MR Images Study In The Middle Cerebral Artery Stenosis

Ischemic stroke patients are not rare in China, especially in the North areas, as we all know, patients with a symptomatic stenosis of middle cerebral artery (MCA) are in high risk of future ischemic stroke. The blood flow with unilateral MCA stenosis or occlusion can be compensated by circle of Willis, and can also be compensated by the collateral circulation from cortical artery, so sometimes these patients have no clinical symptoms, just like cerebral ischemia and anoxaemia. However, cerebral ischemia and anoxaemia will occur in the brain tissue supplied by stenosis artery because of no enough collateral circulation. So it is necessary to find an accessible guideline to evaluate whether the cerebral blood flow in the lesion areas supplied by the lesion side of MCA stenosis is low or not for the selection of vascular stenting and thrombolytic therapy.Part I:The application of MR diffusion and perfusion in the cerebral middle artery stenosisObjective:To discuss the ischemic information with the MR DSC and ASL technique in the unilateral middle artery stenosis and occlusion, and confirm diagnosis value of the ASL perfusion technique in ischemic cerebravascular diseases.Materials and Methods:This study collected a total of 48 cases of TIA patients with unilateral cerebral middle artery sclerosis or occlusion and 8 healthy volunteers, all patients were performed by Siemens Trio Tim 3.0 T superconductive magnetic resonance imaging systems. ALL patients received no drug therapy prior to the study. The mean disease duration was 4.7 years (range=0.4-16.4 years). All the 48 patients with unilateral MCA stenosis were confirmed by MRA angiography. Patients were not included in the study if they have clinical neurological deficits, their most recent episode of relapse within 3 months, or presence of other brain disease. All study protocols were conducted within guidelines from our institutional review board, and consent was obtained by each patient. We performed all the patients'imagings processing blinded to clinical and any other imaging data. We coregistered the individual DWI and PWI data. We obtained the DWI lesion volumes by manually tracing around the edge of the hyperintense lesion on Siemens workstation.On the one hand, we got CBF map after the ASL scan was over. On the other hand, to get the DSC-PWI images, we transfered all raw data into perfusion software bag to get a concentration-time curve. We defined the AIF from the fitted data by averaging the concentration-time data from voxels corresponding to the lumina.We calculated maps of rCBV, rCBF, rMTT, TTP. We normalized the parameter value in each voxels used to define the AIF. An experienced stroke neuroradiologist outlined any PWI lesions visible on the color maps by identifying areas of signal that indicated reduced cerebral perfusion (reduced CBF, abnormal CBV, or increased MTT) compared with the normal perfusion distribution of the contralateral hemisphere. We had thought of the differences between two hemispheres or in the anteroposterior distribution. Each PWI parameter was outlined separately, blinded to all clinical other imaging, and other PWI data.Statistical AnalysisWe compared the median PWI lesion and PWI/DWI mismatch volumes and compared the proportion of patients with or without DWI/PWI mismatch by PWI processing method by theχ2 test. We compared the different PWI volumes with DWI lesion volumes and NIHSS score at baseline and T2-weighed imaging final infarct volume three month later. All analysis were performed in SPSS version 13 for Windows.Results:We compared perfusion data with DSC and ASL in the assessment of the lesion side, P>0.05, without significant difference. We compared the perfusion results between DSC and ASL then found:there were 32 cases in which DSC match ASL, with CBF decreased; ASL> DSC 12 cases, in which 5 cases showed ASL perfusion defects, with DSC perfusion delay; MRA showed unilateral MCA stenosis, while there was no obvious abnormalities in 16 patients in DWI,ASL and DSC. The signal-to-noise ratio (SNR) of DSC-PWI was better than that of ASL-PWI. There were 33 cases that the areas of hypoperfusion were larger than that of DWI, with ischemic penumbra.Conclusion:1,ASL as a completely non-invasive, easy to operate method, can measure CBF data, discriminating the extent of low perfusion in cerebral middle artery stenosis and occlusion,is very helpful for clinic and radiologist to obtain the perfusion information of MCA plaque.2,ASL combination with DWI, can indicate ischemic penumbra for the clinical development of effective treatment programs, can provide help to improve the prognosis of patients with MCA plaque.PartⅡ:Techniques for 3.0T MR imaging of unilateral cerebral middle artery plaqueObjective:To establish a scan protocol for detection of unilateral cerebral middle artery plaque by 3.0T MR, then access the value of each sequence.Materials and Methods:9 healthy volunteers and 56 symptomatic patients with narrow unilateral cerebral middle artery are involved in this study, whose cerebral middle artery was performed by 3.0T MR imaging. The initial protocol was provided from foreign papers. We improved the process until finally get a formal protocol.3.0T magnetic resonance scanner using a multisequence protocol that establish previously(including 3D TOF,T1WI,T2WI,PDWI and T1WI with contrast). We evaluated the sequence from three aspects:range and time of examination, quality of images and capability for discriminating different component of the cerebral middle artery atherosclerotic plaque.Results:After several times of experiences, we got a protocol for detection of cerebral middle artery atherosclerotic plaque in human in vivo by 3.0T magnetic resonance scanner.Black-blood MR imaging including T1WI,T2WI,PDWI were performed and lighten-blood MR imaging including TOF was performed by each patient. We do much works to protect the patients from the harm of MR side-effect.Images by TOF could be used to identify the position of plaque for following scan. Images by T1WI had less flow artifacts and be good at recognize intraplaque hemorrhage, T2WI can distinguish fiberous tissue and lipid-necrotic core. Calcification show low sigal in black-blood and white-blood sequences.Conclusion:We have gotten the protocol for the detection of cerebral middle artery plaque by 3.0T MR imaging.3D TOF can be used to identify stenosis of cerebral middle artery and locate the plaque, and were better for recognizing intraplaque hemorrhage. PDWI had best quality of images and T2WI were better for recognizing fibrous tissue from lipid core.PartⅢ:Characterization of cerebral middle artery plaque by 3.0T MR imaging Objective:To identify the differences of the different components of cerebral middle artery plaque detected by 3.0T MR scanner. To evaluate the capability of classifying and discriminating vulnerable plaque detected by 3.0T MR.Materials and Methods:260 sections detected by 3.0T MR from former study were retrospectively analyzed to sum up the characteristic of different components of cerebral middle artery plaque detected by 3.0T MR. We classified all the cases into five groups types and discriminated soft from hard plaque.We measured the thickness of fibrous-cap, size of lipid-necrotic core.Results:We found that the same componets can show different signal intensity(SI) in different sequence, and SI of fibrous tissue was higher than lipid core's. Mainly fibrous strctues show iso-SI or low SI on TOF, iso-SI or high SI on T1WI, iso or high SI on PDWI and high or iso-SI on T2WI. Lipid structures has iso or low SI on TOF, low/high or iso-SI on T1WI, iso-SI or low SI on PDWI and iso-SI or low SI on T2WI.Calcification have low SI on all contrast-weighed images.Intraplaque hemorrhage have high SI on all sequence.We think multi times contrast enhancement are important in discriminating the components of cerebral middle artery plaque.Multi times contrast enhancement is capable of classifying intermediate to advanced atherosclerotic leisions in the cerebral middle artery plaque and measurement of normalized relative signal intensity can help identifying the type of plaque.The total plaques were classified different groups according to AHA～recommended classification. The thickness of the fibrous cap at the thinnest part and the percentage of lipid-necrotic core in plaque have statistics difference among varied type of plaque.Conclusion:3.0T MR scanner is capable of classifying intermediate to advanced atherosclerotic leisions in the cerebral middle artery plaque and measurement of relative signal intensity can help discriminating the type of plaque.