Diffusion-weighted magnetic resonance imaging versus computed tomography in the diagnosis of acute ischemic stroke

Current treatment protocols using reperfusion therapy for acute ischemic stroke rely on non-contrast computed tomography (NCCT), with most indications including the absence of acute hemorrhage or large volume of infarction in the presence of clinical signs and symptoms. This predictably results in a significant incidence of the administration of reperfusion therapy to patients with "stroke mimics," such as migraine headache or Todd's paralysis after a seizure. Diffusion-weighted imaging (DWI) is a technique based on magnetic resonance imaging (MRI) that may be more sensitive and specific for acute cerebral ischemia than NCCT. In addition, data for techniques such as perfusion-weighted imaging can be acquired with minimal additional time required. This may allow better risk assessment of a clinical response to reperfusion therapy vs. the possibility of hemorrhagic complications. This article describes a methodical review of studies comparing the sensitivity, specificity, positive predictive value, and negative predictive value of DWI vs. NCCT in the evaluation of acute ischemic stroke. Data from studies meeting our screening criteria are combined to produce overall values for each.     

Imaging in acute brain infarction

Imaging in a patient suspected of having suffered an acute stroke is used primarily to clear the patient for thrombolytic therapy, by excluding intracranial hemorrhage and nonstroke causes of the patient's symptoms, within a critical 3-hour window. Noncontrast CT of the brain is the imaging test of choice for the initial evaluation of a patient with suspected acute ischemic stroke. It is rapid and readily available and has a high sensitivity for intracranial hemorrhage. Contrast-enhanced CT angiography and perfusion imaging may provide additional information with only a minimal increase in scanning time. Finally, diffusion-weighted magnetic resonance sequences have a high sensitivity for acute stroke and, with magnetic resonance perfusion imaging, may play an increasing role in the future treatment of stroke.     

Computed tomographic angiography and computed tomographic perfusion imaging of hyperacute stroke

The roles of noncontrast computed tomography (NCCT) and CT angiographic/CT perfusion (CTA/CTP) imaging in the rapid triage of clinically suspected hyperacute stroke patients to appropriate therapy is reviewed. Contraindications to thrombolysis include NCCT hemorrhage (absolute) and significant parenchymal hypodensity (relative). The sensitivity of NCCT for early (<6 h) stroke detection, higher than that of conventional magnetic resonance imaging, is improved further by using nonstandard window and level review settings. CTA/CTP is fast and convenient, adding approximately 10 min to the NCCT examination. CTA/CTP's accuracy in diagnosing ischemia and localizing thrombus to proximal or distal intracranial vessels far exceeds that of clinical examination (including National Institutes of Health stroke scale use), facilitating triage of appropriate candidates to intra-arterial thrombolysis. The size of the ischemic CTP hypodensity (proportional to reduced cerebral blood volume) predicts final infarct volume and clinical outcome; its location can guide the decision to perform intra-arterial thrombolysis, intravenous thrombolysis, or other treatment.     

Expedited computed tomography perfusion and angiography in acute ischemic stroke: a feasibility study

Background

Acute ischemic stroke diagnosis and treatment are among the most challenging in Emergency Medicine. Perfusion computed tomography (CTP) can increase the sensitivity for detecting ischemic stroke and, especially with the addition of CT angiography (CTA), improve decision-making regarding thrombolytic therapy compared to non-contrast computed tomography (NCCT) alone. However, because acute stroke protocols do not generally include procedures for multimodal imaging, they are not commonly performed. In addition, there is concern that additional studies could delay or preclude therapy in patients otherwise eligible for thrombolytic therapy.

Objectives

To demonstrate the feasibility of perfusion CTP and CTA in addition to NCCT of the brain in the emergency assessment of patients with acute ischemic stroke. Methods: Starting January 2008, multimodal (CTP and CTA) imaging was added to NCCT in the Emergency Department (ED) initial assessment of patients with stroke of ≤ 5 h duration. Over the subsequent 9 months, we measured the time from ED arrival to imaging and to recombinant tissue plasminogen activator (rt-PA) treatment and compared these times to patients evaluated with CT alone.

Results

From January to October 2008, 95 patients had CTP and CTA studies in addition to NCCT for acute ischemic stroke. There were no differences between the average time to CT study or to rt-PA treatment between patients evaluated with multimodal CT imaging and patients assessed with NCCT alone.

Conclusions

Combining CTP and CTA with NCCT is feasible and does not adversely increase the time to CT imaging or rt-PA treatment in patients with acute ischemic stroke.     

The detection of nontraumatic subarachnoid hemorrhage: still a diagnostic challenge

Nontraumatic subarachnoid hemorrhage is one of the most elusive diagnoses in emergency medicine; it is a potentially lethal disease that is often considered and rarely found. The current practice as determined by the American College of Emergency Physicians 1996 Clinical Policy on Headache is a noncontrast head computed tomography (CT) followed by diagnostic lumbar puncture (LP) to exclude subarachnoid hemorrhage. Whereas the guideline does not consider pretest probability of subarachnoid hemorrhage in determining which patients require LP after negative head CT, patients' acceptance of LP, technical aspects of performing a LP in patients with nonideal anatomy, and risks associated with LP must all be considered when choosing to proceed with invasive testing. This article outlines the use of current testing modalities including CT, magnetic resonance imaging, angiography and LP to provide an up-to-date understanding of diagnostic testing for subarachnoid hemorrhage.     

MR imaging of the thoracic aorta

MR imaging has been incorporated into the diagnostic algorithm for suspected thoracic aortic pathology, challenging CT and invasive catheter angiography as investigations of choice. Techniques, including spin echo, 3-D steady-state free precession, cardiac cine imaging, phase-contrast flow quantification, and high-resolution contrast-enhanced magnetic resonance angiography, are poised to trump other single competitive modalities. The proliferation of 3-tesla systems has advanced the performance of magnetic resonance, aided by parallel imaging techniques, multiarray surface coils, and powerful gradient coils. This article considers the current status of MR imaging in evaluation of the thoracic aorta, with reference to common clinical indications in clinical practice.     

Advances in diagnostic imaging for peripheral arterial disease

Refinements in both noninvasive and invasive imaging techniques have led to significant improvements in both the diagnosis and treatment of peripheral arterial disease. Multiple complementary imaging modalities are available for evaluating these patients. This article reviews the advantages, disadvantages and recent advances in the commonly used clinical applications of duplex ultrasonography, magnetic resonance angiography, computed tomographic angiography, digital subtraction angiography and intravascular ultrasound for arterial imaging in the lower extremities. It also discusses experimental imaging techniques more recently applied to peripheral arterial disease such as PET, hyperspectral imaging and molecular imaging of atherosclerosis. As more is understood about both lesion and patient characteristics that affect their response to peripheral interventions, clinician selection of the various imaging modalities as well as different peripheral interventions will allow for more effective treatment of patients with peripheral arterial disease.     

Advances in diagnostic imaging for peripheral arterial disease

Refinements in both noninvasive and invasive imaging techniques have led to significant improvements in both the diagnosis and treatment of peripheral arterial disease. Multiple complementary imaging modalities are available for evaluating these patients. This article reviews the advantages, disadvantages and recent advances in the commonly used clinical applications of duplex ultrasonography, magnetic resonance angiography, computed tomographic angiography, digital subtraction angiography and intravascular ultrasound for arterial imaging in the lower extremities. It also discusses experimental imaging techniques more recently applied to peripheral arterial disease such as PET, hyperspectral imaging and molecular imaging of atherosclerosis. As more is understood about both lesion and patient characteristics that affect their response to peripheral interventions, clinician selection of the various imaging modalities as well as different peripheral interventions will allow for more effective treatment of patients with peripheral arterial disease.     

CT and MR Imaging in the Acute Ischemic Stroke Patient: A Nursing Perspective

Historically, computed tomography (CT) head scan is the first diagnostic test for stroke-like symptoms. CT rules out hemorrhage immediately but a magnetic resonance (MR) imaging is more sensitive to early ischemia. New advances in CT and MR imaging techniques provide data to differentiate between reversible and irreversible brain damage with accurate identification of the site of arterial occlusion. The additional data may guide the stroke team in determining if the patient can safely be treated beyond the 0- to 3-hr window. Extending the window for treatment substantially increases the number of patients receiving stroke reversal. Nurses play an integral role in facilitating appropriate treatment and providing care to optimize patient’s clinical outcome. The purpose of this article was to discuss the clinical application of CT and MR imaging, define its purpose in acute ischemic stroke treatment, and guide stroke nurses in understanding the advanced concepts of imaging.     

Neuroimaging of stroke: a review

Advances in neuroimaging technology during the past 30 years have resulted in a virtual explosion in the amount of pathologic information that can be obtained in the clinical stroke setting. This neuroimaging revolution has led to a much better understanding of cerebrovascular and tissue pathology, creating a wide array of opportunities for acute treatment and secondary prevention. Advances include early and accurate detection of ischemic and infarcted tissue and the ability to reveal hypoperfused tissue at risk. Clinicians are increasingly able to noninvasively detect embolic and atherothrombotic intravascular lesions. Vascular lesions associated with stroke can be characterized through endovascular neuroimaging techniques and repaired by various means. In this article, we provide an overview and update on the various techniques used in the neuroimaging of stroke and intracranial hemorrhage, including computed tomography, magnetic resonance imaging, ultrasound, and catheter angiography. We outline the specific role of each modality in clinical practice.     

磁共振血管成像评估颈动脉狭窄的研究进展

颈动脉狭窄是导致缺血性脑卒中的重要原因,早发现和早治疗可显著降低其致死率和致残率。磁共振血管成像以无创、无辐射、软组织分辨率高等特点而在颈动脉狭窄评估方面具有重要意义。作者就时间飞跃法磁共振血管成像(time of flight magnetic resonance angiography,TOF-MRA)、对比增强磁共振血管成像(contrast enhanced MRA,CE-MRA)、四维相位对比磁共振血管成像(four dimensional flow magnetic resonance angiography,4D-Flow-MRA)、零回波时间动脉自旋标记血管成像(zero echo time arterial spin labeling magnetic resonance angiography,zTE-ASL-MRA)、黑血成像技术(black blood,BB)和磁共振同时非增强血管成像和斑块内出血成像(simultaneous noncontrast angiography and intraplaque hemorrhage imaging,SNAP)等磁共振血管成像技术以及磁共振快速成像技术在评估颈动脉狭窄的应用及研究进展予以综述。     

Current imaging concepts of thoracic intervertebral disks.

This article reviews the current concepts of thoracic herniated disks using the radiologic literature as well as our own experience with more than 100 thoracic HNPs. The relative frequency of asymptomatic thoracic HNPs is documented. Points of interest include the optimal technique, criteria for interpretation, strengths and weaknesses of various imaging modalities, including water-soluble myelography, CT myelography, and magnetic resonance imaging. Additionally, the protean clinical manifestations of thoracic HNPs and current operative management are briefly addressed.     

Magnetic Resonance Imaging of Carotid Atherosclerosis and the Risk of Stroke

Stroke attributable to carotid atherosclerosis is a leading cause of mortality and morbidity. The clinical management of carotid atherosclerosis presently relies on the degree of stenosis determined by angiography. Degree of stenosis is limited in stratifying patients’ risk of stroke. Advances in magnetic resonance imaging have resulted in the ability to directly assess atherosclerotic plaque components, morphology, and biomechanical stress levels. Components of atherosclerosis, including lipid-rich necrotic core, fibrous cap thickness/disruption, and intraplaque hemorrhage, are promising emerging indicators of stroke. Information beyond luminal stenosis from magnetic resonance imaging may allow for improved detection of patients at risk of stroke from carotid atherosclerosis. We review the recent literature on the relationship of magnetic resonance imaging detected plaque components and cerebrovascular events. Clinical applications of magnetic resonance imaging of carotid plaque components are discussed.     

Overview of cardiac computed tomography

Cardiac CT (CCT) has evolved rapidly over the past 20 years. Initially designed as a test for myocardial perfusion, CCT has developed into a potent screening test for atherosclerosis and a surrogate for invasive angiography (CT angiography). CT angiography, with high correlation to invasive angiography, is now being increasingly used in clinical practice as an alternative to cardiac catheterization or stress imaging. This technology’s high spatial temporal resolution allows for evaluation of major branches of coronary tree, compared to echocardiography, and nuclear or magnetic resonance imaging. The technology of CCT has undergone rapid transformation in recent years such that new scanners have sub-second image acquisition and multi-row capability (multi-detector CT). This article reviews the current scientific evidence and clinical uses for CCT.     

Emergency department presentations of cerebrovascular disease in children

Five cases of children with cerebrovascular disease presentations to the emergency department (ED) were selected as a series to illustrate the variety of presentation of cerebrovascular disease in children. This series shows that although cerebrovascular disease in children is uncommon, it is likely that cases will occasionally present acutely to an ED. The emergency physician's role in the management of suspected acute strokes in children is that of immediate stabilization, imaging to rule out hemorrhage, other studies to rule out emergent acute disease, and timely consultation for further management. Computed tomography (CT) is useful to detect an acute hemorrhage or old ischemic lesion. Magnetic resonance imaging has superior image resolution over CT, but CT may be more practical initially. Magnetic resonance angiography is a useful part of the stroke workup in children.     

急性肌肉拉伤的MRI应用进展

急性肌肉拉伤是一种急性间接肌肉损伤,常见于日常生活和运动中。仅根据临床症状和体格检查难以准确诊断。常规MRI软组织分辨率高,是急性肌肉拉伤诊断和预后评估的重要手段。近年发展的肌肉MR弹性成像、T2弛豫时间图、磁共振扩散加权成像、扩散张量成像和磁共振波谱具有从微观结构、病理和生理层面为急性肌肉拉伤的诊断提供定量、客观依据的潜力。作者对应用于急性肌肉拉伤的各项MRI技术进行综述。     

Backward somersault as a cause of childhood stroke: a case report of isolated middle cerebral artery dissection in an adolescent boy

Arterial dissection is a rare but serious cause of acute childhood stroke. Here, we present the case of a 15-year-old adolescent boy, an art school student, who suddenly experienced left hemi-paralysis after performing repeated backward somersaults, diagnosed as right-sided middle cerebral artery (MCA) hyperacute infarct due to isolated MCA dissection. Middle cerebral artery dissection in childhood is rare, as in our patient; however, pediatricians and emergency physicians should take MCA dissection into consideration in the differential diagnosis when hyperdense MCA sign is detected from unenhanced cranial computed tomography (CT) of childhood and/or adolescent stroke, with a special history such as backward somersault as in this case. Besides, unenhanced cranial CT and further imaging studies, including CT angiography and magnetic resonance imaging, provide a crucial role in early diagnosis to design proper treatment of acute childhood stroke in the ED.     

Nodal staging in genitourinary cancers

In patients with genitourinary cancers nodal staging is an integral part of the pretreatment evaluation. The presence of nodal metastatic disease plays an important role in predicting prognosis and treatment planning. Although some nodal groups can be evaluated clinically, most patients undergo various imaging studies for nodal staging. Each modality has its own unique attributes and applications. This article reviews various imaging modalities, namely, contrast enhanced computerized tomography, magnetic resonance imaging (MRI), and positron emission tomography, used for nodal staging in patients with genitourinary cancers and highlights their strengths and weaknesses. Emerging novel techniques such as lymphotropic nanoparticle enhanced MRI are also highlighted.     

肺动脉栓塞指数的研究进展

急性肺栓塞(acute pulmonary embolism,APE)是以各种栓子阻塞肺动脉及其分支为其发病原因的一组疾病或综合征,也是临床病死率较高的疾病之一。肺栓塞的诊断方法有螺旋CT、放射性核素肺通气/血流灌注(V/Q)显像、磁共振成像和磁共振肺动脉造影、肺动脉造影。螺旋CT中的多排螺旋CT肺动脉造影诊断肺栓塞的敏感性及特异性较高,因此广泛应用于临床。肺动脉栓塞指数(pulmonary artery obstruction index,PAOI)是通过螺旋CT的多排螺旋CT肺动脉造影进行计算的一种临床指标。本文就PAOI与APE危险分层,PaO2,PaCO2,P(A-a)O2,SaO2,RVd/LVd,MPAd,SVCd,肺动脉高压,D-二聚体等的相关性研究现状作一综述。     

中脑周围非动脉瘤性蛛网膜下腔出血的影像学诊断

目的 中脑周围非动脉瘤性蛛网膜下腔出血(PNSAH)是脑血管造影(CAG)阴性的蛛网膜下腔出血(SAH)中的一种独特且预后较佳的亚型。本探讨其影像学特点和诊断。方法：回顾性分析我科连续收治的30例PNSAH。所有患均进行CT和全脑血管造影，23例进行了MR检查，25例行CT血管造影(CTA)检查。结果：CT上SAH位于脑干周围的脑池内．Fisher分级2—3级。CAG、CTA均无阳性发现，早期MR可见脑池内的出血灶，晚期MR正常。结论：PNSAH具有典型的CT表现，但CAG可明确排除其他部位出血。首次CAG和CTA检查均正常的典型患．1个月后可只行CTA而省略CAG复查。诊断PNSAH必须排除椎基底脑动脉瘤。