MR imaging enhancement patterns as predictors of hemorrhagic transformation in acute ischemic stroke

BACKGROUND AND PURPOSE: Early parenchymal gadolinium enhancement on T1-weighted MR images is predictive of hemorrhagic transformation (HT) in rodent focal ischemia models, but its value in humans is unknown. We sought to investigate gadolinium enhancement in acute ischemic stroke patients to determine their association with subsequent HT. METHODS: We retrospectively examined 22 patients with ischemic stroke who underwent MR imaging within 4.9 hours (+/-1.4) of symptom onset. Patients receiving intravenous tissue plasminogen activator (tPA) (n = 6) were included. Twenty-one patients underwent repeat MR studies at 48 hours, 13 underwent additional MR imaging at 1 week, and one underwent follow-up head CT at 24 hours. Initial images were analyzed for enhancement patterns (vascular, meningeal, parenchymal). Follow-up T2- and T2*-weighted images were evaluated for hemorrhage. RESULTS: In all patients, initial MR images showed vascular enhancement in the vascular territory of the stroke lesion: 19 with vascular enhancement alone and three with vascular and parenchymal enhancement. All three patients with both enhancement patterns had HT: two large and symptomatic, and one asymptomatic (petechial hemorrhage). They received tPA before MR imaging. None of the patients without early parenchymal enhancement developed symptomatic hemorrhage. Six (32%) patients with vascular enhancement alone had petechial hemorrhage at follow-up imaging. In this limited sample, initial mean volumes on diffusion-weighted images, National Institute of Health Stroke Scale scores, and intervals from stroke onset to imaging did not differ between patients with vascular and parenchymal enhancement versus those with vascular enhancement alone. CONCLUSION: Early parenchymal enhancement of stroke lesions may be a good predictor of subsequent symptomatic HT may help identify patients at risk, especially after thrombolytic therapy.     

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   

Multimodal MR examination in acute ischemic stroke

In recent years, combined diffusion-weighted imaging (DWI) with perfusion imaging (PI) has become an important investigational tool in the acute phase of ischemic stroke, as it may differentiate reversible from irreversible brain tissue damage. We consecutively examined 20 subjects within 12 h of stroke onset using a multiparametric magnetic resonance (MR) examination consisting of DWI, mean transit time (MTT) as PI parameter, and MR angiography (MRA). T2-weighted and fluid-attenuated inversion recovery (FLAIR) on day 7 were also acquired in order to obtain final infarct volume. The following MR parameters were considered: volumetric measures of lesion growth and MTT abnormalities, quantification of regional apparent diffusion coefficient (ADC) and visual inspection of MRA findings. Our results showed: (1) an acute DWI lesion was not predictive of lesion growth and the DWI abnormality did not represent the irreversibly infarcted tissue; (2) ADC values in the ischemic penumbra could not predict tissue at risk; (3) the DWI–PI mismatch did not predict lesion growth, and the PI abnormality overestimated the amount of tissue at risk; and (4) patients with proximal middle cerebral artery occlusion had greater initial and final infarct volumes. This study did not demonstrate the prognostic value of a multimodal MR approach in early ischemic stroke; MRA alone provided predictive information about the volumetric evolution of the lesion.     

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.     

急性缺血性脑卒中血管腔内治疗后对比剂外渗影像学研究现状北大核心CSCD

对比剂外渗(CE)和出血性转化(HT)是急性缺血性脑卒中血管腔内治疗(EVT)后的常见并发症,两者有相似的影像学表现,不同的临床治疗方法和转归。早期鉴别诊断CE和HT,对临床治疗和预后至关重要。本文就临床CE影响因素,常规CT、双能CT(DECT)及MRI诊断EVT后CE研究现状作一综述,为预防CE和早期鉴别诊断提供帮助。     

Hepatic cavernous hemangiomas: patterns of contrast enhancement on MR fluoroscopy imaging

PURPOSE: The purpose of this study was to assess the patterns of contrast enhancement of hepatic hemangiomas on gadolinium-enhanced MR fluoroscopy imaging prospectively. METHOD: Investigation was performed on a 0.3-T open MR unit. Gadolinium-enhanced MR fluoroscopy images were obtained in 24 patients with 28 hepatic hemangiomas. Each MR fluoroscopy image was obtained in 2 s and MR fluoroscopy lasted for 10-25 min for each investigation. RESULTS: Three patterns of contrast enhancement were observed in 24 patients on MR fluoroscopy images. Four small lesions were not detected on MR fluoroscopy images. Uniform enhancement was seen in nine lesions (29%), peripheral nodular enhancement progressing centripetally to uniform enhancement was seen in nine lesions (29%), and peripheral nodular enhancement with persistent central hypointensity was seen in six lesions (22%). CONCLUSION: Enhanced MR fluoroscopy technique could obtain dynamic images of hepatic hemangiomas. It can be suggested as a useful technique for the showing of enhancement of hepatic hemangiomas, keeping in mind its low sensitivity in the diagnosis of small hemangiomas.     

Identifying lesion growth with MR imaging in acute ischemic stroke

PURPOSE: To determine whether different MR diffusion- and perfusion-weighted imaging (DWI and PWI) parameters are important in distinguishing lesion growth from the acute lesion and from oligemia. MATERIALS AND METHODS: MR DWI and PWI were acquired from thirteen patients. We defined three regions: (i) LESION - intersection of acute and final lesions, (ii) GROWTH - portion of final lesion not part of acute lesion, and (iii) OLIGEMIA - region of perfusion abnormality not part of either the acute or final lesions. We used logistic regression modeling to distinguish GROWTH from LESION and from OLIGEMIA on a voxel-wise basis using DWI- and PWI-based parameters. Final models were selected based on the Wald statistic and validated by cross-validation using the mean (+/- standard deviation) area under the curve (AUC) from receiver operating characteristic analysis. RESULTS: The final model for differentiating GROWTH from LESION included DWI, the apparent diffusion coefficient (ADC), cerebral blood flow (CBF) and tissue type (AUC = 0.939 +/- 0.028). The final model for differentiating GROWTH from OLIGEMIA included DWI, ADC, CBF, and time-to-peak (AUC = 0.793 +/- 0.106). CONCLUSION: Different MR parameters are important in differentiating lesion growth from acute lesion and from oligemia in acute ischemic stroke.     

Various patterns of perfusion-weighted MR imaging and MR angiographic findings in hyperacute ischemic stroke.

BACKGROUND AND PURPOSE: Various clinical subtypes of patients presenting with sudden-onset ischemic stroke have been recognized, but classification of those types is not simple. We identified various patterns of perfusion-weighted MR imaging and MR angiographic findings in hyperacute ischemic stroke with relation to clinical outcomes. METHODS: Twelve patients with symptoms of acute ischemic stroke due to middle cerebral artery occlusion underwent perfusion-weighted MR imaging and MR angiography within 6 hours after the onset of symptoms. Perfusion-weighted imaging was performed with a conventional dynamic contrast-enhanced T2*-weighted sequence, and cerebral blood volume (CBV) maps were then created. CBV maps and MR angiographic findings were compared with 99mTc-HMPAO brain SPECT scans, short-term outcomes, and follow-up imaging findings. RESULTS: The combined CBV and MR angiographic findings were classified into three patterns: arterial occlusion and decreased CBV (n = 8), arterial occlusion and increased CBV (n = 2), and no arterial occlusion and normal CBV (n = 2). These three patterns were strongly related to SPECT findings, short-term outcomes, and follow-up imaging findings. Perfusion on SPECT decreased markedly in the affected regions in all patients with the first pattern, decreased slightly in the second pattern, and was normal in the third pattern. Symptoms were not significantly changed at 24 hours after onset in any of the patients with the first pattern, but resolved completely in all patients with the latter two patterns. Follow-up imaging showed large infarctions in all patients with the first pattern. Initially, no infarction was seen in the second pattern, but watershed infarction developed later in one of these patients. CONCLUSION: Hyperacute ischemic stroke may be differentiated into three imaging patterns with different clinical outcomes. The combined use of perfusion-weighted MR imaging and MR angiography may play a substantial role in guiding the choice of treatment of this disease.     

Effect of b value on contrast during diffusion-weighted magnetic resonance imaging assessment of acute ischemic stroke

PURPOSE: To examine the effect of varying the diffusion encoding strength (b value) on the contrast (signal difference, Delta S) between damaged and normal tissue during diffusion-weighted magnetic resonance imaging (DWI) assessment of acute ischemic stroke. MATERIALS AND METHODS: Phantoms with diffusion values approximating those expected in acutely infarcted and normal tissue were constructed from a mixture of agar and formaldehyde and imaged at varying b values (0-3000 mm(-2) second). Ten patients were imaged with multiple b values (500-2500 mm(-2) second) within 12 hours of stroke onset. RESULTS: Theoretical calculations showed that for any combination of diffusion coefficients there existed an optimal b value that was higher than the standard setting of 1000 mm(-2) second, and this was confirmed by the phantom studies. In the patients, increasing b from 1000 to 1500 mm(-2) second increased Delta S (average, 22.4%; P = 0.001), but no consistent benefit was seen at b = 2000 mm(-2) second (P = 0.408). This compared favorably with the average optimal b value of 1662 mm(- 2) second calculated from the patients. CONCLUSION: These results suggest that increasing the b value from 1000 to 1500 mm(-2) second would increase contrast between infarcted and normal tissue in the setting of acute ischemic stroke.     

Prediction of hemorrhage in acute ischemic stroke using permeability MR imaging

Increased risk of hemorrhagic transformation (HT) limits the general use of thrombolytic therapy in acute ischemic stroke (AIS). This study shows that early blood-brain barrier defects in AIS can be assessed by using permeability MR imaging. Significantly increased permeability was found in 3 patients who later hemorrhaged. This method indicates the potential for identifying patients at higher risk of HT and offers the use of physiologic imaging rather than time from onset of symptoms to guide treatment decisions.     

Minimum detectable difference of MR diffusion maps in acute ischemic stroke

PURPOSE: To determine the minimum detectable difference (MDD) and investigate variability of region-of-interest (ROI) analysis of apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in acute ischemic stroke. MATERIALS AND METHODS: Ten patients with acute stroke (<24 hours) and moderate-to-large infarcts were imaged using a fast diffusion tensor technique. Four observers repeated three trials, during which each of two ROI types (free-hand polygon and ellipse) were drawn in white and gray matter (WM and GM) on FA and ADC maps. Analysis-of-variance techniques examined tissue and ROI type effects as well as inter- and intraobserver variability. F-tests examined the variability differences between ROI types. RESULTS: The MDD for ADC was 0.160 x 10(-3) mm(2) s(-1) in WM and 0.212 x 10(-3) mm(2) s(-1) in GM. The FA MDD was 0.19 in WM and 0.10 in GM. Tissue but not ROI type affected the mean values for both ADC and FA maps. Intraobserver reliability was substantial, while interobserver reliability was poor-to-moderate. No variability differences were found by ROI types. CONCLUSION: The MDD for WM and GM in normal and ischemic tissue were calculated. Inter- and intraobserver variability and tissue type affect ROI analysis of ADC and FA maps.     

MR contrast enhancement of the normal neonatal brain.

PURPOSETo determine the pattern of enhancement on contrast-enhanced MR studies of the brain in neonates.METHODSContrast-enhanced brain MR studies of 16 neonates were reviewed retrospectively. All infants had normal neonatal courses, normal noncontrast MR findings, and normal neurologic examinations at age 12 months. All enhancing regions within the brain, dura, calvaria, and orbits were recorded. An enhancement factor, F = (Ic-Ip)/Ip, was calculated from region-of-interest intensity measurements in five regions of each hemisphere (basal ganglia, thalami, and three hemispheric locations), where Ic was signal intensity after contrast administration and Ip was the noncontrast signal intensity for each region.RESULTSEnhancement was detected in the choroid plexus, pituitary infundibula, pineal glands, dura, veins and venous sinuses, cranial sutures, and irises of the orbital globes. No enhancement of the brain parenchyma was detected by visual inspection, although some change in signal intensity of the cerebral parenchyma was detected by the region-of-interest intensity measurements, with enhancement factors ranging from 0 to 0.08 (mean, 0.04). No consistent regional variation in enhancement was detected. Because the degree of enhancement was identical to that in the normal adult brain, the slight enhancement detected was attributed to contrast material in capillaries and small venules.CONCLUSIONIn addition to the expected findings of enhancement of the pituitary stalk, the pineal gland, the choroid plexus, the dura, and the cerebral veins, we detected enhancement of the calvarial sutures and ocular irises. No evidence of enhancement of the cerebral parenchyma was detected, suggesting that the blood-brain barrier to gadolinium chelates is intact in the neonatal brain.     

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.     

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 application of perfusion and diffusion MR imaging in acute ischemic stroke.

With the advances in new neuroimaging modalities, the role of imaging of acute ischemic stroke has broadened and progressed from making diagnoses to providing valuable information for patient management. The goal of thrombolytic therapy for acute ischemic stroke should be to salvage the ischemic tissue reversibility that can respond to recanalization and avoid reperfusion of the dead (nonviable) tissue. It is essential to have rapid diagnostic modalities that can distinguish viable ischemic tissue from irreversibly damaged tissue, because there is a risk of reperfusion injury such as hemorrhagic complications with early intervention. Although diffusion magnetic resonance (MR) imaging has been reported to have a high sensitivity and specificity for acute ischemia in acute stroke patients without early reperfusion therapy, the capability to differentiate reversible from irreversible ischemia by diffusion MR imaging has not been established. Perfusion MR imaging techniques provide direct information on parenchymal perfusion status (adequacy of the collateral circulation) and may have the potential for providing important information about tissue viability and/or reversibility for selecting appropriate patients for thrombolytic therapy.     

MR contrast enhancement of intracranial lesions with Gd-DTPA

Gd-DTPA is a paramagnetic contrast agent for MR that produces enhancement of lesions on T1-weighted images. Since it does not cross the intact blood-brain barrier (BBB), Gd-DTPA enhances only those pathologic processes that are associated with breakdown of the BBB and structures or lesions that are devoid of a BBB. Gd-DTPA improves conspicuity, helps characterize and delineate the extent of lesions, and increases the sensitivity for detection of cerebral abnormalities.     

MR测定颈动脉易损斑块特征与急性缺血性脑卒中的关系

目的 分析急性缺血性脑卒中患者症状侧颈动脉粥样硬化病变特征与扩散加权成像(DWI)证实的急性脑梗死(ACI)发生及严重程度的关联性.方法 入组发生单侧肢体症状(颈内动脉供血区)的ACI患者103例,均在发病后1周内行颈动脉磁共振黑血成像(MR-BBI)及头颅常规MRI,测得症状侧颈动脉粥样硬化病变参数(管腔狭窄率、斑块负荷和成分)和相应供血区ACI病灶分布及大小,借此分析症状侧颈动脉斑块特征与ACI发生、大小的关联程度.结果 研究发现,症状侧颈动脉管壁体积标准化指数(PWV)及富脂质核(LRNC)含量是同侧供血区ACI病灶发生及大小的独立危险因素(校正管腔狭窄和临床因素前后,P<0.05).结论 ACI发生及大小与同侧供血颈动脉的斑块易损特征(高斑块负荷和大LRNC)相关联.MR-BBI能细致化评估斑块易损特征,有利于临床分层急性缺血性脑卒中的风险性及严重程度.     

Effect of varying the molecular weight of the MR contrast agent Gd-DTPA-polylysine on blood pharmacokinetics and enhancement patterns

The effects of varying the molecular weight of gadolinium-DTPA (diethylenetriaminepentaacetic acid)—polylysine, a macromolecular magnetic resonance (MR) imaging contrast agent, on blood pharmacokinetics and dynamic tissue MR imaging signal enhancement characteristics were studied in normal rats. Blood elimination half-life, total blood clearance, volume of the central compartment (V_cc) and the steady-state distribution volume (V_ssd) were calculated for four Gd-DTPA-polylysine polymers with average molecular weights of 36, 43.9, 139, and 480 kd and compared with corresponding values for Gd-DTPA (0.57 kd) and Gd-DTPA-albumin (92 kd). Blood elimination half-life increased sevenfold with an increase in molecular weight from 36 to 480 kd. The V_cc values for all polylysine polymers did not differ significantly from the V_cc value for Gd-DTPA-albumin but were significantly smaller than the V_cc value for Gd-DTPA. The V_ssd value for Gd-DTPA did not differ significantly from the V_ssd value for the 36- and 43.9-kd polymers but was significantly larger than the V_ssd values for the 139-and 480-kd polymers and for Gd-DTPA-albumin. On T1-weighted coronal spin-echo MR images, dynamic signal enhancement profiles in liver and kidney for the 36-, 43.9-, and 480-kd Gd-DTPA-polylysine chelates corresponded to the blood pharma-cokinetic data. Increasing molecular weight of Gd-DTPA-polylysine formulations substantially slows blood clearance and produces a prolonged, almost constant tissue signal enhancement for the 60-minute observation period.