中枢神经系统磁共振成象(续)

一、细菌性感染 (一)脑炎 MRI在显示脑炎及水肿反应区域时,T_2加权图象上为高信号异常,如果有点状出血并足够的大,根据血液的化学状态,它们在T_1和T_2加权图象上亦能见到。占位效应用MRI可得到较好的证实,见脑室移位及脑沟裂的受压。脑炎累及多个区域时用MRI比CT好。     

磁共振成象(MRI)诊断脑梗塞的初步体会

本文报告了21例脑梗塞的MRI检查及CT对照检查。脑梗塞在MRI上有其一定的形态,用SE序列T_2加权成象的图象中,脑梗塞可以表现为与脑组织相等或较高的信号,但在较后的回波图象中均表现为明亮的高信号区;MRI对脑梗塞的检查优于X线CT,特别是它能检出X线CT诊断有困难的脑干和小脑内的梗塞病灶,亦可以清楚地显示处于CT平扫为“雾状效应”期的脑梗塞病灶等,从而,为脑梗塞诊断提供了一种敏感性高的影象学方法。     

T_2加权像、液体衰减反转恢复序列与磁共振三维双反转恢复序列对多发性硬化患者脑内病灶的检测比较

目的比较T_2加权像(T_2WI)、液体衰减反转恢复序列(Flair)与磁共振(MRI)三维双翻转恢复序列(3D-DIR)对多发性硬化(MS)患者脑内病变的检测能力。方法收集23例MS患者,采用3.0T MRI分别对23例颅内病变患者行T_2WI、Flair及3D-DIR序列扫描,比较三种序列对MS患者颅内不同部位病变的检出率。结果在总体病灶中,3种方法对皮质病灶及近皮质病灶的检出率差异有统计学意义(P<0.05),与T_2WI和Flair序列相比,3D-DIR对皮质病灶及近皮质病灶的检测更敏感。结论应用MR3D-DIR序列可以提高MS患者皮质病变及近皮质病变的检出率。     

脑囊虫与磁共振成像──附20例分析

报告20例脑囊虫与磁共振成像（MRI）表现。其中脑实质型12例，脑室型6例，混合型2例。脑实质型中4例为单发病灶，2例为多发病灶，其余6例为数量较多的多发病灶。MRI常为小的长T_1低信号与长T_2高信号囊肿。脑室型可见脑室内囊肿壁，有1例可见头节。10例与CF作了对比分析，对于病变大小，范围，数目及部位的显示，MRI均优于CT，特别是微小病灶。     

颅内非肿瘤性疾病的磁共振成像

本文复习了颅内非肿瘤性疾病的磁共振成像(简你MRI)近况,MRI受组织参数(T_1,T_2,ρ和流动效应)和仪器参数(TR,TE)等影响,使图象解释比X线CT复杂,但对某些病理过程的解释比X线CT更为正确.文中重点复习了中枢神经系统绝大多数非肿瘤性疾病的MRI表现,总的看来在非肿瘤性疾病的诊断中MRI优于X线CT.     

中枢神经系统磁共振成像(续)

急性脑实质内出血性病变在MRI的T_1加权图象上呈相对等信号,T_2-W1图像上呈相对低信号,这些征象在高磁场MRI中比较显著。亚急性实质内出血在T_1和T_2加权图象上表现为高信号。MRI在急性蛛网膜下腔出血检查中是不敏感的。在蛛网膜下腔或硬膜下出血的亚急性阶段,MRI比CT更为敏感。血液在轴外积聚时T_1和T_2图像上均呈明亮信号。 为了实用起见,MR对于评价合作病人有急性实质内出血中是最佳之手段,因为蛛网下出血的病人,在急性阶段CT是目前最合适的检查手段,在亚急性阶段MR是最恰当的手段,在可疑CVM病人中,MR是目前最敏感和特异的检查手段。     

CT与MRI对腔隙性梗死的诊断价值分析

目的比较CT与MRI对腔隙性梗死的诊断价值。方法选择腔隙性梗死患者40例为研究对象,均于入院3h内行急诊螺旋CT及MRI检查。以临床诊断为准,观察CT与MRI对腔隙性梗死病灶数量及部位诊断情况。比较CT与MRI对发病24h、24~72h、72h患者脑内病灶及径线5mm、5~10mm和10~15mm病灶检出情况。结果 (1)脑梗死病灶分布于额叶6例,顶叶6例,颞叶6例,枕叶4例,基底节区8例,丘脑3例,脑干3例,小脑4例。40例患者中,CT共显示21例患者存在脑梗死病灶,共显示病灶45处。MRI共显示38例患者存在脑梗死病灶,共显示病灶79处。MRI对脑梗死病灶检出率显著高于CT,差异具有统计学意义(P0.05)。(2)MRI对24h、24~72h脑梗死病灶的检出率显著高于CT,差异具有统计学意义(P0.05)。两者在72h病灶的检出中,差异无统计学意义(P0.05)。(3)其中MRI对径线5mm及5~10mm腔隙性梗死病灶检出率显著高于CT,差异具有统计学意义(P0.05)。在病灶径线10~15mm病灶的检出中,MRI及CT比较差异无统计学意义(P0.05)。结论在腔隙性梗死的诊断中,MRI较CT更具有优势。     

瘤样炎性脱髓鞘病MRI的临床意义

目的分析瘤样炎性脱髓鞘病(TIDD)临床、影像与病理特点,探讨磁共振(MRI)检查对TIDD的诊断价值。方法对39例TIDD患者进行头颅、脊髓CT和MRI扫描,并分析临床和影像学特点。结果病灶在头颅CT均为低密度,常规MRI扫描呈T1WI低信号、T2WI高信号,T1WI增强扫描44%可见"开环征",发病早期DWI可见高信号,FLAIR较T1WI及T2WI更清晰显示病灶及其范围。结论 DWI能发现TIDD早期病变,FLAIR较常规T1WI、T2WI敏感,"开环征"是磁共振诊断TIDD的重要辅助依据。     

海洛因海绵状白质脑病的影像学特征

目的　探讨海洛因海绵状白质脑病 (HSL E)的 CT、MRI和 PET特点。方法　对 2 9例患者的CT、MRI以及 4例患者的 PET资料进行分析。结果　 (1) CT和 MRI显示病变位于双侧小脑、内囊后肢、枕顶叶深部等部位白质 ,病灶广泛且对称 ;(2 ) CT示界限清楚的低密度病灶 ,MRI呈长 T1 WI、长 T2 WI异常信号 ,无水肿 ,快速反转恢复序列 (FL AIR)和增强扫描提示血脑屏障无破坏 ,PET显示为低代谢或无代谢病灶 ;(3)未治疗患者内囊后肢、枕叶和小脑白质无代谢 ,康复期患者代谢明显减低 ;(4 )临床症状改善者和未治疗者小脑皮质代谢降低 ,临床症状明显改善者代谢正常。结论　 HSL E患者的 CT和 MRI改变多局限于白质 ,极为相似。 PET显示病变部位低代谢或无代谢 ,小脑皮质和白质代谢的恢复对 HSL E患者的临床转归非常重要 ,故判断 HSL E患者的转归 ,PET较之 MRI更有价值     

磁共振多层并采扩散峰度成像与传统扩散加权成像识别急性缺血性卒中梗死核心的研究

目的与磁共振成像(magnetic resonance imaging,MRI)传统扩散加权成像(diffusion weighted imaging,DWI)对比,探讨MRI多层并采扩散峰度成像(multi-band EPI diffusion kurtosis imaging,m-DKI)界定急性缺血性卒中梗死核心的准确性。方法选择在发病3~8 h进行MRI检查的急性缺血性卒中患者,所有患者经灌注加权成像(perfusion weighted imaging,PWI)判定不存在缺血半暗带,没有接受静脉溶栓/动脉取栓治疗。基线扫描时加入传统DWI以及m-DKI序列,并在患者发病亚急性期([7±1)d]复查MRI扫描,利用Mricron软件分别对基线MRI检查表观扩散系数(apparent diffusion coefficient,ADC)图,平均扩散峰度(mean kurtosis,MK)图以及复查MRI T_1加权成像(T_1 weighted imaging,T_1WI)责任病灶体积进行测量,分别计算ADC图、MK图与T_1WI责任病灶体积的差值,并进行比较。结果入组的19例患者,1例患者DWI显示缺血病灶,但MK图及复查MRI均未见责任病灶;1例患者病灶位于基底节区附近,影响MK图责任病灶观察及测量。余17例患者MK图显示责任病灶的体积与亚急性期T_1WI责任病灶体积的差值为(0.25±0.37),而ADC图显示责任病灶的体积与亚急性期T_1WI体积的差值为(0.73±0.72)(t=3.968,P=0.001)。MK图责任病灶的体积更接近T_1WI的体积。结论与传统DWI相比,基线m-DKI显示责任病灶的体积更接近复查T_1WI的体积,对最终梗死核心的界定更为准确。     

DWI及MRA在大面积脑梗塞早期诊断中的价值

目的:评价弥散加权磁共振成像DWI和磁共振血管成像MRA对早期大面积脑梗塞的诊断价值。方法:对24例早期大面积脑梗塞的临床和磁共振资料进行分析,全部患者均行DWI及MRA检查。结果:24例早期大面积脑梗塞中,13例急性期CT扫描未检测出确切病灶,DWI扫描全部出现大片异常高信号,病灶检出率为100％。而在常规T2WI检查中,7例为阴性,病灶检出率为69％。MRA发现血管异常24例,表现为供血动脉闭塞,狭窄、硬化。结论: DWI有助于明确早期大面积脑梗塞病变范围,且能区别新旧病灶。MRA能直接显示大面积脑梗塞闭塞的供血脑血管,联合使用DWI和MRA对早期大面积脑梗塞诊断有重要的临床价值,也有利于早期合理的治疗方案制定及预后判断。     

早期脑梗死的临床与磁共振弥散加权成像

目的 从临床角度探讨磁共振弥散加权成像（diffusion weighted imagine,DWI)对早期脑梗死的诊断价值和确定DWI在区分常规MRI上所示的多发梗死灶中急性梗死方面的能力。方法 60例脑梗死均进行MRI常规程序及DWI（程度检查,并由4位经验丰富的医师在不了解患者临床体征的情况下进行阅片、记录出病变所在的详细的神经解剖部位,对同一层面所有的磁共振像进行比较,重点分析信号强度的病灶大小。数据经统计学分析。结果 DWI对超急性合肥市急性期脑梗死可显示T2加权像不能显示的病灶,并随时间延长显影范围逐渐增大,在T2加权像上可显示的病灶中,DWI可更清楚、更全面地显示病灶,大于T2病灶。在急性后期,常规MRI及DWI均有较清晰的影像学改变,恢复期及慢性期,DWI影像学逐渐改变变成等信号、杂信号,部分为囊性信号,且不易显示病灶。结论 DWI能非常可靠地显示超急性及急性脑梗死,而在急性后期及慢性期不如T2WI。其具有区分急性和非急性脑梗死的能力。     

Multiparametric ISODATA analysis of embolic stroke and rt-PA intervention in rat

To increase the sensitivity of MRI parameters to detect tissue damage of ischemic stroke, an unsupervised analysis method, Iterative Self-Organizing Data Analysis Technique Algorithm (ISODATA), was applied to analyze the temporal evolution of ischemic damage in a focal embolic cerebral ischemia model in rat with and without recombinant tissue plasminogen activator (rt-PA) treatment. Male Wistar rats subjected to embolic stroke were investigated using a 7-T MRI system. Rats were randomized into control (n=9) and treated (n=9) groups. The treated rats received rt-PA via a femoral vein at 4 h after onset of embolic ischemia. ISODATA analysis employed parametric maps or weighted images (T1, T2, and diffusion). ISODATA results with parametric maps are superior to ISODATA with weighted images, and both of them were highly correlated with the infarction size measured from the corresponding histological section. At 24 h after embolic stroke, the average map ISODATA lesion sizes were 37.7+/-7.0 and 39.2+/-5.6 mm2 for the treated and the control group, respectively. Average histological infarction areas were 37.9+/-7.4 mm2 for treated rats and 39.4+/-6.1 mm2 for controls. The R2 values of the linear correlation between map ISODATA and histological data were 0.98 and 0.96 for treated and control rats, respectively. Both histological and map ISODATA data suggest that there is no significant difference in infarction area between non-treated and rt-PA-treated rats when treatment was administered 4 h after the onset of embolic stroke. The ISODATA lesion size analysis was also sensitive to changes of lesion size during acute and subacute stages of stroke. Our data demonstrate that the multiparameter map ISODATA approach provides a more sensitive quantitation of the ischemic lesion at all time points than image ISODATA and single MRI parametric analysis using T1, T2 or ADCw.     

Assessment of cerebral infarction by MRI--particularly fogging effect

Fogging effect in cerebral infarction was studied by MRI in a 51-year-old male patient. Initial symptoms consisted of mild disturbance of consciousness and left hemiparesis. MRI examination was performed 2, 13 and 22 days after onset and the results were compared with CT findings during the same period. CT on day 2 revealed a wide of infarction in the region of the middle cerebral artery including the basal ganglia. The presence of a fogging effect was seen by CT on day 12 and MRI revealed a high signal intensity in the region of the basal ganglia in T 1 image, a high signal intensity in the peripheral region and a low signal intensity in the center in T 2 image. It was possible to define the lesion as the ordinary infarcted lesion by the subsequent CT and MRI. MRI indicated the infarct lesion was to be a high signal intensity in T1 image and a high signal intensity in the periphery and a low signal intensity in the center in T 2 image. It was concluded that these findings indicated hemorrhage, strongly suggesting that the cause of the fogging effect was hemorrhagic infarction.     

Early detection of ischemic lesions in the super-acute phase of ischemic cerebrovascular diseases by imaging]

A thrombolytic agent, recombinant tissue plasminogen activator (rt-PA), was recently approved in Japan for use on patients within 3 hrs of the onset of cerebral infarction. In order to salvage cerebral tissue after an ischemic insult, it is crucial to detect the ischemic lesion before it becomes irreversible and to detect the core and penumbra areas of the lesion for guidance in selecting the suitable therapy. In this symposium we discuss the detection of ischemic lesions using plain CT, perfusion CT, and MRI. In the section on plain CT, we present a typical case with early CT signs. In the section on perfusion CT, we report on the feasibility and limitation of the technique for the diagnosis of acute cerebral infarction. In the section on MRI, we study the usefulness of DWI for the early and highly reliable detection of ischemic stroke.     

Diagnosis of acute cerebral infarction using diffusion-weighted imaging by low field (0.2 T) magnetic resonance image]

The purpose of this study is to confirm the diagnosis of acute cerebral infarction on diffusion-weighted imaging using low field (0.2 T) magnetic resonance image(MRI). Acute cerebral infarctions in 51 patients were examined on diffusion-weighted imaging using low field MRI within 48 hours after clinical symptoms. Diffusion-weighted imaging was examined using line scan method. Twenty-four cases were cortical infarction, and twenty-two cases were perforating infarction. In five cases out of 51 cases, ischemic regions were not detected as abnormal high signal intensity area on diffusion-weighted imaging. Four cases of no abnormal detection were transient ischemic attack, and the other one was a perforating infarction. The earliest detection time in cortical infarction cases was 1 hour and 20 minutes. On the other hand, the earliest detection time in perforating infarction cases was 3 hours. Detective ability for acute cerebral infarction on diffusion-weighted imaging by low field MRI was depending on both size and lesion of infarction. That is to say, either small size or brain stem infarction was hard to detect. Thin slice and vertical slice examination for the infarction may improve to diagnose in low field MRI. Our conclusion is acute cerebral infarction was able to be diagnosed on diffusion-weighted imaging by low field as well as high field MRI.     

MRI findings of moyamoya disease in children]

Magnetic resonance imaging (MRI) findings were evaluated in two cases with moyamoya disease. A twelve-year-old girl and a five-year-old boy were admitted to our hospital with the complaints of transient ischemic attack. They were diagnosed as having moyamoya disease by cerebral angiogram. MRI clearly presented cerebral infarction by T2-weighted imaging and multiple small round or tortuous hypo_signal areas around the basal ganglia by proton density weighted imaging. These findings were consistent with moyamoya vessels shown by cerebral angiogram. Moyamoya vessels were visualized more clearly on proton density weighted imaging than on T1-weighted imaging. MRI is less invasive than cerebral angiogram and repeated safely. It might play an important role in a follow-up study of morphological changes on moyamoya vessels.     

Comparison of diffusion-weighted MRI and CT in acute stroke

OBJECTIVE: To compare diffusion-weighted MRI (DWI) and CT with respect to accuracy of localizing acute cerebral infarction; sensitivity, specificity, and interrater reliability for identifying more than one-third middle cerebral artery (MCA) territory involvement; and correlation of acute lesion volume with final infarct volume. METHOD: Nineteen consecutive stroke patients underwent CT and DWI within 7 hours of stroke onset and a follow-up DWI examination 36 hours after symptom onset, which served as the "gold standard" for lesion location and extent of MCA involvement. Each scan was evaluated for acute ischemic lesions by two experienced observers. After 30 days, T2-weighted MRI was obtained for assessment of the final infarct volume. RESULTS: The acute CT and DWI scans were obtained on average 2.6 and 5.1 hours after symptom onset. On DWI the acute lesion was identified correctly in all instances and on CT it was identified correctly in 42 to 63% of patients. Sensitivity for detection of more than 33% MCA involvement was better for DWI (57 to 86%) than for CT (14 to 43%), whereas specificity was excellent for both. Interrater reliability was moderately good for both (kappa, 0.6 for DWI; 0.5 for CT). A positive correlation (r = 0.79; p = 0.001) existed between lesion volume on acute DWI and final infarct volume, whereas no correlation was found between CT volume and final infarct volume. CONCLUSION: When compared with CT, DWI was more accurate for identifying acute infarction and more sensitive for detection of more than 33% MCA involvement. In addition, lesion volume on acute DWI, but not on acute CT, correlated strongly with final infarct volume. Additional studies are required to demonstrate whether these advantages of DWI are clinically relevant in the management of patients with acute stroke.     

CT灌注成像联合CT血管造影诊断超早期缺血性脑血管病的价值

目的 研究CT灌注成像(CTPI)联合CT血管造影(CTA)对超早期缺血性脑血管病(ICVD)的诊断价值。方法 对46例ICVD患者，在发病6h内进行头颅CT平扫、CTPI及CTA检查。结果 (1)CT平扫：显示低密度灶5例，未见异常41例；(2)CTPI：脑血流灌注正常16例，异常30例；(3)CTA：27例患者大脑中动脉(MCA)、大脑前动脉(ACA)不同程度狭窄，2例MCA明显变细，17例CTA图像正常；(4)25例大、中体积脑梗死患者CTPI图像均显示相应灌注缺损区，CTA均显示血管狭窄或闭塞。9例小体积脑梗死患者中，CTPI显示灌注缺损区5例，正常4例；CTA显示血管狭窄2例，正常7例。12例短暂性脑缺血发作(TIA)患者CTPI均正常，2例CTA显示MCA明显变细，远侧血管网增多；其余10例正常。结论 CTPl联合CTA能够超早期诊断ICVD，并可鉴别TIA及不同梗死体积的脑梗死。