Magnetic resonance imaging in the assessment of coronary artery disease

Magnetic resonance imaging (MRI) is gaining importance in cardiology as the noninvasive test of choice for patients with a multitude of cardiovascular problems. Recently, cardiovascular MRI has emerged as an important noninvasive diagnostic modality in the assessment of coronary artery disease. Because of its superior spatial resolution, integration of qualitative and quantitative methodology, and excellent reproducibility, MRI has advantages over conventional noninvasive modalities currently used in the evaluation of coronary artery disease. This article reviews the rapidly expanding recent literature that has now established cardiovascular MRI as an ideal choice in the evaluation of myocardial ischemia (including dobutamine cine MRI and vasodilator perfusion MRI techniques). We further discuss the role of delayed contrast-enhanced MRI and low-dose dobutamine cine MRI for evaluation of myocardial viability. Comparisons with more established techniques, such as dobutamine stress echocardiography, single-photon emission computed tomography perfusion imaging, and positron emission tomography, are reviewed.     

Magnetic resonance imaging in detection and functional assessment of coronary artery disease

The past few years have brought significant improvements in the field of cardiovascular magnetic resonance imaging (MRI), which evolved from an experimental technique to a clinically accepted method of coronary artery disease detection (stress MRI) and viability assessment. In this article, we describe current MRI technology for detection and functional assessment of ischemia, such as dobutamine/atropine MRI, perfusion techniques, viability, and flow reserve in native coronary arteries and grafts. With further refinement in the technology, wide acceptance of cardiovascular MRI is anticipated in clinical practice.     

Técnicas de imagen híbridas en cardiopatía isquémica

Hybrid imaging for ischemic heart disease refers to the fusion of information from a single or usually from multiple cardiovascular imaging modalities enabling synergistic assessment of the presence, the extent, and the severity of coronary atherosclerotic disease along with the hemodynamic significance of lesions and/or with evaluation of the myocardial function. A combination of coronary computed tomography angiography with myocardial perfusion imaging, such as single-photon emission computed tomography and positron emission tomography, has been adopted in several centers and implemented in international coronary artery disease management guidelines. Interest has increased in novel hybrid methods including coronary computed tomography angiography-derived fractional flow reserve and computed tomography perfusion and these techniques hold promise for the imminent diagnostic and management approaches of patients with coronary artery disease. In this review, we discuss the currently available hybrid noninvasive imaging modalities used in clinical practice, research approaches, and exciting potential future technological developments.     

Assessment of Ischemic Heart Disease Using Magnetic Resonance First-Pass Perfusion Imaging

METHODS: Cardiovascular magnetic resonance (MR) perfusion imaging has matured to a point where it can be routinely applied to assess patients with coronary artery disease and ischemic cardiomyopathy. The method has been compared to invasive, catheter-based as well as other noninvasive imaging modalities (echocardiography, single-photon emission computed tomography [SPECT], and positron emission tomography [PET]) for the evaluation of patients with coronary artery disease. Besides qualitative evaluation of MR perfusion images, an absolute quantification of global, regional and transmural myocardial perfusion is possible. A relative or absolute myocardial perfusion reserve has been determined noninvasively with MR perfusion imaging, and can provide good agreement with the invasive assessment. Based on the perfusion reserve, the severity of an epicardial coronary stenosis can be evaluated in patients with known or suspected coronary artery disease. Besides the absence of radiation exposure, MR perfusion imaging offers good temporal and excellent spatial resolution. In particular, the spatial resolution increases the sensitivity and specificity for the detection of coronary artery disease. New parameters such as the "endo-/epimyocardial resting perfusion ratio", may under some circumstances sufficiently enhance the sensitivity for detecting an abnormal perfusion, and thus avoid potentially harmful and expensive stress testing in patients with suspected ischemic heart disease. New revascularization modalities such as therapeutic angiogenesis need to be matched by sensitive imaging tools to prove their benefits. Thus, the optimization of therapeutic angiogenesis may profit from the diagnostic advantages provided by MR perfusion imaging. Furthermore, MR might yield new insights into the pathophysiology of cardiac diseases such as "syndrome X", or might help in the repetitive assessment of heart transplant recipients, possibly obviating the need for further invasive testing. CONCLUSION: The breadth of cardiac MRI allows the combined noninvasive assessment of myocardial perfusion, function, as well as myocardial viability. The combination gives MRI a unique and strong position in the field of noninvasive diagnostic cardiology.     

Myocardial Perfusion and Viability Imaging in Coronary Artery Disease: Clinical Value in Diagnosis,Prognosis, and Therapeutic Guidance

Coronary artery disease is a leading cause of morbidity and mortality worldwide. Noninvasive imaging tests play a significant role in diagnosing coronary artery disease, as well as risk stratification and guidance for revascularization. Myocardial perfusion imaging, including single photon emission computed tomography and positron emission tomography, has been widely employed. In this review, we will review test accuracy and clinical significance of these methods for diagnosing and managing coronary artery disease. We will further discuss the comparative usefulness of other noninvasive tests—stress echocardiography, coronary computed tomography angiography, and cardiac magnetic resonance imaging—in the evaluation of ischemia and myocardial viability.     

Use of cardiac magnetic resonance to assess viability

The accurate differentiation of viable and nonviable myocardium is crucial for therapy planning in patients with coronary artery disease and left ventricular dysfunction. Traditional techniques such as echocardiography, positron emission tomography, single photon emission computed tomography, and dobutamine echocardiography have established roles. Cardiac MRI (CMR) is a rapidly emerging new modality that is used at an increasing number of medical centers in Europe and the United States. This review describes the role of CMR for the assessment of myocardial viability in the setting of acute and chronic ischemic ventricular dysfunction.     

Intravenous myocardial contrast echocardiography for the diagnosis of coronary artery disease

PURPOSE OF REVIEW: Myocardial contrast echocardiography is a recently developed technique that permits the noninvasive assessment of myocardial perfusion. Myocardial contrast enhancement from microbubbles characteristically reflects the myocardial blood volume. The analysis of microbubble kinetics using quantitative myocardial contrast echocardiography permits the evaluation of myocardial blood flow both at rest and during pharmacological stress. RECENT FINDINGS: Myocardial contrast echocardiography has been shown to have good concordance with single photon emission computed tomography for the localization of perfusion abnormalities. As a result of its better spatial resolution and the fact that it tracks myocardial blood flow changes, it seems to have higher sensitivity for the detection of angiographically significant coronary artery disease, while maintaining similar specificity to single photon emission computed tomography. Low mechanical index imaging techniques (real-time myocardial contrast echocardiography) have the advantage of permitting simultaneous analysis of wall motion and perfusion, which is particularly important during dobutamine stress. Myocardial perfusion analysis using real-time myocardial contrast echocardiography has been shown to have higher sensitivity and diagnostic accuracy than wall motion analysis for the detection of coronary artery disease. Quantitative myocardial contrast echocardiography seems to overcome the expertise requirements for appropriate interpretation of myocardial perfusion images, and may have been demonstrated to be an accurate supplemental technique for estimating the severity of coronary artery disease. SUMMARY: Recent technological advances have positioned myocardial contrast echocardiography as a safe and feasible technique for the evaluation of myocardial perfusion. The analysis of myocardial perfusion using myocardial contrast echocardiography has higher diagnostic accuracy than wall motion analysis for detecting coronary artery disease.     

Assessment of myocardial viability with dobutamine stress echocardiography in patients with ischemic left ventricular dysfunction

The noninvasive assessment of myocardial viability has proved clinically useful for distinguishing hibernating and/or stunned myocardium from irreversibly injured myocardium in patients with chronic ischemic heart disease or recent myocardial infarction, with marked regional and/or global left ventricular (LV) dysfunction. Noninvasive techniques utilized for the detection of viability in asynergic myocardial regions include positron emission tomographic imaging of residual metabolic activity, single photon emission tomography (SPECT) of radioisotope uptake with thallium-201, low-dose dobutamine echocardiography assessment of inotropic reserve and myocardial contrast echocardiography for evaluation of microvascular integrity. Of these techniques, dobutamine stress echocardiography is a safe, widely available and relatively inexpensive modality for the identification of myocardial viability for risk stratification and prognosis. Low-dose dobutamine response can accurately predict improvement of dysfunctional yet viable myocardial regions, and thus identify a subset of patients whose LV function will improve following successful coronary revascularization.     

Aktueller Stellenwert von CT und MRT in der Koronardiagnostik

Coronary catheter angiography is the current reference standard for assessing coronary artery disease (CAD). Novel advanced cardiac imaging methods, such as CT and MRI, are opening new opportunities for the noninvasive assessment of morphologic and functional aspects of CAD and provide new options for prevention and for guiding invasive strategies. Especially in patients with low to intermediate pretest likelihood, cardiac CT has been firmly established for ruling out significant CAD (coronary CT angiography) and for evidence-based risk classification (calcium scoring). The strength of cardiac MRI lies in the functional evaluation of CAD. MRI-based myocardial perfusion and function measurements enable accurate evaluation of potential myocardial ischemia. In addition, late enhancement studies enable high resolution imaging of myocardial scar and viability.     

Myocardial perfusion imaging with contrast echocardiography

Advances in myocardial perfusion imaging have firmly established the use of noninvasive techniques capable of providing useful information over a broad range of diagnostic and therapeutic cardiovascular problems. Evaluating regional myocardial perfusion abnormalities is a cornerstone for the diagnosis of coronary artery disease, risk assessment in those with known disease, and determination of myocardial viability. The clinical use of myocardial perfusion imaging and the current limitations of existing techniques continue to promote the development of new technologies capable of assessing microvascular and capillary perfusion abnormalities on a global myocardial level. Myocardial contrast echocardiography is an emerging technique capable of rapidly assessing myocardial perfusion at the capillary level in many different clinical settings. This article focuses on myocardial contrast-enhanced ultrasound perfusion techniques, emphasizing the unique information this modality provides compared with other noninvasive perfusion imaging techniques.     

Advances in imaging for assessment of ischemic heart disease

Cardiac imaging techniques continue to develop for the noninvasive detection and evaluation of patients with coronary artery disease. These techniques include single photon and positron emission tomography along with computed tomography and magnetic resonance imaging. The new myocardial perfusion tracers 99mTc-hexakis-2-methoxyisobutyl-isonitrile and 99mTc-teboroxime have recently come into general use for these purposes, and their role alongside that of more traditional agents is currently being defined using new imaging protocols and instrumentation. 99mTc-hexakis-2-methoxyisobutyl-isonitrile has also been documented as an important research tool for evaluating both at-risk myocardium and the degree of subsequent myocardial salvage following reperfusion therapies for acute myocardial infarction. Antimyosin antibody imaging is another emerging approach in the evaluation of patients with acute myocardial infarction. Metabolic imaging with 18F-fluoro-2-deoxyglucose using positron emission tomography to detect myocardial segments with compromised blood flow but preserved glucose metabolism is currently the best noninvasive method of identifying viable myocardium in patients with left ventricular dysfunction who may benefit from revascularization. Insights from these studies have led to development of the current 201Tl stress-rest reinjection protocols for viability evaluation using single photon emission computed tomography. Positron emission tomography, in combination with blood flow tracers using kinetic modeling, provides accurate estimates of coronary blood flow and flow reserve. The use of these new imaging techniques will allow increasingly accurate evaluation of patients with suspected and proven coronary artery disease in the future.     

Assessment of myocardial viability by radionuclide and echocardiographic techniques: is it simply a sensitivity and specificity issue?

PURPOSE OF REVIEW: The assessment of myocardial viability provides important information that may guide therapeutic decisions in patients with coronary artery disease and left ventricular dysfunction. This review describes methods for assessing myocardial viability using single-photon emission computed tomography, with an emphasis on how to optimize the detection of viable myocardium using current techniques. Relevant comparisons of radionuclide techniques with echocardiographic methods are also discussed. RECENT FINDINGS: The basis for the assessment of myocardial viability using radionuclides is reviewed briefly. Radionuclide techniques provide important prognostic information that may affect the decision on if patients with coronary artery disease should be revascularized or treated medically. Data suggest that dobutamine stress echocardiography may underestimate viability in certain patients. Radionuclide techniques that assess both radiotracer uptake and ventricular function can provide a comprehensive approach to detect viable myocardium in most patients. SUMMARY: The methods for assessing myocardial viability using single-photon emission computed tomography are accurate, reproducible, and widely available. Viability testing should be considered in patients with known coronary artery disease and left ventricular dysfunction. Further studies are warranted to assess the affect of viability assessment on clinical outcomes.     

Magnetic resonance imaging during dobutamine stress in coronary artery disease.

Cine magnetic resonance imaging (MRI) provides a tomographic method of assessing regional ventricular function in any desired plane. It has not been possible to obtain adequate images during dynamic exercise, and this has limited its value in patients with coronary artery disease (CAD). Therefore, an infusion of dobutamine was used to study 25 patients with exertional chest pain and abnormal exercise electrocardiograms. Areas of abnormal wall motion were compared with areas of abnormal myocardial perfusion imaged by dobutamine thallium emission tomography and with coronary arteriography. Twenty-two patients had significant CAD. Twenty-one (96%) of these patients had reversible myocardial ischemia shown by dobutamine thallium tomography, and 20 (91%) had reversible wall motion abnormalities shown by dobutamine MRI. Comparison of abnormal segments of perfusion and wall motion showed 96% agreement at rest, 90% agreement during stress, and 91% agreement for the assessment of functional reversibility. The normalized magnetic resonance signal intensity of the ischemic segments showed a small but significant reduction when compared with that of normal segments (-67 units [9.2%]; p less than 0.05). Dobutamine infusion was well-tolerated, despite causing chest discomfort in 24 patients (96%). Nine patients (36%) developed a minor dysrhythmia that was usually ventricular premature complexes, but this did not limit infusion, and other side effects were mild. The short plasma half-life of dobutamine makes it ideal as a stress agent for imaging techniques (such as MRI), and these results suggest that it is more effective in the provocation of wall motion abnormalities than is dipyridamole in patients with CAD.     

Update in nuclear cardiology

Imaging techniques for the noninvasive detection and evaluation of coronary artery disease continue to develop. New techniques for the quantification of myocardial blood flow by positron-emission tomography, new approaches to metabolic imaging, and new gamma camera technology have the potential to expand the scope of cardiac nuclear medicine in many facilities. Determination of the best and most cost-effective method of assessing myocardial viability in patients with advanced coronary artery disease remains of key interest with research directed at alternative 201Tl imaging protocols, fatty acid metabolism, and viability assessment with the new 99mTc-based myocardial perfusion radiopharmaceuticals. The assessment of endothelial function and determination of coronary flow reserve with 13N-ammonia positron-emission tomography may aid in the identification of preclinical atherosclerosis, and in monitoring disease progression and response to therapy. New information in radionuclide perfusion imaging in young and elderly patients and in those with interventricular conduction disturbances may allow for more accurate identification of coronary artery disease. The role of radionuclide imaging in patients with dilated cardiomyopathy continues to evolve with the development of radiolabeled chemicals of the adrenergic nervous system and their analogues, which will be helpful in the stratification of disease severity. These new imaging techniques promise to increase the accuracy of nuclear cardiology for detection of disease, assessment of function, and prognosis.     

MRI of left ventricular function.

Cardiac magnetic resonance imaging (CMR) is widely recognized as the most accurate noninvasive imaging modality for the assessment of left ventricular (LV) function. By use of state-of-the-art magnetic resonance imaging (MRI) scanners, electrocardiography (ECG)-gated cine images depicting LV function with high contrast and excellent spatial and temporal resolution are readily acquired in breath-holds of 5 to 10 heartbeats. For patients in whom breath-holding and ECG gating are difficult, real-time cine imaging without ECG gating and breath-holding can be performed. LV function can be qualitatively assessed from cine images, or alternatively, parameters such as LV volumes, ejection fraction, and mass may be quantified via computer-based analysis software. In addition, techniques such as myocardial tagging and newer variants can be used to qualitatively or quantitatively assess regional intramyocardial strain, twist, and torsion. Many of the CMR methods have undergone clinical evaluation in the settings of high-dose dobutamine stress testing and determination of myocardial viability. These methods are also very accurate for prognosis in coronary heart disease patients and may be quite useful for the detection of contractile dyssynchrony. When used together with other CMR techniques such as first-pass perfusion imaging or late gadolinium enhancement, CMR of LV function provides a wealth of information in a single imaging study.     

Dobutamine stress echocardiography

Two-dimensional echocardiography is a versatile, accurate, and readily available method for the assessment of cardiac anatomy and function, and extensive experience has been gained in the analysis of left ventricular wall motion. Using modern imaging techniques, regional as well as global wall motion analysis can be performed. Echocardiography can be used in conjunction with a protocol for either exercise or pharmacologic cardiovascular stress in order to identify the distribution and severity of coronary artery disease, with the induction of a regional wall motion abnormality being a sign of myocardial ischemia. The use of dobutamine infusion to accomplish stress echocardiography is a safe, accurate, and practical method for the diagnosis of coronary artery disease in patients unable to exercise. In addition to the evaluation of inducible ischemia, preliminary work is being performed with dobutamine stress echocardiography for the assessment of risk and patient prognosis following acute myocardial infarction and as an indication of tissue viability for myocardium that remains dysfunctional at rest following thrombolytic therapy.     

小剂量多巴酚丁胺负荷磁共振成像对存活心肌的诊断价值

冠心病导致的充血性心力衰竭心功能的恢复则依赖于存活心肌的数量 ,存活心肌的检测方法很多 ,磁共振心肌成像可以获得高质量的、可重复的图像。而不依赖于检查者和患者的状况 ,与超声心动图相比 ,MRI具有较高的诊断正确率。本文综述了小剂量多巴酚丁胺负荷磁共振成像在检测存活心肌方面的诊断指标、对急性心肌梗死和陈旧心肌梗死存活心肌的检测 ,以及和负荷超声心动图在诊断存活心肌方面对比等方面的进展。     

Detection of myocardial contractile reserve by low-dose dobutamine quantitative gated single-photon emission computed tomography in patients with Kawasaki disease and severe coronary artery lesions

We studied 24 patients with severe coronary artery lesions to assess myocardial perfusion and left ventricular contractile reserve simultaneously using low-dose dobutamine quantitative electrocardiographically gated single-photon emission computed tomography in patients with Kawasaki disease. Low-dose dobutamine infusion was started after an injection of technetium-99m tetrofosmin at rest. Myocardial contractile reserve was evaluated using the post-stress and low-dose dobutamine images, and myocardial perfusion was evaluated using the stress and rest images. Quantitative electrocardiographically gated single-photon emission computed tomography during low-dose dobutamine infusion is a useful and safe method for the combined evaluation of myocardial contractile reserve and myocardial perfusion.     

CT Perfusion: Ready for Prime Time

Advancements in computed tomography (CT) technology have revolutionized clinical practice, particularly regarding the noninvasive assessment of coronary artery disease (CAD). The versatility of cardiac CT has rendered multiple applications including assessment of cardiac structure and function, myocardial viability, and coronary anatomy. The merits of cardiac computed tomography angiography (CTA) have been proven for the detection, and particularly the exclusion, of CAD. However, CTA becomes limited in the presence of significant CAD. Its inability to consistently identify lesion-associated ischemia may necessitate additional radionuclide myocardial perfusion imaging. Myocardial computed tomography perfusion imaging (CTP) has emerged as a useful and convenient method to immediately assess myocardial ischemia. In this review, we discuss the current state of CTP including available technology, its performance to date from current literature, and future challenges to this field.     

Myocardial perfusion imaging by magnetic resonance imaging

In the diagnosis and treatment of patients with suspected or known coronary artery disease, noninvasive methodologies for assessing myocardial perfusion have been invaluable. Clinically, nuclear techniques such as single photon emission tomography thallium and sestamibi have predominated. They are limited, however, by the radiation burden, relatively poor spatial resolution, and attenuation artifact caused by soft tissue. In contrast, magnetic resonance imaging (MRI) is notable for its anatomic detail, sharp tissue contrast, excellent spatial and temporal resolution, versatility, and lack of ionizing radiation. It is therefore a potentially attractive alternative to nuclear imaging for the assessment of myocardial perfusion. This review summarizes the principles of MRI myocardial perfusion measurement, discusses recent clinical applications, and highlights future developments in the field.