False-negative diffusion-weighted MR findings in acute ischemic stroke

BACKGROUND AND PURPOSE: Lesions associated with acute stroke are often missed by diffusion-weighted imaging (DWI), suggesting that the sensitivity of this technique for detecting acute ischemic stroke may not be as high as initially thought. Our aim was to estimate the rate of false-negative DWI studies in patients with persistent neurologic deficit due to an ischemic stroke and to identify which stroke lesions are most likely to be missed by DWI. METHODS: We reviewed MR images obtained within 48 hours after stroke onset in 139 patients admitted for symptoms consistent with ischemic stroke in whom the deficit lasted more than 24 hours. Cases of negative initial DWI findings with an ischemic lesion visible on follow-up MR studies and a final diagnosis of arterial ischemic stroke were analyzed in terms of delay between onset of symptoms and initial DWI (MR latency), size and vascular distribution of the lesions, and relationship to findings in patients with positive initial DWI results. RESULTS: We found eight cases (5.8%) of false-negative initial DWI studies, of which four were positive on initial fluid-attenuated inversion recovery (FLAIR) imaging. Follow-up FLAIR/DWI showed a hyperintensity matching clinical presentation in all eight patients. The mean size of the lesion was 0.19 +/- 0.16 cm3. False-negative studies occurred more often in cases of stroke in the posterior (19%) than in the anterior (2%) circulation or when DWI was obtained within 24 hours after symptom onset. Of the six false-negative vertebrobasilar stroke lesions, five were located in the brain stem. In all, 31% of patients with vertebrobasilar ischemic stroke had a false-negative initial DWI study during the first 24 hours. CONCLUSION: A false-negative DWI study is not uncommon during the first 24 hours of ischemic stroke. Vertebrobasilar stroke should therefore not be ruled out on the basis of early negative DWI, especially when symptoms persist and are suggestive of this diagnosis.     

T_2′成像预测急性脑卒中超出扩散加权成像所示的梗死灶范围

目的利用局部磁化率(T2′)对脑内脱氧血红蛋白浓度增加敏感而导致信号丢失的特点,说明横向弛豫时间测定有助于提示存在具有梗死危险的脑组织。材料和方法 本     

Microembolic signals and diffusion-weighted MR imaging abnormalities in acute ischemic stroke.

BACKGROUND AND PURPOSE: The clinical significance of microembolic signals (MESs) detected by transcranial Doppler sonography (TCD) in acute ischemic stroke remains unclear. The purpose of the present study was to assess the findings of diffusion-weighted MR imaging (DWI) and other clinical characteristics in patients with acute ischemic stroke and MESs. METHODS: We performed TCD and DWI within 48 hours and 7 days, respectively, after stroke onset in 28 patients with acute brain infarction. The relationship between the number of MESs and DWI findings, risk factors for stroke, National Institutes of Health Stroke Scale (NIHSS) score on admission, and arterial disease was examined. RESULTS: Ten patients had MESs detected by TCD (MES group) and 18 had no MESs (control group). The frequency of hypertension, diabetes mellitus, hyperlipidemia, and smoking; NIHSS score; blood-coagulation parameters; and interval between stroke onset and DWI study did not differ between the two groups. However, arterial disease was more frequent in the MES group than in the control group. Small, multifocal ischemic lesions (<10 mm in diameter) on DWI were more frequent in the MES group than in the control group. Conventional CT and MR imaging often failed to show these lesions. CONCLUSION: Small, often asymptomatic DWI abnormalities were more frequent in patients with MESs detected by TCD and with large-vessel occlusive diseases than in stroke patients without MESs. TCD and DWI may provide early clues to the mechanism of stroke in the acute phase.     

Clinical MRI of acute ischemic stroke

The most important service that imaging provides to patients with ischemic stroke is to rapidly identify those patients who are most likely to benefit from immediate treatment. This group includes patients who have severe neurological symptoms due to an occlusion of a major artery, and who are candidates for recanalization using intravenous thrombolysis or intra-arterial intervention to remove the occlusion. Outcomes for these patients are determined by symptom severity, the artery that is occluded, the size of the infarct at the time of presentation, and the effect of treatment. MRI provides key physiological information through MR angiography and diffusion MRI that has been proven to be of high clinical value in identify patients who are in need of immediate treatment. Perfusion MRI provides information about the ischemic penumbra, but its clinical value is unproven. In current clinical practice, the time since stroke onset is dominant over physiologic information provided by MRI in treatment decisions. This will change only when clinical trials prove that stroke physiology as revealed by MRI is superior to time from stroke onset in promoting good clinical outcomes.     

Predicting final infarct size using acute and subacute multiparametric MRI measurements in patients with ischemic stroke

PURPOSE: To identify early MRI characteristics of ischemic stroke that predict final infarct size three months poststroke. MATERIALS AND METHODS: Multiparametric MRI (multispin echo T2-weighted [T2W] imaging, T1-weighted [T1W] imaging, and diffusion-weighted imaging [DWI]) was performed acutely (<24 hours), subacutely (three to five days), and at three months. MRI was processed using maps of apparent diffusion coefficient (ADC), T2, and a self-organizing data analysis (ISODATA) technique. Analyses began with testing for individual MRI parameter effects, followed by multivariable modeling with assessment of predictive ability (R(2)) on final infarct size. RESULTS: A total of 45 patients were studied, 15 of whom were treated with tissue plasminogen activator (tPA) before acute MRI. The acute DWI and DWI-ISODATA mismatch lesion size, and the interactions of ADC, T2, and T2W imaging lesion with tPA remained in the final multivariable model (R(2) = 70%). A large acute DWI lesion or DWI < ISODATA lesion independently predicted increase in the final infract size, with predictive ability 68%. Predictive ability increased (R(2) = 83%) when subacute MRI parameters were included along with acute DWI, DWI-ISODATA mismatch, and acute T2W image lesion size by tPA treatment interaction. Subacute DWI > acute DWI lesion size predicted an increased final infarct size (P < 0.01). CONCLUSION: Acute-phase DWI and DWI-ISODATA mismatch strongly predict the final infarct size. An acute-to-subacute DWI lesion size change further increases the predictive ability of the model.     

Combined perfusion- and diffusion-weighted MR imaging in acute ischemic stroke during the 1st week: a longitudinal study

PURPOSE: To compare findings with different magnetic resonance (MR) perfusion maps in acute ischemic stroke. MATERIALS AND METHODS: Combined diffusion-weighted (DW) and perfusion-weighted (PW) MR imaging was performed in 49 patients with acute (<24 hours) stroke, on the 1st and 2nd days and 1 week after stroke. Volumes of hypoperfused tissue on maps of relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF), and mean transit time (MTT) were compared with the volume of infarcted tissue at DW imaging. RESULTS: The mean infarct volume increased from 41 to 65 cm(3) between the 1st and 2nd days (P: <.001; n = 49). On the 1st day, all perfusion maps on average showed hypoperfusion lesions larger than the infarct at DW imaging (P: <.001; n = 49). MTT maps showed significantly (P: <.001) larger hypoperfusion lesions than did rCBF maps, which showed significantly (P: <.001) larger hypoperfusion lesions than did rCBV maps. The sizes of the initial perfusion-diffusion mismatches correlated significantly with the extent of infarct growth (0.479 < r < 0.657; P: 相似文献   

Automatic prediction of infarct growth in acute ischemic stroke from MR apparent diffusion coefficient maps

RATIONALE AND OBJECTIVES: We introduce a new approach to the prediction of final infarct growth in human acute ischemic stroke based on image analysis of the apparent diffusion coefficient (ADC) maps obtained from magnetic resonance imaging. Evidence from multiple previous studies indicate that ADC maps are likely to reveal brain regions belonging to the ischemic penumbra, that is, areas that may be at risk of infarction in the few hours following stroke onset. MATERIALS AND METHODS: In a context where "time is brain," and contrarily to the alternative-and still-debated-perfusion-diffusion weighted image (PWI/DWI) mismatch approach, the DWI magnetic resonance sequences are standardized, fast to acquire, and do not necessitate injection of a contrast agent. The image analysis approach presented here consists of the segmentation of the ischemic penumbra using a fast three-dimensional region-growing technique that mimics the growth of the infarct lesion during acute stroke. RESULTS: The method was evaluated with both numerical simulations and on two groups of 20 ischemic stroke patients (40 patients total). The first group of patient data was used to adjust the parameters of the model ruling the region-growing procedure. The second group of patient data was dedicated to evaluation purposes only, with no subsequent adjustment of the free parameters of the image-analysis procedure. Results indicate that the predicted final infarct volumes are significantly correlated with the true final lesion volumes as revealed by follow-up measurements from DWI sequences. CONCLUSION: The DWI-ADC mismatch method is an encouraging fast alternative to the PWI-DWI mismatch approach to evaluate the likeliness of infarct growth during the acute stage of ischemic stroke.     

Turbo spin-echo diffusion-weighted MR of ischemic stroke.

PURPOSEOur objective was to determine whether a multisection technique, diffusion-weighted half-Fourier single-shot turbo spin-echo (HASTE) imaging, can compensate for the drawbacks common to other diffusion-weighted techniques; specifically, the need for echo-planar technology and the presence of susceptibility artifacts in areas close to the skull base.METHODSForty subjects who were referred to the stroke service with signs of acute (less than 24 hour) neurologic dysfunction were included in this prospective study. MR imaging of the brain was performed with diffusion-weighted echo-planar and diffusion-weighted HASTE sequences. The images obtained with both sequences were analyzed for the presence of hyperintensities corresponding to ischemic lesions as well as for the presence of image artifacts and distortions.RESULTSDiffusion-weighted HASTE images showed areas of hyperintensity corresponding to the infarcts present on diffusion-weighted echo-planar imaging studies without distortion or susceptibility artifacts in all the patients who had a stroke. Twelve patients had no acute ischemic lesions; of these, five had other findings, six had normal findings, and in one patient, a hyperintensity seen on diffusion-weighted echo-planar images proved to be an artifact on diffusion-weighted HASTE images.CONCLUSIONSDiffusion-weighted HASTE is equal to diffusion-weighted echo-planar imaging in the detection of early ischemia. Because of the absence of significant image distortions and other artifacts, diffusion-weighted HASTE permits fast multiplanar imaging in artifact-prone regions, such as the posterior fossa and the inferior frontal and temporal lobes. Diffusion imaging can be performed on conventional systems with strengths of 1.5 T that do not have echo-planar imaging capabilities.     

Reversed discrepancy between CT and diffusion-weighted MR imaging in acute ischemic stroke

PURPOSE: We sought to determine whether an early CT ischemic lesion showing parenchymal hypoattenuation might be undetectable on diffusion-weighted imaging (DWI) in acute cerebral ischemia. MATERIALS AND METHODS: We retrospectively evaluated CT and MR images of 70 consecutive patients with acute middle cerebral artery (MCA) infarction. All patients underwent CT and MR imaging within 6 hours of symptom onset. We determined the presence of reversed discrepancy (RD), defined as an early ischemic lesion showing parenchymal hypoattenuation on CT but no hyperintensity on DWI. CT Hounsfield units (HU), apparent diffusion coefficients (ADCs), and perfusion parameters were calculated for RD lesions. RESULTS: RD was found in 9 (12.9%) patients and at basal ganglia (89%). The mean HU of RD lesion was lower than that of normal tissue (DeltaHU, 2.33 +/- 0.74, P < .001). RD lesions showed no significant decrease of ADC (ADC ratio, 0.97 +/- 0.07, P = .059) and cerebral blood flow (relative CBF, 0.87 +/- 0.20, P > 0.05). Delayed DWI hyperintensity occurred in 8 (88.8%) RD lesions, and all lesions progressed to infarction. In 6 (66%) of 9 patients with RD, Alberto Stroke Program Early CT scores of ischemic lesions were lower on CT than those on DWI. CONCLUSION: RD was uncommonly found mainly in basal ganglia, and all RD lesions progressed to infarction at follow-up. Early CT ischemic lesion showing parenchymal hypoattenuation may be undetectable on DWI, and DWI may underestimate extent of severe ischemic tissue in patients with acute MCA infarction.     

Perfusion differences on SPECT and PWI in patients with acute ischemic stroke

Introduction

The purposes of the present study were to compare the flow defect volumes on perfusion-weighted magnetic resonance imaging (PWI) and ^99mTc-labeled ethylcysteinate dimer (^99mTc-ECD) single photon emission computed tomography (SPECT) at acute and subacute stages of ischemic stroke and to analyze the relationship between the detected flow defects on the two methods and neurological status and clinical outcomes.

Methods

Perfusion defects on PWI and SPECT were measured within 48 h and on day 8 of the onset of stroke from 22 patients with their first-ever acute supratentorial ischemic stroke. The primary neurological status was evaluated prior to the imaging. Clinical outcome was assessed at 3 months after the onset of the stroke.

Results

The volumes of cerebral blood flow (CBF) defects did not differ between SPECT and PWI within the 48-h examinations. However, the volume of CBF defect was significantly larger on SPECT than on PWI on day 8 (p = 0.03). Within the 48-h examinations, the CBF defect volumes on SPECT and PWI were comparably related to the neurological status. On day 8, the CBF defect volume on SPECT showed higher correlation to the neurological status and more precisely predicted the clinical outcomes at 3 months than PWI.

Conclusions

^99mTC-ECD-SPECT and PWI both have ability to detect cerebral hypoperfusion in patients with ischemic stroke but with some differences. The value of SPECT is more accurate in terms of the delayed outcome, such as prognosis and rehabilitation planning.     

MR imaging in acute stroke: diffusion-weighted and perfusion imaging parameters for predicting infarct size

PURPOSE: To investigate the predictive value of the ischemic lesion size, as depicted in the acute stroke phase on diffusion-weighted magnetic resonance (MR) images and time-to-peak (TTP) maps of tissue perfusion imaging, for infarct size, as derived from T2-weighted imaging in the postacute phase. MATERIALS AND METHODS: Fifty patients who underwent diffusion-weighted and perfusion imaging within 1-24 hours after stroke onset and a follow-up T2-weighted investigation after about 8 days were included. Lesion volumes were evaluated by using a semiautomatic thresholding technique. Volumetric results of acute diffusion-weighted and perfusion imaging were analyzed in comparison with follow-up T2-weighted images and in terms of the time difference between symptom onset and initial MR imaging. RESULTS: At diffusion-weighted imaging, the acute lesion defined by a signal intensity increase of more than 20%, compared with the contralateral side, showed the best correlation with the infarct size after 1 week. At perfusion imaging, the best predictor relative to the contralateral side was a delay of more than 6 seconds on TTP maps. Temporal analysis of volumetric results, which depended on the time difference between symptom onset and examination, revealed two patient subgroups. CONCLUSION: Diffusion-weighted imaging helped to predict the size of the lesion on T2-weighted images obtained after about 8 days in patients with a symptom onset of more than 4 hours (r = 0.96), while in patients with a symptom onset of less than 4 hours, perfusion imaging provided important additional information about brain tissue with impaired perfusion.     

Combined stent placement and thrombolysis in acute vertebrobasilar ischemic stroke

BACKGROUND AND PURPOSE: Acute vertebrobasilar ischemic stroke is often associated with high morbidity and mortality with limited therapeutic options. Endovascular treatment with thrombolysis has offered some hope for affected patients; however, overall outcomes have been less than satisfactory. In this report, we present the results of our approach in six consecutive cases of acute vertebrobasilar ischemic stroke by combined proximal vessel stent placement and thrombolysis. METHODS: Six consecutive cases were retrospectively reviewed for the clinical outcome of patients presenting to our institution with acute posterior circulation stroke who underwent cerebral revascularization including proximal arterial stent placement by using balloon-expandable coronary stents and intraarterial thrombolysis. All of these patients were initially evaluated by stroke team neurologists and imaged with MR, including diffusion-weighted imaging documenting acute posterior circulation stroke. MR angiography of the circle of Willis was also obtained. Short-term follow-up was conducted to assess National Institutes of Health stroke scores (NIHSS) and modified Rankin scores. RESULTS: In these six cases, a combined approach of proximal arterial stent placement (five cases of vertebral artery origin and one case of carotid and subclavian stent placement plus vertebral artery revascularization) and thrombolysis was performed at variable times after stroke onset (range, 30 hours to 5 days). Four of the six patients had good basilar artery recanalization (Thrombolysis in Myocardial Infarction [TIMI] grade 0-1 before tissue plasminogen activator thrombolysis and TIMI grade 2 after procedure). Four of six patients had excellent immediate recovery and were discharged to an acute rehabilitation unit or their homes with improved neurologic symptoms and functional status. Two patients died: one patient presented with coma at outset with an NIHSS of 38, and the other patient probably had reocclusion of the basilar artery within 24 hours despite initial postprocedural improvement. CONCLUSION: We demonstrate that, in the setting of acute stroke, stent placement in combination with revascularization and thrombolysis is practical and allows quick access to a clot and simultaneously increases perfusion through collaterals during the thrombolytic process. In particular, basilar thrombolysis may be facilitated by proximal vertebral stent placement as concomitant atheromatous vertebrobasilar stenosis is common.     

Brain ischemia: CT and MRI techniques in acute ischemic stroke

Imaging plays a central role for intravenous and intra-arterial arterial ischemic stroke treatment patient selection.Computed tomography (CT) / CT angiography or magnetic resonance (MR) / MR angiography imaging are used to exclude stroke mimics and haemorrhage, to determine the cause and mechanism of stroke, to define the extension of brain infarct and to identify the arterial occlusion. Imaging may identify the patients that will be benefit more from revascularization therapies independently of the conventional therapeutic time window allowing individualized treatment decisions and improving individual patient outcome. Multiparametric CT/MR imaging may be used to identify the extension of potential viable brain tissue (penumbra) and of irreversible brain lesion (core) using CT perfusion and/or diffusion weighed and perfusion weighted MR imaging. The status of the arterial collateral circulation and the type and extension of the clot may be assessed by imaging.The accuracy and the clinical significance for treatment and patient clinical outcome of different imaging techniques are reviewed.     

Value of diffusion-weighted MR imaging in acute cervical cord injury as a predictor of outcome

Introduction We analyzed the findings of diffusion-weighted (DW) imaging using the single-shot fast spin-echo sequence in acute cervical cord injury and evaluated the usefulness of this method for predicting the prognosis.Methods Our patient group comprised 14 patients examined 2 h to 3 days after injury. First, we visually evaluated the DW imaging findings in all patients. Apparent diffusion coefficient (ADC) maps were also assessed in 13 patients. Second, we assessed follow-up magnetic resonance (MR) examinations obtained in six patients whose DW images showed hyperintensity. Third, we reviewed the functional outcome at discharge.Results The lesions showed hyperintensity in ten patients, and no abnormal signal was noted in the remaining four patients. The ADC maps showed restricted diffusion in all patients with hyperintensity on DW imaging except in one patient for whom the ADC map was unavailable. Repeated MR examinations obtained in six of the ten patients showed either myelomalacia or exacerbation. Seven of the ten patients (70%) required assistance and the other three were independent. Among the four patients without hyperintensity on DW imaging, three (75%) were independent and only one required assistance.Conclusion DW imaging in acute cervical cord injury often reveals restricted diffusion. This finding may predict an unfavorable functional prognosis.     

急性缺血性卒中的MRI早期诊断价值

目的：评价神经影像技术对早期脑梗塞的病灶显示、病变发展及其对治疗的临床应用价值。方法：35例临床初诊急性脑梗塞病人，出现症状后1．5～24h内分别行平扫CT、常规MRI、MR血管成像、弥散（DWI）和灌注（PWI）MR成像；13例行静脉内溶栓治疗并于2w内随访治疗效果。结果：35例中脑出血6例，平扫CT对急性脑梗塞征象显示率为48．3％；29例脑梗塞中，常规MRI、DWI、PWI均显示病灶；T1WI显示病灶范围最小，T2WI、FLAIR序列显示病灶范围逐渐增加；20例同时行DWI和PWI中，13例（65％）出现弥散一灌注不匹配，溶栓治疗7例症状好转（53．3％）。结论：神经影像技术中的DWI和PWI可以在脑梗塞后有效治疗时间窗内显示病灶的大小和血液动力学改变，结合CT平扫和常规MRI序列，有助于尽早溶栓治疗，减轻症状，恢复功能，提高病人生存质量。     

Combined intraarterial/intravenous thrombolysis for acute ischemic stroke

BACKGROUND AND PURPOSE: The intravenous use of recombinant tissue-type plasminogen activator (rTPA) in acute ischemic stroke has been investigated in three large trials. Limited series have reflected outcome after local intraarterial thrombolysis (LIT) in the cerebral territory. The purpose of this study was to evaluate the safety and efficacy of combined intraarterial/intravenous thrombolysis using rTPA (actilyse) for acute ischemic stroke. METHODS: Forty-five patients with acute onset of severe hemispheric stroke and without signs of major cerebral infarction on early CT scans were randomized by order of admission. Twelve patients were treated with 50 mg actilyse (maximal dose, 0.7 mg/kg); three had occlusion of the internal carotid artery and nine had occlusion of the middle cerebral artery. Thrombolysis was started by LIT and continued intravenously within 6 hours of stroke onset. Outcome, assessed after 1 and 12 months according to the modified Rankin scale (MRS), was considered good (MRS score, 0-3) for patients who were functionally independent and poor (MRS score, 4-5) for those who were dependent or had died. RESULTS: In the thrombolysis group, outcome was good in eight patients at 1 month and in 10 patients at 12 months; in the control group, outcome was good in seven (21%) and 11 (33%) patients, respectively. Of the eight patients with a good outcome after thrombolysis, four had complete and one had partial recanalization. In the control group, the rate of intracerebral hemorrhage was 6%. Mortality at 1 month in the thrombolysis and control groups was 17% and 48%, respectively. CONCLUSIONS: Combined intraarterial/intravenous thrombolysis with low-dose rTPA may be a safe and effective treatment for acute ischemic stroke within 6 hours in carefully selected patients.     

Dodecafluoropentane emulsion decreases infarct volume in a rabbit ischemic stroke model

PurposeTo assess the efficacy of dodecafluoropentane emulsion (DDFPe), a nanodroplet emulsion with significant oxygen transport potential, in decreasing infarct volume in an insoluble-emboli rabbit stroke model.Materials And MethodsNew Zealand White rabbits (N = 64; weight, 5.1 ± 0.50 kg) underwent angiography and received embolic spheres in occluded internal carotid artery branches. Rabbits were randomly assigned to groups in 4-hour and 7-hour studies. Four-hour groups included control (n = 7, embolized without treatment) and DDFPe treatment 30 minutes before stroke (n = 7), at stroke onset (n = 8), and 30 minutes (n = 5), 1 hour (n = 7), 2 hours (n = 5), or 3 hours after stroke (n = 6). Seven-hour groups included control (n = 6) and DDFPe at 1 hour (n = 8) and 6 hours after stroke (n = 5). DDFPe dose was a 2% weight/volume intravenous injection (0.6 mL/kg) repeated every 90 minutes as time allowed. After euthanasia, infarct volume was determined by vital stains on brain sections.ResultsAt 4 hours, median infarct volume decreased for all DDFPe treatment times (pretreatment, 0.30% [P = .004]; onset, 0.20% [P = .004]; 30 min, 0.35% [P = .009]; 1 h, 0.30% [P = .01]; 2 h, 0.40% [P = .009]; and 3 h, 0.25% [P = .003]) compared with controls (3.20%). At 7 hours, median infarct volume decreased with treatment at 1 hour (0.25%; P = .007) but not at 6 hours (1.4%; P = .49) compared with controls (2.2%).ConclusionsIntravenous DDFPe in an animal model decreases infarct volumes and protects brain tissue from ischemia, justifying further investigation.     

级联VB-Net分割模型用于急性缺血性脑卒中患者扩散加权成像中缺血核心分割的研究

目的:探讨级联VB-Net深度学习网络对扩散加权成像（DWI）中急性缺血性脑卒中缺血核心检出和分割的价值。方法:回顾性分析2016年12月至2018年12月在河南省人民医院就诊的1 500例急性缺血性卒中患者的MRI资料。将1 500例患者的2 456个病灶依据采集时间按8∶1∶1分为训练集、验证集和测试集。首先在脑D...