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Basic Study of MRI in Identifying Types of Atherosclerotic Plaques with New Vessel Coils

Author: ZhaoBingHui
Tutor: LiMingHua
School: Shanghai Jiaotong University
Course: Medical Imaging
Keywords: Atherosclerotic plaque vulnerability magnetic resonance imaging dynamic contrast-enhancement Multidetetor CT Sonoraphy histopathology
CLC: R445.2
Type: PhD thesis
Year: 2008
Downloads: 193
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Abstract


Current views regard atheroslerosis as a dynamic and progressive disease arising from the combination of endothelial dysfunction and inflammation, and it’s one of the leading causes of morbidity and mortality. Especially“vulnerable plaques”, which are prone to be ruptured, . Especially“vulnerable plaques”, which are prone to be ruptured, were considered to be responsible for two thirds of acute cerebral ischemic infarction , almost heart infarction and cardiogenic sudden death . On the hand, more and more studies insisted that atherosclerotic plaque composition, rather than stenotic severity, was predominantly responsible for plaque rupture. Therefore, the need for noninvasive imaging techniques, for example MRI, multi- detector CT or vessel sonography, to screen vulnerable plaques, monitor plaque progression and the effects of drugs or intervention therapy is enormous.Modern magnetic resonance imagers with a higher magnetic field strength (1.5 or 3.0 Tesla) may offer the advantage of a better signal to noise ratio at a high spatial resolution due to new vessel coils and different contrast agent application. So it’s possible not only to image vessel wall structures and atherosclerotic plaque composition, but also to assess plaque vulnerability for MRI, which was also claimed as one leading imager in distinguishing or monitoring vulnerable plaques.The purpose of this study was to analyze the feasibility of noninvasive high resolution MRI with new vessel coils to identify and characterize vulnerable atherosclerotic plaques in iliac lesions in a rabbit model of atherosclerosis, compared with multi- detector CT and vessel sonography. And also to analyze various distinctions between vulnerable atherosclerotic plaques and stable ones in histopathology, especially the amount of monocytes, macrophages, proliferation of vascular smooth muscle cells(SMCs) and collagen fibers comparatively, correlated to the styles and percentage of dynamic contrast medium enhanced MR imaging for atherosclerotic the plaques. Last, early stage of plaques in carotid lesions in a rabbit model of atherosclerosis were also observed by histopathology, contrasted with noninvasive imagings. the feasibility of high resolution MRI with new vessel coils was also analyzed in screening and distinguishing early stage of plaques, and the potentiality for DCE MRI to monitor the changes of the plaques and the effect of drug, also compared with multi- detector CT and vessel sonography.Part I Analysis of magnetic resonance imaging with multiple contrast and dynamic contrast-enhancement in identifying vulnerable atherosclerotic plaquesMethods Forty adult New Zealand white rabbits were fed by hypercholesterolemic diet, and right iliac arteries including the common and external iliac arteries were examined by multiple contrast and DCE 1.5T MR imaging at intervals 6 to 20 weeks after balloon denudation. For multiple contrast weightings, T1-,T1-/ T2WI with fat suppression , proton density weighted(PDW) and double invention recovery (DIR) were used. Meanwhile, post DCE T1-with fat suppression images were obtained in 1, 5, 15and 25 minutes after a bolus injecting of Gd-DTPA contrast agent. And meanwhile eighteen animals were also scanned by 3.0T MRI, the scanning parameters were as the same as 1.5T MRI. Then a comparative analysis of plaque morphology and components to images was performed at histopathology.Results Eighty atherosclerotic lesions were studied which were located at rabbits’right common or external iliac arteries respectively, including 34 (42.5%) vulnerable plaques and 46(57.5%)stable plaques. From the information presented in this study, The accuracy, sensitivity and specificity of 1.5T MRI with multiple contrast weightings and dynamic contrast- enhancement for the detection of vulnerable plaques were 87.5%, 94.1% and 82.6% respectively, evidently prior to only with multicontrast weightings, which were 73.8%,82.3% and 67.4 % prospectively, p<0.05. And different characteristics were presented between vulnerable and stable plaques after a bolus agent injection. The sensitivity and specificity of 3.0T MRI were higher than 1.5T MRI, especially the accuracy of 3.0T MRA in diagnosing stenosis of artery was evidently prior to 1.5T MRA, p<0.01. However there were consistent contrast-enhancement characteristics of the plaques with 1.5T MRI and 3.0T MRIConclusion MRI with multiple contrast and dynamic contrast- enhancement (DCE) maybe has an important role in evaluating vulnerable atherosclerotic plaques, 1.5T MRI or 3.0T MRI. Especially Gd- DCE MRI is benefit to detect and differentiate vulnerable plaques according to different characteristics of contrast enhancement. And 3.0T MRA is useful in diagnosing stenosis of artery, prior to 1.5T MRA.Part II Analysis of CD31 CD68α-SMA and collagen fibers about atherosclerotic plaque, correlated to characteristics of MRI dynamic contrast-enhancementMethods Fifty-five artery plaques were selected in different arteries and examined by pathology including HE, CD68, CD31α-SMA and Masson stainings, and analyzed quantitatively., and all the plaques were classified into two groups, including twenty-six vulnerable plaques and twenty-nine stable ones. All animals were also examined by DCE 1.5T MR imaging before euthanasia, and pre- and post DCE T1- with fat suppression images were obtained in 1, 5, 15 and 25 minutes after a bolus injecting of Gd-DTPA contrast agent. And the quantity of macrophage, microvessel density,α-SMA and collagenous fibers in the plaques were analyzed and correlated to styles and percentage of contrast-enhancement MR imaging.Results the quantity of macrophage, microvessel density,α-SMA and collagenous fibers in vulnerable plaques was 8.8±1.21 %, 9.01±1.77%, 10.81±2.36%, 22.7±8.91% respectively, evidently different from stable plaques(macrophage 5.82±0.47 %, microvessel density 7.23±1.58 % ,α-SMA 12.16±3.47%, collagenous fibers 30.4±10.25%), P<0.01. On the other hand, contrast-enhancement percentage of MR imaging was positive correlation to macrophage, microvessel density(r value 0.77, 0.66), evidently contrast-enhancement percentage in 1 minutes after a bolus of Gd-DTPA was related to microvessel density (r value 0.78), and contrast-enhancement percentage in 5 minutes closely to macrophage( r value 0.83). However it’s negative to collagenous fibers(r value 0.62). In addition, the size of necrosis and intercellular substance may also influence the contrast-enhancement style.Conclusion The characteristics and style of Gd- DCE MRI were closely correlated to the quantity of macrophage, microvessel density and collagenous fibers in for artery plaques, and also it would reflect the changes of inflammatory and tissue repair in plaques.Part III Analysis of magnetic resonance imaging, Multidetector CT and vessel sonography in identifying vulnerable atherosclerotic plaquesMethods Forty-eight adult New Zealand white rabbits were divided into five groups, including normal group(eight rabbits) and four experiment groups fed with hypercholesterolemic diet (ten rabbits of each group). Each experiment group was examined by MRI, mutidetector CT and vessel sonography in six , ten, fourteen and twenty weeks after balloon denudation respectively. Meanwhile, fifteen experiment animals selected randomly were also done by DSA. Then, a comparative analysis of plaque morphology and components was performed at histopathology including HE、Masson、CD31、CD68 staining and electron microscope examination. Ninety six vessel segments were analyzed pathologically, including sixteen normal vessel segments and eighty segments of atherosclerosis, compared by all imagings.Results Eighty atherosclerotic lesions were studied which were located at rabbits’right common or external iliac arteries respectively, including 34 (42.5%) vulnerable plaques and 46(57.5%)stable plaques. From the information presented in this study, The accuracy, sensitivity and specificity of 1.5T MRI with multiple contrast weightings and dynamic contrast- enhancement for the detection of vulnerable plaques were 87.5%,94.1% and 83.9% respectively, evidently prior to that of multidetector CT and vessel sonography, p<0.01. However, there is no evident difference between MDCT and sonography. On the other hand, the sensitive and negative predictive value of MRI in detecting stable plaques were evidently also prior to MDCT and sonography. And the accuracy of MDCT angiology in diagnosing stenosis of artery was 96.3%,evidently prior to that of MRA and sonography(which was 82.5%,80.0% respectively). Due to MRA and sonography were often influenced by blood flow and the extent of arterial stenosis.Conclusion MRI with multiple contrast and dynamic contrast- enhancement (DCE) maybe has an important role in identifying vulnerable atherosclerotic plaques, prior to MDCT and vessel sonography. And MDCT angiography is a effective implement in diagnosing stenosis of artery.PartⅣThe possiblity of nonivasive imagings in identifying early atherosclerotic plaques and the effect of drug intervention Methods Forty-two adult male New Zealand white rabbits were divided into five groups, including normal group(six rabbits) and three experiment groups fed with hypercholesterolemic diet (twelve rabbits of each group). Meanwhile experiment animals were divided randomly into control group, drug intervention group A (animals were fed with atorvastatin, 5mg/kg/d)and group B(which were fed with atorvastatin 5mg/kg/d and rosiglitazone 1mg/kg/d) after balloon denudation. And thirty days late, they were all examined by MRI, mutidetector CT and vessel sonography at 30 days after balloon denudation respectively. Then, a comparative analysis of plaque morphology and components was performed at histopathology including HE、Masson、CD31、CD68 staining and electron microscope examination. In all, Eighty-four vessel segments were analyzed pathologically, including twelve normal vessel segments and seventy-two segments of early atherosclerosis, compared by all imagings.Results Seventy-two atherosclerotic lesions were studied which were located at rabbits’distal and proximate right common cervical arteries respectively, including 75.0%(54/72) early plaques(AHA I ~ III) and 25.0%(18/72) late plaques. The amount of CD68, CD31 and NF-κB in plaques of each experiment group was more than that of normal groups, and the amount of the drug intervention groups, especially group B, was evidently lower than that of control group. From the information presented in this study, The coincidence of MRI in evaluate the rank of atherosclerosis is 82.1%, higher than MDCT(67.9%)and sonography (70.2%), p<0.05. On the hand, The accuracy of MRI for the detection of early plaques were 75.8%, were also higher than MDCT(59.1%) and sonography(68.2%), p<0.05.Conclusion The pathogenesis and vulnerability of atherosclerosis, especially early plaques, is evidently related with the degree of inflammation. It would be possible to influence the speed of early plaque progress, controlling the inflammation and hyperlipemia. And MRI with early dynamic contrast- enhancement (DCE) maybe has an important role in monitoring early atherosclerotic plaques and the effect of drugs intervention.

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CLC: > Medicine, health > Clinical > Diagnostics > Diagnostic Imaging > Magnetic resonance imaging
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