成人缺血缺氧性脑病MRI特征

目的 分析成人缺血缺氧性脑病患者的MRI表现及其特征。方法 收集18例因各种原因导致缺血缺氧后接受MR检查患者，并对资料进行分析。结果 18例中，17例MRI显示脑内异常信号，累及部位包括大脑皮层、皮层下白质、深部白质、侧脑室周围白质、胼胝体、基底核、海马、丘脑、脑桥及小脑；9例出现全脑萎缩，5例T1WI显示高信号，9例DWI显示扩散受限；5例接受MR增强检查，其中1例大脑皮层见脑回样轻度强化。1例MRI未见明显异常。结论 MRI可发现缺血缺氧性脑病所致脑内广泛异常信号。MRI表现可反映脑缺血缺氧严重程度，并可用于预测治疗效果和评估预后。     

正常足月新生儿脑的MRI信号特点

目的:研究正常足月新生儿脑的MRI信号特点。材料与方法:用0.15T磁共振成像设备SE序列对20例正常足月新生儿进行颅脑T_1和T_2加权成像。以孕期胎龄与出生后日龄之和做为新生儿的实际胎龄。结果与结论:①T_1加权成像脑白质表现低信号,髓鞘化区城为高信号,灰质为稍高信号。髓鞘化的范围和灰白质对比度与新生儿的实际胎龄成正相关;②T_2加权成像,脑白质为较高信号,灰质和髓鞘化区域呈明显的低信号,全组新生儿的灰白质对比均清晰明显;③全组新生儿的侧脑室前角和后角周围的小片白质均呈长T_1和T_2信号特点,与邻近的白质和灰质对比清楚。此属生理现象。     

Magnetic resonance studies on the development of ischemic edema in an early period after occlusion of middle cerebral artery in a rat

The development of ischemic edema after middle cerebral artery occlusion in a rat was studied using T1 and T2-weighted magnetic resonance imaging (MRI). Examinations were performed with Helmholtz coil and multiple echo sequences with TR 1,500 ms and TE 30-240 ms (8 echoes) were used. T2 prolongation was noted already 3 hours after experimental stroke and the values increased during the time of the study. T1-weighted images were much less sensitive for the detection of increased water content. This experiment forms a basis for MR studies on the formation and resolution of cerebral edema and can be useful for studies on efficacy of different medical measures against ischemic edema.     

Perfusion imaging in the pediatric patient

The prevalence of cerebrovascular disease in children is much higher than most clinicians and neuroradiologists suspect, when all primary and secondary causes are considered. Most signal alterations found on MR imaging in childhood central nervous system pathologic conditions result from causes other than a decrease in tissue perfusion. In addition to conventional MR imaging, the ability to assess changes in tissue water by diffusion imaging and tissue perfusion by perfusion-weighted imaging can prove useful to asses cerebral hemodynamics in various pathologic disorders. Exogenous contrast bolus dynamic perfusion-weighted imaging is especially useful in children to differentiate between ischemic injury and other conditions that may alter T2 relaxation, such as demyelination and edema. Perfusion imaging has proved to be a robust and valuable tool to assess the hemodynamic component in childhood CNS disease related to neoplasms and complications from their therapy, cerebrovascular occlusive disease, childhood CNS arteriopathies and trauma.     

对比分析大鼠局灶性脑缺血亚急性期USPIO与Gd-DTPA增强MRI

目的 基于动物模型,对比局灶性脑缺血亚急性期超小型超顺磁性氧化铁(USPIO)与Gd-DTPA增强MRI表现的异同.方法 以6只SD大鼠建立局灶性脑缺血模型,建模成功后将其分为USPIO增强组(n=3)及Gd-DTPA增强组(n=3).对USPIO增强组于建模后第5天以1000 μmolFe2 +/kg体质量静脉注射USPIO,并于24 h后(建模后第6天)行T2W扫描.对Gd-DTPA增强组于建模后第6天行常规T2WI及T1WI后,静脉注射Gd-DTPA行增强T1W扫描,剂量0.2 mmolGd3+/kg体质量. MR检查完成后,取脑组织切片行HE和IgG染色病理观察,对MRI与病理表现进行综合对比分析.结果 USPIO增强组脑缺血灶周围可见T2WI低信号区,MR扫描增强区域与IgG染色提示的血脑屏障破坏区有所差别.Gd-DTPA增强组增强T1WI示脑缺血区明显强化,MR扫描增强区域与IgG染色所示血脑屏障破坏区相一致.结论 大鼠局灶性脑缺血亚急性期USPIO与Gd-DTPA增强MRI具有不同的特征,USPIO图像侧重于反映细胞的反应性增生,而Gd-DTPA图像更利于对血脑屏障破坏的反映.     

Imaging acute ischemic tissue acidosis with pH-sensitive endogenous amide proton transfer (APT) MRI--correction of tissue relaxation and concomitant RF irradiation effects toward mapping quantitative cerebral tissue pH

Amide proton transfer (APT) MRI is sensitive to ischemic tissue acidosis and has been increasingly used as a research tool to investigate disrupted tissue metabolism during acute stroke. However, magnetization transfer asymmetry (MTR(asym)) analysis is often used for calculating APT contrast, which only provides pH-weighted images. In addition to pH-dependent APT contrast, in vivo MTR(asym) is subject to a baseline shift (ΔMTR'(asym)) attributable to the slightly asymmetric magnetization transfer (MT) effect. Additionally, APT contrast approximately scales with T(1) relaxation time. Tissue relaxation time may also affect the experimentally obtainable APT contrast via saturation efficiency and RF spillover effects. In this study, we acquired perfusion, diffusion, relaxation and pH-weighted APT MRI data, and spectroscopy (MRS) in an animal model of acute ischemic stroke. We modeled in vivo MTR(asym) as a superposition of pH-dependent APT contrast and a baseline shift ΔMTR'(asym) (i.e., MTR(asym)=APTR(pH)+ΔMTR'(asym)), and quantified tissue pH. We found pH of the contralateral normal tissue to be 7.03±0.05 and the ipsilateral ischemic tissue pH was 6.44±0.24, which correlated with tissue perfusion and diffusion rates. In summary, our study established an endogenous and quantitative pH imaging technique for improved characterization of ischemic tissue acidification and metabolism disruption.     

Myelin mapping in the living mouse brain using manganese-enhanced magnetization transfer MRI

This work demonstrates manganese-enhanced magnetization transfer (MT) MRI to improve the contrast of myelinated structures in mouse brain in vivo. Systemic administration of manganese chloride led to a reduction of the MT ratio by 23% in white matter and 35% in gray matter. The effect increased their contrast-to-noise ratio by 48% and facilitated a mapping of myelin-rich white matter tissues. Relaxation time measurements revealed the manganese-induced shortening of T1 to be smaller in the corpus callosum (?42%) than in the cortex (?52%) or hippocampus (?60%). These findings are in line with the assumption that a high myelin and correspondingly low water content hinder the free diffusion and uptake of manganese ions. The resulting preferential accumulation of manganese in gray matter structures causes a stronger reduction of the MT saturation in gray matter than in white matter. Extending MRI assessments with conventional MT contrast, manganese-enhanced MT MRI at 76 × 80 × 160 μm³ resolution and 2.35 T field strength allowed for a delineation of small myelinated structures such as the fornix, mammillothalamic tract, and fasciculus retroflexus in the living mouse brain.     

低场磁共振弥散加权成像在急性脑梗死诊断中的应用价值

目的探讨低场磁共振弥散加权成像（DWI）诊断急性脑梗死的价值。方法 2007年7月-2009年9月对48例脑梗死患者行常规MRI扫描和DWI,分析不同时期脑梗死的DWI表现。结果在发病的超急性期及急性期,DWI病灶显示率均为100.0%,T2WI病灶显示率分别为37.5%、73.7%、100.0%。结论低场DWI对急性脑梗死的诊断准确率高,明显优于常规MRI。     

Hindered diffusion of MRI contrast agents in rat brain extracellular micro‐environment assessed by acquisition of dynamic T1 and T2 maps

The knowledge of brain tissues characteristics (such as extracellular space and tortuosity) represents valuable information for the design of optimal MR probes for specific biomarkers targeting. This work proposes a methodology based on dynamic acquisition of relaxation time maps to quantify in vivo MRI contrast agent concentration after intra‐cerebral injection in rat brain. It was applied to estimate the hindered diffusion in brain tissues of five contrast agents with different hydrodynamic diameters (Dotarem® ≈ 1 nm, P846 ≈ 4 nm, P792 ≈ 7 nm, P904 ≈ 22 nm and Gd‐based emulsion ≈ 170 nm). In vivo apparent diffusion coefficients were compared with those estimated in an obstacle‐free medium to determine brain extracellular space and tortuosity. At a 2 h imaging timescale, all contrast agents except the Gd‐based emulsion exhibited significant diffusion through brain tissues, with characteristic times compatible with MR molecular imaging (<70 min to diffuse between two capillaries). In conclusion, our experiments indicate that MRI contrast agents with sizes up to 22 nm can be used to perform molecular imaging on intra‐cerebral biomarkers. Our quantification methodology allows a precise estimation of apparent diffusion coefficients, which is helpful to calibrate optimal timing between contrast agent injection and MRI observation for molecular imaging studies. Copyright © 2012 John Wiley & Sons, Ltd.     

颈动脉蹼的高分辨率磁共振血管壁成像的影像分析

目的探索颈动脉蹼(carotid web,CaW)的高分辨率磁共振血管壁成像(vessel wall magnetic resonance imaging,VW MRI)的信号及形态特点。材料与方法选取经计算机断层扫描血管造影术(computed tomography angiography,CTA)诊断的10例颈动脉蹼的患者,从多序列多方位分析颈动脉蹼磁共振的信号及形态特点。结果颈动脉蹼的磁共振信号特点为T1WI表现为均匀等信号,T2WI表现为稍高信号,抑脂序列信号不减低,增强后明显强化。10例颈动脉蹼患者中出现等信号管壁增厚10例(100%),突向管腔10例(100%),管腔内分隔9例(90%),双腔征8例(80%),瓣膜征6例(60%),对比剂瘀滞3例(30%)。结论颈动脉蹼与既往无明显心血管危险因素患者的缺血性卒中事件具有很高的相关性。VW MRI在颈动脉蹼的影像诊断中具有较高的临床应用价值和特征的影像表现,有利于为颈动脉蹼的未来研究提供参考。     

血管周围间隙的MR表现

目的分析总结血管周围间隙发生部位及MRI表现,提高其诊断符合率。方法随机选择磁共振检查显示有血管周围间隙的病例130例;其中16例进行了MR增强扫描,21例行弥散加权成像;19例行CT检查,4例行CT增强扫描。结果130例病例血管周围间隙均为双侧多发,呈圆形或椭圆形、点状、条状或线状,边界清晰锐利,条形或线形的血管周围间隙多成簇出现,且沿着纤维走行方向排列。发生部位包括前连合两侧(97.69%,127/130)、近大脑凸面的半卵圆中心(85.38%,111/130)、脑干大脑脚处(37.69%,49/130)、极外囊(23.85%,31/130),小脑齿状核旁白质仅见1例。MRI不同序列显示间隙信号与脑脊液信号完全一致,增强扫描无强化征象。随访病例均未发现明显变化。小血管周围间隙见于任何年龄组的所有130例病例,而17例可见大血管周围间隙间隙,其中3例有轻度占位效应。结论血管周围间隙可见于任何年龄,好发生于前连合两侧、近大脑凸面半卵圆中心、脑干大脑脚、极外囊,呈条形或线形、圆形或卵圆形,边界清晰锐利,绝大多数无占位效应,MR成像各种序列显示与脑脊液信号完全一致。     

Application of MAGnetic resonance imaging compilation in acute ischemic stroke

BACKGROUNDSynthetic magnetic resonance imaging (MRI) MAGnetic resonance imaging compilation (MAGiC) is a new MRI technology. Conventional T1, T2, T2-fluid-attenuated inversion recovery (FLAIR) contrast images, quantitative images of T1 and T2 mapping, and MAGiC phase sensitive inversion recovery (PSIR) Vessel cerebrovascular images can be obtained simultaneously through post-processing at the same time after completing a scan. In recent years, studies have reported that MAGiC can be applied to patients with acute ischemic stroke. We hypothesized that the synthetic MRI vascular screening scheme can evaluate the degree of cerebral artery stenosis in patients with acute ischemic stroke.AIMTo explore the application value of vascular images obtained by synthetic MRI in diagnosing acute ischemic stroke.METHODSA total of 64 patients with acute ischemic stroke were selected and examined by MRI in the current retrospective cohort study. The scanning sequences included traditional T1, T2, and T2-FLAIR, three-dimensional time-of-flight magnetic resonance angiography (3D TOF MRA), diffusion-weighted imaging (DWI), and synthetic MRI. Conventional contrast images (T1, T2, and T2-FLAIR) and intracranial vessel images (MAGiC PSIR Vessel] were automatically reconstructed using synthetic MRI raw data. The contrast-to-noise ratio (CNR) values of traditional T1, T2, and T2-FLAIR images and MAGiC reconstructed T1, T2, and T2-FLAIR images in DWI diffusion restriction areas were measured and compared. MAGiC PSIR Vessel and TOF MRA images were used to measure and calculate the stenosis degree of bilateral middle cerebral artery stenosis areas. The consistency of MAGiC PSIR Vessel and TOF MRA in displaying the degree of vascular stenosis with computed tomography angiography (CTA) was compared.RESULTSAmong the 64 patients with acute ischemic stroke, 79 vascular stenosis areas showed that the correlation between MAGiC PSIR Vessel and CTA (r = 0.90, P < 0.01) was higher than that between TOF MRA and CTA (r = 0.84, P < 0.01). With a degree of vascular stenosis > 50% assessed by CTA as a reference, the area under the receiver operating characteristic (ROC) curve of MAGiC PSIR Vessel [area under the curve (AUC) = 0.906, P < 0.01] was higher than that of TOF MRA (AUC = 0.790, P < 0.01). Among the 64 patients with acute ischemic stroke, 39 were scanned for traditional T1, T2, and T2-FLAIR images and MAGiC images simultaneously, and CNR values in DWI diffusion restriction areas were measured, which were: Traditional T2 = 21.2, traditional T1 = -6.7, and traditional T2-FLAIR = 11.9; and MAGiC T2 = 7.1, MAGiC T1 = -3.9, and MAGiC T2-FLAIR = 4.5.CONCLUSIONThe synthetic MRI vascular screening scheme for patients with acute ischemic stroke can accurately evaluate the degree of bilateral middle cerebral artery stenosis, which is of great significance to early thrombolytic interventional therapy and improving patients’ quality of life.     

MR弥散张量成像在中枢神经系统的临床应用

DWI是一种较新的MR成像技术,图像对比与组织内水分子运动的不同有关,水分子的运动用表观扩散系数表示,DWI对急性脑缺血的早期诊断有重要的临床价值;DTI可用于评估各向同性及各向异性扩散.DTI主要用于评估影响脑白质尤其是白质纤维束完整性的疾病.本文主要对DWI、尤其是DTI在中枢神经系统中的临床应用现状作一综述.     

弥散加权磁共振成像在急性脑梗塞中的应用

目的　分析弥散加权磁共振成像（ＤＷＩ） 在急性脑梗塞中的表现规律。方法　用单次激发平面回波弥散加权ＭＲＩ和常规ＭＲＩ技术检查了３２ 例急性脑梗塞患者,以陈旧性脑梗塞１０ 例为对照,比较其敏感性,并测量其在ＤＷＩ、Ｔ２ ＷＩ上的梗塞面积,比较其关系。结果　ＤＷＩ在全部急性期患者中均显示出梗塞灶,而Ｔ２ ＷＩ只显示了２３ 例患者且发病时间均大于６ 小时。其梗塞面积显示：在２４ 小时内ＤＷＩ大于Ｔ２ ＷＩ。结论　ＤＷＩ较常规Ｔ２ ＷＩ能更早地发现脑缺血的改变,为超早期脑梗塞的临床诊断和治疗提供依据并可动态观察疗效。     

Basic concepts of MR imaging, diffusion MR imaging, and diffusion tensor imaging

MR image contrast is based on intrinsic tissue properties and specific pulse sequences and parameter adjustments. A growing number of MRI imaging applications are based on diffusion properties of water. To better understand MRI diffusion-weighted imaging, a brief overview of MR physics is presented in this article followed by physics of the evolving techniques of diffusion MR imaging and diffusion tensor imaging.     

脑干白质纤维束磁共振扩散张量成像研究

目的：使用磁共振扩散张量成像方法对脑干白质束进行研究。方法：30名健康志愿者进行MR检查，检查包括常规T1WI，T2WI以及扩散张量序列。结果：在脑干不同解剖水平，锥体束、锥体交叉、内、外侧丘系在各向异性（FA）图像上均显示为高信号，在彩色张量图像上分别显示为红色（横向走行）、蓝色（上下走行）和绿色（前后走行）的纤维束，而这些结构在常规T1WI、T2WI上均不能得到显示。结论：扩散张量成像可以无创性检查脑干白质束。     

评估量化超急性期缺血性脑卒中发病时间窗的研究

目的利用高场MR多模态成像序列评估及找出脑卒中的早期迹象影像证据,为早期rt-PA溶栓治疗时间窗提供直观和个体化的影像学信息。材料与方法利用线栓法栓塞右侧大脑中动脉,制备MCAO大鼠模型10只,在不同的时间点采用DWI、病灶的表观扩散系数（ADC）和常规T2WI评估MCAO大鼠模型脑缺血性病变区域的特性。通过MRS、并应用LCModel后处理来绝对定量在不同的时间点病灶内局部特异性代谢物浓度的变化。结果10只MCAO大鼠,6 h内T2WI均未显示明确病变灶;而大脑中动脉梗塞10 min后,DWI均能在大脑中动脉供血相应纹状体区及顶叶皮层区显示出异常的高信号,与DWI相应病变区ADC图均显示有异常的低信号。MRS研究发现,大脑中动脉梗塞1 h后病变中心区对比相应对侧正常区Lac峰明显增高,NAA峰明显下降;谷氨酸和牛磺酸绝对浓度2 h内逐渐上升达峰值,随后3 h段明显下降。结论 MR多模态成像序列,特别是利用T2WI、DWI及1H MRS可定性诊断超早期缺血性脑卒中,并能评估及量化超急性脑卒中发病时间窗,为筛选适合rt-PA溶栓治疗者提供客观和个体化的影像学信息。     

Magnetic resonance imaging of fetal developmental anomalies

Fetal developmental anomalies consist of central nervous system malformations, brain injury, and tumors. Overlap is often seen especially between malformation and injury because malformation may be genetically determined or related to external causative agent, whereas brain injury may be, on one hand, caused by malformation as with intracranial vascular malformation and, on another, can cause brain malformation when cerebral insult occurs during organogenesis and histogenesis. The goal of this review was not to describe by magnetic resonance imaging (MRI) all fetal developmental anomalies encountered in utero; it is most likely to focus on fetal brain anomalies that either are most commonly seen in fetal tertiary care facility or are extremely challenging for MRI. Consequently, the potential of advanced MR techniques such as proton MR spectroscopy and diffusion tensor imaging is also described especially when a challenge is highlighted. This review is therefore organized in subchapters as follows. The first section gives the place of MRI in prenatal development and cites the standard protocol and the advanced techniques. The rules of fetal brain MRI, the challenge and pitfalls, and the selection of MRI cases follow as 3 subchapters. Also, abnormalities are described as 3 separate subchapters entitled ventriculomegalies (hydrocephalus), malformations, and brain injury.     

不同MRI检查方法诊断早期脑缺血价值的实验研究

目的评价各种MRI检查方法在早期脑缺血动物模型中的诊断价值.方法线栓法制备大鼠局灶性大脑中动脉闭塞/再通模型.应用弥散加权成像(DWI)、超顺磁氧化铁(SPIO)灌注T2WI和常规MRI检查,在不同时间点对模型进行观察.结果DWI在脑缺血的30～90 min可显示高信号区,但缺血范围显示不清;SPIO灌注T2WI在缺血1 h时可显示脑血流低灌注区,无法观察病理改变;T2WI上高信号在脑缺血后6～12 h,可确切观察缺血范围;T1WI无异常发现.结论早期脑缺血的MRI诊断应综合应用不同的成像方法.     

3.0T磁共振T2*成像技术在缺血性脑梗死并发微小出血灶的应用

目的 分析缺血性脑梗死并发微小出血灶(CMB)的发生率、分布特点以及微小出血灶发生的相关危险因素.方法 对93例缺血性脑梗死患者行MRI T1WI、T2WI、DWI、3DTOFMRA及T2*WI检查,分析MRI表现.结果 36例(38.71%)合并微小出血灶,其中11例为急性脑梗死并CMBs,15例为陈旧性脑梗死并CMBs,7例为陈旧性脑梗死再发急性脑梗死并CMBs,3例为脑白质内缺血变性灶并CMBs.结论 T2*WI技术能敏感地检测CMBs,对临床治疗具有指导意义.