The imaging of ischaemic stroke

Magnetic resonance imaging in the management of Crohn's disease: a systematic review and meta-analysis

Objectives

Crohn’s disease (CD) is a condition that can occur in any part of the gastrointestinal tract, although usually forms in the colon and terminal ileum. Magnetic resonance imaging (MRI) has become a beneficial modality in the evaluation of small bowel activity. This study reports on a systematic review and meta-analysis of magnetic resonance enterography for the prediction of CD activity and evaluation of outcomes and possible complications.

Methods

Following the PRISMA guidelines, a total of 25 low-risk studies on established CD were selected, based on a QUADAS-II score of ≥ 9.

Results

A sensitivity of 90% was revealed in a pooled analysis of the 19 studies, with heterogeneity of χ² = 81.83 and I² of 80.3%. Also, a specificity of 89% was calculated, with heterogeneity of χ² = 65.12 and I² of 70.0%.

Conclusion

It was concluded that MRI provides an effective alternative to CT enterography in the detection of small bowel activity in CD patients under supervision of radiologist for assessment of disease activity and its complications. Its advantages include the avoidance of radiation exposure and good diagnostic accuracy.

MCA-DN: Multi-path convolution leveraged attention deep network for salvageable tissue detection in ischemic stroke from multi-parametric MRI

BACKGROUND AND OBJECTIVE

Accurate and timely treatment of ischemic stroke can restore the blood flow in the affected area and reduce the risk of disability and death. Identification and localisation of both direct and collateral blood flow restriction from MRI using computational intelligence play a crucial role in assisting manual diagnosis decisions in stroke treatment.

METHOD

A novel multi-path convolution leveraged attention based deep network (MCA-DN) is proposed to address this challenge. MCA-DN combines multi-path convolution derived attention making different weighted filters in each attention convolution sub-path, with interactions on the same level of abstraction. This facilitates the network to focus on voxels with enhanced weighted activations, directing to a plausible lesion. Such a proposition of acquiring attention by embedding multiple filter paths, also prioritizes the selective activation of multi-parametric MRI sequences. The multi-path convolution assisted attention block allows the network layers to gain more insights on the input tensor, enabling the expansion of hypothesis search space with a controlled parameter count.

RESULTS

The algorithm is evaluated on 139 patients of 3 datasets with 4 sub-datasets, including 2 benchmarked challenge datasets of ISLES-2015, 2017. MCA-DN achieved parametric measures of Dice similarity coefficient: 77.3 %, sensitivity: 82.8 %, and specificity: 98.8 %, for stroke segmentation, outperforming the five state-of-the-art methods in the field with encouraging success.

CONCLUSION

Competitive performance of the MCA-DN demonstrates immense potential to assist patient-specific stroke treatment planning by estimating the benefit of reperfusion.

Ischemic Lesion Segmentation using Ensemble of Multi-Scale Region Aligned CNN

The first and foremost step in the diagnosis of ischemic stroke is the delineation of the lesion from radiological images for effective treatment planning. Manual delineation of the lesion by radiological experts is generally laborious and time-consuming. Sometimes, it is prone to intra-observer and inter-observer variability. State of the art deep architectures based on Fully Convolutional Networks (FCN) and cascaded CNNs have shown good results in automated lesion segmentation. This work proposes a series of enhancements over the learning paradigm in the existing methods, by focusing on learning meticulous feature representations through the CNN layers for accurate ischemic lesion segmentation from multimodal MRI. Multiple levels of losses, integration of features from multiple scales, an ensemble of prediction maps from sub-networks are employed to enable the CNN to correlate between features seen from different receptive fields. To allow for progressive refinement of features from block to block, a custom dropout module has been proposed that suppresses noisy features. Multi-branch residual connections and attention mechanisms were also included in the CNN blocks to enable the integration of information from multiple receptive fields and selectively weigh significant features. Also, to tackle data imbalance both at voxel and sample level, patch-based modeling and separation of concerns into classification & segmentation functional branches are proposed. By incorporating the above mentioned architectural enhancements, the proposed deep architecture was able to achieve better segmentation performance against the existing models. The proposed approach was evaluated on the ISLES 2015 SISS dataset, and it achieved a mean dice coefficient of 0.775. By combining sample classification and lesion segmentation into a fully automated framework, the proposed approach has yielded better results compared to most of the existing works.

Dijabetesna ketoacidoza kod bolesnika sa cerebrovaskularnim insultom - uzroci, mehanizmi, dijagnostika i naše smernice za terapiju

Although cerebrovascular disease may be a well recognised trigger for diabetic ketoacidosis (DKA), literature data on the precise mechanisms, characteristics, or treatment guidelines are rare. The risk of developing an ischemic stroke is doubled in adults with diabetes compared to people with normal glucose metabolism. It is important to point out that even children with DKA have a significantly increased risk of cerebrovascular insult and that they can have a stroke with a frequency of about 10%. Given the significant overlap of symptoms between these two diseases, it can be assumed that attributing DKA symptoms as a manifestation of stroke is not uncommon, especially in elderly and less communicative patients. In addition, pH, bicarbonate concentration, and anion gap are not routinely measured in all diabetics suffering from stroke, at least not in secondary health institutions.Children who develop cerebrovascular stroke during DKA often at the beginning have a preserved consciousness or only mild confusion or lethargy. After a few hours, with the institution of therapy, however, loss of consciousness may occur accompanied by signs of increased intracranial pressure. It was previously thought that the cause was too fast fluid replacement. Recent data suggest that reperfusion injury may be a more likely mechanism. Although most of these studies relate to younger individuals with ketoacidosis, it is clear that at least some of them may be operative in adult DKA. Literature therapeutic guidelines for adult diabetics with stroke-related diabetic ketoacidosis are almost lacking, although it is clear that they could not be the same as those utilised in population with normal glucose metabolism. In this paper, we have tried to define our treatment guidelines for these particular patients.

Ischemic stroke segmentation in multi-sequence MRI by symmetry determined superpixel based hierarchical clustering

Automated estimation of ischemic stroke evolution across different brain anatomical regions has immense potential to revolutionize stroke treatment. Multi-sequence Magnetic Resonance Imaging (MRI) techniques provide information to characterize abnormal tissues based on their anatomy and physical properties. Asymmetry of the right and left hemispheres of the brain is an important cue for abnormality estimation but using it alone is susceptible to occasional error due to self-asymmetry of the brain. A precise estimate of the symmetry axis is therefore essential for accurate asymmetry identification, which holds the key to the proposed method. The proposed symmetry determined superpixel based hierarchical clustering (SSHC) method initially estimates the lesion from inter-hemispheric asymmetry. This asymmetry further determines the thresholding parameter for hierarchically clustering the superpixels leading to an automated and accurate lesion delineation. A multi-sequence MRI based pipeline also combines the estimations from individual sequences. SSHC is evaluated on different sequences of the Loma Linda University (LLU) dataset with 26 patients and the Ischemic Stroke Lesion Segmentation (ISLES'15) dataset with 28 patients. SSHC eliminates the need for manual determination of threshold for combining the superpixel clusters and is more reliable as it derives the information from the quick estimation of asymmetry. SSHC outperforms the state-of-the-art resulting in a high Dice similarity score of 0.704±0.27 and a recall of 0.85±0.01 which are 6% and 35% respectively higher than the challenge winning method. SSHC thus demonstrates a promising potential in the automated detection of (sub-)acute adult ischemic stroke.

A review of magnetic resonance enterography-based indices for quantification of Crohn's disease inflammation

Magnetic resonance enterography (MRE) is a leading radiological modality in Crohn's disease (CD) and is used together with laboratory findings and endoscopic examinations for the evaluation of patients during initial diagnosis and follow up. Over the years, there has been great progress in the understanding of CD and there is a continuous strive to achieve better monitoring of patients and to develop new modalities which will predict disease course and thus help in clinical decisions making. An objective evaluation of CD using a quantification score is not a new concept and there are different clinical, endoscopies, radiological and combined indices which are used in clinical practice. Such scores are a necessity in clinical trials on CD for evaluation of disease response, however, there is no consensus of the preferred MRE score and they are not routinely used. This review presents MRE-based indices in use in the last decade: the Magnetic Resonance Index of Activity (MaRIA), the Clermont score, the Crohn's Disease Magnetic Resonance Imaging (MRI) Index (CDMI), the Magnetic Resonance Enterography Global Score (MEGS) and the Lemann index. We compare the different indices and evaluate the clinical research that utilized them. The aim of this review is to provide a reference guide for researchers and clinicians who incorporate MRE indices in their work. When devising future indices, accumulated data of the existing indices must be taken into account, as each of the current indices has its own strengths and weakness.

Dynamic Susceptibility Contrast Magnetic Resonance Imaging Protocol of the Normal Canine Brain

Perfusion magnetic resonance imaging (MRI), specifically dynamic susceptibility MRI (DSC-MRI) is routinely performed as a supplement to conventional MRI in human medicine for patients with intracranial neoplasia and cerebrovascular events. There is minimal data on the use of DSC-MRI in veterinary patients and a DSC-MRI protocol in the veterinary patient has not been described. Sixteen normal dogs, 6 years or older were recruited for this study. The sample population included 11 large dogs (>11 kg) and 5 small dogs (<11 kg). DSC-MRI was performed on a 1.5-T MRI using an adjusted protocol inherent to the MRI. Contrast media was injected using an automatic power injector. Injections were made after five MR measurements were obtained. Following image acquisition, an arterial input function (AIF) graph mapping the transit time of contrast within the cerebral arteries was generated. The manually selected time points along this graph were used to compute perfusion maps. A dose and rate of 0.1 mmol/kg gadolinium-based contrast media at 3 ml/s followed by 10 ml saline flush at 3 ml/s was used in all dogs greater than 11 kg. In all dogs >11 kg, a useable AIF and perfusion map was generated. One dog less than 11 kg received the same contrast dose and rate. In this patient, the protocol did not generate a useable AIF. The remainder of the dogs less than 11 kg followed a protocol of 0.2 mmol/kg gadolinium-based contrast media at 1.5 ml/s with a 10 ml saline flush at 1.5 ml/s. A useable AIF and perfusion map was generated in the remaining dogs <11 kg using the higher contrast dose and slower rate protocol. This study establishes a contrast dose and administration rate for canine DSC-MRI imaging that is different in dogs greater than 11 kg compared to dogs less than 11 kg. These protocols may be used for future applications to evaluate hemodynamic disturbances in canine intracranial pathology.

In vivo measurement of cerebral blood flow: a review of methods and applications

This article reviews the concepts of cerebral blood flow for the clinician involved in the management of patients with carotid stenosis and/or ischaemic stroke. Methods of assessing cerebral blood flow in vivo using nuclear medicine, magnetic resonance and X-ray computed tomography are described. Applications of magnetic resonance and X-ray computed tomographic methods are reviewed and illustrated by examples from the authors' radiological practice.

Radiological investigation of acute stroke 1: non-enhanced computed tomography

Radiology plays a central part in the acute stroke management pathway, with its role now widened beyond establishing the diagnosis. This article reviews the role of the non-enhanced computed tomography brain scan, particularly focusing on the hyper-acute presentation of stroke from a radiological perspective.

CT volume/density ratio as the marker of ischaemic brain injury

OBJECTIVES

We believe that the CT volume/density ratio (VDR) of infarcted area reflects the degree of brain tissue damage during ischaemic stroke (IS).

PATIENTS AND METHODS

Forty six patients with IS were prospectively enrolled into the study. CT scan was performed on days 1 and 10 of hospitalization. S100BB serum level, gelatinase activities (MMP-2 and MMP-9) and neurological examination (NIHSS) were performed on days 1, 5 and 10 of IS. After 3 months, 42 patients were examined by functional disability scales: Barthel index (BI) and modified Rankin scale (mRS).

RESULTS

The VDR of ischaemic focus correlated well with the average S100BB serum level, MMP-9 serum activity and NIHSS score. The weak but statistically significant relationships were noticed between the VDR vs BI and mRS estimated 3 months after stroke.

CONCLUSION

VDR reflects well the damage ratio of brain tissue during IS. In addition, the study underlines the relationship between VDR vs patients' neurological status and disability after IS.

Diabetic ketoacidosis-associated stroke in children and youth

Diabetic ketoacidosis (DKA) is a state of severe insulin deficiency, either absolute or relative, resulting in hyperglycemia and ketonemia. Although possibly underappreciated, up to 10% of cases of intracerebral complications associated with an episode of DKA, and/or its treatment, in children and youth are due to hemorrhage or ischemic brain infarction. Systemic inflammation is present in DKA, with resultant vascular endothelial perturbation that may result in coagulopathy and increased hemorrhagic risk. Thrombotic risk during DKA is elevated by abnormalities in coagulation factors, platelet activation, blood volume and flow, and vascular reactivity. DKA-associated cerebral edema may also predispose to ischemic injury and hemorrhage, though cases of stroke without concomitant cerebral edema have been identified. We review the current literature regarding the pathogenesis of stroke during an episode of DKA in children and youth.

Multimodal MRI segmentation of ischemic stroke lesions

The problem addressed in this paper is the automatic segmentation of stroke lesions on MR multi-sequences. Lesions enhance differently depending on the MR modality and there is an obvious gain in trying to account for various sources of information in a single procedure. To this aim, we propose a multimodal Markov random field model which includes all MR modalities simultaneously. The results of the multimodal method proposed are compared with those obtained with a mono-dimensional segmentation applied on each MRI sequence separately. We constructed an Atlas of blood supply territories to help clinicians in the determination of stroke subtypes and potential functional deficit.

Comparison of two imaging protocols for acute stroke: unenhanced cranial CT versus a multimodality cranial CT protocol with perfusion imaging

The aim of the study was to validate a multimodality cranial computed tomography (CCT) protocol for patients with acute stroke in the United Arab Emirates as a basic imaging procedure for a stroke unit. Therefore, a comparative study was conducted between two groups: retrospective, historical group 1 with early unenhanced CCT and prospective group 2 undergoing a multimodality CCT protocol. Follow-up unenhanced CCT>48 h served as gold standard in both groups. Group 1: Early unenhanced CCT of 50 patients were evaluated retrospectively, using Alberta Stroke Program Early CT Score, and compared with the definite infarction on follow-up CCT. Group 2: 50 patients underwent multimodality CCT (unenhanced CCT, perfusion studies: cerebral blood flow, cerebral blood volume, mean transit time and CT angiography)<8 h after clinical onset and follow-up studies. Modified National Institute of Health Stroke Scale was used clinically in both groups. Group 1 showed 38 men, 12 women, clinical onset 2-8 h before CCT and modified National Institute of Health Stroke Scale 0-28. Group 2 included 38 men, 12 women, onset 3-8 h before CCT, modified National Institute of Health Stroke Scale 0-28. Sensitivity was 58.3% in group 1 and 84.2% in group 2. Computed tomography angiography detected nine intracranial occlusions/stenoses. The higher sensitivity of the multimodality CCT protocol justifies its use as a basic diagnostic tool for the set-up of a first-stroke unit in the United Arab Emirates.

Stroke Imaging at 3.0 T

Stroke is a devastating disease with a complex pathophysiology. It is a major cause of death and disability in North America. To fully characterize its extent and effects, one requires numerous specialized anatomical and functional MR techniques, specifically diffusion-weighted imaging, MR angiography, and perfusion-weighted imaging. The advent of 3.0 T clinical scanners has the potential to provide higher quality information in potentially less time compared with 1.5 T stroke-specific MR imaging protocols. This article gives a brief overview of stroke, presents the principles and clinical applications of the relevant MR techniques required for diagnostic stroke imaging at high field, and discusses the advantages, challenges, and limitations of 3.0 T imaging as they relate to stroke.

Applying instance-based techniques to prediction of final outcome in acute stroke

OBJECTIVE

Acute cerebral stroke is a frequent cause of death and the major cause of adult neurological disability in the western world. Thrombolysis is the only established treatment of ischemic stroke; however, its use carries a substantial risk of symptomatic intracerebral hemorrhage. A clinical tool to guide the use of thrombolysis would be very valuable. One of the major goals of such a tool would be the identification of potentially salvageable tissue. This requires an accurate prediction of the extent of infarction if untreated. In this study, we investigate the applicability of highly flexible instance-based (IB) methods for such predictions.

METHODS AND MATERIALS

Based on information obtained from magnetic resonance imaging of 14 patients with acute stroke, we explored three different implementations of the IB method: k-NN, Gaussian weighted, and constant radius search classification. Receiver operating characteristics analysis, in particular area under the curve (AUC), was used as performance measure.

RESULTS

We found no significant difference (P = 0.48) in performance for the optimal k-NN (k = 164, AUC = 0.814 +/- 0.001) and Gaussian weight (sigma = 0.17, AUC = 0.813 +/- 0.001) implementations, while they were both significantly better (P < 1 x 10(-6) for both) than the constant radius implementation (R = 0.28, AUC = 0.809 +/- 0.001). Qualitative analyses of the distribution of instances in the feature space indicated that non-infarcted instances tends to cluster together while infarcted instances are more dispersed, and that there may not exist a stringent boundary separating infarcted from non-infarcted instances.

CONCLUSIONS

This study shows that IB methods can be used, and may be advantageous, for predicting final infarct in patients with acute stroke, but further work must be done to make them clinically applicable.

Acute Stroke Assessment with CT: Do We Need Multimodal Evaluation?

PURPOSE

To assess detection of stroke and prediction of extent of infarction with multimodal computed tomographic (CT) evaluation (unenhanced CT, perfusion CT, and CT angiography) in patients suspected of having acute stroke.

MATERIALS AND METHODS

Forty-four consecutive patients with a mean National Institutes of Health Stroke Scale score of 10.45 and suspected of having ischemic stroke of the anterior circulation were examined with multi-detector row CT within 8 hours (mean, 3.05 hours) of onset of symptoms. All evaluations were performed with the knowledge that acute stroke was suspected but without detailed clinical information. The extent of ischemia or final infarction on the baseline unenhanced CT scan and follow-up images was assessed with the Alberta Stroke Program Early CT score. Different perfusion maps and follow-up images were assessed to determine the percentage of the ischemia-affected hemisphere. Each component, as well as the multimodal CT evaluation, was compared with follow-up unenhanced CT scans or magnetic resonance images after a mean time of 2.32 days.

RESULTS

Multimodal CT revealed true-positive findings in 30 of 41 patients and true-negative findings in three, resulting in a sensitivity of 78.9%. Unenhanced CT, CT angiography, and perfusion CT showed sensitivities of 55.3%, 57.9%, and 76.3%, respectively. In eight patients, small infarctions (mean size, 1.47 cm) that were proved at follow-up were missed with all modalities at initial multimodal CT. With perfusion CT, four of these small infarctions were missed within the white matter of the section levels. Maps of cerebral blood flow showed the best correlation with the final size of infarction with an r(2) value of 0.71.

CONCLUSION

The presented multimodal CT evaluation improves detection rate and prediction of the final size of infarction in comparison with unenhanced CT, CT angiography, and perfusion CT alone.

Stroke in children

Stroke is defined as the sudden occlusion or rupture of cerebral arteries or veins resulting in focal cerebral damage and neurological deficits. Forms of stroke resulting from vascular occlusion are arterial ischemic stroke (AIS) and sinovenous thrombosis (SVT) and those resulting from vascular rupture are called hemorrhagic stroke. Stroke in children is relatively rare and frequently results in a lack of recognition and delay in diagnosis. The etiologies of stroke in children are legion and multiple risk factors coexist unlike unifactorial etiology in adults. Heart disease whether congenital or acquired, malformations, metabolic and hematological disorders and vasospastic conditions like migraine are seen more often in childhood strokes. The purpose of diagnostic evaluation includes confirmation of the presence of a cerebrovascular lesion, exclusion of other types of neurological dysfunction and identification of etiology of the stroke. The treatment of stroke in children has been primarily directed toward stabilizing systemic factors and management of the underlying causes. Various antithrombotic and non antithrombotic therapies are discussed. The use of anticoagulant therapy appears to be increasing in pediatric AIS. Mortality after stroke in children ranges from 20% to 30% depending on the location and the underlying cause. Residual neurological dysfunction is present in more than 50% of survivors.

Cerebral perfusion imaging using contrast-enhanced MRI

New developments in fast magnetic resonance imaging (MRI) have enabled imaging of cerebral haemodynamics. This article describes the theory behind perfusion imaging and provides an overview of the most commonly used MRI technique. Limitations of this technique are described, and the potential clinical applications are discussed, with particular attention to the role of perfusion imaging in the context of stroke and brain tumour.

Diffusion weighted magnetic resonance imaging in stroke

Diffusion weighted magnetic resonance imaging has evolved from an esoteric laboratory experiment to a critical aspect of routine clinical care of the patient presenting with symptoms suspicious of acute ischemic stroke. The purpose of this article is to review the basis of diffusion weighted imaging (DWI), to consider its application in acute stroke and to recognize potential pitfalls and stroke mimics that might be encountered. Included in the discussion are comments on the elimination of 'T2 shine through' phenomena as well as construction of pixel-by-pixel maps of the apparent diffusion coefficient (ADC). Furthermore, discussion of techniques such as parallel imaging (using SENSE) and PROPELLER sequences will be introduced as methods potentially allowing DWI to be utilized in areas usually associated with prohibitive susceptibility artifact (e.g. the base of the brain). Finally, the concept of interventional therapeutic approaches to salvaging ischemic tissue is introduced, both in terms of the ischemic penumbra (defined by a diffusion/perfusion mismatch) and also in terms of the potential reversibility of the diffusion-weighted hyperintensity, associated with the lesion core.

Imaging of haemorrhagic stroke

Computed tomography (CT) is the reference standard for the imaging of acute non-traumatic intracranial haemorrhage. The sensitivity with which CT detects haemorrhage falls with time and lumber puncture remains mandatory for the exclusion of subarachnoid haemorrhage (SAH). Magnetic resonance (MR) imaging is, however, superior to CT in the subacute and chronic stages after haemorrhage. MR in addition offers pathophysiological information that can help with assessment of both the aetiology of and complications arising from both SAH and intra-parenchymal haemorrhage.

Brain imaging in psychiatry: what has it done for the patient?

From a research perspective, it is easy to become excited by the kinds of findings that neuroimaging has delivered in psychiatry; by allowing us to view the undisturbed living brain, we now have a better picture of neurobiological characteristics of different conditions. But what does it add to the clinical management of psychiatric illnesses?

Spinal-cord injury

More than a decade ago, spinal-cord injury meant confinement to a wheelchair and a lifetime of medical comorbidity. The physician's armamentarium of treatments was very limited, and provision of care for individuals with spinal-cord injury was usually met with frustration. Advances in the neurosciences have drawn attention to research into spinal-cord injury. Nowadays, advanced interventions provide high hope for regeneration and functional restoration. As scientific advances become more frequent, scepticism is giving way to the ideas that spinal-cord injury will eventually be repairable and that strategies to restore function are within our grasp. We address the present understanding of spinal-cord injury, its cause, pathophysiology, diagnosis, and treatment, and look at promising research avenues. We also discuss new treatment options, including functional electric stimulation and part-weight-supported walking.