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The Study of USPIO Enhanced MRI to Detect Atherosclerotic Plaques in the Hypercholesterolemic Rabbit
[Abstract] Objective:USPIO is an MRI contrast agent, whichaccumulates in macrophages and induces magnetic susceptibility. We evaluated the ability of USPIO enhancedMRI to quantify unstable atherosclerotic plaque of hypercholesterolemia rabbits.
Methods: Atherosclerosis model had been established by double balloon aorta injury in hypercholesterolemia rabbit. The rabbits were examined by MRI with USPIO for 6 days. To define the RIO of vessel wall and detect the SNR, we draw the curve chart follow the change of SNR for one week and find the optimal time of reinforcement. To detect USPIO were swallowing in unstable atherosclerotic plaque by pathological study.
Results: Luminal irregularities are visible in the injured aorta four days after injection of USPIO in the images of MIP. The signal intensity of injured arterial wall was gradually decreasing and the lowest on the fourth day. The percentage reduction in luminal area in the injured aorta strongly correlated with the Perl-positive (y=172.1x+0.6; r=0.78; P<0.05).
Conclusions: USPIO enhanced MRI is helpful to detect the vulnerable plaque of hypercholesterolemia rabbits.
[Key word] Arteriosclerosis; plaque; Magnetic resonance imaging (MRI); Ultrasmall Superparamagnetic Particle of Iron Oxide (USPIO); animal model; Rabbit
动脉粥样硬化是系统性疾病，患者早期可无任何临床症状，但粥样硬化不稳定斑块容易破裂，形成血栓引起急性缺血症状或者是血栓脱落导致急性的血管栓塞，引发心脏猝死、中风、心肌梗死等，致死、致残率极高[1]。如果能够早期检测出不稳定斑块，将可为临床采取提前干预措施提供有力的帮助。动脉粥样硬化不稳定斑块中含有大量巨噬细胞，能够吞噬特异性对比剂超微超顺磁氧化铁微粒（ultrasmall superparamagnetic particle of iron oxide，USPIO)，在MR的磁场中产生顺磁性，在T2加权和T2*加权扫描序列上信号减低，用于判断粥样硬化斑块的稳定性[2-5]。本文旨在探索USPIO增强MRI判断粥样硬化斑块稳定性的价值。
一、材料和方法
1.动脉粥样硬化模型建立
新西兰大白兔20只，雌雄各半，体重1.8-2.2KG左右，4周龄，由上海长海医院动物实验中心提供。实验组15只，对照组5只。所有动物普通饲料饮食观察一周后，实验组动物行经髂动脉球囊内膜损伤腹主动脉[6]辅助高脂饮食（1％的胆固醇，8％猪油，10％蛋黄粉，71％的基础饲料）12周，对照组普通饲料喂养12周。
2．MRI扫描
MRI扫描均在Siemens, AVANTO 1.5T扫描仪上完成。兔腹部专用线圈。扫描范围为双肾平面之间的腹主动脉约15cm。采用True-fisp序列定位，扫描参数为TR：40s，TE:18s,flip:20°，视野（FOV）：18cm，矩阵256×128，层厚：3mm。扫描序列TSE序列的T2WI，TOF－2D及增强T2WI， TOF-2D。所有动物扫描先进行MRI平扫，然后经耳缘静脉缓慢注射对比剂USPIO（1ml/kg，用生理盐水稀释至10ml，速率0.15ml/s）进行增强MRI扫描，连续跟踪扫描6天。USPIO由东南大学生物医学工程系纳米技术与纳米材料实验室顾宁教授及张宇教授惠赠，浓度20mg/ml，直径约20nm，外包酒石酸。
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