Gadolinium-enhanced magnetic resonance imaging in acute myocardial infarction

To evaluate the usefulness of the paramagnetic contrast agent Gadolinium-DTPA (diethylenetriaminepentaacetic acid) in Magnetic Resonance Imaging of acute myocardial infarction, we studied a total of 45 patients with a first acute myocardial infarction by ECG-gated magnetic resonance imaging before and after intravenous administration of 0.1 mmol/kg Gadolinium-DTPA. All patients received thrombolytic treatment by intravenous streptokinase. The magnetic resonance imaging studies were performed after a mean of 88 h (range 15-241) after the acute onset of acute myocardial infarction. Five patients without evidence of cardiac disease served as controls. Spin-echo measurements (TE 30 ms) were made using a Philips Gyroscan (0.5 Tesla) or a Teslacon II (0.6 Tesla). The 45 patients were divided into four groups of patients. In Group I (5 patients) Gadolinium-DTPA improved the detection of myocardial infarction by Gadolinium-DTPA. In Group II (20 patients) the magnetic resonance imaging procedure was repeated every 10 min for up to 40 min following administration of Gadolinium-DTPA. Optimal contrast enhancement was obtained 20-25 min after Gadolinium-DTPA. In Group III (27 patients) signal intensities were significantly higher in the patients who underwent the magnetic resonance imaging study more than 72 h (mean 120) after the acute event, suggesting increased accumulation of Gadolinium-DTPA in a more advanced stage of the infarction process. In Group IV (45 patients) Gadolinium-DTPA was administered in an attempt to distinguish between reperfused and nonreperfused myocardial areas after thrombolytic treatment for acute myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)     

急性心肌梗死后心脏MRI的作用

摘要背景对心肌梗死处理措施的进步大大减少了其发病率和死亡率。方法在经过急性治疗后,一些诊断和预后的问题仍然有待解决,因此心脏影像起着重要的作用。结果有些病人在梗死后将经受早期机械性并发症,而其他病人可能会有严重的心室功能障碍。此外,许多病人要承担遗留的冠状动脉疾病的重大负担,这些冠状动脉疾病解释了功能性缺血性状态和(或)疑似心肌缺血范围的生存能力。结论在评价心脏功能、压力负荷实验和心肌组织表征方面,心脏磁共振成像(CMR)显示出其无与伦比的优势。     

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.     

Cardiac rupture in acute myocardial infarction: post-mortem MR imaging

We assessed acute myocardial infarction (AMI) with cardiac rupture in an autopsy using magnetic resonance (MR) imaging in vitro and histological staining. Cardiac MR imaging in vitro generated high resolution images of myocardial thinning, rupture, and epicardial hemorrhage. High signal intensity (SI) on T(1) weighted images (WI) and low SI on T(2)WI of the rupture site corresponded with acute myocardial necrosis, edema, and hemorrhage. A rupture site rich in erythrocytes after AMI might affect SI on T(1) and T(2)WI in cardiac MR imaging.     

Proton magnetic resonance of early myocardial infarction in rats

In vitro (10 MHz) proton magnetic resonance (MR) was used to study myocardial infarction 30 hours after ligation of the left coronary artery in rats. The location of large anterolateral myocardial wall infarcts was confirmed when the rats were killed. In vitro measurements of control animals (n = 7) showed T1 prolongation in right as compared with left ventricles (559 +/- 41 vs. 522 +/- 35 milliseconds [sd]; P less than .02); this correlated with a higher water content and is believed to be caused by increased extracellular compartment size. Infarcted myocardium (n = 9) had lower T1 relaxation times than control left ventricle anterior walls (480 +/- 37 vs. 522 +/- 35 milliseconds; P less than .01) despite increased water content (78 +/- 1.1% vs. 76.5 +/- 6%; P less than .01) and a mild increase in T2 values. We conclude that the MR characteristics of myocardial infarction in rats differ from those of other models, possibly because of differences in infarct sizes and rates of proteolysis within the damaged tissues.     

Left ventricular thrombus formation after acute myocardial infarction as assessed by cardiovascular magnetic resonance imaging

Introduction

Left ventricular (LV) thrombus formation is a feared complication of myocardial infarction (MI). We assessed the prevalence of LV thrombus in ST-segment elevated MI patients treated with percutaneous coronary intervention (PCI) and compared the diagnostic accuracy of transthoracic echocardiography (TTE) to cardiovascular magnetic resonance imaging (CMR). Also, we evaluated the course of LV thrombi in the modern era of primary PCI.

Methods

200 patients with primary PCI underwent TTE and CMR, at baseline and at 4 months follow-up. Studies were analyzed by two blinded examiners. Patients were seen at 1, 4, 12, and 24 months for assessment of clinical status and adverse events.

Results

On CMR at baseline, a thrombus was found in 17 of 194 (8.8%) patients. LV thrombus resolution occurred in 15 patients. Two patients had persistence of LV thrombus on follow-up CMR. On CMR at four months, a thrombus was found in an additional 12 patients. In multivariate analysis, thrombus formation on baseline CMR was independently associated with, baseline infarct size (g) (B = 0.02, SE = 0.02, p < 0.001). Routine TTE had a sensitivity of 21–24% and a specificity of 95–98% compared to CMR for the detection of LV thrombi. Intra- and interobserver variation for detection of LV thrombus were lower for CMR (κ = 0.91 and κ = 0.96) compared to TTE (κ = 0.74 and κ = 0.53).

Conclusion

LV thrombus still occurs in a substantial amount of patients after PCI-treated MI, especially in larger infarct sizes. Routine TTE had a low sensitivity for the detection of LV thrombi and the interobserver variation of TTE was large.     

Cardiac index after acute ST-segment elevation myocardial infarction measured with phase-contrast cardiac magnetic resonance imaging

Objectives

Phase-contrast CMR (PC-CMR) might provide a fast and robust non-invasive determination of left ventricular function in patients after ST-segment elevation myocardial infarction (STEMI).

Methods

Cine sequences in the left-ventricular (LV) short-axis and free-breathing, retrospectively gated PC-CMR were performed in 90 patients with first acute STEMI and 15 healthy volunteers. Inter- and intra-observer agreement was determined. The correlations of clinical variables (age, gender, ejection fraction, NT pro-brain natriuretic peptide [NT-proBNP] with cardiac index (CI) were calculated.

Results

For CI, there was a strong agreement of cine CMR with PC-CMR in healthy volunteers (r: 0.82, mean difference: -0.14 l/min/m², error?±?23 %). Agreement was lower in STEMI patients (r: 0.61, mean difference: -0.17 l/min/m², error?±?32 %). In STEMI patients, CI measured with PC-CMR showed lower intra-observer (1 % vs. 9 %) and similar inter-observer variability (9 % vs. 12 %) compared to cine CMR. CI was significantly correlated with age, ejection fraction and NT-proBNP values in STEMI patients.

Discussion

The agreement of PC-CMR and cine CMR for the determination of CI is lower in STEMI patients than in healthy volunteers. After acute STEMI, CI measured with PC-CMR decreases with age, LV ejection fraction and higher NT-proBNP.

Key Points

? Cine CMR and PC-CMR correlate well in healthy volunteers.? Agreement is lower in STEMI patients.? Cardiac Output should be measured with one method longitudinally.? Cardiac output decreases with age after myocardial infarction.

     

Evaluation of heart perfusion in patients with acute myocardial infarction using dynamic contrast-enhanced magnetic resonance imaging

PURPOSE: To investigate the diagnostic ability of quantitative magnetic resonance imaging (MRI) heart perfusion in acute heart patients, a fast, multislice dynamic contrast-enhanced MRI sequence was applied to patients with acute myocardial infarction. MATERIALS AND METHODS: Seven patients with acute transmural myocardial infarction were studied using a Turbo-fast low angle shot (FLASH) MRI sequence to monitor the first pass of an extravascular contrast agent (CA), gadolinium diethylene triamine pentaacetic acid (Gd-DTPA). Quantitation of perfusion, expressed as Ki (mL/100 g/minute), in five slices, each having 60 sectors, provided an estimation of the severity and extent of the perfusion deficiency. Reperfusion was assessed both by noninvasive criteria and by coronary angiography (CAG). RESULTS: The Ki maps clearly delineated the infarction in all patients. Thrombolytic treatment was clearly beneficial in one case, but had no effect in the two other cases. Over the time-course of the study, normal perfusion values were not reestablished following thrombolytic treatment in all cases investigated. CONCLUSION: This study shows that quantitative MRI perfusion values can be obtained from acutely ill patients following acute myocardial infarction. The technique provides information on both the volume and severity of affected myocardial tissue, enabling the power of treatment regimes to be assessed objectively, and this approach should aid individual patient stratification and prognosis.     

Magnetic resonance imaging of acute myocardial infarction in pigs using Gd-DTPA

Six pigs with coronary artery occlusion were investigated with MR imaging before and subsequently for about 2.5 hours at repeated intervals after the intravenous administration of Gd-DTPA (0.4 mmol/kg). The animals were sacrificed after a total occlusion time of 6 hours and the hearts were excised. The excised hearts were then reexamined in the MR equipment and stained with TTC (triphenyl tetrazolium) in order to define areas of infarction. Four control hearts with 6-hour-old infarctions were only imaged ex vivo without any previous administration of contrast media. In vivo, there was no clear demarcation of infarction with or without Gd-DTPA. Ex vivo, without any contrast media, the infarctions were poorly discriminated with a discretely increased signal intensity relative to normal myocardium in the T2 weighted images. Gd-DTPA was found to accumulate in the infarctions, which caused an elevated signal intensity most pronounced in the T1 weighted images. This considerably improved the delineation of the infarcted area.     

Intravenous myocardial imaging performed serially early and late after acute myocardial infarction

The accuracy and sensitivity of myocardial imaging using intravenous Rb-81 in delineating the extent and subsequent changes in regional myocardial perfusion abnormalities were examined serially in 12 patients one to 510 days after an acute myocardial infarction. Definite regions of decreased Rb-81 uptake were noted in 10 patients with transmural infarction. There was excellent correlation between the site of perfusion abnormalities, the electrocardiographic infarct location and the region of segmental wall motion disorders. Follow-up studies revealed in 8 of 11 patients a decrease in the extent of the perfusion defect, which was associated with an improvement in the extent and/or severity of regional wall motion disorders. Conversely, wall motion abnormalities did not change in the remaining three patients in whom perfusion abnormalities persisted unchanged. We conclude that intravenous myocardial imaging permits visualization of myocardial perfusion abnormalities early after acute myocardial infarction. Serial imaging allows detection of changes in the extent of perfusion abnormalities, and, thus, might provide useful information with respect to the patient's prognosis and the effects of therapeutic interventions.Dr. O'Rourke is a Teaching Scholar of the American Heart Association. Supported in part by National Heart and Lung Institute Myocardial Infarction Research Unit Contract NOI-HV-81332 and Arteriosclerosis Grant # HL 14197     

Practical applications of diffusion magnetic resonance imaging in acute cerebral infarction

This article attempts to answer the most common questions on the use of diffusion magnetic resonance imaging to distinguish between acute cerebral infarction and transient ischemic attack in patients who present with the symptoms of stroke.     

Gated magnetic resonance imaging for assessment of cardiac function and myocardial infarction

Gated magnetic resonance imaging (MRI) is a promising noninvasive imaging modality capable of evaluating cardiac function and blood flow in the great vessels. MRI detects acute and chronic myocardial infarctions in experimental animals and in man.     

Value of t2-weighted magnetic resonance imaging early after myocardial infarction in dogs: comparison with bis-gadolinium-mesoporphyrin enhanced T1-weighted magnetic resonance imaging and functional data from cine magnetic resonance imaging.

RATIONALE AND OBJECTIVES: Magnetic Resonance Imaging (MRI) has proved to provide noninvasive methods to investigate the functional repercussion of myocardial infarction and to measure infarct size with specific contrast agents. In this study, we evaluate whether the combination of T2-weighted and contrast-enhanced T1-weighted MRI could detect and discern necrotic and ischemic, but salvageable, myocardium. METHODS: Reperfused myocardial infarction was surgically induced in 14 dogs. T1- and T2-weighted MRI was performed 6 hours after administration of the necrosis avid contrast agent Gadophrin-2 at 0.05 mmol/kg. Gradient-echo cine MRI series were performed at baseline and at 6 hours. Quantification of myocardial infarction was performed with triphenyltetrazolium chloride staining. RESULTS: There was a strong correlation between of postcontrast T1-weighted MRI and histomorphometry (r2 = 0.98, P < 0.01). T2-weighted MRI overestimated the infarct size by 10.5% +/- 4.3% of left ventricular area. A good correlation was found between hyperintense areas on T2-weighted images and the percentage of dysfunctional areas on cine MRI (r2 = 0.84, P < 0.01). In regions with increased signal intensity on T2-weighted MRI, a decreased maximal systolic thickening (11.8% +/- 4.9%, P = 0.043) was found. CONCLUSION: In this study, the difference between the hyperintense areas on T2-weighted and enhanced T1-weighted images after myocardial infarction likely represents viable myocardium.     

Clinical implications of microvascular obstruction and intramyocardial haemorrhage in acute myocardial infarction using cardiovascular magnetic resonance imaging

Objectives  

To investigate the clinical implications of microvascular obstruction (MVO) and intramyocardial haemorrhage (IMH) in acute myocardial infarction (AMI).     

急性心肌梗死心血管MRI中微血管阻塞和心肌内出血的临床意义

目的评估急性心肌梗死(AMI)时微血管阻塞(MVO)和心肌内出血(IMH)的临床意义。方法选取90例首次心肌梗死、主要行经皮冠状动脉介入(PCI)治疗的病人。于介入治疗     

Contrast-enhanced magnetic resonance imaging in the assessment of myocardial infarction and viability

Contrast-enhanced magnetic resonance imaging (MRI) can be used to visualize the transmural extent of myocardial infarction with high spatial resolution. The aim of this review is to provide an overview of the use of contrast-enhanced MRI for characterization of ischemic myocardial injury in comparison to other imaging methods and its relevance in clinical syndromes related to coronary artery disease. Infarcted myocardium appears hyperenhanced compared with normal myocardium when imaged by a delayed-enhancement MRI technique with the use of an inversion-prepared T₁-weighted sequence after injection of gadolinium chelates, such as gadolinium-diethylenetriamine pentaacetic acid. Experimental and clinical studies indicate that the extent of delayed enhancement is reproducible and closely correlates with the size of myocardial necrosis or infarct scar as determined by established in vitro and in vivo methods. Furthermore, MRI appears to be more sensitive than other imaging methods in detecting small subendocardial infarctions. The transmural extent of delayed enhancement potentially predicts functional outcome after revascularization in acute myocardial infarction and chronic ischemic heart disease, indicating that it can accurately discriminate between infarction and dysfunctional but viable myocardium. Further experience from clinical trials is needed to understand the association of delayed enhancement with clinical outcomes. Financial assistance was provided by EC-FP6-project DiMl (LSHB-CT-2005-512146) and Finnish Foundation for Cardiovascular Research.     

Quantitative magnetic resonance imaging can distinguish remodeling mechanisms after acute myocardial infarction based on the severity of ischemic insult

The type and extent of myocardial infarction encountered clinically is primarily determined by the severity of the initial ischemic insult. The purpose of the study was to differentiate longitudinal fluctuations in remodeling mechanisms in porcine myocardium following different ischemic insult durations. Animals (N = 8) were subjected to coronary balloon occlusion for either 90 or 45 min, followed by reperfusion. Imaging was performed on a 3 T MRI scanner between day‐2 and week‐6 postinfarction with edema quantified by T2, hemorrhage by T2*, vasodilatory function by blood‐oxygenation‐level‐dependent T2 alterations and infarction/microvascular obstruction by contrast‐enhanced imaging. The 90‐min model produced large transmural infarcts with hemorrhage and microvascular obstruction, while the 45 min produced small nontransmural and nonhemorrhagic infarction. In the 90‐min group, elevation of end‐diastolic‐volume, reduced cardiac function, persistence of edema, and prolonged vasodilatory dysfunction were all indicative of adverse remodeling; in contrast, the 45‐min group showed no signs of adverse remodeling. The 45‐ and 90‐min porcine models seem to be ideal for representing the low‐ and high‐risk patient groups, respectively, commonly encountered in the clinic. Such in vivo characterization will be a key in predicting functional recovery and may potentially allow evaluation of novel therapies targeted to alleviate ischemic injury and prevent microvascular obstruction/hemorrhage. Magn Reson Med, 70:1095–1105, 2013. © 2012 Wiley Periodicals, Inc.     

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.