拉伸指数模型DWI对大鼠急性脑缺血的研究

目的:探讨拉伸指数模型多b值扩散加权成像(DWI)对大鼠急性脑缺血的诊断价值。方法:SD大鼠实验组18只、对照组9只术前行3.0T MRI检查,包括T1WI和T2WI、单b值(1000s/mm2)DWI、动脉自旋标记灌注成像(ASL-PWI)和多b值(0～4000s/mm2共12个b值)DWI,其中ASL-PWI可计算相对脑血流量(rCBF),多b值DWI采用拉伸指数模型,一次成像可得到Mono-ADC、F、DDC和α参数值。MRI检查后对实验组大鼠行右侧大脑中动脉闭塞(MCAO)的急性脑缺血手术,对照组行假手术,分别于术后0.5、3、6、9、12、18和24h行上述MRI检查,观察各时间点各参数的动态变化规律。最后,对大鼠脑缺血区行病理TTC染色确定实际脑梗死情况。结果:术后0.5h实验组右侧脑缺血区的rCBF值(0.470±0.002)较术前(0.990±0.010)明显下降、3h以后逐渐升高(从术后3h的0.980±0.006升至24h的1.970±0.070);实验组右侧脑缺血区F值术后缓慢升高(从术后0.5h的0.58±0.74升至0.76±0.57),在术后12、18和24h实验组双侧脑F值的差异有统计学意义(P值分别为0.031、0.004和0.001)。实验组双侧脑术后0.5～24.0h的DDC值为右侧(0.40±0.02)×10-3～(0.58±0.03)×10-3 mm2/s、左侧(0.46±0.03)×10-3～(0.49±0.06)×10-3 mm2/s,均较术前值[右侧(1.18±0.05)×10-3、左侧(1.01±0.05)×10-3 mm2/s]降低,且在各时间点均低于对照组,差异有统计学意义(P值0.0083～0.0163);术后各时间点实验组右侧的α值均小于对照组右侧(P值范围0.0205～0.0443),其DDC值和Mono-ADC值之间有强相关性(r=0.9051,P<0.0001),且α值随着DDC值的升高而减低。结论:多b值DWI的拉伸指数衰减模型的各参数值所表现出的特征性可能为大鼠急性缺血脑组织中水分子不均一的扩散状态提供了一定的参考价值。     

拉伸指数与单指数模型DWI对单侧大脑前循环动脉狭窄者的评价

目的:以单侧大脑前循环动脉不同程度狭窄的患者为研究对象,比较DWI的拉伸指数模型、单指数模型的各参数值在左、右半球之间的差异。方法:对申请头颈部动脉CTA检查的患者,在无MRI检查禁忌及患者知情同意的情况下行单指数和拉伸指数模型的扩散加权检查。采用的b值序列是:0、5、10、20、50、100、200、400、600、1000、1500、2000、3000s/mm2,通过工作站计算表观扩散系数(ADC)值、分布扩散系数(DDC)值和α值三个参数。根据颈内动脉系统是否狭窄及狭窄程度将患者分为A(无狭窄)、B(轻、中度狭窄)、C(重度狭窄或闭塞)三组,统计各组左右两侧大脑中动脉供血区的各参数值,运用非参数秩和检验法比较两侧值的组间差异及组内差异。结果:进入统计分析的患者共39例,其中A组11例,B组13例,C组15例。经统计学检验发现,ADC值、DDC值的左右侧差值及左右侧比值的对数值的各组间比较、C组的组内比较差异均有统计学意义(P<0.05);B组DDC值的左右侧差值及左右侧比值的对数值的组内比较差异均有统计学意义(P<0.05);B组ADC值的左右侧差值比较差异无统计学意义(P>0.05),左右侧比值的对数值的比较差异有统计学意义(P<0.05)。α值的上述差异均无统计学意义(P>0.05)。结论:运用多b值DWI技术定量分析大脑前循环狭窄时,单指数模型的ADC值和拉伸指数模型的DDC值在无动脉狭窄和狭窄者之间的差异均有明显体现,而DDC值对不同程度狭窄者之间的差异更敏感。     

大鼠急性缺血性脑卒中双指数扩散加权成像研究

目的:探讨大鼠急性缺血性脑卒中MRI及双指数扩散加权成像的动态变化.方法:30只成年雄性Wistar 大鼠随机分为大脑中动脉闭塞(MCAO)永久缺血组11只、缺血再灌注组11只及对照组8只,于术前及术后0.5、3、6、12和24 h分别行单b值、多b值DWI及T2 WI扫描,分析表观扩散参数(ADC)、慢速扩散系数(ADCsl.w)、快速扩散系数(ADCfast)和快速扩散所占容积分数(Afast)的动态变化,以24 h TTC组织染色作为病理对照.结果:永久缺血组ADC、ADCsl.w和Afast先降低,6h到达最低,而后轻度上升;ADCfast缺血后降低,并持续在一个较低水平.缺血再灌注组ADC、ADCslow、ADCfast和Afast于再灌注1.5h回升,但仍低于正常水平,而后逐渐下降,至24 h到达最低水平,且此时与永久缺血组各参数差异均无统计学意义(P＞0.05).ADCfast永久缺血组与再灌注组只在3h时差异有统计学意义(P＜0.05),Afast再灌注组与对照组只在3h时差异无统计学意义(P＞0.05).结论:多b值扩散加权成像可显示缺血不同时间点细胞内、外水分子的扩散受限情况及细胞内、外水分子的转移过程.     

Diffusion weighted MR imaging of acute Wernicke's encephalopathy

We report a case of Wernicke's encephalopathy in which diffusion-weighted MR images demonstrated symmetrical hyperintense lesions in the paraventricular area of the third ventricles and medial thalami. Apparent diffusion coefficient mapping showed isointensity in the aforementioned areas. Diffusion-weighted MR images may provide evidence of vasogenic edema associated with thiamine deficiency, proven in the histopathology of experimental animals. In addition, diffusion-weighted MRI has many advantages over T2 or FLARE-weighted brain MRI in detecting structural and functional abnormalities in Wernicke's encephalopathy.     

Diffusion weighted MR imaging in non-infarct lesions of the brain

Diffusion weighted imaging (DWI) is a relatively new method in which the images are formed by the contrast produced by the random microscopic motion of water molecules in different tissues. Although DWI has been tried for different organ systems, it has been found its primary use in the central nervous system. The most widely used clinical application is in the detection of hyperacute infarcts and the differentiation of acute or subacute infarction from chronic infarction. Recently DWI has been applied to various other cerebral diseases. In this pictorial paper the authors demonstrated different DWI patterns of non-infarct lesions of the brain which are hyperintense in the diffusion trace image, such as infectious, neoplastic and demyelinating diseases, encephalopathies - including hypoxic-ischemic, hypertensive, eclamptic, toxic, metabolic and mitochondrial encephalopathies - leukodystrophies, vasculitis and vasculopathies, hemorrhage and trauma.     

单指数及双指数模型DWI对缺血性脑卒中患者的评价

目的:比较不同时期缺血性脑卒中(ischemic stroke,IS)单指数及双指数模型DWI参数的差异。方法:收集经临床综合确诊为IS的患者32例(超急性期12例、急性期10例、亚急性期10例),所有患者行常规DWI(b=1 000 s/mm2)及多b值DWI(b=20~5 000 s/mm2)成像,应用单指数模型测量缺血核心区和对侧镜像区域ADC值,应用双指数模型测量缺血核心区和对侧镜像区域快速表观扩散系数(ADCfast)、慢速表观扩散系数(ADCslow)、快速扩散成分比(ffast)。结果:超急性期、急性期、亚急性期IS患侧缺血核心区ADC、ADCfast、ADCslow均低于对侧镜像区,双侧比较差异均有统计学意义(均P0.05);超急性期、急性期、亚急性期ffast均低于对侧镜像区,双侧比较差异均有统计学意义(均P0.05);超急性期、急性期、亚急性期患侧r ADC、r ADCfast及r ADCslow组比较差异均无统计学意义(均P0.05)。结论:常规DWI单指数ADC只能反映脑组织扩散受限的程度,可用来诊断IS;多b值DWI双指数ADC可反映脑组织灌注和扩散的信息,能对IS早期诊断和治疗提供重要依据。     

Diffusion/perfusion MR imaging of acute cerebral ischemia

In vivo echo-planar MR imaging was used to measure apparent diffusion coefficients (ADC) of cerebral tissues in a comprehensive noninvasive evaluation of early ischemic brain damage induced by occlusion of the middle cerebral artery (MCA) in a cat model of acute regional stroke. Within 10 min after arterial occlusion, ADC was significantly lower in tissues within the vascular territory of the occluded MCA than in normally perfused tissues in the contralateral hemisphere. Sequential echo-planar imaging was then used in conjunction with bolus injections of the magnetic susceptibility contrast agent, dysprosium DTPA-BMA, to characterize the underlying cerebrovascular perfusion deficits. Normally perfused regions of brain were identified by a dose-dependent 35-70% loss of signal intensity within 6-8 s of contrast administration, whereas ischemic regions appeared relatively hyperintense. These data indicate that sequential diffusion/perfusion imaging may be useful in differentiating permanently damaged from reversibly ischemic brain tissue.     

Diffusion weighted imaging in prostate cancer

Diffusion-weighted imaging has generated substantial interest in the hope that it can be developed into a robust technique to improve the accuracy of MRI for the evaluation of prostate cancer. This technique has the advantages of short acquisition times, no need for intravenous administration of contrast medium, and the ability to study diffusion of water molecules that indirectly reflects tissue cellularity. In this article, we review the existing literature on the utility of DWI in tumour detection, localisation, treatment response, limitations of the technique, how it compares with other imaging techniques, technical considerations and future directions.     

Demonstration of acute retinal ischemia on diffusion weighted magnetic resonance imaging

In this case, we demonstrate the ability of diffusion weighted magnetic resonance imaging to localize retinal ischemia in a patient with acute vision loss. MRI is widely used for the evaluation of acute stroke, but there has only been one other case report showing the ability of DWI to rapidly localize retinal pathology, including central retinal artery occlusion [1]. Central retinal artery occlusion is an ocular emergency presenting with acute, painless loss of vision as a result of retinal ischemia. This case demonstrates the role of diffusion weighted imaging as an adjunctive test in the prompt diagnosis and management of central retinal artery occlusion. As the technology improves, we anticipate diffusion weighted imaging will become more sensitive for the identification of acute retinal ischemia and other retinal pathologies.     

扩散和灌注加权成像对兔脑缺血半暗带的量化

目的:探讨磁共振扩散加权成像(DWI)和灌注加权成像(PWI)在对被挽救缺血半暗带(IP)评价中的价值。方法:将制作成功的58只兔大脑中动脉闭塞(MCAO)模型随机分为永久缺血组(A组)和缺血再灌注组(B组);A组再按缺血1、3、6、12、24、48 h分组(A_1～6组),B组再按缺血1h后再灌注0、2、5、11、23、47h分组(B_(1～6)组)。然后,对各组行I)WI和PWI检查。结果:缺血再灌注组DWI像上异常信号区面积明显小于永久缺血组;缺血24h,梗死范围基本稳定。缺血1h,当表观扩散系数(ADC)比值、相对脑血容量(rCBV)比值和相对平均通过时间(rMTT)比值分别为(73.40±4.33)%、(46.83±9.89)%、1.58±0.04时,该区可能为IP;当ADC比值和rCBV比值分别低于(58.83±6.06)%和(22.87±8.19)%、rMTT比值大于1.94±0.1时,缺血脑组织将会发生不可逆性坏死。结论:DWI结合PWI能够快速、有效地评价IP。     

兔骨骼肌缺血模型扩散张量成像研究

目的 初步探讨MR DTI在定量评估兔后肢缺血模型骨骼肌缺血中的应用价值.方法 对14只新西兰大白兔进行结扎并切除一侧后肢股动脉,成功建立兔后肢缺血模型共12只,分别于术后3 d(12只)、10 d(10只)、28 d(7只)、56 d(5只)对两侧小腿行DTI检查,并在每个时间点留取病理组织.观察两侧肌组织在DWI、本征向量(λ)_1图、λ_2图、λ_3图、ADC图和部分各向异性(FA)图上的表现,并测量后组肌群的λ_1、λ_2、λ_3、ADC值和FA值,采用配对t检验比较两侧小腿的差异,并与病理组织对照.结果 术后3 d手术侧ADC值升高(ADC_(术侧)=1.72±0.16,ADC_(健侧)=1.53±0.16,t=6.48,P<0.01),其中λ_2和λ_3 2个特征矢量值升高明显(入_(2术侧)=1.70±0.15,入_(2健侧)=1.51±0.06,t=10.87,P<0.01;入_(3术侧)=1.17±0.12,λ_(3健侧)=0.88±0.12,t=6.67,P<0.01),FA值急骤下降(FA_(术侧)=0.24±0.04,FA_(健侧)=0.39±0.03,t=-10.61,P<0.01);术后10 d缺血骨骼肌ADC值及λ_2、λ_3值下降,但两侧仍有差异(ADC_(术侧)=1.65±0.16,ADC_(健侧)=1.50±0.12,t=6.42,P<0.01;λ_(2术侧)=1.62±0.32,λ_(2健侧)=1.48±0.31,t=5.09,P<0.01);λ_(3术侧)=1.11±0.13,λ_(3健侧)=0.85±0.09,t=6.26,P<0.01),λ_1值恢复正常(λ_(1术侧)=2.20±0.21,λ_(1健侧)=2.18±0.20,t=0.87,P=0.40);术后28 d ADC及λ_3值恢复正常(ADC_(术侧)=1.51±0.16,ADC_(健侧)=1.55±0.14,t=-1.35,P=0.23;λ_(3术侧)=0.95±0.10,λ_(3健侧)=0.92±0.06,t=1.70,P=0.14),但λ_2及FA值仍有差异(λ_(2术侧)=1.45±0.23,λ_(2健侧)=1.52±0.95,t=-3.56,P=0.012;FA_(术侧)=0.35±0.02,FA_(健侧)=0.40±0.03,t=-3.83,P<0.01);术后56 d各观测指标均恢复正常(ADC_(术侧)=1.57±0.18,ADC_(健侧)=1.58±0.23,t=-0.71,P=0.52;λ_(1术侧)=2.18±0.18;λ_(1健侧)=2.24±0.14;t=-0.22,P=0.10;λ_(2术侧)=1.64±0.13,λ_(2健侧)=1.59±0.15,t=0.89,P=0.42;λ_(3术侧)=0.89±0.1,λ_(3健侧)=0.91±0.07,t=-1.64,P=0.18;FA_(术侧)=0.39±0.03,FA_(健侧)=0.41±0.02,t=-0.83,P=0.47).组织学观察,在缺血后3、10 d见肌肉损害,28 d后缺血肌肉逐渐恢复,56 d恢复正常形态.结论 DTI可以定量且较准确地评估动物后肢缺血模型随时间推移发生的肌肉组织损伤及修复过程.     

Quantitative regional brain water measurement with magnetic resonance imaging in a focal ischemia model

Therapeutic approaches to cerebral edema require an understanding of both the magnitude and location of changes in brain water content. It is desirable to have a sensitive, accurate means of measuring brain water noninvasively so that effective therapies for cerebral edema in stroke, head trauma, and other conditions can be investigated. In this work, a three-dimensional magnetic resonance imaging technique that is able to provide both spin density and T₁ simultaneously is described. This method was used to quantitate regional changes in brain water content in a rat model of focal cerebral ischemia. Brain water contents estimated from both relative spin density and relative T₁ measurements made in vivo were compared with ex vivo measurements of relative tissue water content based on the wet-dry technique. Correlation coefficients of 0.95 and 0.98 were obtained between the wet-dry measurements and magnetic resonance measurements of T₁ and spin density, respectively. Notably, the slope of the relationship between T₁ and tissue water content changed dramatically after the injection of a paramagnetic contrast agent while precontrast and postcontrast spin density measurements remained essentially invariant. In addition, a plot of absolute spin density (obtained by normalizing spin density from agar gelatin phantoms of different water contents to the spin density of a sample of 100% water) was linearly related to wet-dry measurements with a slope of 0.99 (R² = 0.99).     

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.     

急性征兆性脑外伤扩散张量成像研究

目的 探讨急性征兆性脑外伤患者脑内微结构的变化.方法 对12例急性征兆性脑外伤患者以及13例性别、年龄、受教育程度、利手均匹配的健康对照者进行全脑扩散张量成像(DTI)及临床行为认知评估,采用的评估量表包括:汉密顿抑郁量表(HAMD),临床痴呆量表(CDR),疲劳严重程度量表(FSS),脑震荡后遗症评分(PSS),简易精神状态检查量表(MMSE),任务A、任务B(Trial-making A、Trial-making B).应用基于纤维束示踪的空间统计得出2组间有差异的脑区,应用方差分析得出行为认知差异.结果 与健康组对照,急性征兆性脑外伤患者存在广泛的各向异性分数(FA)值降低区域(P＜0.05,TFCE校正),尤其在边缘-皮层下结构.2组间在CDR,PSS,Trial-making A、Trial-making B有显著差异(P＜0.01),在MMSE、FSS有差异(P＜0.05),在HAMD无差异.结论 DTI能全面、准确地评估征兆性脑外伤患者脑组织微结构的改变,为临床治疗提供依据.     

Diffusion weighted imaging of bone marrow pathologies

Diffusion weighted imaging of non-CNS tissue has attracted much attention during the last years. Its capability of probing the microstructure of a biologic tissue at a sub-millimeter range is used to evaluate its diffusion capacity, which is tissue specific and can be used for tissue characterization. Processes involving bone marrow where the primary target for DWI during the last years. Most experience has been gained for differentiating benign from pathologic vertebral compression fractures, which can be reliably done when quantitative diffusion measurements are available. However, preliminary results exist indicating that this non-invasive technique may be a potential tool for therapy monitoring, which will revise the management of cancer patients. Moreover, this will be the first non-invasive and quantifiable tool for evaluating the effectiveness of modern tumor treatment. In this article, we will give an overview on the current status of DWI in the evaluation of bone marrow alterations; on currently available DWI techniques and a short out-look on future aspects of DWI in bone marrow pathologies.     

急性一氧化碳中毒脑损伤的磁共振扩散张量成像

目的：利用磁共振扩散张量成像(DTI )评估急性一氧化碳(CO)中毒患者的脑结构损伤情况。方法25例急性(5.0 d±1.44 d) CO 中毒患者和37例性别、年龄、利手、受教育程度匹配的健康志愿者进行 DTI 扫描,获得扩散张量纤维束成像(DTT)图像,并分别测量双侧小脑半球(齿状核)、黑质、海马、额叶白质(侧脑室前角前下方、侧脑室体部上方)、尾状核头、苍白球、丘脑、内囊前肢、内囊后肢、枕叶白质(视中枢)、顶叶白质(侧脑室体部上方)及胼胝体膝部、压部共26个感兴趣(ROI)的各向异性分数(FA)值和表观扩散系数(ADC)值,进行组间配对 t 检验。结果病患组双侧苍白球、双侧内囊前肢、双侧黑质、右侧小脑、左侧额叶下部白质、右额叶上下部白质、胼胝体膝部的 FA 值显著低于对照组(P <0.05)。病患组右侧黑质、左侧苍白球的 ADC 值显著降低(P <0.05),病患组右额叶上下部白质及双侧枕叶白质 ADC 值显著升高(P <0.05)。结论急性 CO 中毒患者广泛脑微结构受损,提示脑微结构的原发损伤可能是 CO 中毒迟发性脑病潜在的病理生理基础。     

Diffusion weighted imaging: Technique and applications

Diffusion weighted imaging (DWI) is a method of signal contrast generation based on the differences in Brownian motion. DWI is a method to evaluate the molecular function and micro-architecture of the human body. DWI signal contrast can be quantified by apparent diffusion coefficient maps and it acts as a tool for treatment response evaluation and assessment of disease progression. Ability to detect and quantify the anisotropy of diffusion leads to a new paradigm called diffusion tensor imaging (DTI). DTI is a tool for assessment of the organs with highly organised fibre structure. DWI forms an integral part of modern state-of-art magnetic resonance imaging and is indispensable in neuroimaging and oncology. DWI is a field that has been undergoing rapid technical evolution and its applications are increasing every day. This review article provides insights in to the evolution of DWI as a new imaging paradigm and provides a summary of current role of DWI in various disease processes.