In Vivo Detection Of Carotid Atherosclerotic Plaque In Human By Multi-sequence Magnetc Resonance Imaging: A 3.0 Tesla MRI Study

Stroke is the second most common cause of death and major cause of disability worldwide.Vulnerable plaque in the carotid bifurcation is an important risk factor for (recurrent) stroke and is used in therapeutic decision making,which is important to be detected.Given sufficient resolution,MRI can visualize carotid plaque structure and quantify differences in morphology and composition.But there are still little 3.0T MRI study.In our study,we get the protocol in 3.0T MRI for detecting carotid atherosclerosis plaque and try to characterize the plaque.PartⅠ:Techniques for 3.0T MR imaging of carotid plaque in vivoObjective:To Establish a scan protocol for detection of carotid plaque in vivo by 3.0T MR Imaging,and then assess the value of each sequence.Materials and Methods:9 Young healthy volunteers and 6 symptomatic patients with narrow carotid are involved in this study,whose carotid artery was undergoing 3.0T MR imaging.The initial protocol was provided by GE company.With the help of engineers,we are improving the process until finally get a formal protocal.Twenty seven symptomatic patients with narrow carotid including 4 patients who underwent a CEA within a week after MRI examination were examined by a 3.0T magnetic resonance scanner using a multisequence protocol that establish previously(including 3D TOF,DIR T1WI,PDWI,T2WI).We evaluated the sequence from three aspects:range and time of examination,quality of images and capability for discriminating different component of carotid atherosclerotic plaque.Results:We get a protocal for detection of carotid atherosclerotic plaque in human in vivo by a 3.0T magnetic resonance scanner.And we teached patients and used pulse gate-control to reduc movement artifacts,used DIR(Double Inversion Recovery) before T1WI to reduce flow artifacts,used SCIC(surface coil intensity correction) for black-blood MR imaging to enhance the signal of plaque regions,used TONE for TOF to reduce pre-saturation and extend range to ensure the quality of goal sections.We also did some works to protect the patients from the harm of MRI sideeffects.Images by TOF could be used to identify the position of plaque for following scan.Images by DIR T1WI had less flow artifacts and be good at recognise intraplaque hemorrhage,but took more time to get.Images by PDWI had best quality to define plaques.Images by T2WI can be used to distinguish fibrous tissue and lipid-necrotic core.Calcification need images by black-blood and white-blood sequences to indentify.Finally we acquired 197 sections for subsequent analyse,including 21 sections compared with pathology sections.Conclusions:we've gotten the protocal for the detection of carotid plaque by 3.0T MR imaging in human in vivo and evaluated it.3D TOF can be used to indentify stenosis of carotid artery and locate the plaque,and were better for recognizing calcification.DIR T1WI had less flow artifacts and were better for recognizing intraplaque hemorrhage.PDWI had best quality of images and T2WI were better for recognizing fibrous tissue from lipid core.PartⅡ:Characterization of carotid atherosclerotic plaque by 3.0T MR imagingObjective:To get the characteristic of different components of carotid atherosclerotic plaque detecting by 3.0T MRI.To evaluate the capability of classifing and indentifing vulnerable plaque detected by 3.0 T MRI.Materials and Methods:197 sections detected by 3.0T MRI from former sduty including 21 sections compared with pathology sections were involoved in this part to sum up the characteristic of different components of carotid atherosclerotic plaque detected by 3.0T MRI.Based on the result and AHA classification,we grouped them into five types(typeⅢ,typeⅣ～Ⅴa,typeⅤb,typeⅤc and typeⅥ) and soft/hard plaque.Then we measured thickness of fibrous-cap,size of lipid-necrotic core, O-nrSI(Overall normalized relative Signal Intensity),overall CT value for assessment statistically.Results:We found that the same component can show varied signal intensity(SI) in a sequence,but SI of fibrous tissue was higher than lipid core's.Mainly fibrous structure has iso-SI or low SI on TOF,iso-SI or high SI on T1WI,iso-SI or high SI on PDWI and high or iso-SI on T2WI.Lipid structure 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-weighted images.Intraplaque hemorrhage have high SI on all four sequences.Though our study and articles by others,we think multicontrast MRI was needed to indentify the component and that higher SI in fibrous tissus than lipid core's was important.In vivo 3.0T multicontrast MRI is capable of classifying intermediate to advanced atherosclerotic lesions in the human carotid artery and measurement of normalized relative signal intensity can help indentifying the type of plaque.The total count of plaques through the AHA-recommended classification are as follows:typeⅢlesions 45 sections(22.84%),typeⅣ～Ⅴa lesions 26 sections(13.20%),typeⅤb lesions 4 sections(2.02%),typeⅤc lesions 96 sections(48.74%),typeⅥlesions 26 sections(13.20%),and soft plaque 52 sections(26.40%) with hard plaque 52 sections(73.60%).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.Our research demonstrated a statistically significant differences of relative signal intensity before and after normalization,so we've took the normalized relative signal intensity(nrSI) as parameters.Our data show that O-nrSI is a useful parameter to type the plaques,which required multi-sequence.Considered the interference on overall CT value by existence of calcification,we choose the images without calcification as research objects.We cannot determine which type of a plaque by CT value.So we argue that MRI is better than CT on showing composition of carotid plaque.Conclusions:In vivo 3.0T multicontrast MRI is capable of classifying intermediate to advanced atherosclerotic lesions in the human carotid artery and measurement of normalized relative signal intensity can help indentifying the type of plaque.O-nrSI was a useful parameter.