Magnetic resonance imaging for the assessment of myocardial viability

The identification of myocardial viability in the setting of left ventricular (LV) dysfunction is crucial for the prediction of functional recovery following revascularization. Although echocardiography, positron emission tomography (PET), and nuclear imaging have validated roles, recent advances in cardiac magnetic resonance (CMR) technology and availability have led to increased experience in CMR for identification of myocardial viability. CMR has unique advantages in the ability of magnetic resonance spectroscopy (MRS) to measure subcellular components of myocardium, and in the image resolution of magnetic resonance proton imaging. As a result of excellent image resolution and advances in pulse sequences and coil technology, magnetic resonance imaging (MRI) can be used to identify the transmural extent of myocardial infarction (MI) in vivo for the first time. This review of the role of CMR in myocardial viability imaging describes the acute and chronic settings of ventricular dysfunction and concepts regarding the underlying pathophysiology. Recent advances in MRS and MRI are discussed, including the potential for dobutamine MRI to identify viable myocardium and a detailed review of the technique of delayed gadolinium (Gd) contrast hyperenhancement for visualization of viable and nonviable myocardium.     

Is myocardial stress perfusion MR-imaging suitable to predict the long term clinical outcome after revascularization?

Introduction

Aim of our study was to evaluate, whether myocardial ischemia or myocardial infarction (MI) depicted by myocardial stress perfusion MR imaging (SP CMR) can predict the clinical outcome in patients with coronary artery disease (CAD).

Materials and method

220 patients were included. Myocardial perfusion was assessed at stress and at rest, using a 2D saturation recovery gradient echo sequence (SR GRE) and myocardial viability by late gadolinium enhancement magnetic resonance images (LGE CMR). MR-images were assessed in regard of presence and extent of MI and ischemia. Patients were monitored for major adverse cardiac events (MACE) (monitoring period: 5–7 years). MACE were correlated with the initial results of SP CMR.

Results

Ischemia was found in 143 patients, MI in 107 patients. Number of MACE was in patients with normal SP CMR 0 (51 patients), with ischemia 21 (62 patients), with MI 14 (26 patients), with ischemia and MI 52 (81 patients). In all patients with severe MACE (MI, death) and in 63 of those with recurring symptoms LGE CMR revealed MI at baseline.

Conclusion

Negative SP CMR indicates low risk for MACE. In patients with stress induced ischemia, MACE might occur even after myocardial revascularization. The presence of MI proved by LGE CMR is associated with a significantly increased risk for MACE.     

Assessment of myocardial viability by MR imaging

Diagnosis of myocardial viability after infarction focuses on the prediction of functional improvement of dysfunctional myocardium after revascularization therapy. Magnetic resonance imaging provides different approaches for the detection of myocardial viability. Measurement of end-diastolic wall thickness is easy to perform and has a high sensitivity, but a low specificity, and can only be used 4 months after myocardial infarction due to infarct healing processes. Low-dose dobutamine stress has a good sensitivity with a high specificity for the prediction of wall motion improvement, but this is only true for patients with a singular dysfunctional area and only slightly depressed cardiac function. Late enhancement allows for direct visualization of necrotic or scarred tissue. By measuring the transmural extent of late enhancement, the probability of mechanical improvement can precisely be given. Imaging of microvascular obstruction by first-pass perfusion or late enhancement gives additional information on viability and patient prognosis. Metabolic imaging techniques, such as ³¹P-MR spectroscopy and ²³Na-MR imaging, provide further insights into the mechanisms of myocardial infarction and viability. In conclusion, cardiac MRI offers several clinically usable approaches for the assessment of myocardial viability and will probably become the method of choice in the near future. Electronic Publication     

Utility of cardiac magnetic resonance in the diagnosis of suspected “MINOCA”: a case series and literature review

Myocardial infarction with nonobstructive coronary artery (MINOCA) is a common condition in clinical practice with multiple specific causes, such as plaque rupture, plaque erosion, and epicardial coronary vasospasm. There must be an ischemic mechanism responsible for the myocyte injury and an exclusion of nonischemic mechanisms that can mimic myocardial infarction, and then a diagnosis of MINOCA can be made. Cardiac magnetic resonance (CMR) plays an essential role in the diagnosis and differential diagnosis of MINOCA, which cannot only exclude myocarditis, Takotsubo syndrome, and cardiomyopathies, but also provide imaging confirmation of acute myocardial infarction. In this study, we presented 2 typical cases with the clinical presentation of acute myocardial infarction but normal or nonobstructive epicardial coronary arteries. Further CMR examinations showed different patterns of late gadolinium enhancement (LGE) in these 2 cases, one case with subendocardial LGE of the anterolateral wall and the other one with subepicardial LGE of the lateral wall, which indicated 2 different mechanisms for the myocyte injury. Subsequently, these 2 patients received different treatment regimens and were discharged with improved symptoms. In conclusion, CMR should be a mandatory test in patients with suspected MINOCA, because it can not only make a clear diagnosis, but also play an important role in guiding clinical decision-making.     

Assessment of acute reperfused myocardial infarction with delayed enhancement 64-MDCT

OBJECTIVE: The purpose of this study was to evaluate the utility of delayed enhancement 64-MDCT in the assessment of myocardial infarct size in a porcine model of acute reperfused myocardial infarction. CT can be used for noninvasive assessment of coronary artery stenosis, but to our knowledge, evaluation of myocardial viability in the subacute phase of acute myocardial infarction has not been validated. We performed delayed enhancement imaging on six domestic swine 5 days after reperfused acute myocardial infarction and assessed the relation between delayed enhancement patterns in vivo and the extent of viable and nonviable myocardium at postmortem histochemical analysis. CONCLUSION: Delayed enhancement imaging with 64-MDCT can be used for accurate assessment of the size of reperfused acute myocardial infarcts.     

Myocardial Fibrosis in Hypertrophic Cardiomyopathy Demonstrated by Integrated Cardiac F-18 FDG PET/MR

Hypertrophic cardiomyopathy (HCM) is a common condition defined as a diffuse or segmental left ventricular (LV) hypertrophy with a nondilated and hyperdynamic chamber as well as cardiac arrhythmias. Cardiac MR (CMR) imaging is a key modality for evaluation of HCM. In addition to the assessment of LV wall thickness, LV function and aortic flow, CMR is capable of estimation of late gadolinium enhancement (LGE) in affected myocardium which has been shown to have a direct correlation with incidence and severity of arrhythmias in HCM. In patients with HCM, LGE on CMR is presumed to represent intramyocardial fibrosis. Meanwhile, F-18 FDG myocardial PET has been sporadically studied in HCM, mostly for evaluation of the metabolic status of a hypertrophic myocardial segment, especially after interventions or to demonstrate partial myocardial fibrosis. We presented here the case of a 25-year-old male patient referred for simultaneous F-18 FDG cardiac PET/MR for the evaluation of septal hypertrophy. The PET/MR revealed myocardial fibrosis in the septum associated with FDG-defect and LGE.     

Optimized cardiac magnetic resonance imaging inversion recovery sequence for metal artifact reduction and accurate myocardial scar assessment in patients with cardiac implantable electronic devices

Late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) is the gold standard for imaging myocardial viability. An important application of LGE CMR is the assessment of the location and extent of the myocardial scar in patients with ventricular tachycardia (VT), which allows for more accurate identification of the ablation targets. However, a large percentage of patients with VT have cardiac implantable electronic devices (CIEDs), which is a relative contraindication for cardiac magnetic resonance imaging due to safety and image artifact concerns. Previous studies showed that these patients can be safely scanned on 1.5 T scanners provided that an adequate imaging protocol is adopted. Nevertheless, imaging patients with a CIED result in metal artifacts due to the strong frequency off-resonance effects near the device; therefore, the spins in the surrounding myocardium are not completely inverted, and thus give rise to hyperintensity artifacts. These artifacts obscure the myocardial scar tissue and limit the ability to study the correlation between the myocardial scar structure and the electro-anatomical map during catheter ablation. In this study, we developed a modified inversion recovery technique to alleviate the CIED-induced metal artifacts and improve the diagnostic image quality of LGE images in patients with CIEDs without increasing scan time or requiring additional hardware. The developed technique was tested in phantom experiments and in vivo scans, which showed its capability for suppressing the hyperintensity artifacts without compromising myocardium nulling in the resulting LGE images.     

Cardiovascular magnetic resonance in mild to moderate clozapine‐induced myocarditis: Is there a role in the absence of electrocardiographic and echocardiographic abnormalities?

Clozapine is an atypical, neuroleptic medication that can cause myocarditis. While the “gold standard” for diagnosis of myocarditis is perceived to be via myocardial biopsy, cardiovascular magnetic resonance (CMR) has also proven its utility in this respect, primarily through its ability to detect myocardial scar by late‐gadolinium enhancement (LGE). Until recently, however, clozapine‐induced myocarditis specifically has not been known to be associated with LGE on CMR. In that particular case, LGE was demonstrated in a patient with clozapine‐induced myocarditis. However, quite important, that patient also had specific abnormalities on the electrocardiogram (ECG) and echocardiogram that corresponded to the area of LGE demonstrated by CMR. We highlight a case series of three patients with clozapine‐induced myocarditis and provide a literature review to discuss and critically appraise the true incremental diagnostic value of CMR in such patients with normal ECG and echocardiography. J. Magn. Reson. Imaging 2010;31:1473–1476. © 2010 Wiley‐Liss, Inc.     

Late gadolinium enhancement on cardiac magnetic resonance imaging: is it associated with a higher incidence of nonsustained ventricular tachycardia in patients with idiopathic dilated cardiomyopathy?

Purpose  

Late gadolinium enhancement (LGE) during cardiac magnetic resonance imaging (MRI) can be seen in patients with myocardial fibrosis accompanied by myocardial infarction and cardiomyopathy. Some idiopathic dilated cardiomyopathy (DCM) patients have fibrosis in the myocardium and show LGE during cardiac MRI. The purpose of this study was to investigate the clinical significance of LGE in patients with DCM.     

磁共振心功能电影序列快速多参数对比评估危重症STEMI患者的扫描技术探索

目的 阐述磁共振心功能电影序列(CINE)在危重症急性ST段抬高型心肌梗死(STEMI)患者扫描及后处理对比分析中的应用价值.方法 选取临床确诊的危重症STEMI患者1例,通过心脏磁共振成像(CMR)序列的快速优化组合,重点对比分析心功能成像序列,分享扫描经验和技术要点.结果 CMR全部检查时间仅为18 min,CIN...     

The size does not matter - the presence of microvascular obstruction but not its extent corresponds to larger infarct size in reperfused STEMI

Background

Microvascular obstruction (MVO) is a cardiac magnetic resonance (CMR) marker of no-reflow in ST-segment elevation myocardial infarction (STEMI). It remains unresolved whether the infarct size corresponds only to the presence of MVO or also to its extent.

Methods

The study included 53 patients with first STEMI (median age 61.5 years, 77% male) treated with percutaneous coronary intervention (PCI) who underwent CMR after median 5 days from PCI. Small MVO was defined as patchy, non-confluent spots of dark areas of absent contrast surrounded by late gadolinium enhancement (LGE). Large MVO was defined as confluent areas of MVO comprising a large amount of the infarct zone.

Results

Microvascular obstruction was observed in 32 patients (60%) including 18 patients with small MVO (36%) and 14 patients with large MVO (24%). Patients with MVO were more likely to have TIMI 0/1 grade flow on initial angiogram, higher levels of necrotic markers, larger infarct size, larger left ventricular end-diastolic and end-systolic volume and lower ejection fraction in comparison to patients without MVO. These differences were not observed between patients with large and small MVO.

Conclusions

The presence of MVO but not its extent corresponds to larger infarct size in STEMI.     

Peri-infarct dysfunction in post-myocardial infarction: assessment of 3-T tagged and late enhancement MRI

Objective

To determine LV function at different distances from myocardial infarction (MI) by using 3-T tagged MRI and late gadolinium enhancement (LGE).

Methods

Cardiac MR images were acquired from 21 patients with previous MI. The harmonic phase (HARP) method was used to calculate radial and circumferential strain (RS, CS). The two strains were synchronised by subtracting the CS from the RS at the same time, and this was defined as the efficient strain (ES). Peak strain (P-RS, P-CS, P-ES) and time to peak strain (T-RS, T-CS, T-ES) were used as estimates of contractile function. Based on the presence of LGE, myocardium was classified into infarct, border zone, adjacent and remote areas.

Results

P-RS and P-ES were significantly greater for remote than for adjacent and infarct areas. P-CS values were significantly greater for remote and border zone than for infarct areas. T-RS and T-ES were significantly shorter for remote and border zone than for infarct areas. T-CS was significantly shorter for border zone than for infarct areas.

Conclusion

Contractile dysfunction demonstrated by peak strain was correlated with location at different distances from the infarct. In the border zone, contractile deformation was characterised as earlier T-RS, T-CS and T-ES and greater P-CS than in the infarct area.     

Noninvasive assessment myocardial viability: Current status and future directions

Observations of reversibility of cardiac contractile dysfunction in patients with coronary artery disease and ischemia were first made more than 40 years ago. Since that time a wealth of basic science and clinical data has been gathered exploring the mechanisms of this phenomenon of myocardial viability and relevance to clinical care of patients. Advances in cardiac imaging techniques have contributed greatly to knowledge in the area, first with thallium-201 imaging, then later with Tc-99m-based tracers for SPECT imaging and metabolic tracers used in conjunction with positron emission tomography (PET), most commonly F-18 FDG in conjunction with blood flow imaging with N-13 ammonia or Rb-82 Cl. In parallel, stress echocardiography has made great progress also. Over time observational studies in patients using these techniques accumulated and were later summarized in several meta-analyses. More recently, cardiac magnetic resonance imaging (CMR) has contributed further information in combination with either late gadolinium enhancement imaging or dobutamine stress. This review discusses the tracer and CMR imaging techniques, the pooled observational data, the results of clinical trials, and ongoing investigation in the field. It also examines some of the current challenges and issues for researchers and explores the emerging potential of combined PET/CMR imaging for myocardial viability.     

Cardiovascular magnetic resonance reveals similar damage to the heart of patients with becker and limb‐girdle muscular dystrophy but no cardiac symptoms

Cardiac involvement in patients with a sarcoglycanopathy (limb‐girdle muscular dystrophy) has been described previously; however, this is the first cardiovascular magnetic resonance (CMR) study in such a patient demonstrating an interesting pattern of myocardial damage using late gadolinium enhancement (LGE) imaging. Moreover, the wall motion abnormality and the subepicardial pattern of LGE in this patient with a sarcoglycanopathy is in agreement with the findings in another patient with Becker muscular dystrophy. The predominance of LGE in the subepicardial layers of the left ventricular inferolateral wall suggests that such a myocardial damage pattern represents a nonspecific cardiac phenotype in response to exaggerated mechanical stress in this region, at least in patients with a sarcoglycanopathy or dystrophinopathy. J. Magn. Reson. Imaging 2009;30:876–877. © 2009 Wiley‐Liss, Inc.     

Takotsubo Cardiomyopathy: Role of Cardiac MRI

We present a case of Takotsubo Cardiomyopathy (TC) which is a non ischemic cardiomyopathy. It is stress related and also known as broken heart syndrome. The patient presented to our emergency department with symptoms of chest pain and breathlessness. The patient was diagnosed as acute coronary syndrome and various tests including ECG, Screening ECHO, Coronary CT and Cardiac Magnetic Resonance (CMR) were done before arriving at the diagnosis of TC. Currently CMR is the modality of choice as it detects the wall motion abnormalities (WMA), presence of wall edema and late gadolinium enhancement (LGE) characteristics can be well appreciated. No intervention was done and the case was managed medically.     

Multicontrast late gadolinium enhancement imaging enables viability and wall motion assessment in a single acquisition with reduced scan times

Purpose

To determine the accuracy of multicontrast late enhancement imaging (MCLE) in the assessment of myocardial viability and wall motion compared to the conventional wall motion and viability cardiac magnetic resonance imaging (MRI) pulse sequences.

Materials and Methods

Forty‐one patients with suspected myocardial infarction were studied. Patients underwent assessment of cardiac function with cine steady‐state free‐precession (SSFP), followed by late gadolinium enhancement (LGE) imaging using inversion recovery gradient echo scanning (IR‐GRE) sequence and MCLE. MCLE was compared to cine SSFP in the assessment of wall motion, ejection fraction (EF), left ventricular (LV) mass, LV end‐diastolic volume (EDV), and to IR‐GRE for measuring infarct size.

Results

MCLE, IR‐GRE, and SSFP imaging demonstrated excellent agreement in the assessment of EF, LV infarct size, and LV mass (r > 0.95, P < 0.001 for all measures), as well as in the assessment of wall motion (κ statistic 0.75).

Conclusion

MCLE provided coregistered images for the assessment of viability and wall motion without loss of accuracy in the assessment of quantitative cardiac parameters. MCLE provides accurate quantitative cardiac assessment with reduced scan times compared to the conventional sequences and thus may be used as an alternative to conventional cine SSFP and IR‐GRE imaging. J. Magn. Reson. Imaging 2009;30:771–777. © 2009 Wiley‐Liss, Inc.     

Technetium 99m sestamibi in the assessment of acute myocardial infarction.

Technetium 99m sestamibi is a promising new radiopharmaceutical that can assess myocardium at risk, infarct size, and treatment efficacy in acute myocardial infarction. The minimal redistribution of this radiopharmaceutical makes it ideal for the measurement of myocardium at risk, as demonstrated by several animal studies. The high-count density images are readily quantitated, and techniques have been developed and validated for this purpose. Early clinical studies have shown that myocardium at risk varies widely, even for a coronary occlusion in a similar location, a finding similar to that reported previously in several different animal infarction models. The clinical use of this radiopharmaceutical to measure final infarct size and treatment benefit, or myocardial salvage, has now been demonstrated using both planar and tomographic imaging techniques. Evidence of benefit is often evident by 18 to 48 hours after reperfusion therapy, although the full extent of improvement is not evident until later. The current 6-hour shelf life and 30-minute preparation time are logistical barriers to widespread clinical use. This radiopharmaceutical provides a new, powerful measurement tool for the assessment of treatment efficacy in acute myocardial infarction that is probably superior to other currently available methods.     

Assessment of myocardial viability by MRI.

Assessment of myocardial viability has become an important issue in patients presenting with either acute myocardial infarction or presenting with chronic ischemic left ventricular dysfunction. In patients with viable myocardium recovery of left ventricular function can be anticipatedm, spontaneously in patients with acute myocardial infarction or following revascularization in patients with ischemic cardiomyopathy. In contrast, patients without viable tissue are not likely to improve in left ventricular function. Currently, nuclear imaging techniques and dobutamine stress echocardiography are used for assessment of viability; recent studies with magnetic resonance imaging (MRI) have however demonstrated the potential usefulness of this technique for the assessment of viability. Various parameters, derived from resting MRI, can be used as markers of myocardial viability, including the end-diastolic wall thickness, systolic wall thickening and signal intensity without contrast-enhancement. Other studies have combined the information from resting MRI with the assessment of contractile reserve during dobutamine stimulation. Finally, recent studies have evaluated the use of contrast-enhanced MRI to detect viable myocardium. All of these parameters are potentially useful and MRI provide an alternative approach for the assessment of viable myocardium.     

Infarct sizing by scintigraphic techniques and nuclear magnetic resonance imaging

Assessment of myocardial infarct size is the cornerstone in the evaluation of interventions designed to salvage myocardium, such as thrombolytic therapy and urgent coronary angioplasty. Enzymatic methods have probably the highest accuracy but can only be used in the very early phase of infarction. The electrocardiogram allows a reasonable estimate of infarct size, but its confidence limits are wide, and in inferior wall infarction the estimates are unreliable. In recent years, radionuclide techniques have been successfully used to identify, localize and determine infarct size in the course of acute myocardial infarction. These scintigraphic measurements have provided important diagnostic, therapeutic and prognostic information based on the extent of myocardial damage. Nuclear magnetic resonance imaging, particularly with contrast enhancement, is one of the methods that have the greatest potential in accurately delineating myocardial infarct size. Nuclear medicine procedures, on the other hand, employ more biologically oriented tracers and offer promise in view of their ability to monitor biochemical alterations as an effect of therapy in the course of myocardial infarction.     

心脏磁共振延迟强化技术进展

心脏磁共振（CMR）延迟强化是诊断心肌梗死、心肌病及评估病变范围最重要的检查技术。目前临床应用的单次激发相位敏感反转恢复（SS-PSIR）序列、自由呼吸运动伪影校正PSIR（MOCO-PSIR）序列和非血流依赖黑血延迟强化（FIDDLE）序列,相比常规采用的PSIR序列能够实现呼吸、心脏运动伪影及血池信号抑制,可明显改善影像质量,有利于更好地指导治疗并进行预后评价。就多种CMR延迟强化技术原理及应用作一综述。