急性脑静脉闭塞脑损伤治疗时间窗初探:DWI与病理学对照实验研究

目的:探讨急性脑静脉闭塞模型脑实质损伤治疗时间窗的存在及其意义.方法:选择新西兰大白兔28只随机分为2组(实验组24只,对照组4只),实验组动物经一侧颈内静脉注入醋酸纤维素聚合物(CAP),分别于术后1、3、6、12、24和48 h行T1WI、T2WI和扩散加权成像(DWI)检查.各时间点MR扫描后取兔脑组织做胶质纤维酸性蛋白(GFAP)表达的免疫组化研究及电镜观察.结果:DWI、T2WI、GFAP的表达和电镜检查均能显示急性脑静脉闭塞模型脑实质损伤及其变化.DWI在术后1 h即能显示脑实质病变(ADC值下降),术后3 h DWI和T2WI均能显示病变;术后6 h前,DWI上有扩散异常的脑组织容积明显大于T2WI上异常高信号区的容积(t=13.69,P＜0.01);术后12、24和48 h病变区ADC值逐渐回升,T2WI上病变容积与DWI上的扩散异常区的容积比较,差异无显著性意义(t值分别为1.467、0.996和2.017,P＞0.05).术后1 h病变区GFAP阳性细胞增多,染色加深,胞体增大,突起增粗增长,术后3～6 h变化更明显,病理学改变以血管源性水肿为主,12 h后出现脑组织大量坏死.对照组未见上述各种异常表现.结论:DWI可准确评价急性脑静脉闭塞模型脑实质损伤程度,结合GFAP的表达,在探讨急性脑静脉闭塞脑损伤的治疗时间窗的存在及其意义中具有重要价值,在其发生发展过程中确实存在潜在的治疗时间窗.     

急性脑静脉闭塞CT灌注成像的实验研究

目的观察脑静脉闭塞模型脑实质损害区CT灌注成像（CTP）变化规律,探讨该模型在该病研究中的价值。方法新西兰大白兔28只,随机分为2组（实验组24只,对照组4只）。一侧颈内静脉注入醋酸纤维素聚合物（CAP）合并双侧颈外静脉结扎术后1、3、6、12、24和48h行CTP检查对各组模型的脑血流动力学改变进行观察。结果实验组21只造模成功,其中3h及12h组各有1只在CTP上无明显异常表现,有19只CTP检查示脑血流灌注异常。术后1～3h,病变区脑血容量（CBV）轻度增加或正常,脑血流量（CBF）轻度降低,平均通过时间（MTT）稍延长;6～12h后病变中心区主要表现为CBV和CBF降低,MTT延长,而病变边缘区CBV增加或正常或轻度降低,CBF降低,MTT缩短;12～24h后病变中心区和边缘区CBV和CBF均明显降低,MTT明显延长。各时段病变中心区和边缘区的CBV%、CBF%、MTT%的差异均有统计学意义（P值均〈0.05）。对照组未见上述各种异常表现。结论 CT灌注成像可准确、敏感地反映急性脑静脉闭塞模型的血流动力学改变。     

大鼠超急性期脑缺血的磁共振扩散加权成像研究

目的：利用磁共振扩散加权成像（DWI）评价大鼠超急性期脑缺血的诊断价值。方法：12只Wistar雄性大鼠,采用线栓法制作右侧大脑中动脉闭塞（MCAO）脑缺血模型,分别于栓塞后1h和6h行大鼠冠状位磁共振DWI、T2WI和T1WI检查,并测量缺血区DWI异常高信号的体积、表观扩散系数（ADC）值,将所测值进行比较。磁共振检查结束后处死大鼠,断头取脑行TTC染色,并与DWI结果进行比较。结果：大鼠MCAO后1h进行MRI扫描右侧大脑中动脉供血区DWI可见异常稍高信号,ADC为低信号,T2WI和T1WI均未见异常信号;MCAO后6hDWI可见明显高信号,较1hADC值显著减低（P〈0.01）,DWI上梗死灶体积显著扩大（P〈0.01）,T2WI显示缺血区异常高信号,T1WI可见稍低信号。TTC染色者均显示脑梗死灶,与MCAO后6h的DWI显示脑缺血范围一致。结论：DWI对超急性期脑梗死较常规MRI敏感,是超急性期脑缺血重要的检查方法。     

猫急性脑静脉闭塞模型的MR扩散加权成像与病理学对照研究

目的用MR扩散加权成像(DWI)和病理学方法对急性脑静脉闭塞动物模型进行评价。方法家猫22只,用随机数字表法分为2组(手术组18只,假手术组4只)。采用开颅上矢状窦穿刺注射液体栓塞剂醋酸纤维素聚合物(CAP)联合双侧颈外静脉结扎制备急性脑静脉闭塞动物模型,在术后1、3、6、12、24、48h用DWI、T2WI、液体衰减反转恢复序列(fluid attenuated inversionrecovery,FLAIR)对模型行连续MR扫描,测量异常高信号最大层面相对面积(rs)比例、相对表观扩散系数(rADC)值,并和大体标本、光学显微镜及电子显微镜作对照研究。结果仅DWI能显示早期脑实质病变,3h后,DWI、T2WI及FLAIR均能显示病变,24h后,DWI呈高、等混杂信号改变。术后1h,与对照组比较,rADC下降至(50.2±6.9)%,3~12h间,rADC缓慢上升。平均上升速率每小时8.7%,12~24h间,rADC又下降,平均下降速率每小时4.75%,24~48h,rADC又缓慢上升至接近对照组的水平。1h和48h时间点,rADC差异有统计学意义(t=10.2335,P<0.01)。大体病理学14只猫上矢状窦及桥静脉及皮层静脉内见CAP凝固呈铸型改变,12h后窦旁皮层病变区被伊文思蓝不同程度蓝染。显微病理学见术后1~3h以细胞内毒性水肿为主,3~24h血管源性水肿逐渐出现并占优势,24~48h出现出血性脑梗死。假手术组4只猫均未见上述各种异常表现。结论DWI能区分脑静脉闭塞后的脑水肿类型,早期评价脑组织损伤的程度。     

猫急性脑静脉闭塞模型的建立

目的 建立一个稳定的急性脑静脉闭塞动物模型。材料与方法 家猫22只,随机分为2组(手术组18只,假手术组4只)。采用开颅上矢状窦穿刺注射液体栓塞剂——醋酸纤维素聚合物(CAP)联合双侧颈外静脉结扎制备急性脑静脉闭塞动物模型,在术后1、3、6、12、24、48h用扩散加权成像(DWI)、T2WI技术对模型行MRI扫描,并和大体标本、光镜及电镜对照研究。结果 手术组14只造模成功。由于手术误操作,1、6、12、24h组各1只实验失败。1、3、48h组各1只脑实质MRI表现阴性。24h组1只脑皮层异常信号面积太小,未做MRI定量分析。10只猫脑病变位于上矢状窦旁皮层及皮层下。仅DWI能显示早期脑实质病变,3h后,DWI、T2WI均能显示病变。大体病理学14只上矢状窦及窦旁额、顶叶桥静脉及皮层静脉内见CAP凝固呈铸型改变,12h后窦旁皮层病变区被伊文思蓝不同程度蓝染。显微病理学见术后1～3h以细胞内毒性水肿为主,3～24h血管源性水肿逐渐出现并占优势．24～48h出现静脉性脑梗死、脑出血。假手术组4只均未见上述各种异常表现。结论 上矢状窦穿刺注射CAP联合双侧颈外静脉结扎制备急性脑静脉闭塞动物模型的方法是可行的。     

超急性脑梗死再灌注扩散加权-灌注磁共振成像及病理变化

目的应用扩散-灌注(DWI-PI)磁共振成像技术对改良线栓法建立的超急性脑梗死再灌注模型进行实验研究,并与病理结果对照.明确该技术对超急性脑梗死再灌注的评价作用.材料与方法 50只SD大鼠,随机分成5组,A组(10只)行假手术作对照,其余按栓塞时间30 min、1、3、6 h均分成B、C、D、E 4组;行DWI、PI和常规质子密度加权成像(PDWI)、T2WI、T1WI扫描;DWI和PI原始图像重建获得表观扩散系数(ADC)、脑血容量(CBV)、脑血流量(CBF)、平均通过时间(MTT)参数形态图.观察各栓塞时间点和再灌注2、24 h后各项参数变化,并将其结果与四氮唑红(TTC)染色和病理观察对比.结果 A组DWI、PI成像无异常信号,病理观察和TTC染色无变化.B组再灌注2 h DWI高信号消失,ADC值恢复正常化(88.27±1.92)%,24 h继发性ADC值降低和DWI高信号;C组再灌注2 h后ADC值轻度升高,24 h明显降低;D、E组再灌注2、24 h ADC值轻度降低或基本不变;各组再灌注后24 h DWI显示病灶范围无明显扩大.A、B组再灌注后PI各参数指标(CBV、CBF、MTT)恢复和维持正常,而D、E组的信号强度-时间曲线图有3种表现,分别为高灌注、低灌注和正常灌注.超急性脑梗死再灌注后DWI显示的缺血范围与TTC异常染色(白色)范围无显著性差异(方差分析,P＞0.05).结论在超急性脑梗死中大脑中动脉栓塞30 min再灌注后初次DWI异常信号消散是暂时的,以后会发生继发性DWI异常信号,再灌注后初次DWI异常信号消散区24 h后观察到神经元坏死;再灌注可限制病灶进一步扩大,保护缺血半影区.     

超急性脑梗死再灌注弥散加权--灌注磁共振成像实验研究

目的　应用弥散 -灌注磁共振成像技术对改良线栓法建立的超急性脑梗死再灌注模型进行实验研究。明确该技术对超急性脑梗死再灌注的评价作用。方法　 90只SD大鼠 ,随机分成 5组 ,A组 ( 10只 )假手术做对照 ,其余按栓塞时间 3 0min、1、3、6h均分成B、C、D、E 4组 ;行DWI、PI和常规T2 WI、T1WI扫描 ;DWI和PI原始图像重建获得ADC、CBV、CBF、MTT参数形态图。观察各栓塞时间点再灌注 2、2 4h后各项参数变化。结果　A组DWI、PI成像无异常信号。B组再灌注 2hDWI高信号消失 ,ADC值恢复正常化 ( 88.2 7%± 1.92 % ) ,2 4h继发性ADC值降低和DWI高信号 ;C组再灌注 2h后ADC值轻度升高 ,2 4h明显降低 ;D、E组再灌注 2、2 4hADC值轻度降低或基本不变 ;各组再灌注后 2 4hDWI显示病灶范围无明显扩大。A、B组再灌注后PI各参数指标 (CBV、CBF、MTT)恢复和维持正常 ,而D、E组的信号强度 -时间曲线图有 3种表现 ,分别为高灌注、低灌注和正常灌注。结论　在超急性脑梗死中MCAo 3 0min再灌注后初次DWI异常信号消散是暂时的 ,以后会发生继发性DWI异常信号 ;再灌注可限制病灶进一步扩大 ,保护缺血半影区     

家犬脑挫裂伤扩散加权成像研究

目的:探讨脑挫裂伤的扩散加权像(DWI)表现及其价值。方法:家犬10只,200g砝码1.3m高以自由坠落方式复制脑挫裂伤动物模型,分6个时间点(1h、24h、72h、5天、8天和14天)行常规MRI及DWI检查,各时段检查结束后处死家犬,取伤处脑组织行病理检查。结果:伤后1~24h,DWI上挫伤周围带扩散受限ADC值降低(P=0.001,P=0.000,P<0.05),呈环状或不规则点、片状高信号,病变中心不均匀低信号。DWI比T2WI显示病变的范围更大且更清楚。病理示局部点状出血,灶性坏死,神经细胞肿胀。伤后72h~5天,DWI上信号强度稍低,ADC值开始升高;高信号周围深部白质水肿区扩散不受限,ADC值升高(P=0.001,P=0.002,P<0.05);T2WI较DWI显示病变范围大。病理示炎性细胞浸润,可见血管周围炎、肉芽及纤维瘢痕形成。此后ADC值逐渐升高,14天时无统计学意义(P=0.119,P>0.05)。炎性反应及胶质增生更加显著,可见肉芽肿形成。结论:DWI能从分子水平动态反映脑挫裂伤的病理生理变化,急性期DWI较T2WI显示病变敏感,范围更大,有利于了解脑挫裂伤的严重程度。     

64层螺旋CT脑灌注成像评价急性脑梗死溶栓前后脑血流动力学改变

目的探讨64层螺旋CT脑灌注成像(CTP)在评价急性脑梗死溶栓疗效中的应用价值。资料与方法20例急性脑梗死患者于发病3~10h行常规CT平扫和CTP检查,其中16例行静脉溶栓、4例行动脉溶栓治疗。溶栓后2~7天复查CT平扫和CTP。对溶栓治疗前后病变区的脑血流量(CBF)、脑血容量(CBV)和达峰时间(TTP)进行定性和定量比较分析。结果20例中5例头颅CT平扫发现早期脑梗死征象,15例常规CT平扫未发现异常,CTP均发现与临床症状对应的脑灌注异常区,表现为CBF、CBV降低,TTP延迟。溶栓后15例脑灌注异常范围缩小,CBF和CBV增加,TTP缩短;3例脑灌注异常区范围扩大,CBF、CBV进一步降低,TTP延迟更加显著;2例出现局部过度灌注。统计学分析结果显示溶栓治疗后多数患者脑灌注情况明显改善,缺血边缘区CBF和TTP与溶栓前差异有统计学意义(P<0.05),缺血中心区CBF和CBV与溶栓前差异无统计学意义(P>0.05)。结论脑CTP检查能够观察溶栓治疗前后脑血流动力学指标的变化,为评价急性脑梗死患者的溶栓疗效提供重要依据。     

急性脑静脉闭塞磁共振扩散张量成像的实验研究

目的 对急性脑静脉闭塞模型进行磁共振扩散张量成像(DTI),观察脑实质损害的扩散规律及脑白质纤维束的完整性.材料与方法取家猫30只随机分为手术组(n=24)和假手术组(n=6).手术组制备急性脑静脉闭塞动物模型,假手术组仅行开颅上矢状窦暴露.术后采用常规MRI和DTI对各组模型脑实质损害病灶进行连续动态观察,测最病变区的平均扩散系数(ADCav)和各向异性分数(FA)值,计算病变区与健侧区的ADCav、FA比值.用纤维示踪技术(FT)显示脑白质纤维柬的完整性,并与病理学对照.结果 手术组24只猫,9只常规MRI检查为阴性;15只猫脑实质出现异常信号,术后1 h ADCav值较健侧降低,3 h后ADCav值较健侧逐渐增高,12 h后增高明显.FA值于术后各时问点均降低.各时间点病变区与健侧ADCav、FA值差异有统计学意义(P<0.05).各时间点ADCav、FA比值差异有统计学意义(F值分别为62.07、9.37.P<0.05).术后1 h,FT显示脑白质纤维束移位和穿过病灶区,6 h后脑白质纤维束断裂、破坏,12 h后脑白质纤维束于病灶边缘处中断.术后1 h病灶区出现细胞毒性脑水肿,3 h后以血管源性水肿为主,12 h后出现静脉性脑梗死、脑出血.假手术组未见上述异常表现.结论 DTI能清楚显示并定量判断急性脑静脉闭塞脑实质损害的动态变化规律,FT能更好地显示脑白质纤维柬的受损和移位.     

Ultrasound contrast agents: properties, principles of action, tolerance, and artifacts

The concept of contrast imaging was introduced to ultrasound almost 30 years ago. The development of ultrasound contrast agents (USCAs), initially slowed by technical limitations, has become more dynamic during the past decade. The ideal USCA should be non-toxic, injectable intravenously, capable of crossing the pulmonary capillary bed after a peripheral injection, and stable enough to achieve enhancement for the duration of the examination. While satisfying cost-benefit requirements, it should provide not only Doppler but also gray-scale enhancement. Already, Doppler examinations are improved by using USCAs when studying deep and small vessels, vessels with low or slow flow, or vessels with a non-optimal insonation angle. Ultrasound contrast agents also enhance detection of flow within abnormal vessels, including tumor vascularization and stenotic vessels, and provide better delineation of ischemic areas. Research is focusing on the development of specific contrast imaging sequences that allow detection of tissue enhancement similar to that obtained with CT or MRI. These sequences take advantage of the nonlinear behavior of the microbubbles within the ultrasound field, bringing real-time perfusion imaging for liver, kidney, and the myocardium into reach. New objectives include targeted agents that could further widen USCA applications to specific delivery of active drugs such as anticoagulants or cytotoxic compounds. The combination of new generations of USCAs and new ultrasound image sequences appears to be very promising and currently represents a significant part of ultrasound research.     

A monitoring,feedback, and triggering system for reproducible breath-hold MR imaging

A technique is described that provides improved reproducibility of breath-holding for MR image acquisition by monitoring the superior-inferior (S/I) position of the diaphragm. The method incorporates detection of the level of inspiration using an MR signal, rapid display to the patient of diaphragm position to enable breath-hold adjustment, and triggering of image data acquisition once appropriate position is attained. The response time of the system is short, approximately 10 ms. Studies in six volunteers using this method demonstrate a considerable decrease in the S/I range of diaphragm position over 10 consecutive periods of suspended respiration. The mean range is 1.3 mm with the system, while it is 8.3 mm without using it is expected that this method will be of assistance in many abdominal and cardiothoracic studies that use breath-hold techniques.     

Monitoring of Clinical Imaging Guidelines Part 3: Norms,Standards, and Regulations

It is known that the use of imaging in clinical situations is not always optimal, leading to suboptimal health care and potential radiation risk. There may be overuse of imaging, underuse, or use of the wrong modality. The use of clinical imaging guidelines is likely to improve the use of imaging, but roadblocks exist. Some of these relate to regulatory oversight and mandates. There is wide variation by country and region in the regulatory setting, ranging from actual absence of regulatory authorities to mandated availability of clinical imaging guidelines in the European Community. Collaborative efforts to ensure that clinical imaging guidelines are at least available is a good starting point. Regulatory oversight and support are necessary to ensure the use of clinical imaging guidelines. Regulations should address 3 areas: availability, clinical utilization, and adherence to and revision of guidelines. The use of both internal and external audits, with the aim of both use of and adherence to guidelines and quality improvement, is the best tool for enhancing use. The major challenges that need to be addressed, collaboratively, to ensure the dissemination and use of clinical imaging guidelines are the development of regulations, of regulatory structures that can be effectively deployed, and of benchmarks for adherence and for utility.     

Ultrafast imaging: Principles,pitfalls, solutions,and applications

Ultrafast MRI refers to efficient scan techniques that use a high percentage of the scan time for data acquisition. Often, they are used to achieve short scan duration ranging from sub‐second to several seconds. Alternatively, they may form basic components of longer scans that may be more robust or have higher image quality. Several important applications use ultrafast imaging, including real‐time dynamic imaging, myocardial perfusion imaging, high‐resolution coronary imaging, functional neuroimaging, diffusion imaging, and whole‐body scanning. Over the years, echo‐planar imaging (EPI) and spiral imaging have been the main ultrafast techniques, and they will be the focus of the review. In practice, there are important challenges with these techniques, as it is easy to push imaging speed too far, resulting in images of a nondiagnostic quality. Thus, it is important to understand and balance the trade‐off between speed and image quality. The purpose of this review is to describe how ultrafast imaging works, the potential pitfalls, current solutions to overcome the challenges, and the key applications. J. Magn. Reson. Imaging 2010;32:252–266. © 2010 Wiley‐Liss, Inc.     

Ex Vivo Evaluation of Ferromagnetism,Heating, and Artifacts of Breast Tissue Expanders Exposed to a 1.5-T MR System

Three breast tissue expanders were evaluated for compatibility with MR imaging (1.5 Tesla). The metallic components of the breast tissue expanders were shown to be nonferromagnetic, heating .2°C and the artifacts varied. These results indicate that MR procedures may be performed safely in patients with these implants; however, artifacts may obscure Implant leaks or breast lesions if located near and metal portion of the breast tissue expanders.     

Diffusion and Perfusion Characteristics of MELAS (Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Stroke-Like Episode) in Thirteen Patients

Objective

We analyzed the diffusion and perfusion characteristics of acute MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode) lesions in a large series to investigate the controversial changes of the apparent diffusion coefficient (ADC) that were reported in prior studies.

Materials and Methods

We analyzed 44 newly appearing lesions during 28 stroke-like episodes in 13 patients with MELAS. We performed a visual assessment of the MR images including the ADC and perfusion maps, comparison of the ADC between the normal and abnormal areas, comparison of % ADC between the 44 MELAS lesions and the 30 acute ischemic infarcts. In addition, the patterns of evolution on follow-up MR images were analyzed.

Results

Decreased, increased, and normal ADCs were noted in 16 (36%), 16 (36%), and 12 (27%) lesions, respectively. The mean % ADC was 102 ± 40.9% in the MELAS and 64 ± 17.8% in the acute vascular infarcts (p < 0.001), while perfusion imaging demonstrated hyper-perfusion in six acute MELAS lesions. On follow-up images, resolution, progression, and tissue loss were noted in 10, 4, and 17 lesions, respectively.

Conclusion

The cytotoxic edema gradually evolves following an acute stroke-like episode in patients with MELAS, and this may overlap with hyper-perfusion and vasogenic edema. The edematous swelling may be reversible or it may evolve to encephalomalacia, suggesting irreversible damage.