【作者】 张水兴；

【导师】 梁长虹；

【作者基本信息】 第一军医大学 ， 医学影像与核医学， 2007， 博士

【摘要】 研究目的1．探讨SPIO应用于MR脑灌注成像的可行性。2．研究SPIO在MR脑灌注成像的方法学及质量控制；优化选择其应用于PWI的最适剂量。3．与Gd-DTPA相比较，探讨SPIO在大鼠超急性脑梗塞MRPWI的应用价值。4．探讨SPIO灌注成像联合弥散加权成像对大鼠超急性脑梗死再灌注的评价作用。材料与方法1．健康新西兰大白兔30只，随机法平均分为A、B、c、D、E五个小组，每小组各6只。其中A、B、C、D四个小组分别给予不同剂量的SPIO（4umolFe／kgBW，8umolFe／kgBW，16umolFe／kgBW，32umolFe／kgBW），E组设为对照，给予0.2mmol／kgBW的Gd-DTPA。全部动物行磁共振灌注成像（MR PWI）扫描，获得相应信号强度-时间曲线图并分别计算灰质、白质的SRR_max和rCBV值，进一步比较其Q_rCBV和Q_SRRmax值。MR检查结束后，B、D、E三组各取1只实验兔脑切片行普鲁士蓝染色。2．30只Wistar大鼠，随机法平均分成A₁、B₁两组，A₁组为8umolFe／kg体重SPIO MR PWI组，B₁组为0.2mmol／kg体重Gd-DTPA MR PWI组，两类不同对比剂剂量的选择是以在正常脑组织的MR PWI中获得相同的最大信号强度变化为标准。全部动物均在左侧大脑中动脉栓塞时间一小时后行MR PWI扫描。PWI原始图像重建获得病灶中心区以及脑缺血半暗带CBV、CBF、MTT参数形态图。比较两组各项参数变化并与病理检查及红四氮唑染色（TTC）对照。3．30只Wistar大鼠，随机法平均分成A₂、B₂两组，分别于左侧大脑中动脉栓塞时间1h、5h后再灌注2h，于再灌注前后分别行PWI、DWI和常规FSE T₂WI、SE T₁WI扫描，PWI扫描时对比剂选用8umolFe／kg体重的SPIO；PWI和DWI原始图像重建获得ADC、CBV、CBF、MTT参数形态图。观察各栓塞时间点再灌注2h后各项参数变化并与病理检查及红四氮唑染色（TTC）对照。4．对比剂：本实验所用SPIO为Resovist，由先灵公司提供。Resovist又名SHU555A（ScheringAG Berlin，Germany．国内相应产品的商品名为内二显），是由羧基右旋糖苷（Carboxydextran）包裹的氧化铁颗粒，平均直径61.1nm，氧化铁核心颗粒直径4.2nm，浓度为0.5mmol Fe／ml。外被的羧基右旋糖苷使其具有良好的水溶性及稳定性，另外还含有40mg／ml甘露醇及2mg／ml乳酸，37℃时pH值6.5。结果1．SPIO能快速团注，在四个不同剂量的SPIO都能对正常兔脑灰白质有良好的分辨。各组相应参数值(Q_rCBV／Q_SRRmax)分别为：1.98±0.07／1.85±0.11，2.09±0.11／1.88±0.06，2.09±0.07／2.06±0.25，1.50±0.01／1.49±0.09，2.05±0.03／1.94±0.12。A、B、C三组（4umolFe／kgB W，8umolFe／kgBW，16umolFe／kgBW）随着对比剂剂量的加大，Q_rCBV值和Q_SRRmax值未见显著性差异；而D组（32umolFe／kgBW）Q_rCBV值和Q_SRRmax值显著低于A组（P＜0.01）。2．SPIO在四个不同剂量组均获得满意的信号强度-时间曲线图。但当剂量达到一定范围时（16umolFe／kgBW以上），随着注射剂量的增加，灌注的信号强度-时间曲线显示信号强度恢复到稳态水平的距离加大，我们将此现象称为“信号丢失”，C组（16umolFe／kgBW）及D组（32umolFe／kgBW）分别为10％、20％。3．静脉注射SPIO 6小时后D组（32umolFe／kgBW）实验兔脑切片Prussian blue染色显示胞浆中含有铁颗粒，而注射SPIO 1小时后B组（8umolFe／kgBW）实验兔脑切片Prussian blue染色呈阴性。4．A₁、B₁两组大鼠在脑缺血中心区以及病灶边缘区（即影像半暗带）所获得的信号-时间曲线基本一致，分别比较各兴趣区rCBV、rMTT及TTP值，均无显著性差异。5．A₂、B₂两组再灌注2h后ADC值轻度降低或基本不变；A₂组再灌注后2h DWI显示病灶范围稍有减小，B₂组则无明显缩小。A₂组再灌注后影像半暗带区PWI各参数指标恢复和维持正常，而B₂组的信号强度-时间曲线图有3种表现，分别为高灌注、低灌注和正常灌注。结论1．SPIO应用于MR脑灌注是可行的，适宜剂量范围在4～16umolFe／kgBW，推荐最适剂量为8umolFe／kgBW。2．在急性脑梗塞的MRPWI应用中，SPlO与Gd-DTPA同样有效，且所需剂量更小，因此，SPIO在颅脑灌注具有广阔的应用前景。3．在超急性脑梗死再灌注可限制病灶进一步扩大，保护缺血半影区。应用SPIO磁共振脑灌注成像联合MR DWI能反映急性脑缺血再灌注后脑损伤的变化，同时又能反映再灌注后脑组织血流灌注情况。4．高剂量组SPIO（32umolFe／kgBW）铁颗粒能透过正常实验兔血脑屏障，可能与多种转运机制有关。更多还原

【Abstract】 Objective1. To study the feasibility of cerebral perfusion weighted imaging（PWI） using superparamagnetic iron oxide particles in normal rabbits.2. To investigate the methodology and quality control of cerebral MR PWI using superparamagnetic iron oxide particles, and a prospective study was undertaken to determine the proper contrast agent dose of SPIO used in PWI.3. To compare the evaluation of perfusion weighted imaging（PWI） using Gd-DTPA and the superparamagnetic iron oxide particles in the experimental model of hyperacute cerebral infarction in rats.4. To assess the role of diffusion-perfusion MRI using SPIO in evaluating the experimental model of hyperacute cerebral infarction reperfusion in rats.Materials and Methodes1. All 30 rabbits were randomly divide into 5 groups（n=6 for each）, group A, B, C, D were divided according to the different dose of SPIO（4, 8, 16 and 32umolFe/kgBW） and group E was operated for control study with 0.2mmol/kgBW Gd-DTPA. The dynamic MR perfusion imaging sequence was acquired in each group. The signal intensity time curves were analyzed in gray matter and white matter, the parameters (rCBV, SRR_max, Q_rCBV, Q_SRRmax) were calculated and compared in all groups and correlated with control group. The pathologic examination of Prussian blue was practised in three normal rabbits coming from group B, D and E.2. All 30 Wistar rats were randomly divided into 2 groups（n=15 for each）, group A₁, and B₁ for the different contrast agents PWI. After occluding the left middle cerebral artery with thread about 1 hour in all rats, the dynamic MR perfusion imaging sequence was acquired after intravenous bolus injections of 8umolFe/kgBW SPIO in group A₁ and 0.2mmol/kgBW Gd-DTPA in group B₁, respectively. The doses were chosen to obtain similar maximum signal change in normally perfused brain. The perfusion parameters at the regions of interest（ROI） in the core area and the penumbra area with ischemia lesion on the perfusion image were measured and compared. The data were correlated with pathologic findings and TTC stain.3. All 30 Wistar rats were randomly divide into 2 groups（n=15 for each）, group A₂ and B₂, which were divided according to time intervals of 1 hour and 5 hours after occluding the left middle cerebral artery with thread and reflowed about 2 hours. The MR sequences included diffusion weighted imaging（DWI）, perfusion weighted imaging（PWI）, FSE T₂WI, SE T₁WI during their occlusion and 2 hours after reperfusion. The perfusion parameters were calculated and correlated with light, electron microscopic findings and TTC stain.4. Contrast medium: Resovist was an alternative SPIO in our study. Resovist compromised SPIO microparticles coated with carboxydextran and an overall hydrodynamic diameter of 61.1 nm as measured with photon-correlation spectroscopy. The polycrystalline iron oxide core consisted of multiple single crystals, each 4.2nm in diameter as measured with electron microscopy. The carboxydextran coating ensured aqueous solubility of the microparticles and prevented aggregation. Resovist contained 0.5mmol/L of iron per liter, including 40mg/mL mannitol and 2mg/mL of lactatic acid, adjusted to a PH of 6.5 at 37℃.Results1. SPIO enabled rapid injections and a dose-dependent strong reduction in gray and white matter signal intensity in all groups. The parameters (Q_rCBV/Q_SRRmax) values were 1.98±0.07/1.85±0.11, 2.09±0.11/1.88±0.06, 2.09±0.07/2.06±0.25,1.50±0.01/1.49±0.09 and 2.05±0.03/1.94±0.12 for group A, B, C, D and E, respectively, without significant difference in group A, B and C and with significant difference between group A and D（P＜0.01）.2. The signal-time curve could be obtained satisfactorily through MR PWI in all groups. A decrease in normalized signal instensity of approximately 10% and 20% remained for the duration of the acquisitions after intravenous adminastration of 16umolFe/kgBW and 32umolFe/kgBW, which was defined as signal drop.3. The iron particles on Prussian blue stain was found within the brain cells after intravenous administration of 32umolFe/kgBW about 6 hours, but none was found in group B（SumolFe/kgBW） at 1 hour.4. The similar first-passage profiles were found in the core area and the penumbra area with ischemia lesions in this rat stroke model for Gd-DTPA and SPIO. The parameters （CBV, MTT, TTP） values of PWI for ischemic penumbra in group A₁ and B₁ had not statistical disparity.5. In groups A₂ and B₂, ADC was slightly decreased or unchanged after reflow. It could be seen that the initial DWI high-intensity signal shadow disappeared slightly in group A₂ and unchanged in group B₂. Although parameters （CBV, CBF, MTT） values of PWI for ischemic penumbra in group A₂ recovered and remained normal, but in group B₂, there were 3 typical fashions of appearance after reperfusion in ischemic penumbra, which included hyperperfusion, hypoperfusion and normal perfusion respectively.Conclusion1. SPIO could be used in the study of MR perfusion weighted imaging in the brain. The proper contrast agent dose was 4～16umolFe/kgBW and the dose of 8umolFe/kgBW may be chosen firstly.2. The efficacy of the SPIO used in the MR PWI was similar to Gd-DTPA for diagnosis of the perfusion reduction in the rat stroke model. The strong susceptibility effects may be achieved with small injection volumes.3. The ischemic penumbra could be protected by recanalisation in hyperacute cerebral infarction. Combination DWI with PWI using SPIO could evaluate the extent of the ischemic lesions and detect hemodynamic changes in hyperacute cerebral infarction.4. The iron particles of SPIO could permeate blood-brain-barrier of normal rabbits after intravenous adminastration of 32umolFe/kgBW, which may be relative with multiple transport factors.更多还原