Quantitative analysis of regional left ventricular function after myocardial infarction in the pig assessed with cine magnetic resonance imaging

To assess the accuracy of quantitative analysis of global and regional wall motion and wall thickening of the left ventricle with cine magnetic resonance (MR), images obtained in eight pigs before and after myocardial infarction were compared with those obtained using gadolinium diethylenetriaminepen-taacetic acid (Gd-DTPA)-enhanced multislice spin-echo MR imaging and determination of pathology. The region with abnormal wall motion and wall thickening, as determined with cine MR imaging, identified the same region of infarction as indicated by Gd-DTPA-enhanced spin-echo MR imaging and pathology. Within the infarcted region wall motion and wall thickening analyzed with the centerline method were significantly reduced. We conclude that the use of quantitative analysis of cine MR images accurately determines localization and extent of regional left ventricular dysfunction in the infarcted heart in vivo. This analysis using dedicated software including the centerline method allows sequential assessment of regional left ventricular function in normal and infarcted hearts.     

Prediction of myocardial recovery by dobutamine magnetic resonance imaging and delayed enhancement early after reperfused acute myocardial infarction

The purpose was to study dobutamine magnetic resonance cine imaging (DOB-MRI) and delayed myocardial contrast enhancement (DE) early after reperfused acute myocardial infarction (AMI) for the predicion of segmental myocardial recovery and to find the optimal dose of dobutamine. Fifty patients (56±12 years, 42 males) with reperfused AMI underwent DOB-MRI and DE studies 3.5 (1–19) days after reperfusion. In DOB-MRI systolic wall thickening (SWT) was measured in 18 segments at rest and during dobutamine at 5, 10 and 20 μg*kg⁻¹*min⁻¹. Dysfunctional segments were identified and the extent of DE was measured for each segment. Segmental recovery was examined after 8 (5–15) months. Two hundred-forty-eight segments were dysfunctional with presence of DE in 193. DOB-MRI showed the best prediction of recovery at 10 μg*kg⁻¹*min⁻¹ of dobutamine with sensitivity of 67%, specificity of 63% and accuracy of 66% using a cut-off value for SWT of 2.0 mm. DE revealed a sensitivity of 68%, specificity of 65% and accuracy of 67% using a cut-off value of 46%. Combined analysis of DOB-MRI and DE did not improve diagnostic performance. Early prediction of segmental myocardial recovery after AMI is possible with DOB-MRI and DE. No improvement is achieved by dobutamine >10 μg*kg⁻¹*min⁻¹ or a combination of DOB-MRI and DE.     

兔急性心肌梗死后左心室重塑的MRI研究

目的 观察兔急性心肌梗死( AMI)后心功能随时间演变的规律,探讨MRI影像特征及心功能指标的变化与左心室重塑的关系.方法 日本长耳白兔45只,采用开胸结扎法建立心肌梗死模型.分别于术后即刻(0周)和术后1、2、4、6、8周共6个时间点行在体MR检查,测定各项心功能指标,包括:左心室舒张末期容积(EDV)、每搏输出量(Sv)、射血分数(EF)、射血率峰值(PER)、充盈率峰值(PFR).比较心肌梗死后心功能参数随时间变化的规律.在每个时间点随机取5只动物的心脏离体标本,行MR扩散张量成像(DTI),测量ADC值、各向异性分数(FA)值.不同时间点的心功能参数组间比较采用重复测量方差分析,各时间点梗死区心肌及不同区域心肌的FA值与ADC值的比较采用单因素方差分析,相邻2组均数的比较采用LSD-t检验.结果 随着梗死时间的延长,左心室EDV呈现增加趋势,由术前的(2.21±0.35) ml增加到术后8周时的(3.15±0.57)ml,但差异无统计学意义(F=1.384,P =0.220).EF则由(57.31±11.11)％下降至(34.71±8.72)％,呈明显下降趋势,差异有统计学意义(F =27.134,P=0.001).EF随着EDV增加呈现下降趋势,线性回归分析得出一次方程:y=- 5.58x± 57.7 (F=8.855,P=0.005).随梗死时间的延长,PER由(27.31±13.06) ml/s下降至(17.31±6.41) ml/s (F=2.105,P=0.037),而PFR则由(23.79±14.15) ml/s下降至(12.07±6.91) ml/s (F =2.366,P=0.011).梗死区FA值随着梗死时间的延长而下降,由0.442±0.093下降至0.107±0.037(F=12.61,P=0.001),而ADC值则由(5.07±1.15)×10-4 mm2/s上升至(6.39±0.78)×10-4 mm2/s(F=4.166,P=0.022),差异均有统计学意义.梗死区、边缘区和外围区的FA值分别为0.201±0.049、0.316±0.127、0.323 ±0.117,ADC值分别为(6.19±1.78)×10-4、(5.44±2.63)×10-4、(5.29±2.02)×10-4 mm2/s,差异均有统计学意义(F=3.896,P =0.004;F =3.248,P=0.018).FA、ADC值在梗死区与边缘区比较差异均有统计学意义(t=7.327,P=0.001:t =3.292,P=0.005),而边缘区和外围区的FA值、ADC值的差异无统计学意义(t=1.024,P=0.129;t=1.467,P=0.164).结论 MR心功能测定可以动态监测AMI后心室功能性重塑过程,通过DTI可以反映心室结构性重塑过程的心肌微观察结构的改变.MRI可以作为心肌梗死后左心室重塑的一种可行性的评价方法.     

磁共振心肌灌注成像及心肌活力分析诊断急性心肌梗死的价值

目的:研究磁共振心肌灌注成像及心肌活力分析在诊断急性心肌梗死中的价值。方法:选择37例急性心肌梗死患者作为观察组,同时选出37例无心血管疾病的正常志愿者作为对照组,均行灌注成像和心肌活力分析,观察2组相应心肌信号强度平均值、首过最大上升斜率及首过时间。结果:磁共振心肌灌注成像延迟期观察组梗死心肌的信号强度平均值为73.23±35.24,对照组正常心肌(对应观察组梗死区)为17.99±8.15,2组对比差异具有统计学意义(P<0.01);观察组梗死心肌的首过最大上升斜率平均值为32.85±20.69,对照组正常心肌(对应观察组梗死区)为44.68±23.60,2组对比差异具有统计学意义(P<0.01)。观察组患者心肌梗死区首过时间平均为(5.04±1.74)s,对照组正常心肌(对应观察组梗死区)为(2.82±1.82)s,2组对比差异具有统计学意义(P<0.01)。结论:磁共振心肌灌注成像及心肌活力分析可用于诊断急性心肌梗死。     

心血管MR成像在缺血性心脏病中的应用

缺血性心脏病（IHD）不同阶段的病理组织学改变与病人预后和生活质量密切相关。心血管MR（CMR）成像技术具有多参数、多成像序列,能对IHD进行早期诊断,评价微血管阻塞、心肌内出血、瘢痕心肌和舒张末期心室壁厚度,通过对急慢性心肌梗死进行早期诊断和远期风险评估,为病人的早期治疗及降低预后风险提供信息。就CMR在急慢性IHD心肌组织特征、风险评估和病人远期预后方面的应用予以综述。     

增强超高速MRI在犬慢性心肌梗塞的初步应用

目的：应用超高速磁共振成像（ＭＲＩ）观察犬慢性心肌梗塞的心肌灌注。材料与方法：采用聚氯乙烯狭窄器闭胸制备犬慢性心肌梗塞模型。心肌灌注成像的参数包括预备反转脉冲１８０°；ＴＥ２毫秒；ＴＲ４．９毫秒；翻转角８°及采集矩阵６４×６４。静脉注射钆－二乙烯三胺五乙酸（Ｇｄ－ＤＴＰＡ）的同时，在３２秒内获得连续图像。结果：左旋支（ＬＣＸ）或左前降支（ＬＡＤ）致窄术５～１０个月后呈９５％狭窄或闭塞。４条犬左心室壁运动减弱，３条犬为运动消失。在光、电镜下见心肌发生纤维化。注射Ｇｄ－ＤＴＰＡ后，右室、左室及心肌信号逐渐明显增强，正常心肌信号远高于梗塞区心肌（Ｐ＜０．０１）。结论：本研究结果显示Ｇｄ－ＤＴＰＡ增强超高速ＭＲＩ能非创伤地评价心肌缺血     

31P MR波谱在诊断国人心肌梗死中的价值

目的 采用＾３１Ｐ磁共振波谱（＾３１Ｐ ＭＲＳ）测定国人心肌梗死（ＭＩ）病人和正常志愿者心肌细胞内的多种能量代谢化合物含量以及比值,评价＾３１Ｐ ＭＲＳ在心肌缺血领域中的应用价值。方法 １５例ＭＩ病人均经过临床和冠状动脉造影证实,８例健康志愿者为正常对照组。采用西门子１．５ＴＭａｇｎｅｔｏｎ ６３ ＳＰ ＭＲ扫描机,三维－化学位移成像（３Ｄ－ＣＳＩ）定位技术。７例病人经皮冠状动脉腔内成形术（ＰＴＣ     

Left ventricular aneurysm: comprehensive assessment of morphology, structure and thrombus using cardiovascular magnetic resonance

AIM: To demonstrate that cardiac magnetic resonance (CMR) techniques provide unique and definitive information on the presence, location, size and nature of left ventricular aneurysm and pseudoaneurysm, the presence of thrombus and the viability of myocardium. METHOD: A retrospective study of 27 patients with a final diagnosis of left ventricular aneurysm or pseudoaneurysm, who underwent CMR at a tertiary referral centre in the period between 2000 and 2003. RESULTS: In 7 cases the correct diagnosis of true aneurysm was confirmed; in 7 cases previously unsuspected thrombus was identified; in 7 cases an unsuspected pseudoaneurysm was identified; and in a further 6 cases a previously unsuspected aneurysm was identified. CONCLUSION: CMR refined the diagnosis in the majority of patients with left ventricular aneurysm, and should be considered in all cases of confirmed or suspected left ventricular aneurysm.     

Determinants and impact of microvascular obstruction in successfully reperfused ST-segment elevation myocardial infarction. Assessment by magnetic resonance imaging

Microvascular obstruction (MVO) is an important and independent determinant of post-infarct remodeling. Fifty-two patients with a successfully reperfused ST-segment elevation acute myocardial infarction (MI) were studied with MRI in the first week and at 4 months post-infarction. On early (i.e., 2–5 min) post-contrast MRI, MVO was detected in 32 patients with an MVO to infarct ratio of 36.3 ± 24.9%. On late (i.e., 10–25 min) post-contrast MRI, MVO was detected in only 27 patients, with an MVO to infarct ratio of 15.9 ± 13.9%. MVO infarcts (n = 32) were associated with higher cardiac enzymes (troponin I, P = 0.016), and lower pre-revascularization thrombolysis in myocardial infarction (TIMI) flow (P = 0.018) than non-MVO infarcts (n = 20). Infarct size was larger in MVO infarcts (25.0 ± 14.3 g) than non-MVO infarcts (12.5 ± 7.9 g), P = 0.0007. Systolic wall thickening in the infarct and peri-infarct area, and left ventricular (LV) ejection fraction (EF) were worse in MVO (46.1 ± 7.2%) than non-MVO infarcts (50.5 ± 6.6%, P = 0.038). At 4 months, MVO infarcts showed more adverse remodeling and lack of functional improvement, whereas non-MVO infarcts improved significantly (LV EF at 4 months, MVO, 47.5 ± 7.8%, P = 0.31; non-MVO, 55.2 ± 10.3%, P = 0.0028). In the majority of patients with successfully reperfused ST-segment elevation MI, MVO is observed, whose present and maximal extent can be best evaluated on early post-contrast MRI. Presence of MVO is associated with more extensive infarctions, and characterized by greater adverse LV remodeling and lack of functional recovery.     

Left ventricular thrombus complicated by acute limb ischemia in a patient with HIV

Left ventricular thrombus typically occurs in patients with impaired left ventricular function such as aneurysm, dilated cardiomyopathy, or post-myocardial infarction. Untreated HIV infection is known to increase the risk of venous thromboembolism and cardiovascular disease. However, the pathophysiology remains uncertain; some studies have proposed chronic inflammation as the underlying etiology. Nonetheless, left ventricular thrombus is extremely rare among persons living with HIV with no known underlying cardiac disease. Herein, we report an unusual case of a 55-year-old homeless and heterosexual male with past medical history of HIV, who has mildly reduced left ventricular function and a nonmobile, medium size left ventricular thrombus. Patient was initially treated with therapeutic dose of enoxaparin, and subsequently developed acute embolic occlusion of right femoral artery that lead to an above knee amputation. To our knowledge, left ventricular thromboembolism complicated with acute embolic ischemia in persons living with HIV is extremely rare. The presenting case will definitely add to the current body of knowledge and will raise awareness among physicians, in recognizing the rare association between HIV and arterial thromboembolism.     

Value of magnetic resonance imaging in patients with a recent myocardial infarction: Comparison with planar thallium-201 scintigraphy

The diagnostic accuracy of spin-echo Magnetic Resonance (MR) imaging in the detection and localization of a recent myocardial infarction (mean 4 days old) was compared to planar thallium-201 scintigraphy in 20 patients with a documented myocardial infarction. A control group of 10 subjects underwent a similar MR imaging procedure without thallium-201 scintigraphy. T1-weighted MR images (TE 30 msec) showed abnormal thinning of the infarcted left ventricular wall during systole (<50% of the opposite wall) in 11 patients (55%). On T2-weighted multi-echo MR images, (TE 30–60–90–120 msec) abnormally increased signal intensity was found in 17 patients and coincided with the location of the infarction. Thallium-201 scintigraphy detected the infarction in 18 patients. Comparison of T2-MR imaging and thallium-201 scintigraphy showed concordant findings in 82% of the left ventricular segments. In 9% of segements, thallium uptake was reduced with normal T2-MR and in 9% we found a normal thallium uptake with abnormal T2-MR findings. In all subjects of the control group, T1-MR images were normal, and only one subject showed increased signal intensity on T2-MR images. We conclude that the diagnostic accuracy of MR imaging in detecting a myocardial infarction is similar to that of T1-201 scintigraphy.     

T2-weighted cardiovascular magnetic resonance imaging

Technical advances in T2-weighted cardiovascular MR (CMR) imaging allow for accurate identification and quantification of tissue injuries that alter myocardial T2 relaxation. Of these, myocardial edema is of special relevance. Increased myocardial water content is an important feature of ischemic as well as nonischemic cardiomyopathies, which are often associated with acute myocardial inflammation. In this article, we review technical considerations and discuss clinical indications of myocardial T2-weighted imaging.     

Q-wave regression after acute myocardial infarction assessed by Tl-201 myocardial perfusion SPECT

BACKGROUND: The actual relationship between the interval change of myocardial thallium 201 (Tl-201) radioactivity in the infarct area and the pattern of Q-wave regression is still unknown. This study was conducted to evaluate their relationship after acute myocardial infarction (AMI). METHODS AND RESULTS: A total of 30 patients who had a first Q-wave AMI (11 without Q-wave regression and 19 with Q-wave regression) were retrospectively included. Two sets of 12-lead surface electrocardiograms and Tl-201 myocardial perfusion images were obtained 0 to 2 months and 14 to 84 months after the AMI event, respectively. The acute/subacute redistribution Tl-201 radioactivity was similar between the patients with and those without Q-wave regression. However, the patients with Q-wave regression had higher chronic redistribution Tl-201 radioactivity than those without Q-wave regression. Moreover, the patients with Q-wave regression presented a higher gradient in the redistribution Tl-201 radioactivity between the chronic and acute/subacute images than those without Q-wave regression. CONCLUSIONS: This study supports the role of functional recovery of stunning and/or hibernating myocardium in the disappearance of Q waves after AMI.     

Categorization of aortic aneurysm thrombus morphology by magnetic resonance imaging

Background

Magnetic resonance imaging (MRI) has been proposed for qualitative categorization of intraluminal thrombus morphology. We aimed to correlate the qualitative MRI categorization previously described to quantitative measurements of signal intensity and to compare morphological characteristics of intraluminal thrombus specimens to the appearance on magnetic resonance imaging.

Methods

Thirty-four patients undergoing open surgery for abdominal aortic aneurysm had a preoperative MRI obtained with a 1.5 T magnet. Qualitative categorization was performed (blinded and in consensus) and correlated to intraluminal thrombus to muscle signal-intensity ratios. Morphology of intraluminal thrombus specimens collected during surgery were compared to the magnetic resonance imaging categories and specimen weight was correlated to thrombus volume measured on preoperative computer tomography angiography.

Results

Blinded MRI categorization resulted in agreement in 22 out of 34 intraluminal thrombi (Kappa value 0.3, p = 0.006). Medians (p = 0.004) and distribution (p = 0.002) of signal-intensity ratios varied significantly across the three MRI categories obtained by consensus. Heterogeneous and homogenous specimen appearance corresponded to similar appearances on MRI in 78% and 55% respectively, resulting in an overall Kappa = 0.4 (p = 0.04). Intraluminal thrombus volume and weight correlated well (r_s 0.831, p < 0.001) with a mean difference of 60 g (95% CI 38–80 g), without proportional bias.

Conclusion

Qualitative evaluation of intraluminal thrombus morphology based on MRI can be quantified by measuring signal-intensity ratios. Concurrently a fair agreement to blinded qualitative evaluation of thrombus specimens can be obtained. However, the evaluation is impaired by loss of a large proportion of thrombus during sampling.     

Analysis of microvascularity after reperfused acute myocardial infarction using the maximum slope method of contrast-enhanced magnetic resonance imaging

PURPOSE: The aim of this study was to analyze microvas-cularity after reperfused acute myocardial infarction (AMI) using the maximum slope method of contrastenhanced cardiac magnetic resonance imaging (CMR). MATERIALS AND METHODS: CMR and resting (201)T1 single photon emission computed tomography (SPECT) images were obtained in 30 consecutive patients after reperfused AMI and 10 controls. After bolus injection of gadolinium diethylenetriamine pentaacetic acid, first-pass CMR images were obtained using the True-FISP sequence. Time-intensity curves were generated by measuring the signal intensity in the myocardium and left ventricle. The arterial input function was obtained from the left ventricular time-intensity curve. On the basis of the maximum slope method, the microvascular index (MVI) was calculated by dividing the maximum initial upslope of the myocardium by the initial upslope of the left ventricle. RESULTS: The MVI was significantly lower in the segments related to the occluded coronary artery. MVIs in segments with (201)Tl uptake of 50%-59% of peak were significantly lower than in those with (201)Tl uptake of 60%-69%. MVIs in segments with (201)Tl uptake of <50% of peak were significantly lower than in those with (201)Tl uptake of 50%-59%. CONCLUSION: This study presents a method that directly assesses microvascularity after reperfused AMI.     

Monitoring bone marrow‐originated mesenchymal stem cell traffic to myocardial infarction sites using magnetic resonance imaging

How stem cells promote myocardial repair in myocardial infarction (MI) is not well understood. The purpose of this study was to noninvasively monitor and quantify mesenchymal stem cells (MSC) from bone marrow to MI sites using magnetic resonance imaging (MRI). MSC were dual‐labeled with an enhanced green fluorescent protein and micrometer‐sized iron oxide particles prior to intra‐bone marrow transplantation into the tibial medullary space of C57Bl/6 mice. Micrometer‐sized iron oxide particles labeling caused signal attenuation in T₂*‐weighted MRI and thus allowed noninvasive cell tracking. Longitudinal MRI demonstrated MSC infiltration into MI sites over time. Fluorescence from both micrometer‐sized iron oxide particles and enhanced green fluorescent protein in histology validated the presence of dual‐labeled cells at MI sites. This study demonstrated that MSC traffic to MI sites can be noninvasively monitored in MRI by labeling cells with micrometer‐sized iron oxide particles. The dual‐labeled MSC at MI sites maintained their capability of proliferation and differentiation. The dual‐labeling, intra‐bone marrow transplantation, and MRI cell tracking provided a unique approach for investigating stem cells' roles in the post‐MI healing process. This technique can potentially be applied to monitor possible effects on stem cell mobilization caused by given treatment strategies. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

心肌梗死延迟增强三维与二维MR成像对比研究

目的 比较屏气三维快速小角度激励序列(3D-FLASH)延迟增强扫描与多次屏气二维快速FLASH(2D-turboFLASH)延迟增强扫描的图像质量及量化梗死面积有无差异.方法 15例心肌梗死患者行单次屏气3D-FLASH及多次屏气2D-反转恢复快速FLASH(IR-turboFLASH)延迟增强检查,以2D序列为标准,比较两者测虽心肌梗死面积比值.同时比较3D图像与2D-原始图、2D-相位敏感重组图的对比噪声比(CNR)并进行视觉评分.采用配对t检验、随机区组设计的方差分析分别对心肌梗死面积及各图像CNR进行分析.结果 3D序列测量心肌梗死面积比值(31.28%)与2D测量结果(30.91%)间差异无统计学意义(t=-0.505,P=0.621),相关性好(r=0.990).2D-相位敏感重组图CNR较其他两者低(3D、2D-原始图及2D-相位敏感重组图CNR分别为43.43±20.67、34.10±14.29和7.59±2.59),且差异具有统计学意义(F=24.376,P<0.01).但视觉评分2D-相位敏感重组图显示正常心肌与梗死心肌对比度最好,而背景噪声最明显(3D组、2D-原始图组及2D-相位敏感图组图像总体质量评分分别为2.33、2.13和2.73,背景噪声分别为2.67、2.53和1.20).结论 屏气3D-FLASH延迟增强扫描量化心肌梗死面积准确性高,图像质量良好,适合临床运用.但受屏气及时间影响大,且需准确选择反转时间.