, I-CWI had higher degrees of steno-occlusion of the ipsilateral middle cerebral artery, ipsilateral carotid artery, and contralateral middle cerebral artery. E-CWI showed no significant differences. All the 3 arteries were independent cerebrovascular risk factors for I-CWI confirmed by multivariate binary logistic regression analysis. I-CWI had higher degrees of steno-occlusion of the ipsilateral middle cerebral artery compared with E-CWI. No significant differences were found among arteries associated with the circle of Willis.The ipsilateral middle cerebral artery, carotid artery, and contralateral middle cerebral artery were independent cerebrovascular risk factors for I-CWI. No cerebrovascular risk factor was identified for E-CWI.