Partial rescue of the perfusion deficit area by thrombolysis

PURPOSE: To investigate the evolution of the perfusion deficit area following systemic thrombolysis with recombinant tissue plasminogen activator (rtPA) in a clinical study on acute cerebral ischemia. MATERIALS AND METHODS: We performed volumetric measurements of the acute ischemic lesions in MR images of perfusion (TTP, MTT, and rCBV) and in diffusion-weighted (DW) images, as well as the manifest stroke lesions in T2-weighted MR images on day 8. We compared the data of 29 patients who were subjected to systemic thrombolysis with those of 18 patients who were not eligible for thrombolysis. RESULTS: In the treated patients there were prominent MTT/DWI and TTP/DWI mismatches (P < 0.0006). The acute TTP volumes were smaller than the acute MTT volumes, but as large as the T2 lesions on day 8. The MTT/T2 lesion volume reduction was significant (P < 0.03) in patients who received the GPIIb/IIIa receptor antagonist tirofiban (N = 13) in addition to the low-dose rtPA. This corresponded to a greater neurological improvement compared to patients who received rtPA alone (P < 0.05). In contrast, in the nontreated patients the initial MTT and TTP lesion volumes were of similar magnitude and predicted the T2 lesions on day 8. In the treated and nontreated patients the TTP lesion signified the viability threshold of acute ischemia, which corresponded to a rCBF of 25 +/- 11 mL/100 g/min. CONCLUSION: The perfusion deficit area comprises the ischemic core that is destined to undergo necrosis, and an ischemic rim that is salvageable by systemic thrombolysis.     

DWI、MRA在急性脑缺血中的联合诊断价值

目的探讨磁共振弥散加权成像（DWI）与磁共振血管成像（MRA）在急性期脑缺血中的联合诊断价值。方法收集经临床和影像学确诊为急性脑梗死的患者40例,所有患者行常规MRI、FLIAR、DWI及MRA检查。对MRA原始图像进行最大密度投影（MIP）重建,选取病灶中心和健侧相应部位8×8像素大小区域,测定各自的表观扩散系数（ADC）,并计算rADC值。结果 40例患者的DWI图像均显示与临床症状及体征相符的病灶,尤其是在超急性期,病灶具有较高的信号强度和清晰度。MRA检查均获得清晰血管图像,结果显示动脉硬化3例,动脉狭窄或闭塞28例;40例中,24例大面积病灶的血管病变阳性率为100%。DWI显示病灶解剖定位均与MRA上血管异常解剖定位有较好的一致性。结论 DWI对脑梗死超急性期、急性期均有很高的敏感性,MRA对颅内大血管及其部分分支的狭窄或闭塞情况均能很好地显示。通过DWI和MRA联合扫描进行比较,可以对应显示同一区域脑实质和脑血管情况,进一步判定责任血管。     

脑梗死rADC值变化与临床分期相关性的初步研究

目的:分析脑梗死各临床分期的相对表现扩散系数(rADC)值变化,探讨rADC值的大小与临床分期的相关性。方法:收集22例脑梗死患者,分别于超急性期(<12h)、急性期(13～72h)、亚急性期(4～14d)、慢性期(15d)行常规序列和磁共振扩散加权成像(DWI)检查。测量各期病灶的ADC值,并计算rADC值,统计不同分期rADC值有无差异。按rADC值大小对临床各期病例进行统计,分析rADC值的大小与临床分期的相关性。结果:脑梗死rADC值在超急性期下降,急性期进一步下降;于亚急性期、慢性期逐渐上升。脑梗死病灶各期的rADC值有明显差异;脑梗死不同分期与rADC值大小有相关性。结论:根据脑梗死rADC值大小可判断其临床发病时间。     

Reproducibility of T2* blood volume and vascular tortuosity maps in cerebral gliomas.

The development of anti-angiogenic therapies for tumors has led to a demand for imaging-based surrogate markers of the angiogenic process. The utility of such markers is highly dependent on their test-retest reproducibility. This paper presents a formal assessment of the reproducibility of measurements of relative blood volume (rBV), normalized rBV (rBVnorm), and vascular tortuosity as estimated by measurement of relative recirculation (rR). The study was conducted in 11 patients with glioma who were scanned on two occasions 36-56 hours apart. The observed reliability estimates were used to calculate 95% confidence limits for detection of differences between groups and for changes in individual cases. The results show that measurement of rBV or rBVnorm in consecutive studies is statistically capable of reliably detecting changes in excess of 15% in between group studies and 25% in individual patients. Measurement of vascular tortuosity using is less reproducible but is able to confidently identify changes in excess of 30% in group studies and 35% in individuals.     

慢性脑缺血脑血流动力学的PCMRI研究

目的 应用相位对比磁共振成像(PCMRI)技术测量中老年人慢性脑缺血大脑中动脉(MCA)血流动力学参数,探讨不同程度慢性脑缺血脑血流动力学变化的模式.方法 对中老年人进行常规头颅MRI扫描,筛选出正常组12例、轻度脑缺血组16例和明显脑缺血组13例,3组均行双侧MCA PCMRI扫描,利用工作站上QFLOW软件进行后处理,获得1次心动周期内双侧MCA的时相-流速曲线及相关血流动力学参数;记录双侧MCA的血管断面面积、峰值流速(PV)、平均流速(MV)、平均流量(MF).采用SPSS17.0统计软件比较3组间血流动力学各参数的差异.结果 3组间双侧MCA血管断面面积、MV、MF及右侧MCA PV的单向方差分析比较均有统计学差异(P值均＜0.05).慢性脑缺血患者双侧MCA的时相-流速曲线较正常中老年人收缩期波峰变低、变钝、变宽,舒张期和收缩期两波峰连线变平.结论 PCMRI可反映不同程度慢性脑缺血患者脑动脉血流动力学变化模式的差异.     

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。     

Time evolution of cerebral perfusion and apparent diffusion coefficient measured by magnetic resonance imaging in a porcine stroke model

PURPOSE: To demonstrate the feasibility of sequential diffusion-weighted (DW) and perfusion-weighted (PW) magnetic resonance imaging (MRI) of a recently developed porcine stroke model and to evaluate the evolution of cerebral perfusion and the apparent diffusion coefficient (ADC) over time. Materials and Methods In five pigs, DW imaging (DWI) and PW imaging (PWI) was carried out for 7 hours after stroke onset, starting 1 hour after middle cerebral artery occlusion (MCAO). RESULTS: The DWI lesion volume increased significantly with time, and final DWI lesion volume correlated well with lesion area on histological sections (r = 0.910). T2 changes could be recognized 3 hours after stroke onset. At 1 hour the ADC ratio (ischemic lesion/contralateral side) was reduced to 0.81 in the caudate-putamen and to 0.87 in the cortex, and the cerebral blood flow ratio was reduced to 0.40 in the caudate-putamen and 0.51 in the cortex. CONCLUSION: The level of flow reduction in the caudate-putamen and the cortex after 1 hour is in good correlation with human thresholds of irreversible and reversible ischemic damage, and accordingly, this model might be a model for mechanisms of infarct evolution and therapeutic intervention.     

MRA 联合DWI对急性脑卒中动脉狭窄的诊断价值

 目的 探讨核磁共振血管成像(MRA)联合磁共振弥散加权成像(DWI)序列对急性脑卒中动脉狭窄的诊断价值。方法 选取2015-03至2018-03入院的80例急性卒中患者为研究对象,对其MRA、DWI 以及高分辨核磁血管(HR-MRA)检查结果进行回顾性分析,以HR-MRA诊断结果为金标准,将MRA及MRA联合DWI的诊断结果进行比较。结果 MRA诊断为基底动脉狭窄的灵敏度、特异度、准确率分别为50.00%、96.87%和87.50%,MRA联合DWI检查,诊断为基底动脉狭窄的灵敏度、特异度、准确率分别为75.00%、96.87%、92.50%,后者灵敏度和准确率均高于前者。MRA诊断为大脑中动脉的灵敏度、特异度、准确率分别为63.15%、70.49%和68.75%,MRA联合DWI诊断为大脑中动脉的灵敏度、特异度、准确率分别为89.47%、86.88%、87.5%,联合诊断各项指标均高于MRA诊断。结论 相比单独MRA检查,MRA联合DWI能更准确判断动脉狭窄的部位。     

Simultaneous diffusion MRI measurements from multiple perfused rat hippocampal slices.

Rat brain slices provide a controllable tissue model in which to investigate the biophysical basis of diffusion-weighted magnetic resonance (MR) signal changes observed clinically in nervous tissue after ischemic injury. This study describes a new multislice perfusion chamber that allows for the simultaneous acquisition of diffusion-weighted MR images from multiple perfused rat hippocampal slices (eight slices in the present study). These images had a signal-to-noise ratio (SNR) of 48 +/- 3 at b = 8080 s/mm(2), which was sufficient to analyze the multicomponent diffusion properties of water in rat hippocampal slices. The tissue water diffusion parameters (f(fast) = 0.527 +/- 0.041, D(fast) = 1.268 +/- 0.087 x 10(-3) mm(2)/s, and D(slow) = 0.060 +/- 0.003 x 10(-3) mm(2)/s) were stable for at least 8 hr after slice procurement (ANOVA, P > 0.05), suggesting that it may be possible to study the acute temporal evolution of diffusion changes in multiple brain slices following experimental perturbation.     

Interleukin-1 exacerbates focal cerebral ischemia and reduces ischemic brain temperature in the rat.

The proinflammatory cytokine interleukin-1 (IL-1) is a key mediator of inflammation in cerebral ischemia, but its precise mechanisms of action remain elusive. Temperature is critical to outcome in brain injury and given the importance of IL-1 in pyrogenesis this has clear mechanistic implications. IL-1 exacerbates ischemia independently of core (rectal) temperature. However, it is temperature in the ischemic brain that influences outcome and rectal temperature is likely to be a poor surrogate marker. This study tested the hypothesis that IL-1 exacerbates cerebral ischemia by increasing ischemic brain temperature. Wistar rats undergoing transient middle cerebral artery occlusion received either 4 microg/kg IL-1 (n=9) or vehicle (n=10) intraperitoneally. NMR-generated maps of brain temperature, tissue perfusion, and the trace of the diffusion tensor were collected during occlusion, early reperfusion, and at 24 hr. IL-1 significantly increased ischemic damage at 24 hr by 35% but rectal temperature did not vary significantly between groups. However, ischemic brain was 1.7 degrees C cooler on reperfusion in IL-1-treated animals (vs. vehicle) and a corresponding reduction in cerebral blood flow was identified in the ischemic striatum. Contrary to the stated hypothesis, IL-1 reduced ischemic brain temperature during reperfusion and this may be due to a reduction in tissue perfusion.     

SWI在脑静脉血管畸形诊断中的价值

目的 探讨磁敏感加权成像(SWI)在诊断脑静脉血管畸形(CVM)中的特点,以提高诊断准确率.方法 回顾分析70例CVM患者的影像资料,将SWI与常规MR对比,评价SWI对CVM检出的优越性.结果 70例患者SWI均得到明确显示,T1WI发现病灶55例,T2WI发现病灶59例,常规MR呈管状或条形流空信号,且只显示明显扩张的髓静脉及增粗的引流静脉,而SWI较常规MR更敏感更清晰地显示所有扩张的髓静脉呈放射状汇入增粗的引流静脉,呈现特征性的“水母头”状表现.结论 SWI比常规MR对CVM的检出更为敏感,结合常规MR能够做出CVM的定性诊断,有利于临床治疗及预后.     

Contrast agent dose effects in cerebral dynamic susceptibility contrast magnetic resonance perfusion imaging

Purpose

To study the contrast agent dose sensitivity of hemodynamic parameters derived from brain dynamic susceptibility contrast MRI (DSC‐MRI).

Materials and Methods

Sequential DSC‐MRI (1.5T gradient‐echo echo‐planar imaging using an echo time of 61–64 msec) was performed using contrast agent doses of 0.1 and 0.2 mmol/kg delivered at a fixed rate of 5.0 mL/second in 12 normal subjects and 12 stroke patients.

Results

1) Arterial signal showed the expected doubling in relaxation response (ΔR2*) to dose doubling. 2) The brain signal showed a less than doubled ΔR2* response to dose doubling. 3) The 0.2 mmol/kg dose studies subtly underestimated cerebral blood volume (CBV) and cerebral blood flow (CBF) relative to the 0.1 mmol/kg studies. 4) In the range of low CBV and CBF, the 0.2 mmol/kg studies overestimated the CBV and CBF compared with the 0.1 mmol/kg studies. 5) The 0.1 mmol/kg studies reported larger ischemic volumes in stroke.

Conclusion

Subtle but statistically significant dose sensitivities were found. Therefore, it is advisable to carefully control the contrast agent dose when DSC‐MRI is used in clinical trials. The study also suggests that a 0.1 mmol/kg dose is adequate for hemodynamic measurements. J. Magn. Reson. Imaging 2009;29:52–64. © 2008 Wiley‐Liss, Inc.     

正常儿童脑组织成分变化--扩散张量成像的研究

目的　应用扩散张量成像分析正常儿童脑实质的扩散特性 ,研究儿童脑组织的成熟规律。方法　对 63名正常儿童 (年龄 2d～ 9岁 )行头部扩散张量成像 ,于ADC图上测量不同部位脑组织平均扩散度 ,并对其进行统计分析。结果　 (1)婴儿期脑灰质、白质的ADC值存在显著性差异 ,ADC图可见明显灰白质对比 ;(2 )婴儿期脑白质ADC值的降低快于灰质 ;(3 )各部位脑实质ADC值均随年龄增加而降低 ,与年龄呈指数负相关 ,具有统计学意义。结论　扩散张量成像可反映活体脑组织的成分变化 ,可用于评价儿童脑发育情况     

Diffusion weighted fMRI at 1.5 T

Functional magnetic resonance imaging (fMRI) is capable of detecting task-induced blood oxygenation changes using susceptibility sensitive pulse sequences such as gradient-recalled echo-planar imaging (EPI). The local signal increases seen in the time course are believed to be due to an increase in oxygen delivery that is incommensurate with oxygen demands. To help isolate the sources of functional signal changes, the authors have incorporated various forms of diffusion weighting Into EPI pulse sequences to characterize the apparent mobility of the functionally modulated protons. Results suggest that the majority of the functional signal at 1.5 T arises from protons that have apparent diffusion coefficients that are approximately four or five times higher than that of brain tissue. This implies that significant functional signal sources are either protons within the vascular space or protons from the perivascular space that is occupied by cerebro-spinal fluid.     

MRI在脑微出血与腔隙性脑梗死相关性研究中的应用

目的:利用MRI研究脑微出血(CMBs)与腔隙性脑梗死的相关性。方法:收集颅脑MRI受检者284例,行常规MRI序列及磁敏感加权成像(SWI)序列扫描。记录CMBs及腔隙性脑梗死位置、数目,分析CMBs、腔隙性脑梗死分布位置以及病变程度,分别统计皮层-皮层下区(CSC区)、基底节-丘脑区(DGM区)、幕下区(IT区)的CMBs、腔隙性脑梗死数目并进行相应分级;再根据脑内所有CMBs及腔隙性脑梗死数目总和对每例患者进行分级,分析两者在发病部位、病变等级之间相关性,统计各年龄组CMBs、腔隙性脑梗死发生率。利用SPSS 13.0软件对数据进行统计分析。结果:284例受检者中腔隙性脑梗死215例,CMBs 97例,腔隙性脑梗死患者CMBs发生率约40%。CMBs、腔隙性脑梗死数目分别为1～93、1～41个不等;CMBs、腔隙性脑梗死具有共同的好发部位,CSC区rs=0.450,P=0.004;DGM区,rs=0.406,P=0.000;IT区,rs=0.441,P=0.000。CSC区、DGM区、IT区的CMBs病变程度随腔隙性脑梗死病变程度的升高而升高(P=0.000);脑内所有CMBs与腔隙性脑梗死病变程度呈显著相关性(P=0.000);腔隙性脑梗死、CMBs的发生率随年龄的增大而升高。结论:颅脑MRI常规扫描序列结合SWI序列检测腔隙性脑梗死和CMBs,可以更加科学指导脑血管患者的诊断治疗、跟踪观察及预后判断。     

A serial MR study of cerebral blood flow changes and lesion development following endothelin-1-induced ischemia in rats.

The vasoconstrictive peptide endothelin-1 (ET-1) has been used previously to transiently occlude the middle cerebral artery (MCA) in rats. However, the duration of the resulting reduction in cerebral blood flow (CBF) and the reperfusion characteristics are poorly understood. In this study perfusion and T(2)-weighted MRI were used together with histology to characterize the cerebral perfusion dynamics and lesion development following ET-1 injection. Twenty-two rats received an intracerebral injection of ET-1 adjacent to the MCA. CBF was reduced to 30-50% of control levels, and a significant reduction persisted for 16 h in the cortex and 7 h in the striatum. The lesion size measured by T(2)-weighted imaging at 48 h correlated with the final infarct size measured by histology at 7 d. The sustained reduction in CBF and the gradual development of the ischemic lesion resemble human stroke evolution, suggesting that this model may be useful for evaluating therapeutic agents, particularly when treatment is delayed.     

3.0TMRI常规序列及MRA对可逆性脑血管收缩综合征的诊断价值

目的：探讨 MRI 各序列与 MRA 对可逆性脑血管收缩综合征(RCVS)的诊断价值。方法回顾性分析明确诊断的5例RCVS 患者的临床资料和 MRI 及 MRA 显示的异常血管分布、形态、脑实质病变信号特点。结果5例 MRA 结果均显示颅内外大动脉呈非动脉硬化性、非炎症性、多发节段性狭窄与扩张,典型者呈“串珠样”改变,有4例并发颅脑病变,其中1例合并后部可逆性脑病综合征(PRES),局部皮层蛛网膜下腔出血1例,分水岭区脑梗死3例。5例治疗后3个月复查 MRI 及 MRA 完全恢复正常。结论MRI 及 MRA 能清楚显示脑血管形态,观察脑实质的继发性病变,对临床治疗和预后的评估具有重要的指导意义。     

Comparison of diffusion-weighted MRI and MR volumetry in the evaluation of early treatment outcomes after preoperative chemoradiotherapy for locally advanced rectal cancer

Purpose:

To compare diffusion‐weighted imaging (DWI) and magnetic resonance (MR) volumetry for predicting treatment outcomes of locally advanced rectal cancers with preoperative chemoradiotherapy (CRT).

Materials and Methods:

This prospective study was approved by our Institutional Review Board. Thirty‐four patients underwent three MR examinations: pre‐CRT (before CRT), early CRT (2 weeks after CRT initiation), and post‐CRT (before surgery). The tumor apparent diffusion coefficient (ADC), ADC increase rate, and volume reduction rate were compared between responders and nonresponders using three reference standards: downstaging, modified Response Evaluation Criteria in Solid Tumors (mRECIST), and tumor regression grade (TRG). For DWI and volumetry, differences between responders and nonresponders were assessed by receiver operating characteristic analysis.

Results:

The median early tumor volume reduction rate of responders, subgrouped by downstaging and mRECIST (47.97% and 53.97%, respectively), was significantly higher than that of nonresponders (20.94% and 20.36%; P = 0.0024 and 0.0001, respectively), but there were no significant differences in pre‐CRT ADC and early ADC increase rate using all references. When using the downstaging and mRECIST, the diagnostic performance of early tumor volume reduction rate (Az = 0.81 and 0.94, respectively) was higher than that of pre‐CRT ADC (Az = 0.55 and 0.62; P = 0.033 and 0.007) and early ADC increase rate (Az = 0.58 and 0.64; P = 0.055 and 0.01) for predicting the treatment outcome. For TRG, there were no significant differences between DWI and volumetry.

Conclusion:

Early tumor volume reduction rate at the second week after CRT initiation may be a better indicator than DWI based on the mean ADC measurements for predicting CRT treatment outcome. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.