急性、亚急性、慢性心肌梗塞在Gd—DTPA增强MRI上的信号表现

目的：通过对Gd-DTPA增强前后MRI上急性、亚急性和慢性心肌梗塞区的心肌信号变化规律的总结，期望对心肌梗塞作出定性定量的诊断。材料和方法：32例不同时期心肌梗塞及12例正常心脏做了Gd-DTPA增强前后MRI扫描，增强后为动态观察。结果：10例急性心肌梗塞和10例亚急性心肌梗塞均见到心肌的异常强化信号；12例慢性心肌梗塞中仅4侧(38%)见到异常强化信号。正常心肌为均匀一致的轻度信号增强，不同时期的心肌梗塞异常信号范围不同，信号率的动态变化规律也不同。结论：Gd—DTPA增强MRI及动态观察可以显示心肌梗塞的部位，范围及为心肌梗塞的分期提供依据．     

急性心肌梗塞早期溶栓治疗成功

急性心肌梗塞溶栓的疗效用梗塞区再灌注、心肌活力及灌注成功后心肌细胞功能有否恢复等指标来评价。正电子发射体层摄影(PET)、MRI和频谱图是有潜力的无创技术。新近证实,用~(85)铷能确定心肌灌注程度,~(19)氟脱氧葡糖或~(13)碳软脂酸能评价心肌代谢。Saeed等指出,新MR造影剂磷酸吡哆醛锰能确定心肌梗塞和再灌注的部位。用闭塞鼠的冠状动脉产生心肌梗塞模型,给顺磁剂后2分时,图象上梗塞区信号弱,正常心肌信号增强。2分及以后,正常心肌增强小,梗塞区和再灌注区增强明显。区别闭塞和再灌注心肌梗塞也可用其他顺磁剂,CT用碘造影剂。最近Saeed等用磁化造影剂显示,灌注区信号消失,闭塞梗塞区亮,再灌注区暗。但上述影象技术并未用于临床。     

急性、亚急性、慢性心肌梗塞在Gd－DTPA增强MRI上的信号表现

通过对Ｇｄ－ＤＴＰＡ增强前后ＭＲＩ上急性、亚急性和慢性心肌梗塞区的心肌信号变化规律的总结，期望对心肌梗塞作出定性定量的诊断。材料和方法：３２例不同时期心肌梗塞及１２例正常心脏做了Ｇｄ－ＤＴＰＡ增强前后ＭＲＩ扫描，增强后为动态观察。结果：１０例急性心肌梗塞和１０例亚急性心肌梗塞均见到心肌的异常强化信号：１２例慢性心肌梗塞中仅４例（３３％）见到异常强化信号。正常心肌为均匀一致的轻度信号增强。不同时期的心肌梗塞异常信号范围不同，信号率的动态变化规律也不同。结论：Ｇｄ－ＤＴＰＡ增强ＭＲＩ及动态观察可以显示心肌梗塞的部位、范围及为心肌梗塞的分期提供依据。     

急性心肌梗塞的MRI特征及其超微病理基础

目的　探讨急性心肌梗塞后不同心肌损伤区的MRI特征及其超微病理学基础。方法　结扎兔冠状动脉左前降支 2 4h制作AMI模型 10只 ,行常规MRI、对比剂动态增强MRI、电影MRI及多巴酚丁胺负荷试验。放射微球测定心肌血流量 ,伊文氏蓝和TTC染色确定缺血和梗塞心肌 ,并制作电镜标本观察肌原纤维和线粒体的改变 ,测定病变值和对损伤程度分级。结果　AMI后T1信号无明显改变 ,T2 信号增高 ,40 %可见病变局部心肌壁变薄 ,60 %可见病变邻近左室腔内异常血流高信号 ;正常、缺血和梗塞心肌动态增强时间 -信号强度曲线表现不同 ;cine -MRI表现为局部室壁变薄、运动减弱 ,多巴酚丁胺负荷表现为室壁变厚、运动增强。病变心肌较正常肌含水量显著增高而血流显著减少。正常、缺血及梗塞心肌线粒体体密度、数密度存在显著差异。结论　AMI的MRI表现与心肌超微结构损伤程度及残余血流量有关     

造影增强MRI对急性心肌梗塞的评价

ＭＲＩ技术的发展及及ＭＲＩ造影剂的应用，能有效地评价急性心肌梗塞：①可以直接显示梗塞灶，表现为Ｔ２加权上病灶信号高于正常心肌，增强后病灶信号增强大于正常心肌。②可以区别梗塞心肌是否获得再灌注，表现为Ｔ２加权象上再灌注梗塞心肌信号高于非再灌注心肌，增强再灌注后梗塞心肌信号强化更明显，倾向于均匀强化；非再灌注心肌磁化相对较弱，倾向于不均匀强化；但两信号改变有交叉重叠。③可以测定梗塞大小及其动态变化。     

Gd-DTPA动态增强MRI评价心肌微血管损伤

目的：探讨Gd-DTPA动态增强MRI评价心肌微血管损伤的可行性。方法：制作急性犬心肌梗死动物模型，在活体上用放射微球^99Tc—MAA测量心肌血流量，0．5％伊文蓝染色区分缺血心肌；心脏离体后用3％TTC染色区分梗死心肌，SP免疫组化染色观察心肌微血管并计算微血管体积分数。犬离体心脏左冠状动脉插管后作MRI平扫及Gd—DTPA动态增强扫描，测量正常、缺血和梗死心肌的信号强度，绘制时间-信号强度曲线。结果：在T1WI上，心肌信号强度无明显差异；在T2WI上，病变心肌信号强度较正常增高；Gd-DTPA灌注动态增强扫描，正常心肌时间-信号强度曲线呈下降形，危险心肌呈上升形，梗死心肌呈平直形，灌注晚期病变区呈明显环状强化。正常、危险和梗死心肌血流量、微血管体密度差异显著。结论：急性心肌梗死后心肌间质水肿、心肌含水量增加致T2WI信号增高。Gd-DTPA动态增强时间-信号强度曲线上升的斜率及峰值可以反映心肌微血管损伤及组织水肿的程度。     

应用非离子造影剂心肌MRI评估亚急性心肌梗塞信号强度变化

已有动物试验证明钇二酰胺(Omniscan)注射液是一种新的非离子MR造影剂,这种造影剂可以对心肌梗塞提供持久的特异性增强作用。它对正常和梗塞心肌的特异性增强作用有益于诊断和确定心肌梗塞的范围。作者首次报道注射钆二酰胺对自旋回波T_1加权(T_1WI)增强梗塞心肌和正常心肌信号强度的影响。作者观察了12例亚急性心肌梗塞     

磁共振成像诊断陈旧性心肌梗塞的初步评价

目的：探讨ＭＲＩ在评价陈旧性心肌梗塞的形态和功能中的应用价值。材料和方法：对７例陈旧性心肌梗塞进行ＭＲＩ检查，观察心脏形态学变化、心室壁运动、二尖瓣和主动脉瓣开闭功能，测量左室功能。结果：左室壁限局性变薄６例，其中３例在变薄的左室壁邻近部位见血流信号异常增高，左室壁节段性运动减弱，１例室壁瘤形成。左室射血分数降低。１例见二尖瓣有轻度返流。增强扫描（２例）显示梗塞心肌与正常心肌的增强有明显差异。结论：ＭＲＩ能为临床提供心肌的局部和整体功能、梗塞心肌的信号改变、心脏的瓣膜功能及心肌灌注等信息     

超顺磁性氧化铁在肝脏局灶性病变中的定性研究

目的 探讨超顺磁性氧化铁（SPIO）增强MRI在肝脏局灶性病变的定性能力。材料与方法 43例怀疑肝占位者经常规MRI和Gd-DTPA增强后1－7后,行SPIO增强检查。其中31例经手术病理证实,12例经随访、实验室生化检查及临床资料证实。分析平扫MRI及SPIO增强后病灶的信号变化,并与Gd-DTPA动态增强结果相对照。结果 43例共12种病变、单发病灶21例,多病灶22例。包括原发性肝细胞肝癌22例,血管瘤5例,囊肿4例,转移性肝癌5例,肝硬化结节4例,局灶性结节增生（FNH）5例,其他病变6例。22例多发病灶中有8例合并1或2种病变。SPIO增强后,肝细胞肝癌T1WI为等或略高信号,T2WI为较高信号;血管瘤T1WI为较高信号,T2WI信号同平扫为高信号;囊肿T1WI、T2WI信号无改变;肝硬化结节T2WI为等信号同正常肝实质;FNH T2WI信号明显下降。其余病变的诊断SPIO增强不具有特征性,须与Gd-DTPA动态增强相结合。结论 SPIO具有一定的定性能力Gd-DTPA增强相结合,可帮助提高肝局灶性病变诊断和鉴别诊断的准确性。     

正常心脏Gd－DTPA动态增强MRI的表现

目的：探讨正常心脏心肌在Ｇｄ－ＤＴＰＡ动态ＭＲＩ上的信号表现及动态变化规律。材料和方法：１２例正常心脏于０．３５～０．３８ＴＭＲＩ机上作Ｇｄ－ＤＴＰＡ增强前后ＭＲＩ检查，增强后为动态观察。结果：左心室前壁、侧壁、下壁以及室间隔的信号强度在增强前其差别无统计意义（Ｐ＞０．０５）；增强后及其动态观察中，各时间段内各部心肌信号率差别无统计意义（Ｐ＞０．０５）。正常心肌增强后呈均匀一致强化，最大强化是在增强后５分钟内，随增强时间延长而递减。结论：正常心肌在Ｇｄ－ＤＴＰＡＭＲＩ增强前后的信号均匀一致，局部心肌信号增高或减低应视为病理改变。     

Low-dose gadobenate dimeglumine versus standard-dose gadopentate dimeglumine for delayed contrast-enhanced cardiac magnetic resonance imaging

RATIONALE AND OBJECTIVES: The purpose of our study was to compare gadopentate dimeglumine (Gd-DTPA) and gadobenate dimeglumine (Gd-BOPTA) for the evaluation of myocardial infarction (MI) and in the grading transmural extent on late-contrast enhanced cardiac magnetic resonance imaging. MATERIALS AND METHODS: Twenty-three patients with clinically proven MI were examined with the use of 0.2 mmol/kg Gd-DTPA and 0.1 mmol/kg Gd-BOPTA in 2 days interval. All patients were examined with the use of segmented two-dimensional inversion-recovery turbo fast-field echo pulse sequence with an inversion time 210-300 milliseconds. Fifteen minutes time delay was used on both examinations after the injection of contrast agent. Contrast-to-noise ratio between normal myocardium and infarcted myocardium and signal intensity ratio (SIR) of the enhanced myocardium to blood pool was derived and compared for each contrast agent. RESULTS: A total of 61 infarcted segments were analyzed. All of the infarcted segments were visualized on both Gd-BOPTA and Gd-DTPA enhanced images. There was statistically no significant difference between 0.2 mmol/kg Gd-DTPA and 0.1 mmol/kg Gd-BOPTA in the mean contrast-to-noise ratio (10.19 versus 10.22; P = .96), SNR (14.29 versus 14.25; P = .96), and SIR (4.34 versus 4.21; P = .38) of the infarcted segments. Intraobserver agreement (kappa) between Gd-DTPA and Gd-BOPTA were R1 = 91% and R2 = 86%. Interobserver agreements between the readers were Gd-DTPA = 85% and Gd-BOPTA = 88%. CONCLUSION: According to our data, the diagnostic efficacy of 0.1 mmol/kg dose Gd-BOPTA is equivalent to that of 0.2 mmol/kg Gd-DTPA for the assessment of MI on delayed enhanced magnetic resonance images.     

Serial assessment of myocardial infarction by using gated MR imaging and Gd-DTPA

In order to assess the usefulness of Gd-DTPA in the evaluation of myocardial infarction, 17 patients were examined with gated MR imaging. Scans were made by using a spin-echo pulse sequence before and after IV administration of 0.15 mmol/kg of Gd-DTPA. The images were made at four intervals (average of 5, 12, 30, and 90 days) after the onset of the infarction. Gd-DTPA uptake at the infarcted area was graded as marked, moderate, or no increase in signal intensity by visual inspection. At these four time intervals, an area of increased signal intensity in the infarcted myocardium was detected on T1-weighted images after administration of Gd-DTPA in 14 (82%) of 17 cases, 16 (94%) of 17 cases, six (38%) of 16 cases, and three (21%) of 14 cases, respectively. Markedly increased signal intensity in infarcted areas was shown on T1-weighted images with Gd-DTPA at 5 and 12 days. The ratio of gadolinium uptake in the infarcted area to that in normal myocardium also was evaluated. At 5 and 12 days, the mean increase in signal intensity in the infarcted area was significantly higher than that in a normal area, but not at 30 and 90 days. Increased signal intensity also was apparent on T2-weighted images without Gd-DTPA at 5 and 12 days; however, the use of late echo reduced the signal-to-noise ratio, leading to image degradation. Uptake of Gd-DTPA was a positive marker in acute myocardial infarction, but no significant uptake of Gd-DTPA occurred in chronic myocardial infarction.     

Differentiation of reversible and irreversible myocardial injury by MR imaging with and without gadolinium-DTPA

The current study evaluated the capability of magnetic resonance (MR) imaging to distinguish myocardium subjected to reversible and irreversible ischemic injury. Nine dogs underwent left anterior descending coronary arterial occlusion for 15 minutes (reversible injury) and nine for 1 hour (irreversible injury), followed by reperfusion for 24 hours in both groups. Six dogs from each group received 0.5 mmol/kg of gadolinium-DTPA intravenously; the remaining dogs received no contrast media. In the dogs with irreversible injury but no contrast media, there were prolonged T1 and T2 of the infarcted myocardium and adequate visualization of the infarct. The percentage of contrast between normal and infarcted myocardium was greatest on T2-weighted images. In the group with irreversible injury and contrast media, Gd-DTPA produced significant T1 shortening of injured myocardium, with resultant high signal intensity of the infarct, and significantly enhanced contrast compared with the group that did not receive Gd-DTPA. In the dogs with reversible injury, there were no regional differences in intensity or relaxation times. MR has the capability to distinguish myocardium with irreversible injury from that with reversible injury. The difference of T1 between normal and reperfused infarcted myocardium is increased by Gd-DTPA; thus, contrast between these two is enhanced on MR images.     

Reperfused and nonreperfused myocardial infarction: diagnostic potential of Gd-DTPA--enhanced MR imaging

Forty-five patients with suspected acute myocardial infarction were examined with magnetic resonance (MR) imaging before and serially up to 30 minutes after intravenous injection of gadolinium diethylenetriaminepentaacetic acid (DTPA), 0.1 mmol/kg of body weight. Coronary angiography after thrombolytic therapy was performed in all patients to assess reperfusion. Intensity ratios between both reperfused and nonreperfused infarcted areas and normal myocardium increased significantly up to 15-20 minutes after administration of Gd-DTPA and were still elevated 30 minutes after injection (P less than .0001). In accordance with the findings in experimental studies, four distribution patterns of infarct enhancement were observed. The overlap in enhancement patterns and similar maximal intensity ratios after Gd-DTPA administration for both reperfused and nonreperfused infarcts preclude a reliable differentiation on the basis of these factors alone. Significant enhancement of both reperfused and nonreperfused infarcts allows adequate infarct imaging up to at least 30 minutes after administration of Gd-DTPA.     

Occlusive myocardial infarction: investigation of bis-gadolinium mesoporphyrins-enhanced T1-weighted MR imaging in a cat model

PURPOSE: To test whether bis-gadolinium mesoporphyrins-enhanced magnetic resonance (MR) imaging can accurately depict irreversibly damaged myocardium in occlusive myocardial infarction. MATERIALS AND METHODS: Ten cats were subjected to 90 minutes of occlusion of the left anterior descending coronary artery. Bis-gadolinium mesoporphyrins-enhanced T1-weighted MR imaging was performed in the cats for 6 hours. Histopathologic examinations with 2'3'5-triphenyl tetrazolium chloride (TTC) staining and electron microscopy were performed on the resected specimens. The time course and pattern of signal intensity enhancement were evaluated. The size of the infarcted myocardium was estimated on the MR images by measuring the size of the signal intensity-enhanced area. RESULTS: In eight of 10 cats, it was impossible to distinguish infarcted myocardium from normal myocardium at visual inspection of T1-weighted MR images. The contrast ratio between infarcted and normal myocardium did not increase significantly over time. In one of the two remaining cats, a doughnut pattern of signal intensity enhancement was noted. The other cat showed intensely homogeneous enhancement of infarcted myocardium at MR imaging. The size of the area of signal intensity enhancement at MR imaging in these two cats was accurately mapped to that of the infarction on the TTC-stained specimens. CONCLUSION: Occlusive myocardial infarction cannot be accurately detected at bis-gadolinium mesoporphyrins-enhanced MR imaging.     

Cardiac tumors: assessment with Gd-DTPA enhanced MR imaging

Previous studies have shown the value of MR imaging for the identification of cardiac masses. The distinction of intramural tumors from normal myocardium may be equivocal because of the similarity of signal intensity between tumor and normal myocardium on ECG-gated SE images. The purpose of this study was to assess the role of Gd-DTPA for improving the contrast between cardiac tumors and myocardium. Four patients with established or suspected cardiac tumors were imaged with a 1.5 T imager. The T1-weighted images (TR = RR interval, TE = 20-30 ms) were obtained before and immediately after the intravenous injection of Gd-DTPA, at a dosage of 0.1 mmol/kg. Tumors were identified in three patients. All tumors were isointense to the myocardium in precontrast images but demonstrated differential enhancement relative to myocardium after the administration of Gd-DTPA. Two tumors were hyperintense relative to myocardium, and the third was mostly hypointense, surrounded by a hyperintense rim. In the remaining case, no tumor was found and the myocardium was homogeneously enhanced on postgadolinium images. Gadolinium DTPA can produce differential enhancement of tumor from normal myocardium and therefore demonstrate intramural masses.     

Alterations in T1 of normal and reperfused infarcted myocardium after Gd-BOPTA versus GD-DTPA on inversion recovery EPI

This study tested whether Gd-BOPTA/Dimeg or Gd-DTPA exerts greater relaxation enhancement for blood and reperfused infarcted myocardium. Relaxivity of Gd-BOPTA is increased by weak binding to serum albumin. Thirty-six rats were subjected to reperfused infarction before contrast (doses = 0.05, 0.1, and 0.2 mmol/kg). ΔR1 was repeatedly measured over 30 min. Gd-BOPTA caused greater ΔR1 for blood and myocardium than did Gd-DTPA clearance of both agents from normal and infarcted myocardium was similar to blood clearance; plots of ΔR1myocardium/ΔR1blood showed equilibrium phase contrast distribution. Fractional contrast agent distribution volumes were approximately 0.24 for both agents in normal myocardium, 0.98 and 1.6 for Gd-DTPA and Gd-BOPTA, respectively, in reperfused infarction. The high value for Gd-BOPTA was ascribed to greater relaxivity in infarction versus blood. It was concluded that Gd-BOPTA/Dimeg causes a greater ΔR1 than Gd-DTPA in regions which contain serum albumin.     

Magnetic resonance imaging of myocardial infarction using albumin-(Gd-DTPA), a macromolecular blood-volume contrast agent in a rat model

Magnetic resonance (MR) contrast enhancement of acute myocardial infarction was studied in rats using albumin-(Gd-DTPA), a paramagnetic macromolecule with prolonged intravascular retention after intravenous injection. Histologic examination and distribution measurements of radiolabeled microspheres confirmed induction of regional myocardial infarction after ligation of the left coronary artery. ECG-gated spin-echo images at 2.0 Tesla, employing short, T1-weighted pulse sequence settings, demonstrated time-persistent and significant (P less than .05) enhancement of normal myocardium (66%) and an even greater enhancement of the infarcted area (100%), for as long as 60 minutes after injection of 160 mg/kg albumin-(Gd-DTPA). The contrast difference between normal and infarcted myocardium was increased significantly (P less than .05) after administration of albumin-(Gd-DTPA). The prolonged enhancing effects of albumin-(Gd-DTPA) on MR images are useful for evaluating regional differences in blood volume and capillary integrity between normal and infarcted myocardium.     

MRI of acute myocardial ischemia: comparing a new contrast agent, Gd-DTPA-24-cascade-polymer, with Gd-DTPA

A new macromolecular contrast agent, gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA)-24-cascade-polymer, was compared with Gd-DTPA for time-dependent delineation of acute myocardial ischemia. Acute myocardial ischemia was produced in 12 rats by occluding the anterior branch of the left coronary artery for 20-40 minutes. Dynamic spin-echo magnetic resonance imaging (MRI) was performed for 30 minutes after injection of Gd-DTPA (n = 6) or the cascade polymer (n = 6) using equimolar doses (0.1 mmol of Gd/kg). The contrast agent-induced changes in signal intensity (deltaSI) in normal and ischemic myocardium were observed. In normal myocardium, both contrast agents caused a sharp increase in deltaSI, followed by a decline to baseline values over the 30-minute period. Enhancement in the ischemic myocardium was attenuated. Gd-DTPA showed greater deltaSI in ischemic myocardium than the cascade polymer, which gave rise to virtually no enhancement. Significant differences (P<0.05) in signal enhancement between normal and ischemic myocardium persisted for only 6 minutes using Gd-DTPA but for 18 minutes with the cascade polymer. Use of Gd-DTPA-24-cascade-polymer extends the temporal window of dynamic contrast-enhanced MRI for the differentiation of ischemic and normal myocardium. Identification of the ischemic zone is easier with the cascade polymer, which demonstrates virtually no signal enhancement in this territory.