磁共振Propeller技术消除伪影的临床应用

目的:探讨Propeller技术在临床的应用价值。方法:日常工作中随机对19例磁共振头颅检查中出现躁动或有固定金属异物患者,应用Propeller技术进行成像,与常规T2FRFSE序列、DWI序列进行对比扫描。其中因躁动产生运动伪影进行PropellerT2加权成像11例,因金属异物产生伪影进行PropellerDWI成像8例,同时进行PropellerT2WI、DWI成像5例。结果:19例应用Propeller技术进行T2WI、DWI成像消除因运动、金属引起的伪影均获得满意图像。结论:应用PropellerT2WI、DWI成像技术明显消除患者因运动或金属异物造成的伪影,可生成高分辨无伪影具有临床诊断意义的理想图像。     

PROPELLER FSE磁共振扩散加权技术在诊断超急性和急性脑梗死中的价值

目的比较螺旋桨扫描技术(PROPELLER FSE)和平面回波成像(EPI)两种扩散加权成像(DWI)序列,探讨PROPELLER技术在DWI的应用价值。资料与方法选取67例临床疑诊急性脑梗死的患者分别行PROPEL-LER FSE DWI、EPI DWI和常规T1WI、T2WI、T2WI液体衰减反转恢复序列(FLAIR)检查,比较两种不同的DWI序列的图像质量,病灶检出率和对病变的显示程度。结果67例EPI DWI图像均不同程度地存在磁化率伪影,67例PROPELLER FSE DWI图像未见明显伪影及变形。67例中共发现并确诊46个急性脑梗死灶(4例为颅内多发病灶),其中病灶位于颅底区域12个,非颅底区域34个。PROPELLER FSE DWI和EPI DWI均可分辩出所有非颅底区域梗死灶。对12个颅底病灶PROPELLER FSE DWI检出率达100%,而EPI DWI可以明确诊断的7个,检出率达58.3%,病灶形态显示不充分或变形者3个,占25%,漏诊2个,漏诊率为16.7%。所有颅底区域病灶EPI DWI上信噪比(SNR)低于相应PROPELLER FSE DWI的SNR(t=-2.874,P<0.05)。结论PROPELLER FSE DWI能提高图像SNR,有效消除颅底磁化率伪影,改善图像质量,提高颅底病变的检出率。     

磁共振Propeller技术消除头部伪影的临床应用

目的探讨Propeller技术在头部伪影消除的应用价值。方法对21例磁共振头颅日常检查中出现躁动或不能自控患者，用Propeller技术进行T2WI扫描，与常规T2FRFSE序列进行对比；5例DWI序列磁敏感伪影明显者进行Propeller DWI扫描，与常规DWI进行对比。结果21例应用Propeller技术进行T2VI扫描明显减少或消除了运动伪影，5例Propeller DWI明显消除磁敏感效应引起的伪影，均生成较满意图像。结论应用PropellerT2WI及DWI成像技术可以明显减少或消除患者因运动及磁敏感效应造成的伪影，显著提高图像质量，获得具有临床诊断价值的理想图像。     

磁共振弥散加权成像对急性皮层下脑梗塞的评价

目的 研究磁共振弥散加权成像（DWI）诊断急性皮层下脑梗塞的准确性以及对急性与非急性皮层下脑梗塞的鉴别诊断。材料与方法 对32例临床诊断为急性皮层下脑梗塞的患者和20例对照者在不同时间内进行常规MRI检查和弥散加权MRI检查,并用盲法进行对照观察。对所有病例的病变部位均按神经解剖进行准确定位并与患者的症状、体征相联系。结果 DWI诊断急性皮层下脑梗塞的敏感性、特异性及准确性分别为97％、95％和96％。32例中有3例常规MRI检查未发现急性梗塞性。另20例常规MRI检查均显示为多发梗塞,而DWI只显示单个急性病灶,且患者的症状、体征与DWI上显示的病灶相符。结论 DWI对诊断急性皮层下脑梗塞有很高的准确性,能发现常规T2WI不能发现的早期脑梗塞,并能鉴别急性与非急性梗塞。     

MRI常规扫描序列与EPI序列对弥漫性轴索损伤诊断的对比研究

目的评价MRI常规FSET2WI、SET1WI序列与EPI序列对弥漫性轴索损伤的诊断价值.材料与方法42例弥漫性轴索损伤患者均进行MRI常规FSET2WI、SET1WI和EPI扫描.29例检查前静脉注射5～10毫克安定.结果FSET2WI、SET1WI序列运动伪影的发生率分别为83.3%、71.4%;EPI序列无一例出现运动伪影.EPI病灶与正常脑白质的对比度显著低于FSET2WI序列(p＜0.001),空间分辨率较FSET2WI、SET1WI序列差,信噪比最高.EPI共显示143个病灶,为FSET2WI显示病灶(174个)的82.2%,SET1WI序列显示133个病灶.对于直径大于1cm的病灶,EPI病灶显示数为FSET2WI序列的91.7%.FSET2WI、SET1WI序列所见的DAI主要并发症,EPI序列大都能显示.结论EPI的对比度与分辨率不如FSET2WI,对脑内小病灶、出血灶及脑底部病灶的显示还存在一定的限度,但EPI扫描时间极短,图像信噪比高、无运动伪影,能保证对脑内大多数病灶的显示,对弥漫性轴索损伤的诊断有重要的诊断价值,尤其对伴有烦噪的急性脑外伤患者或病情不允许进行长时间检查的患者,EPI可代替FSET2WI进行检查.     

磁共振弥散加权成像在诊断急性脑梗塞中的价值

目的探讨磁共振弥散加权成像(DWI)在急性脑梗塞诊断中的价值,及对急性与非急性脑梗塞鉴别诊断价值。方法回顾性分析25例急性脑梗塞患者。均先行CT平扫,后行常规MRI及DWI检查。结果超急性期脑梗塞4例,CT呈阴性,常规MRI序列未见明显异常,而DWI均显示不同程度高信号;急性期脑梗塞21例只有2例CT显示新病灶,9例常规MRI(T2WI)显示新病灶,而DWI明显优于常规序列。结论 DWI对超急性期、急性期脑梗塞有高度的特异性和敏感性,能准确可靠地显示病灶的部位和范围,而且可以鉴别新旧梗死灶。     

磁共振弥散加权成像对急性脑梗塞的诊断价值

目的：评价磁共振弥散加权成像对急性脑梗塞的诊断价值及对急性和非急性脑梗塞的鉴别诊断价值。方法：对临床怀疑急性脑中风35例患者，进行常规T2WI和DWI检查，并采用盲法进行对照观察。对DWI图像上出现的异常高信号的病变部位进行准确定位，并判断病变部位与临床症状与体征是否相符，对DWI图像上出现的异常高信号与FSE序列T2WI像上的表现进行对照观察。结果：35例在DWI像上均出现异常信号，其中3例是在发病后6h内进行MRI检查，而在常规T2WI像上未显示异常信号；2例是在发病后12h内进行检查，而在常规T2WI像上仅表现稍高信号；10例患者在发病后12～24h内进行检查，20例患者在发病后24-72h进行检查，在T2WI和DWI像上均出现异常高信号；其中8例在FSE T2WI像上表现为多发脑梗塞病灶，而在DWI像上显示为单一异常高信号。在DWI像上诊断急性脑梗塞的敏感性及特异性均为100％。结论：DWI图像比常规T2WI图像对诊断急性脑梗塞有较高的敏感性及特异性，能发现常规T2WI像不能发现的超早期脑梗塞，并能鉴别急性和非急性脑梗塞，故DWI图像在诊断急性脑梗塞具有十分重要的诊断价值。     

MR螺旋桨扫描技术在消除伪影方面的临床应用

目的探讨螺旋桨扫描技术（periodically rotated overlapping parallel lines enhanced reconstruction，PROPELLER）在临床的应用价值。方法对10例健康志愿者在头部晃动状态下、64例头颅MR检查中出现躁动不合作或口腔有固定金属异物的患者，应用PROPELLER技术进行T2WI和（或）扩散加权成像（DWI），与常规T2WI和（或）DWI进行对比。64例患者中，脑梗死40例（其中脑干梗死16例），脑梗死伴脑出血1例，脑转移瘤3例，癫痫、病毒性脑炎和高血压等20例。56例为运动伪影，8例为金属异物引起的磁敏感伪影。结果10例健康志愿者PROPELLER T2W图像质量明显优于常规T2WI。分别对10例志愿者和56例患者的常规T2WI、DWI与PROPELLER T2WI、DWI的图像进行比较，显示因运动产生的伪影，导致图像质量降低，无法达到诊断要求；采用PROPELLER T2WI，均显著消除伪影的影响，病变显示清晰，诊断明确。8例因固定义齿产生的磁敏感伪影，采用PROPELLER DWI，均明显消除伪影干扰，获得有诊断价值的图像。结论应用PROPELLER T2WI、DWI技术，明显消除患者因运动或金属异物造成的伪影，可生成高分辨率、无伪影、具有临床诊断意义的理想图像。     

扩散加权成像诊断超急性和急性脑梗塞的应用价值

目的:探讨DWI和ADC图诊断超急性和急性脑梗塞的价值.材料和方法:14例脑梗塞患者(超急性期6例,急性期8例)采用1.5T MR机进行扫描,对DWI、ADC图及常规T1WI、T2WI进行对比研究分析.结果:超急性和急性脑梗塞DWI均表现为高信号,ADC图均表现为低信号,DWI对病变显示达100%.6例超急性期脑梗塞患者仅DWI可显示病变而常规T1WI、T2WI无任何相应的异常发现.全部病灶ADC值均低于其相对应的正常脑组织.结论:DWI对急性脑梗塞诊断敏感、准确,且能对脑梗塞作定量分析.     

O.5T磁共振机弥散加权像诊断急性脑梗塞

目的分析0.5T磁共振机的弥散加权像(DWI)对急性脑梗塞诊断的临床价值。材料与方法计算50例健康志愿者正常脑组织各不同部位的表观弥散系数(ADC)值,并对急性脑梗塞发作后3～12小时的10名患者进行DWI及常规T1WI、T2WI、FLAIR及MRA检查。结果测得正常人额、顶、枕叶脑白质、半卵圆中心、基底节、脑干、小脑半球、脑脊液部位的ADC平均值。对于临床患者,DWI可明确显示急性期脑梗塞病灶,常规T1WI、T2WI、FLAIR均不能显示或显示不清。结论以DWI为主,结合T1WI、T2WI、FLAIR及MRA序列能非常准确、可靠的诊断急性脑梗塞。     

Improved image quality and detection of acute cerebral infarction with PROPELLER diffusion-weighted MR imaging

PURPOSE: To compare periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) multishot fast spin-echo diffusion-weighted magnetic resonance (MR) imaging with single-shot echo-planar diffusion-weighted MR imaging for image quality and visualization of acute cerebral infarction. MATERIALS AND METHODS: Seventy subjects (35 men, 35 women; mean age, 55 years +/- 24 [SD]) who were suspected of having acute cerebral infarction (symptom duration, 2.8 days +/- 2.7) underwent PROPELLER and echo-planar MR imaging (b = 1,000 sec/mm(2)). Two neuroradiologists compared unlabeled images for presence of artifacts, visualization of infarction, and their preference of images. Interobserver agreement and image comparison were assessed by using the kappa statistic and the chi(2) test, respectively. RESULTS: PROPELLER MR imaging reduced susceptibility artifacts (n = 70 subjects), which limited visualization of temporal (echo-planar, n = 64; PROPELLER, n = 0; P <.01, chi(2) test), frontal (echo-planar, n = 58; PROPELLER, n = 1; P <.01), and parietal lobes (echo-planar, n = 5; PROPELLER, n = 0; P <.05) and cerebellum (echo-planar, n = 36; PROPELLER, n = 0; P <.01) and brainstem (echo-planar, n = 23; PROPELLER, n = 0; P <.01). Acute infarction (n = 31 subjects) was better demonstrated at PROPELLER MR imaging (PROPELLER better, n = 18; echo-planar better, n = 1; PROPELLER and echo-planar equal, n = 12; P <.01, chi(2) test). PROPELLER MR imaging was preferred in all (n = 70) but one case in which the lesion lay within the intersection gap (PROPELLER preferred, n = 69; echo-planar preferred, n = 1; P <.01, chi(2) test). CONCLUSION: With a short increase in imaging time, PROPELLER MR imaging offers better image quality and detection of acute cerebral infarction than does echo-planar MR imaging.     

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.     

急性脑梗塞磁共振弥散加权成像的演变特征

目的：研究临床急性脑梗塞病变在弥散加权（DW）MRI上的表现规律。材料和方法：用单次激发平面回波弥散加权MRI和MRI其他技术对47例脑梗塞患者和14例非脑梗塞患者进行了对比研究。分别测量梗塞灶ACD图、DWI和T2WI的信号强度，绘出时间-信号强度图。分别在DWI和T2WI上测量梗塞面积．比较两者的关系。结果：急性脑梗塞发病后局部ACD逐渐降低．至12h达到峰值．以后逐渐升高。弥散加权MRI对急性脑梗塞病变非常敏感和特异，发病3h内T2WI为阴性，DW－MRI全部显示了梗塞灶；发病24h内T2WI所显示的梗塞灶面积明显小于DWI。发病7天内梗塞灶在DWI上与正常脑信号比均＞2．0．非脑梗塞病变均＜2．0。结论：急性脑梗塞病变在DW．MRI上有特征性演变规律，DW．MRI能快速、敏感、准确地诊断急性脑梗塞     

弥散加权MRI在脑梗塞诊断中的初步应用

目的：探讨弥散加权ＭＲＩ（ＤＷＩ）对早期脑梗塞诊断的敏感性和对急性与非急性脑梗塞的鉴别诊断价值。材料和方法：３１例脑梗塞（４例超急性,７例急性,１２例亚急性,８例慢性）患者行头颅单次激发回波平面弥散加权ＭＲＩ和常规ＭＲＩ扫描。结果：超急性、急性和亚急性脑梗塞在ＤＷＩ上均表现为高信号,其中４例超急性脑梗塞常规ＭＲＩ阴性。慢性脑梗塞除１例（发病１５天）ＤＷＩ表现为高信号,其余表现为混杂信号、等信号或低信号。６例患者常规ＭＲＩ显示多发脑梗塞灶,但ＤＷＩ显示１个急性高信号病灶。结论：ＤＷＩ对急性脑梗塞,尤其是超急性脑梗塞较常规ＭＲＩ具有更高的敏感性;ＤＷＩ还可以鉴别急性和非急性脑梗塞。     

Diffusion-weighted MR of acute cerebral infarction: comparison of data processing methods.

BACKGROUND AND PURPOSESome investigators have proposed that either calculated diffusion trace images or apparent diffusion coefficient (ADC) maps, which require imaging with multiple diffusion sensitivities and/or postacquisition image processing, are essential for the accurate interpretation of diffusion-weighted images in acute stroke because of the possible pitfalls of regional diffusion anisotropy, magnetic susceptibility artifacts, and confounding T2 effects, all of which alter signal on diffusion-weighted MR images. The purpose of our study was to compare the sensitivity, specificity, and accuracy of simple, orthogonal-axis diffusion-weighted imaging for the diagnosis of early cerebral infarction with three other sets of postacquisition-processed images: isotropic diffusion-weighted, diffusion trace-weighted, and diffusion trace images.METHODSTwenty-six consecutive adult patients with signs and symptoms consistent with a clinical diagnosis of early cortical and/or subcortical cerebral infarction and 17 control subjects were studied with multisection, single-shot, spin-echo echo-planar diffusion-weighted imaging at 1.5 T to generate a set of three orthogonal-axis diffusion-weighted images. Isotropic diffusion-weighted, diffusion trace-weighted, and diffusion trace (mean ADC) images were then generated off-line and all four sets of images were interpreted blindly by two neuroradiologists.RESULTSThe average sensitivity, specificity, and accuracy for the orthogonal-axis diffusion-weighted images were 98.1%, 97.1%, and 97.7%, respectively. The average sensitivity, specificity, and accuracy for isotropic diffusion-weighted images were 88.5%, 100%, and 93% respectively. The average sensitivity, specificity, and accuracy for diffusion trace-weighted images were 82.7%, 73.6%, and 79.1%, respectively. The average sensitivity, specificity, and accuracy for diffusion trace images were 50.0%, 85.3%, and 64.0%, respectively.CONCLUSIONOrthogonal-axis diffusion-weighted images have the highest sensitivity and accuracy and very high specificity for early cerebral infarction. Our data contradict the contention that quantitative diffusion maps, requiring imaging with multiple diffusion sensitivities and/or subsequent image processing, are necessary for clinical stroke imaging.     

DTI常用扫描序列原理及比较

磁共振弥散张量成像技术是利用水分子的弥散各向异性进行成像,可用于脑白质纤维研究,常用扫描技术包括单次激发平面回波成像(EPI),线阵扫描弥散成像,导航自旋回波弥散加权成像(LSDI),半傅立叶探测单发射快速自旋回波成像等。每种成像技术各有其优缺点,EPI扫描时间短,图像信噪比高,但存在化学位移伪影、磁敏感性伪影、几何变形;LSDI精确度高,几乎无伪影及变形,但扫描时间过长;导航自旋回波弥散加权成像运动伪影少,但扫描时间长;半傅立叶探测单发射快速自旋回波成像扫描时间短,但图像模糊。综合比较,单次激发平面回波成像是用于临床研究较适宜的方法。     

Diffusion-weighted imaging with navigated interleaved echo-planar imaging and a conventional gradient system.

PURPOSE: To demonstrate the technical feasibility and precision of a navigated diffusion-weighted (DW) MR imaging method with interleaved echo-planar imaging and test its diagnostic sensitivity for detection of ischemic stroke. MATERIALS AND METHODS: Apparent diffusion coefficient (ADC) measurements were performed in phantoms, and six healthy adult volunteers were examined to determine intrasubject (precision) and intersubject (reference range) variations in absolute ADC and relative ADC (rADC) measurements. DW imaging maps and lesion rADC values were also obtained in 34 consecutive stroke patients to evaluate the sensitivity and reliability of DW-interleaved echo-planar imaging for detection of ischemic brain damage. RESULTS: Phantom and volunteer ADC values were in excellent agreement with published data. The intrasubject variation of rADC was 6.2%. The ADC precision ranged from 6.5% in the subcortical white matter in the frontal lobe to 12.9% in the head of the caudate nucleus. Interleaved echo-planar imaging enabled rapid acquisition of high-quality images of the entire brain without substantial artifacts. Within the 1st week, the sensitivity of DW-interleaved echo-planar imaging for detection of acute infarction was 90% (18 of 20 true-positive studies) and independent of lesion location. CONCLUSION: DW-interleaved echo-planar imaging with phase navigation and cardiac triggering is robust, reliable, and fast. With high sensitivity for detection of early ischemic infarction, it is useful for examining stroke patients by using MR systems with conventional gradient hardware.     

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.