Multimodality imaging in coronary artery disease – “The more the better?”

Multimodality imaging in coronary artery disease (CAD) comprises a combination of information from more than one imaging technique. These combinations, performed in a side-by-side or fusion mode, include computed tomography (CT) and single photon emission computed tomography (SPECT), positron emission tomography (PET) and CT, and PET with magnetic resonance imaging (MRI). Data thus obtained lead to either a summative or synergistic gain of information. For instance, morphology (coronary plaques/stenosis) can be depicted by coronary CT angiography, whereas functional aspects of CAD such as myocardial perfusion abnormalities or myocardial metabolism can be evaluated by the complementary technique in order to separate a hemodynamic significant coronary stenosis from a hemodynamic non-significant stenosis. Distinguishing these two entities has an important impact on patient management. Beyond the diagnostic yield, some of these combinations in multimodality imaging also have prognostic implications. In this article, we will describe different multimodality imaging approaches (CT/SPECT, PET/CT and PET/MRI) for evaluation of CAD in patients with suspected or known CAD and put them into the context of current knowledge.     

Cardiac PET,CT, and MR: What Are the Advantages of Hybrid Imaging?

Cardiac hybrid imaging combines different imaging modalities in a way where both modalities equally contribute to image information. Hybrid positron emission tomography-computed tomography (PET-CT) imaging is a promising tool for evaluation of coronary artery disease (CAD) because it enables detection of coronary atherosclerotic lesions by CT angiography and their consequences on myocardial blood flow by PET perfusion in a single study. This appears to offer superior diagnostic accuracy in patients with intermediate risk for CAD compared with stand-alone imaging. Novel, commercially available hybrid scanners containing PET and magnetic resonance as well as development of targeted probes to evaluate molecular and cellular disease mechanisms are expected to provide many new applications for cardiac hybrid imaging. This article focuses on the advantages of cardiac hybrid imaging in the detection of CAD in light of currently available clinical data and discusses the potential future applications.     

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.     

Hybridbildgebung in Diagnostik und Therapie der chronischen Myokardischämie

Clinical studies have consistently shown that there is only a very weak correlation between the angiographically determined severity of coronary artery disease (CAD) and disturbance of regional coronary perfusion. On the other hand, the results of randomized trials with a fractional flow reserve (FFR)-guided coronary intervention (DEFER, FAME I, FAME II) showed that it is not the angiographically determined morphological severity of coronary artery disease but the functional severity determined by FFR that is critical for prognosis and the indications for revascularization. A non-invasive method combining the morphological image of the coronary anatomy with functional imaging of myocardial ischemia is therefore particularly desirable. An obvious solution is the combination of coronary computed tomography angiography (CCTA) with a functional procedure, such as perfusion positron emission tomography (PET), perfusion single photon emission computed tomography (SPECT) or perfusion magnetic resonance imaging (MRI). This can be performed with fusion imaging or with hybrid imaging using PET-CT or SPECT-CT. First trial results with PET CCTA and SPECT CCTA carried out as cardiac hybrid imaging on a 64 slice CT showed a major effect to be a decrease in the number of false positive results, significantly increasing the specificity of CCTA and SPECT. Although the results are promising, due to the previously high costs, low availability and the additional radiation exposure, current data is not yet sufficient to give clear recommendations for the use of hybrid imaging in patients with a low to intermediate risk of CAD. Ongoing prospective studies such as the SPARC or EVINCI trials will bring further clarification here.     

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.     

Assessment of cardiac computed tomography-myocardial perfusion imaging - promise and challenges -

Cardiac computed tomography (CT) has evolved rapidly over the last decade into a reliable imaging modality for the non-invasive assessment of coronary artery disease. With the advancement in multi-detector CT technology, there has developed an increasing body of evidence that suggests that the role of cardiac CT can be extended to include functional assessment of the myocardium not only at rest but also during stress. Simultaneous anatomical and functional assessment approaches will have a number of advantages such as evaluation of the transmural extent of myocardial perfusion defects (including small subendocardial perfusion defects), reduced risk associated with multiple sources of radiation, and short image acquisition time. Although initial results hold some promise, CT myocardial perfusion imaging is a modality in the early stages of development and further work and studies are required to define, validate, and optimize this technique. This review will provide an overview of this novel perfusion imaging method, its underlying principles, evolution, limitations and future directions.     

SPECT Imaging for Detecting Coronary Artery Disease and Determining Prognosis by Noninvasive Assessment of Myocardial Perfusion and Myocardial Viability

Basic knowledge of active and passive transport mechanisms for concentrating monovalent cations in myocardial cells led to the investigation of the application of radioisotopes of potassium, thallium, rubidium, and ammonia to the in vivo noninvasive assessment of regional myocardial perfusion and viability utilizing gamma camera or positron emission tomographic (PET) imaging technology. Subsequently, technetium-99m (Tc-99m)-labeled isonitriles (sestamibi and tetrofosmin), which bind to mitochondrial membranes, emerged as superior imaging agents with single photon emission tomography (SPECT) imaging. When any of these imaging agents are injected intravenously during either exercise or pharmacologic stress, myocardial defects in tracer uptake represent either abnormal regional flow reserve or myocardial scar reflecting of coronary artery disease (CAD). The major clinical indications for stress SPECT or PET myocardial perfusion imaging are for detection of CAD as the cause of chest pain and risk stratification for prognostication. Patients with normal stress myocardial perfusion scans have an excellent prognosis with <1.0% annual rate future annual death or nonfatal infarction. The greater the extent and severity of ischemic perfusion defects (defects seen on stress images but improve on resting images), the greater the subsequent death or infarction rate during follow-up. Rest imaging alone is performed for determination of myocardial viability in patients with CAD and severe left ventricular dysfunction. Myocardial segments showing >50% uptake compared to normal uptake have a better long-term outcome with revascularization than with medical therapy with enhanced left ventricular function and improved survival. Other applications of SPECT imaging include the evaluation of cardiac sympathetic function, assessment of myocardial metabolism in health and disease, and molecular imaging of coronary atherosclerosis and myocardial stem cell therapy.     

Assessment of myocardial perfusion and viability by Positron Emission Tomography

An important evolution has taken place recently in the field of cardiovascular Positron Emission Tomography (PET) imaging. Being originally a highly versatile research tool that has contributed significantly to advance our understanding of cardiovascular physiology and pathophysiology, PET has gradually been incorporated into the clinical cardiac imaging portfolio contributing to diagnosis and management of patients investigated for coronary artery disease (CAD). PET myocardial perfusion imaging (MPI) has an average sensitivity and specificity around 90% for the detection of angiographically significant CAD and it is also a very accurate technique for prognostication of patients with suspected or known CAD. In clinical practice, Rubidium-82 (⁸²Rb) is the most widely used radiopharmaceutical for MPI that affords also accurate and reproducible quantification in absolute terms (ml/min/g) comparable to that obtained by cyclotron produced tracers such as Nitrogen-13 ammonia (¹³N-ammonia) and Oxygen-15 labeled water (¹⁵O-water). Quantification increases sensitivity for detection of multivessel CAD and it may also be helpful for detection of early stages of atherosclerosis or microvascular dysfunction. PET imaging combining perfusion with myocardial metabolism using ¹⁸F-Fluorodeoxyglucose (¹⁸F FDG), a glucose analog, is an accurate standard for assessment of myocardial hibernation and risk stratification of patients with left ventricular dysfunction of ischemic etiology. It is helpful for guiding management decisions regarding revascularization or medical treatment and predicting improvement of symptoms, exercise capacity and quality of life post-revascularization. The strengths of PET can be increased further with the introduction of hybrid scanners, which combine PET with computed tomography (PET/CT) or with magnetic resonance imaging (PET/MRI) offering integrated morphological, biological and physiological information and hence, comprehensive evaluation of the consequences of atherosclerosis in the coronary arteries and the myocardium.     

Cardiac PET-CT

Integrated positron emission tomography computed tomography (PET/CT) scanners allow a true integration of the structure and function of the heart. Myocardial perfusion PET provides a high sensitivity (91%) and specificity (89%) for the diagnosis of obstructive coronary artery disease (CAD). But, as with single photon emission CT, relative perfusion PET often uncovers only the territory subtended by the most severe coronary stenosis, leading to underestimation of the extent of CAD. In contrast, quantitative PET provides a noninvasive assessment of myocardial blood flow and coronary flow reserve and improves detection of preclinical and multivessel coronary atherosclerosis. Similarly, CT coronary angiography is an accurate means to image the entire continuum of anatomic coronary atherosclerosis from nonobstructive to obstructive CAD. However, not all coronary stenoses are hemodynamically significant and <50% of the patients with obstructive CAD on CT angiography demonstrate stress induced perfusion defects. Stress PET data complement the anatomic information on the CT angiogram by providing instant readings about the ischemic burden of coronary stenoses. Thus, combined PET/CT may be potentially superior to CT angiography alone for the guiding revascularization decisions. Further, fusion of the PET and CT angiogram images allows identification of the culprit stenosis in patients presenting with chest pain. Finally, the advances in molecular imaging and image fusion may soon make noninvasive detection of vulnerable coronary plaques a clinical reality. In summary, integrated PET/CT is a powerful new noninvasive modality that offers the potential for refined diagnosis and management of the entire spectrum of coronary atherosclerosis.     

Advances in rubidium PET and integrated imaging with CT angiography

The role of rubidium-82 (Rb-82) positron emission tomography (PET) in the evaluation and care of patients with suspected coronary artery disease is evolving in conjunction with advances in PET instrumentation, data analysis, and clinical research. Instrumentation developments such as three-dimensional acquisition, new scintillator materials, and x-ray CT help to improve the quality of Rb-82 images. New approaches to kinetic modeling and software tools for analysis of clinical Rb-82 studies are being developed and evaluated, enabling quantification of absolute myocardial blood flow and flow reserve. Recent clinical research studies are providing new insights into the value of Rb-82 cardiac imaging compared with single photon emission CT myocardial perfusion imaging. Integrated x-ray CT angiography and Rb-82 PET perfusion imaging on hybrid PET/CT systems is an exciting new prospect. Complementary anatomical and functional information on atherosclerosis and ischemia can be provided in a single imaging session for better diagnosis and risk stratification of patients with coronary artery disease.     

Positron emission tomography

Positron emission tomography (PET) is currently the most sophisticated scintigraphic imaging technique developed for in-vivo quantification of cardiac physiology and biochemistry. The state-of-the-art PET technology allows delineation of regional tracer activity with high spatial and temporal resolution. A large number of radiopharmaceuticals have been developed to study myocardial perfusion enabling accurate diagnosis and localization of coronary artery disease (CAD) and energy metabolism. More recently, newer tracers such as radiolabeled catecholamine analogues allow the pre- and postsynaptic evaluation of cardiac autonomic innervation. Metabolic imaging with PET represents currently the gold standard for tissue viability assessment with well-validated diagnostic and prognostic information. F-18 deoxyglucose has been also used in combination with SPECT or coincidence imaging providing comparable clinical information but without need for the expensive and rarely available imaging technology of PET. The assessment of coronary flow reserve is the most sensitive scintigraphic method to i) detect vascular abnormalities before their hemodynamic significance, ii) diagnose and define the extent of CAD, and iii) to monitor the effects of (non)pharmacological intervention on regional and global cardiac flow. C-11 hydroxyephedrine (HED) allows imaging of sympathetic neuronal function. the course of cardiac reinnervation after cardiac transplantation was demonstrated with C-11 HED PET, and preliminary evidence suggests that this technique might provide prognostic information on sympathetic neuronal status in congestive heart failure, too. The functional and prognostic relevance of PET imaging together with the increased availability of lower cost instrumentation imaging will define its future role in the diagnosis, assessment of extent, prognosis and in the therapeutic decision making of cardiac disease.     

Untersuchung der Myokardperfusion mit der Positronen-Emissions-Tomographie

Positron emission tomography (PET) of the heart has gained widespread scientific and clinical acceptance with regard to two indications: 1) The detection of perfusion abnormalities by qualitative and semiquantitative analyses of perfusion images at rest and during physical or pharmacological stress using well-validated perfusion tracers, such as N-13 ammonia, Rb-82 rubidium chloride, or O-15 labeled water. 2) Viability imaging of myocardial regions with reduced contractility by combining perfusion measurements with substrate metabolism as assessed from F-18 deoxyglucose utilization. This overview summarizes the use of PET as a perfusion imaging method. With a sensitivity > 90% in combination with high specificity, PET is today the best-validated available nuclear imaging technique for the diagnosis of coronary artery disease (CAD). The short half-life of the perfusion tracers in combination with highly sophisticated hard- and software enables rapid PET studies with high patient throughput. The high diagnostic accuracy and the methological advantages as compared to conventional scintigraphy allows one to use PET perfusion imaging to detect subtle changes in the perfusion reserve for the detection of CAD in high risk but asymptomatic patients as well as in patients with proven CAD undergoing various treatment forms such as risk factor reduction or coronary revascularization. In patients following orthotopic heart transplantation, evolving transplant vasculopathy can be detected at an early stage. Quantitative PET imaging at rest allows for detection of myocardial viability since cellular survival is based on maintenance of a minimal perfusion and structural changes correlate to the degree of perfusion reduction. Furthermore, quantitative assessment of the myocardial perfusion reserve detects the magnitude and competence of collaterals in regions with occluded epicardial collaterals and, thus, imaging of several coronary distribution territories in one noninvasive study. The cost of PET in combination with the cost of a cyclotron facility together with the demanding methological problems have limited the availability of perfusion PET to a few sophisticated centers. Therefore, quantitative PET investigations of myocardial perfusion have been performed predominantly for scientific purposes, and the cost-effectiveness of PET in the everyday clinical setting is not yet finally proven. However, the unique possibilities of PET to study non-invasively and quantitatively myocardial perfusion and metabolism as well as cardiac innervation and pharmacokinetics of cardiac drugs have established cardiac PET as a scientific tool of the highest quality for the future.     

Multi-slice computed tomography coronary angiography: anatomic vs functional assessment in clinical practice.

Non-invasive imaging plays an increasingly important role in the diagnosis and risk stratification of coronary artery disease (CAD). Several techniques such as stress echocardiography and myocardial perfusion imaging have become available to assess cardiac function and myocardial perfusion. With the arrival of multi-slice computed tomography coronary angiography (CTA), non-invasive imaging of coronary anatomy has also become possible. Studies concerning the diagnostic accuracy have demonstrated a good agreement with conventional coronary angiography resulting in a sensitivity and specificity of approximately 86% and 96%, respectively. The high negative predictive value of 97% renders it particularly useful to rule out the presence of CAD in patients with an intermediate pretest likelihood. Moreover, comparative studies have demonstrated that anatomic imaging with CTA may provide information complementary to the traditionally used techniques for functional assessment. From these studies can be derived that only approximately 50% of significant stenoses on CTA are functionally relevant; a large proportion of significant (>50%) lesions on CTA does not result in perfusion abnormalities. Alternatively, many patients with a normal perfusion CTA show considerable atherosclerosis on CTA. Therefore, the combined use of these techniques may enhance the assessment of the presence and extent of CAD. In the future diagnostic algorithms, combining non-invasive anatomic and functional imaging need to be evaluated in large patient populations to establish their efficacy, safety, and cost effectiveness. Importantly, these investigations should result in the development of comprehensive guidelines on the use of CTA in clinical practice as well.     

Non-invasive assessment of low- and intermediate-risk patients with chest pain

Coronary artery disease (CAD) remains a significant global public health burden despite advancements in prevention and therapeutic strategies. Common non-invasive imaging modalities, anatomic and functional, are available for the assessment of patients with stable chest pain. Exercise electrocardiography is a long-standing method for evaluation for CAD and remains the initial test for the majority of patients who can exercise adequately with a baseline interpretable electrocardiogram. The addition of cardiac imaging to exercise testing provides incremental benefit for accurate diagnosis for CAD and is particularly useful in patients who are unable to exercise adequately and/or have uninterpretable electrocardiograms. Radionuclide myocardial perfusion imaging and echocardiography with exercise or pharmacological stress provide high sensitivity and specificity in the detection and further risk stratification of patients with CAD. Recently, coronary computed tomography angiography has demonstrated its growing role to rule out significant CAD given its high negative predictive value. Although less available, stress cardiac magnetic resonance provides a comprehensive assessment of cardiac structure and function and provides a high diagnostic accuracy in the detection of CAD. The utilization of non-invasive testing is complex due to various advantages and limitations, particularly in the assessment of low- and intermediate-risk patients with chest pain, where no single study is suitable for all patients. This review will describe currently available non-invasive modalities, along with current evidence-based guidelines and appropriate use criteria in the assessment of low- and intermediate-risk patients with suspected, stable CAD.     

Comprehensive cardiac CT study: evaluation of coronary arteries, left ventricular function, and myocardial perfusion--is it possible?

With advances in multidetector computed tomography (MDCT) technology, the new generation of 64-slice MDCT scanners with submillimeter collimation and a faster gantry rotation allows imaging of the entire heart in a single breath-hold with excellent temporal and spatial resolution. This potentially permits a comprehensive assessment of coronary anatomy, left ventricular function, and myocardial perfusion. As will be seen in this review of the current literature regarding 16- and 64-slice MDCT, there is great promise for a comprehensive cardiac computed tomography (CT) study. The available data support the notion that CT coronary angiography may be an alternative to invasive coronary angiography in symptomatic patients with a low to intermediate likelihood of having coronary artery disease. By use of the same data acquired for CT coronary angiography, evaluation of global and regional left ventricular function and myocardial perfusion can be added to the MDCT evaluation without additional exposure to contrast medium or radiation and may provide a more conclusive cardiac workup in these patients. The potential applications and limitations of coronary stenosis detection, global and regional left ventricular function, and myocardial perfusion assessment by MDCT will be reviewed. The full potential of cardiac MDCT is just beginning to be realized.     

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.     

Developments in nuclear cardiology: transition from single photon emission computed tomography to positron emission tomography-computed tomography

Recent advances in positron emission tomography (PET) instrumentation have paralleled those of multichannel computed tomography (CT) for cardiac applications. Whereas multichannel CT angiography provides information on the presence and extent of anatomical luminal narrowing of epicardial coronary arteries, stress myocardial perfusion PET provides information on the downstream functional consequences of such anatomic lesions. With the advent of hybrid PET/CT systems, such complementary information of anatomy and physiology can be realized immediately at the same imaging session. By acquiring dynamic, gated myocardial perfusion data, PET studies provide insight into impairment of regional coronary blood flow reserve and microvascular endothelial dysfunction. This paper presents recent developments in PET detector materials, acquisition modes, combined PET/CT scanners, rubidium-82 (Rb-82) gated myocardial perfusion studies and analysis methods for absolute myocardial blood flow quantification.     

Usefulness of cardiac magnetic resonance imaging for coronary artery disease detection

Cardiac magnetic resonance imaging (cMRI) is a promising non-invasive technique to assess the presence of coronary artery disease (CAD), which is free of ionizing radiation and iodine contrast. cMRI can detect CAD by angiographic methods or indirectly by perfusion stress techniques. While coronary angiography by cMRI remains limited to research protocols, stress perfusion cMRI is currently being applied worldwide in the clinical setting. Studies have shown good correlation between adenosine-induced stress myocardial perfusion cMRI and single-photon-emission computed tomography or positron emission tomography to detect CAD. Quantitative methods to analyze cMRI perfusion data have been developed in an attempt to provide a more objective imaging interpretation. Standardization of such quantitative methods, with minimal operator dependency, would be useful for clinical and research applications. Myocardial perfusion reserve (MPR), calculated using Fermi deconvolution technique, has been compared with well established anatomical and physiological CAD detection techniques. MPR appears to be the most accurate quantitative index to detect anatomical and hemodynamically significant CAD. Beyond physiological assessment of CAD, cMRI provides information regarding regional and global left ventricular function and morphology, myocardial infarction size, transmurality and viability. Such comprehensive information would require the performance of multiple tests if other modalities were used. This article describes current applications of cMRI for evaluation of patients with CAD.     

Cardiac Imaging in the Diagnosis of Coronary Artery Disease

Coronary artery disease (CAD) continues to be a leading cause of morbidity and mortality worldwide. Although invasive coronary angiography has previously been the gold standard in establishing the diagnosis of CAD, there is a growing shift to more appropriately use the cardiac catheterization laboratory to perform interventional procedures once a diagnosis of CAD has been established by noninvasive imaging modalities rather than using it primarily as a diagnostic facility to confirm or refute CAD. With ongoing technological advancements, noninvasive imaging plays a pre-eminent role in not only diagnosing CAD but also informing the choice of appropriate therapies, establishing prognosis, all while containing costs and providing value-based care. Multiple imaging modalities are available to evaluate patients suspected of having coronary ischemia, such as stress electrocardiography, stress echocardiography, single-photon emission computed tomography myocardial perfusion imaging, positron emission tomography, coronary computed tomography (CT) angiography, and magnetic resonance imaging. These imaging modalities can variably provide functional and anatomical delineation of coronary stenoses and help guide appropriate therapy. This review will discuss their advantages and limitations and their usage in the diagnostic pathway for patients with CAD. We also discuss newer technologies such as CT fractional flow reserve, CT angiography with perfusion, whole-heart coronary magnetic resonance angiography with perfusion, which can provide both anatomical as well as functional information in the same test, thus obviating the need for multiple diagnostic tests to obtain a comprehensive assessment of both, plaque burden and downstream ischemia. Recognizing that clinicians have a multitude of tests to choose from, we provide an underpinning of the principles of ischemia detection by these various modalities, focusing on anatomy vs physiology, the database justifying their use, their prognostic capabilities and lastly, their appropriate and judicious use in this era of patient-centered, cost-effective imaging.     

Positron emission tomography in ischemic heart disease

Non-invasive assessment of ischemic heart disease remains a challenging task, even with a large armory of diagnostic modalities. Positron emission tomography (PET) is an advanced radionuclide technique that has been available for decades. Originally used as a research tool that contributed to advances in the understanding of cardiovascular pathophysiology, it is now becoming established in clinical practice and is increasingly used in the diagnosis and risk stratification of patients with ischemic heart disease. PET myocardial perfusion imaging has a mean sensitivity and specificity of around 90% for the detection of angiographically significant coronary artery disease, and is also highly accurate for assessing the prognosis of patients with ischemic heart disease. Depending on the radiotracer used, it can provide information not only on myocardial perfusion but also on myocardial metabolism, which is essential for viability assessment. The potential of this imaging technique has been further increased with the introduction of hybrid scanners, which combine PET with computed tomography or cardiac magnetic resonance imaging, offering integrated morphological and functional information and hence comprehensive assessment of the effects of atherosclerosis on the myocardium. The scope of this review is to summarize the role of PET in ischemic heart disease.