Imaging acute ischemic stroke

A NIRS-Based Technique for Monitoring Brain Tissue Oxygenation in Stroke Patients

Stroke is a global health issue caused by reduced blood flow to the brain, which leads to severe motor disabilities. Measuring oxygen levels in the brain tissue is crucial for understanding the severity and evolution of stroke. While CT or fMRI scans are preferred for confirming a stroke due to their high sensitivity, Near-Infrared Spectroscopy (NIRS)-based systems could be an alternative for monitoring stroke evolution. This study explores the potential of fNIRS signals to assess brain tissue in chronic stroke patients along with rehabilitation therapy. To study the feasibility of this proposal, ten healthy subjects and three stroke patients participated. For signal acquisition, two NIRS sensors were placed on the forehead of the subjects, who were asked to remain in a resting state for 5 min, followed by a 30 s motor task for each hand, which consists of opening and closing the hand at a steady pace, with a 1 min rest period in between. Acomplete protocol for placing sensors and a signal processing algorithm are proposed. In healthy subjects, a measurable change in oxygen saturation was found, with statistically significant differences (females p = 0.016, males p = 0.005) between the resting-state and the hand movement conditions. This work showed the feasibility of the complete proposal, including the NIRS sensor, the placement, the tasks protocol, and signal processing, for monitoring the state of the brain tissue cerebral oxygenation in stroke patients undergoing rehabilitation therapy. Thus this is a non-invasive barin assessment test based on fNIRS with the potential to be implemented in non-controlled clinical environments.

West Nile virus encephalomyelitis in an immunocompromised patient

We report a case of a 50-year-old immunocompromised woman who presented with acute encephalopathy and gait ataxia due to severe West Nile virus encephalomyelitis. The patient remarkably improved following early and sustained aggressive immunomodulation. Diagnosing West Nile neuroinvasive disease could be challenging without biochemical evidence of West Nile virus nucleic acid in the cerebrospinal fluid, a specific but not sensitive test. Although the neuroimaging findings in our patient could be considered "typical" for West Nile neuroinvasive disease, there is an overlap with the imaging abnormalities seen in other neuroinflammatory disorders presenting with acute leukoencephalopathy. Hence, we review West Nile neuroinvasive disease imaging characteristics and the differential diagnosis of acute leukoencephalopathy.

Incidence, outcomes, and associated factors of isolated striatocapsular infarct after mechanical thrombectomy

OBJECTIVE

To describe baseline and procedural characteristics and clinical outcomes of isolated striatocapsular infarct (iSCI) after mechanical thrombectomy in patients with large-vessel occlusion of the anterior cerebral circulation and its clinical outcome.

METHODS

We performed a longitudinal study including all patients treated with mechanical thrombectomy at our centre between 2015 and 2017; patients were divided into 2 groups (iSCI and non-iSCI) according to whether they presented iSCI in a control CT scan at 24 hours.

RESULTS

Of the 83 patients identified, 22.9% developed an iSCI. There were no statically significant differences in baseline characteristics or in reperfusion times. Patients presenting iSCI showed better collateral circulation and better reperfusion rates in the bivariate analysis. No significant difference was observed for mortality at discharge or at 3 months, or for functional prognosis at 3 months.

CONCLUSIONS

Even if successful reperfusion is achieved, iSCI is a common sequela, independently of reperfusion time, especially in patients with good collateral circulation.

Incidence, outcomes, and associated factors of isolated striatocapsular infarct after mechanical thrombectomy

OBJECTIVES

To describe baseline and procedural characteristics and clinical outcomes of isolated striatocapsular infarct (iSCI) after mechanical thrombectomy in patients with large-vessel occlusion of the anterior cerebral circulation andits clinical outcome.

METHODS

We performed a longitudinal study including all patients treated with mechanical thrombectomy at our centre between 2015 and 2017; patients were divided into 2 groups (iSCI and non-iSCI) according to whether they presented iSCI in a control CT scan at 24h.

RESULTS

Of the 83 patients identified, 22.9% developed an iSCI. There were no statically significant differences in baseline characteristics or in reperfusion times. Patients presenting iSCI showed better collateral circulation and better reperfusion rates in the bivariate analysis. No significant difference was observed for mortality at discharge or at 3 months, or for functional prognosis at 3 months.

CONCLUSIONS

Even if successful reperfusion is achieved, iSCI is a common sequela, independently of reperfusion time, especially in patients with good collateral circulation.

Concerns in the Blurred Divisions between Medical and Consumer Neurotechnology

Neurotechnology has traditionally been central to the diagnosis and treatment of neurological disorders. While these devices have initially been utilized in clinical and research settings, recent advancements in neurotechnology have yielded devices that are more portable, user-friendly, and less expensive. These improvements allow laypeople to monitor their brain waves and interface their brains with external devices. Such improvements have led to the rise of wearable neurotechnology that is marketed to the consumer. While many of the consumer devices are marketed for innocuous applications, such as use in video games, there is potential for them to be repurposed for medical use. How do we manage neurotechnologies that skirt the line between medical and consumer applications and what can be done to ensure consumer safety? Here, we characterize neurotechnology based on medical and consumer applications and summarize currently marketed uses of consumer-grade wearable headsets. We lay out concerns that may arise due to the similar claims associated with both medical and consumer devices, the possibility of consumer devices being repurposed for medical uses, and the potential for medical uses of neurotechnology to influence commercial markets related to employment and self-enhancement.

Predictive value of Alberta stroke program early CT score for perfusion weighted imaging - diffusion weighted imaging mismatch in stroke with middle cerebral artery occlusion

This study aimed to quantitatively assess the consistency and correlation between perfusion weighted imaging (PWI)/ diffusion weighted imaging (DWI) Alberta Stroke Program Early CT Score (ASPECTS) mismatch and PWI/DWI mismatch.Sixty-eight acute ischemic stroke with middle cerebral artery occlusion who underwent magnetic resonance imaging before thrombectomy were eligible. DWI volume, PWI volume and PWI-DWI mismatch were measured. DWI-, PWI-, PWI-DWI ASPECTS were evaluated. Statistical analysis was performed to compare the correlation between volume and ASPECTS of DWI-, PWI- and PWI-DWI mismatch. Receiver operating characteristic curve analysis was used to assess the predictive value of the PWI-DWI ASPECTS mismatch for the occurrence of PWI-DWI mismatch in acute ischemic stroke patients with middle cerebral artery occlusion.Of 68 patients, the DWI volume, PWI volume and PWI-DWI mismatch volume were (27.76 ± 17.53) mL, (167.09 ± 59.64) mL and (139.33 ± 58.18) mL respectively. DWI-ASPECTS was 6.75 ± 1.90 with the interobserver agreement was κ=0.98 (95% CI, 0.95-0.99); PWI-ASPECTS was 3.09 ± 2.11 with the interobserver agreement was κ=0.95 (95% CI, 0.91-0.99); PWI-DWI ASPECTS mismatch was 6.75 ± 1.90. Spearman's rank correlation analysis revealed that PWI-DWI mismatch volume was negatively correlated with PWI-DWI ASPECTS mismatch (r = -0.802; P = .000). Receiver operating characteristic analysis showed that when the PWI-DWI ASPECTS mismatch cut point was ≥ 2, the under curve of PWI-DWI ASPECTS mismatch for predicting PWI-DWI mismatch was 0.954 (95%CI, 0.911-0.998), with the sensitivity and specificity were 84.00% and 100% respectively.PWI-DWI ASPECTS mismatch may represent a convenient surrogate for penumbra in clinical trials.

GAMER MRI: Gated-attention mechanism ranking of multi-contrast MRI in brain pathology

INTRODUCTION

During the last decade, a multitude of novel quantitative and semiquantitative MRI techniques have provided new information about the pathophysiology of neurological diseases. Yet, selection of the most relevant contrasts for a given pathology remains challenging. In this work, we developed and validated a method, Gated-Attention MEchanism Ranking of multi-contrast MRI in brain pathology (GAMER MRI), to rank the relative importance of MR measures in the classification of well understood ischemic stroke lesions. Subsequently, we applied this method to the classification of multiple sclerosis (MS) lesions, where the relative importance of MR measures is less understood.

METHODS

GAMER MRI was developed based on the gated attention mechanism, which computes attention weights (AWs) as proxies of importance of hidden features in the classification. In the first two experiments, we used Trace-weighted (Trace), apparent diffusion coefficient (ADC), Fluid-Attenuated Inversion Recovery (FLAIR), and T1-weighted (T1w) images acquired in 904 acute/subacute ischemic stroke patients and in 6,230 healthy controls and patients with other brain pathologies to assess if GAMER MRI could produce clinically meaningful importance orders in two different classification scenarios. In the first experiment, GAMER MRI with a pretrained convolutional neural network (CNN) was used in conjunction with Trace, ADC, and FLAIR to distinguish patients with ischemic stroke from those with other pathologies and healthy controls. In the second experiment, GAMER MRI with a patch-based CNN used Trace, ADC and T1w to differentiate acute ischemic stroke lesions from healthy tissue. The last experiment explored the performance of patch-based CNN with GAMER MRI in ranking the importance of quantitative MRI measures to distinguish two groups of lesions with different pathological characteristics and unknown quantitative MR features. Specifically, GAMER MRI was applied to assess the relative importance of the myelin water fraction (MWF), quantitative susceptibility mapping (QSM), T1 relaxometry map (qT1), and neurite density index (NDI) in distinguishing 750 juxtacortical lesions from 242 periventricular lesions in 47 MS patients. Pair-wise permutation t-tests were used to evaluate the differences between the AWs obtained for each quantitative measure.

RESULTS

In the first experiment, we achieved a mean test AUC of 0.881 and the obtained AWs of FLAIR and the sum of AWs of Trace and ADC were 0.11 and 0.89, respectively, as expected based on previous knowledge. In the second experiment, we achieved a mean test F1 score of 0.895 and a mean AW of Trace = 0.49, of ADC = 0.28, and of T1w = 0.23, thereby confirming the findings of the first experiment. In the third experiment, MS lesion classification achieved test balanced accuracy = 0.777, sensitivity = 0.739, and specificity = 0.814. The mean AWs of T1map, MWF, NDI, and QSM were 0.29, 0.26, 0.24, and 0.22 (p < 0.001), respectively.

CONCLUSIONS

This work demonstrates that the proposed GAMER MRI might be a useful method to assess the relative importance of MRI measures in neurological diseases with focal pathology. Moreover, the obtained AWs may in fact help to choose the best combination of MR contrasts for a specific classification problem.

Impaired cerebral autoregulation and neurovascular coupling in middle cerebral artery stroke: Influence of severity?

We aimed to assess cerebral autoregulation (CA) and neurovascular coupling (NVC) in stroke patients of differing severity comparing responses to healthy controls and explore the association between CA and NVC with functional outcome. Patients admitted with middle cerebral artery (MCA) stroke and healthy controls were recruited. Stroke severity was defined by the National Institutes of Health Stroke Scale (NIHSS) scores: ≤4 mild, 5-15 moderate and ≥16 severe. Transcranial Doppler ultrasound and Finometer recorded MCA cerebral blood flow velocity (CBFv) and blood pressure, respectively, over 5 min baseline and 1 min passive movement of the elbow to calculate the autoregulation index (ARI) and CBFv amplitude responses to movement. All participants were followed up for three months. A total of 87 participants enrolled in the study, including 15 mild, 27 moderate and 13 severe stroke patients, and 32 control subjects. ARI was lower in the affected hemisphere (AH) of moderate and severe stroke groups. Decreased NVC was seen bilaterally in all stroke groups. CA and NVC correlated with stroke severity and functional outcome. CBFv regulation is significantly impaired in acute stroke, and further compromised with increasing stroke severity. Preserved CA and NVC in the acute period were associated with improved three-month functional outcome.

A New Era of Extended Time Window Acute Stroke Interventions Guided by Imaging

Ischemic stroke is one of the most debilitating and deadliest conditions worldwide. Intravenous t-PA is the current standard treatment within 4 hours after onset of symptoms. Recent randomized controlled trials have demonstrated the efficacy of neurointerventional intra-arterial treatment in acute ischemic stroke. About 20% of acute ischemic stroke are classified as wake-up strokes, which falls out of the conventional treatment time window. New evidence suggests that some patients with longer time from symptom onset (up to 24 hours) may benefit from thrombectomy, probably in part due to variations in collateral circulation among individual patients. Advanced imaging can play a crucial role in identifying patients who could benefit from endovascular intervention presenting within extended treatment time windows. In this article, we review the advanced imaging algorithm for ischemic stroke workup in the multiple studies published to date and summarize the results of the clinical trials for late ischemic stroke that can be clinically useful.

Risk Factors for Perceptual-versus-Interpretative Errors in Diagnostic Neuroradiology

BACKGROUND AND PURPOSE

Diagnostic errors in radiology are classified as perception or interpretation errors. This study determined whether specific conditions differed when perception or interpretation errors occurred during neuroradiology image interpretation.

MATERIALS AND METHODS

In a sample of 254 clinical error cases in diagnostic neuroradiology, we classified errors as perception or interpretation errors, then characterized imaging technique, interpreting radiologist's experience, anatomic location of the abnormality, disease etiology, time of day, and day of the week. Interpretation and perception errors were compared with hours worked per shift, cases read per shift, average cases read per shift hour, and the order of case during the shift when the error occurred.

RESULTS

Perception and interpretation errors were 74.8% (n = 190) and 25.2% (n = 64) of errors, respectively. Logistic regression analyses showed that the odds of an interpretation error were 2 times greater (OR, 2.09; 95% CI, 1.05-4.15; P = .04) for neuroradiology attending physicians with ≤5 years of experience. Interpretation errors were more likely with MR imaging compared with CT (OR, 2.10; 95% CI, 1.09-4.01; P = .03). Infectious/inflammatory/autoimmune diseases were more frequently associated with interpretation errors (P = .04). Perception errors were associated with faster reading rates (6.01 versus 5.03 cases read per hour; P = .004) and occurred later during the shift (24th-versus-18th case; P = .04).

CONCLUSIONS

Among diagnostic neuroradiology error cases, interpretation-versus-perception errors are affected by the neuroradiologist's experience, technique, and the volume and rate of cases read. Recognition of these risk factors may help guide programs for error reduction in clinical neuroradiology services.

Imaging Brain Collaterals: Quantification, Scoring, and Potential Significance

Leptomeningeal collaterals provide the primary source of perfusion to ischemic brain tissue following the onset of acute ischemic stroke and are becoming an important imaging biomarker for stroke therapy triage. Collateral circulation is predictive of infarct growth, end infarct volume, and response to endovascular therapy. The strength of the collateral circulation varies among patients and is partially dependent on genetic and modifiable risk factors. Collateral circulation may be assessed by standard angiographic techniques, including digital subtraction angiography, computed tomography and magnetic resonance (MR) angiography, as well as a growing array of advanced MR techniques including arterial spin labeling and dynamic MR angiography. Simple scoring systems are used to estimate the relative strength of the collateral circulation for a given patient, although there are some discrepancies in the predictive value of these systems. In this review, we discuss methods and techniques for determining the robustness of the collateral circulation and the role of the collateral circulation in acute ischemic stroke assessment and triage.