心脏MRI对心肌顿抑设置中收缩储备及透壁心肌坏死范围的对比研究

<正>目的对比研究心脏MRI产生的射血分数(EF),通过低剂量多巴酚丁胺输注时的射血分数(EFD)、透壁梗死累及大于50%心肌壁厚度(ETN)程度,预知主要不良心脏事件(MACEs)和首次ST段抬高心     

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     

超声、磁共振对冬眠心肌及其存活性的实验研究

目的:探讨超声和MR评价冬眠心肌及其存活性的价值。材料和方法:通过Ameroid环套扎猪冠脉的左回旋支完成6个冬眠心肌模型,分别于术前、术后2、5周进行超声和MR检查。结果:超声显示左室侧后壁运动异常区,在5、10μg/(kg.min)多巴酚丁胺刺激下,室壁运动改善,在20μg/(kg.min)多巴酚丁胺刺激下,有2头猪室壁运动恶化。MR显示2头猪有心内膜下梗死,与病理结果一致,判断的坏死心肌范围术后5周较2周时缩小;有1头猪病理显示缺血而MR灌注成像未见缺血节段。结论:多巴酚丁胺负荷超声及MR灌注成像可以识别冬眠心肌,MRI延迟显像高信号可能高估坏死心肌。     

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。     

低剂量多巴酚丁胺负荷MR结合心肌标记技术在心肌缺血中的应用

目的评价采用心肌标记技术的低剂量多巴酚丁胺负荷MR用于检测缺血心肌室壁运动异常的价值。方法8只犬通过结扎左冠状动脉前降支第一对角支远侧建立急性心肌梗死模型后,行低剂量多巴酚丁胺负荷下的电影MR(c ine-MR)和采用心肌标记技术的低剂量多巴酚丁胺负荷下的c ine-MR,分析和对比左心室壁运动。结果c ine-MR扫描负荷前后的左心室各节段室壁运动得分指数(wallmotion score index,WMSI)有显著差异(1.44±0.16 vs 1.32±0.16,P=0.002),采用标记技术扫描负荷前后也有显著差异(1.48±0.12 vs 1.21±0.10,P=0.001)。而且,2种不同方法检测的负荷下的WMSI也有明显差异(1.32±0.16 vs 1.21±0.10,P=0.049)。结论采用心肌标记技术的低剂量多巴酚丁胺负荷下的c ine-MR比未采用心肌标记技术检测出更多的室壁运动异常,它是一种客观准确评价室壁运动异常的工具。     

双核素心肌显像预测PCI术后心功能改善的评价

目的:探讨多巴酚丁胺201Tl负荷-再分布/硝酸甘油介入99Tcm-MIBI门控心肌灌注显像预测PCI术后心功能改善的作用.方法:69例临床怀疑有冠心病拟行经皮冠状动脉介入治疗(PCI)的病人进行多巴酚丁胺201 Tl负荷-再分布显像,显像结束后行硝酸甘油介入99Tcm-MIBI门控心肌灌注显像.心肌显像后2周内69例病人全部进行了经皮冠状动脉介入治疗.PCI术前及术后3个月心脏超声测定左室射血分数(LVEF).结果:①69例病人PCI术后左心室功能较术前有改善(△LVEF=4.78±2.4,t=2.02,P值<0.05).②左心室功能降低组术后心功能提高值明显高于左心室功能正常组(△LVEF=5.3±2.0对LVEF=3.1±2.9,t=2.83,P<0.05).③可逆性灌注缺损心肌节段数>3组术后心功能提高值明显高于可逆性灌注缺损心肌节段数≤3组(△LVEF=5.8±1.6对△LVEF=4.4±1.4,t=2.45,P<0.05).结论:多巴酚丁胺201Tl负荷-再分布/硝酸甘油介入99Tcm-MIBI门控心肌灌注显像能准确检出缺血且存活心肌,对PCI术后心功能改善有很好的预测价值.     

多巴酚丁胺超声心动图检测存活心肌的局限性研究

目的利用小剂量多巴酚丁胺超声心动图（LDDE）识别存活心肌,并对冠脉再通术前后心脏收缩功能进行对比研究,阐述多巴酚丁胺（Dobu）超声心动图检测存活心肌的局限性。方法选择急性前壁心梗（AMI）4周后左前降支（LAD）完全闭塞或濒临闭塞病变,拟行介入性治疗（PCI）的患者20例,PCI术前进行LDDE,根据收缩性储备功能（CR）分组：有CR组和无CR组,对术前静息、术前小剂量Dobu、术后静息状态下进行左室舒张末容积指数（EDVI）、左室收缩末容积指数（ESVI）、室壁运动积分指数（WMSI）、左室射血分数（LVEF）进行分组对比分析。结果 LDDE术前判断无收缩功能的心肌（无CR组）,PCI术后部分恢复收缩功能（占32%）,其LVEF术前、术后对比亦有明显差异（P〈0.05）。结论多巴酚丁胺超声心动图术前检测存活心肌具有一定的局限性。     

比较小剂量多巴酚丁胺负荷MRI和延迟强化MRI预测陈旧心肌梗死心功能恢复的价值

目的 比较小剂量多巴酚丁胺负荷MRI和延迟强化MRI预测陈旧心肌梗死心功能恢复价值.方法 10例陈旧心肌梗死病人于10 d内行小剂量多巴酚丁胺负荷(5～10 μg·kg-1·min-1)心脏电影MRI和延迟强化心脏MRI,所有病人均行血运重建术, 3～6月后再次行静息MRI心脏电影检查评价心功能恢复情况.结果 10例患者中38个心肌节段室壁运动异常,其中24个节段血运重建后功能恢复,14个节段功能未恢复.小剂量多巴酚丁胺负荷MRI和延迟强化MRI预测心功能恢复的敏感性、特异性、准确性分别为95.7% vs 85.7%(P=0.094＞0.05)、85.7%vs 78.5% (P=0.50＞0.05)、 92.1% vs 78.9%.ROC曲线下面积小剂量多巴酚丁胺负荷MRI和延迟强化MRI分别为0.91和0.79.结论 小剂量多巴酚丁胺负荷MRI与延迟强化MRI预测陈旧心肌梗死心功能恢复诊断能力相当.     

MRI评估心肌活性

心肌梗塞后心肌活性的诊断是为了评估血运重建后梗塞心肌功能恢复的可能性。MRI提供了多种评估心肌活性的方法。测量舒张期室壁厚度是一种易于操作的方法，这种方法敏感性高，但特异性低，只有在梗塞4个月后才能使用。低剂量多巴酚丁胺负荷实验对预测室壁运动的恢复情况有很好的敏感性和特异性，但其仅适用于单一节段的心肌功能障碍且心功能只有轻度下降的病人。延迟增强可直接显示坏死心肌和疤痕组织。通过判断坏死心肌延迟增强后的透壁程度，能够精确判断心肌舒缩能力恢复的可能性。首过灌注显示微血管阻塞，延迟增强能提供有关病人心肌活性及预后的信息。代谢成像技术，例如31^P和23^Na磁共振波谱可提供有关心肌梗死机制及活性方面进一步的信息。综述MRI评估心肌活性的方法和机制。     

多巴酚丁胺负荷用于猪缺血心肌18F-FDG代谢显像的价值

目的 探讨多巴酚丁胺负荷情况下实验猪缺血心肌对18F-脱氧葡萄糖(FDG)的摄取情况.方法 15头中华小型猪,于冠状动脉左前降支近中段放置动脉环,造成慢性冠状动脉狭窄.分别在静息和多巴酚丁胺负荷试验时,进行99Tcm-甲氧基异丁基异腈(MIBI)心肌灌注和18F-FDG心肌代谢SPECT显像.99Tcm-MIBI心肌血流灌注图像用17段4分法进行半定量分析,通过测量心肌短轴感兴趣区(ROI)放射性计数,对缺损的可逆程度进行定量分析.18F-FDG心肌代谢图像分析通过在原始投影数据上勾画ROI,计算心脏与肝脏的平均放射性比值(H/Li)、心脏与右肺尖的平均放射性比值(H/L).所有实验猪均行冠状动脉造影检查.结果 冠状动脉造影发现,所有实验猪的冠状动脉左前降支狭窄均大于50%.99Tcm-MIBI药物负荷和静息显像时的心肌血流灌注半定量评分分别为(9.5±8.3)和(8.3±8.4)分,两者差异有显著性(P＜0.05).缺损可逆程度比值为1.17±0.14.18F-FDG图像分析发现在静息情况下,H/Li比值为1.06±0.10,H/L比值为1.40±0.18;而在多巴酚丁胺负荷情况下,心脏对18F-FDG的摄取相对增加H/Li比值为1.25±0.15(P＜0.0001),与缺血可逆程度呈明显正相关(r=0.64,P=0.007),H/L比值为1.77±0.33(P=0.001),与缺血可逆程度呈明显正相关(r=0.51,P＜0.05).结论多巴酚丁胺负荷可使缺血心肌增加对18F-FDG的摄取.     

Gd(ABE-DTTA)-enhanced cardiac MRI for the diagnosis of ischemic events in the heart

PURPOSE: To demonstrate that contrast-enhanced MRI (ceMRI) with the aid of Gd(ABE-DTTA) is able to detect ischemic events in the heart in a canine ischemia/reperfusion (30/40 minutes) model. MATERIALS AND METHODS: ECG-gated, T1-weighted MR image sets (four to five slices each) with three-minute time resolution were collected in transiently LAD-occluded dogs. Following the acquisition of control image sets, ischemia was started by occluding the LAD. Either Gd(ABE-DTTA) (N = 6) or Gd(DTPA) (N = 6) was injected, and imaging was continued for 30 minutes of ischemia and 40 minutes of reperfusion. The contrast agent (CA)-induced MRI signal intensity enhancement (SIE) and contrast were monitored. Microspheres measured myocardial perfusion (MP) to verify areas of ischemia and reperfusion. RESULTS: SIEs of 86% +/- 3% and 97% +/- 3% in nonischemic, and 25% +/- 5% and 29% +/- 8% in ischemic regions were found within three minutes of onset of ischemia with Gd(ABE-DTTA) and Gd(DTPA), respectively. For the rest of the 30 minutes of ischemia, with Gd(ABE-DTTA) SIE of 60% +/- 3% and 25% +/- 5% persisted in the nonischemic and ischemic regions, respectively. With Gd(DTPA), however, SIE in the nonischemic areas decreased rapidly after the first three minutes of ischemia, while SIE in the ischemic areas increased, abolishing contrast. Thus, there was a persistent contrast with Gd(ABE-DTTA) and a short-lived contrast with Gd(DTPA) during ischemia. Furthermore, with Gd(ABE-DTTA) some contrast was still visible in the early reperfusion period. CONCLUSION: Gd(ABE-DTTA) in an ischemia/reperfusion model induces a persistent MRI contrast between regions of normal and ischemic myocardium, and verifies reperfusion. Therefore, it can be used to detect myocardial ischemic events.     

Quantification of myocardial blood flow using model based analysis of first‐pass perfusion MRI: Extraction fraction of Gd‐DTPA varies with myocardial blood flow in human myocardium

For the absolute quantification of myocardial blood flow (MBF), Patlak plot‐derived K1 need to be converted to MBF by using the relation between the extraction fraction of gadolinium contrast agent and MBF. This study was conducted to determine the relation between extraction fraction of Gd‐DTPA and MBF in human heart at rest and during stress. Thirty‐four patients (19 men, mean age of 66.5 ± 11.0 years) with normal coronary arteries and no myocardial infarction were retrospectively evaluated. First‐pass myocardial perfusion MRI during adenosine triphosphate stress and at rest was performed using a dual bolus approach to correct for saturation of the blood signal. Myocardial K1 was quantified by Patlak plot method. Mean MBF was determined from coronary sinus flow measured by phase contrast cine MRI and left ventricle mass measured by cine MRI. The extraction fraction of Gd‐DTPA was calculated as the K1 divided by the mean MBF. The extraction fraction of Gd‐DTPA was 0.46 ± 0.22 at rest and 0.32 ± 0.13 during stress (P < 0.001). The relationship between extraction fraction (E) and MBF in human myocardium can be approximated as E = 1 ? exp(?(0.14 × MBF + 0.56)/MBF). The current results indicate that MBF can be accurately quantified by Patlak plot method of first‐pass myocardial perfusion MRI by performing a correction of extraction fraction. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.     

Use of gadolinium-DTPA as a myocardial perfusion agent: potential applications and limitations for magnetic resonance imaging

To establish the effect of the paramagnetic contrast agent gadolinium diethylenetriaminepentaacetic acid ([Gd]DTPA) on myocardial magnetic resonance relaxation parameters T1 and T2, and its relationship to myocardial perfusion, we administered [Gd] DTPA 0.2 mM/kg to two groups of dogs. Group I had severe, resting myocardial ischemia induced by coronary occlusion, followed in 2 min by [Gd]DTPA infusion and heart excision 1 min later. Group II had a variable reduction in blood flow. In Group II the coronary vasodilator dipyridamole was infused to enhance blood flow to the normal myocardium before [Gd]DTPA was given. In Group I [Gd]DTPA caused a significant difference in T1 between the normal and severely ischemic zones; changes in T1 correlated with the severity of myocardial ischemia. Although vasodilatation delivered more Gd-DTPA to the normal myocardium in Group II, the lack of further decrease in T1 suggested that it was cleared more rapidly. Thus, [Gd]DTPA permits the detection and characterization of severe, resting myocardial ischemia by magnetic resonance techniques. Using the experimental techniques described in this study, less severe flow differences caused by vasodilatation and resultant hyperemia are not detected.     

Cine magnetic resonance with dobutamine following a myocardial infarct

PURPOSE: Dobutamine cine MRI is a new diagnostic imaging technique in the pretreatment (revascularization) assessment of myocardial infarction patients. We report the results of a comparative study of the diagnostic yield of dobutamine cine MRI with that of stress echocardiography in the assessment of viable myocardium. We also propose a new method for analysis of cine MR images, employing digital subtraction, aimed at decreasing subjectivity in the quantitative assessment of myocardial wall thickening. MATERIAL AND METHODS: Twenty-six patients (21 men and 5 women) with a history of myocardial infarction who were scheduled for revascularization were submitted to stress echocardiography and dobutamine cine MRI to evaluate contractile recovery of the segments considered akinetic or hypokinetic at baseline echocardiography. Dobutamine was administered in growing doses (5, 10, 15 gamma/kg/min). We considered 16 segments of the left ventricle in each patient. We performed a quantitative analysis of systolic wall thickening on individual cine MR frames both by manual measurements and by digital subtraction. RESULTS: In the 416 segments studied, we found 307 normokinetic, 64 scarred and 45 viable segments with stress echocardiography, versus 302 normokinetic, 83 scarred and 31 viable segments with dobutamine MRI. Wall thickening analysis on Cine MR images showed 268 normal, 68 scarred and 80 viable segments, versus 274 normal, 58 scarred and 84 viable segments with digital subtraction. Three months after revascularization 15 patients were examined to check contractile recovery of the segments considered as viable. Echocardiography had 79% sensitivity and 97% specificity, while cine MRI had 96% and 86%, respectively. Quantitative assessment of systolic wall thickening by cine MRI and digital subtraction had 96% sensitivity and 91% specificity, with no statistically significant differences between the two techniques. In patients with anteroseptal wall myocardial infarction stress echocardiography had 75% sensitivity and 97% specificity. In the subgroup of 13 patients with diaphragmatic or inferior wall infarction echocardiography sensitivity dropped to 68%, versus 96% of cine MRI, but its specificity was higher, namely 97 versus 86%. CONCLUSIONS: In anteroseptal infarction, echocardiography permits to distinguish viable myocardium and scarred myocardial tissue with good sensitivity and specificity, but cine MRI performs better. In inferolateral or diaphragmatic infarction, cine MRI has much higher sensitivity than stress echocardiography and thus makes the technique of choice to evaluate viable myocardium in these sites. The digital subtraction technique is as accurate as manual measurements, but reduces the error rate and permits quicker evaluation, particularly in subendocardial thickening.     

Magnetic resonance imaging for ischemic heart disease

Cardiac MRI has long been recognized as an accurate and reliable means of evaluating cardiac anatomy and ventricular function. Considerable progress has been made in the field of cardiac MRI, and cardiac MRI can provide accurate evaluation of myocardial ischemia and infarction (MI). Late gadolinium (Gd)-enhanced MRI can clearly delineate subendocardial infarction, and the assessment of transmural extent of infarction on late enhanced MRI has been shown to be useful in predicting functional recovery of dysfunctional myocardium in patients after MI. Stress first-pass contrast-enhanced (CE) myocardial perfusion MRI can be used to detect subendocardial ischemia, and recent studies have demonstrated the high diagnostic accuracy of stress myocardial perfusion MRI for detecting significant coronary artery disease (CAD). Free-breathing, whole-heart coronary MR angiography (MRA) was recently introduced as a method that can provide visualization of all three major coronary arteries within a single three-dimensional (3D) acquisition. With further improvements in MRI techniques and the establishment of a standardized study protocol, cardiac MRI will play a pivotal role in managing patients with ischemic heart disease.     

肺癌与结核球的MRI增强研究

目的：研究肺癌增强ＭＲＩ的表现和病理基础，探讨增强ＭＲＩ在肺癌诊断中的作用。材料与方法：对１９例原发周围型支气管肺癌，１０例结核球行常规和动态增强ＭＲＩ检查，分析其表现并与病理对照。测量病灶实体的增强程度，绘出动态时间－信号强度曲线。结果：所有肺癌在静脉注入Ｇｄ－ＤＴ－ＰＡ后均有强化，表现为三种形式：均匀型、不均匀型和厚壁空洞型；结核球多数表现为薄壁环形增强；各种增强形式有不同的病理基础。肺癌组平均增强７１％，明显高于结核球组（４１％，Ｐ＜０．０１）；肺癌的动态增强时间－信号强度曲线也与结核球不同，结论：肺癌的增强形式和增强程度与结核球不同，因而Ｇｄ－ＤＴＰＡ增强ＭＲＩ有助于肺癌的鉴别     

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.     

急性缺血再灌注心肌磁共振成像实验研究

目的：通过MR灌注成保评价急性梗死心肌组织血流灌注特点。方法：采用结扎左前降支90min存灌注的方法建立为存灌注梗死心肌组，对6只犬行MRI灌注成保及延迟扫描，观察犬心肌缺血存灌注模型梗死心肌MRI特点。结果：犬心肌缺血存灌注梗死心肌MR灌注成保表现为灌注缺损区，延迟扫描表现为高信号。结论：MR灌注成保有助于评价心肌血流，诊断心肌缺血存灌注梗死心肌。     

双源双能量CT成像评估猪急性心肌缺血再灌注损伤的实验研究

目的 评价双源双能量CT(DECT)成像诊断猪急性心肌缺血再灌注损伤的可行性和准确性.方法 8只猪通过开胸结扎冠状动脉左前降支(LAD)或第一对角支(D1)建立再灌注损伤模型,术后行DECT心肌灌注成像扫描.检查结束后立即处死动物,取出心脏,进行氯化三苯基四氮唑(TTC)染色,分析心肌缺血再灌注损伤范围.以病理结果为参照,测量损伤区、非损伤区的CT值以及损伤区面积.将左心室壁分为17个节段,确定DECT心肌灌注碘图、DECT(140、100和平均加权120 kV)3组图像和大体病理上心肌损伤的节段数.以病理结果为金标准分别评价DECT心肌灌注碘图、3组图像显示心肌损伤的敏感性、特异性和一致性.利用方差检验分析损伤区和非损伤心肌不同管电压条件的CT值、大体病理和DECT 3组图像所测量损伤区重量的差异.结果 8只猪DECT心肌灌注碘图见心尖前壁、心尖间隔灌注稀疏甚至缺损,DECT 3组图像中再灌注损伤区CT值均较正常心肌明显降低.与病理金标准对照,DECT心肌灌注碘图诊断再灌注损伤的敏感性、特异性分别为85.2％ (23/27)、86.2％ (94/109),Kappa值为0.62;DECT3组图像的敏感性、特异性和Kappa值:140 kV组分别为88.9％ (24/27)、92.7％ (101/109),0.76;100 kV组分别为85.2％ (23/27)、89.0％(97/109),0.67;平均加权120 kV组分别为88.9％ (24/27)、91.7％ (100/109),0.74.DECT 3组图像测量损伤心肌重量与大体病理所测值之间差异无统计学意义(F=0.419,P=0.741).结论 DECT心肌灌注成像可用于检测猪急性心肌缺血再灌注损伤,与病理诊断一致性较好.