Cardiac imaging | |
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![]() An MRI of a 13 year old female's heart beating. | |
ICD-10-PCS | B2 |
MeSH | D057791 |
Cardiac imaging refers to minimally invasive imaging of the heart using ultrasound, magnetic resonance imaging (MRI), computed tomography (CT), or nuclear medicine (NM) imaging with PET or SPECT. These cardiac techniques are otherwise referred to as echocardiography, Cardiac MRI, Cardiac CT, Cardiac PET and Cardiac SPECT including myocardial perfusion imaging.
A physician may recommend cardiac imaging to support a diagnosis of a heart condition.
Medical specialty professional organizations discourage the use of routine cardiac imaging during pre-operative assessment for patients about to undergo low or mid-risk non-cardiac surgery because the procedure carries risks and is unlikely to result in the change of a patient's management. [1] Stress cardiac imaging is discouraged in the evaluation of patients without cardiac symptoms or in routine follow-ups. [2]
Echocardiography is regularly utilized to diagnose, manage, and monitor patients with suspected or established heart ailments, making it a highly prevalent diagnostic imaging technique in cardiology due to its speed and efficiency. [3]
Transthoracic echocardiography (TTE) uses ultrasonic waves for continuous heart chamber and blood movement visualization. It is the most commonly used imaging tool for diagnosing heart problems, as it allows non-invasive visualization of the heart and the blood flow through the heart, using a technique known as Doppler.
TTE is commonly used to evaluate patients with coronary artery disease. [4] Stress echocardiography is used to diagnose coronary artery disease and assess myocardial viability. [4]
Transesophageal echocardiography is an invasive procedure that involves inserting a flexible probe with an ultrasound transducer into the esophagus, providing closer access to the heart and surrounding structures. [5] This procedure allows for better imaging of the aorta, pulmonary artery, heart valves, atria, atrial septum, left atrial appendage, and coronary arteries. It can also be used during cardiac surgery to monitor the patient and assess the success of surgical interventions. [5] TTE can visualize non-dilated coronary arteries and measure coronary artery flow using harmonic imaging, contrast agents, and high-frequency transducers. This noninvasive and low-cost method can help diagnose and manage patients with suspected or confirmed CAD by demonstrating pathologic coronary artery flow patterns at rest and with pharmacological stress. [6]
Transesophageal echocardiography creates clearer images of the heart and surrounding blood vessels than traditional transthoracic echocardiography (TTE). TEE is especially useful for patients with obesity or chronic obstructive pulmonary disease (COPD) who may have difficulty obtaining high-quality images using TTE. [5]
However, TEE has several disadvantages, including the need for a team of medical personnel to perform the procedure, the necessity of the patient to follow specific guidelines before the procedure, longer procedure time, and potential discomfort for the patient requiring general anesthesia. TEE is also limited by available anatomy and may require a second procedure, such as esophagogastroduodenoscopy, to visualize the anatomy for safety. [5]
Additionally, TEE has some risks associated with it, such as esophageal perforation and adverse reactions to medication. [5]
3D TEE is a technology developed to improve upon the limitations of 2D tomography. With the introduction of the matrix TEE probe, 3D TEE can collect real-time 3D images that provide a comprehensive view of the heart structures, leading to better understanding and decision making during cardiac procedures. The technique acquires a volumetric data set and displays it in custom orientations, allowing for greater depth and understanding of heart structures compared to 2D echocardiography. [7]
The introduction of ultrasound contrast agents for contrast echocardiography has significantly improved the usefulness of echocardiography in diagnosing and assessing coronary artery disease. [8] Ultrasound contrast is used for assessing left ventricular ejection fraction at rest and during stress echocardiography. Contrast echocardiography can simultaneously assess regional myocardial function and perfusion, allowing for the non-invasive diagnosis of coronary artery disease. It has several advantages compared to other non-invasive imaging techniques, such as being performed without radiation exposure and potential nephrotoxicity. Contrast echocardiography requires intravenous administration of an ultrasound contrast agent during contrast specific ultrasound imaging. [8]
Magnetic resonance imaging visualizes the heart by detecting hydrogen atoms using superconducting magnets, particularly those attached to water and fat molecules. [9] These hydrogen atoms possess a property known as nuclear spin. Although the direction of this spin is usually random, the spin can be aligned using a powerful magnetic field. [9] Faint electromagnetic signals are emitted by these hydrogen atoms when their alignment is temporarily disturbed which can be detected and used to create an image of the heart. [10]
Cardiovascular magnetic resonance (MR) technology is able to measure the size, shape, function, and tissue characteristics of the heart in a single session. [11] It is also commonly used to determine ventricular function and for the evaluation of structural heart disease. [12] It is more reproducible than echocardiography with less inter-observer variability, allowing for more precise reference ranges to better distinguish health from disease. [11] Additionally, MR lacks ionizing radiation and does not have any known long-term effects, making it safe for repeated imaging. [13]
Additional benefits from cardiac MRI include the ability to detect scar within the heart using late gadolinium enhancement, and identify other abnormalities of the heart muscle itself such as infiltration with iron or amyloid protein. [11] Disadvantages of MRI include lengthy protocols and the potential for claustrophobia. Furthermore, an MRI scan cannot be performed in some people who have metallic implants such as some types of pacemakers, defibrillators, although many modern pacemakers are safe for use within an MRI scanner. [14] Other metal structures such as artificial valves and coronary stents are generally not problematic. However, MR is less widely available and may be more difficult for patients to tolerate than other noninvasive modalities, requiring physician monitoring for complex cases. [13]
Recent development in deep learning and convolutional neural network techniques have made it possible to analyze and quantify some aspects of cardiac MRI automatically. [15] The use of cardiac MRI is projected to increase through greater availability of scanners and more widespread knowledge about its clinical application.
Computed tomography (CT) provides simultaneous evaluation of multiple systems. [12] A downside to CT scans are that they subject the patient to ionizing radiation, but technological improvements are lessening the amount. CT is best employed in low-to-intermediate-risk patients and is often used when other noninvasive tests are equivocal or abnormal. The Wells' score for pulmonary embolism or the Diamond-Forrester chest pain criteria and Thrombolysis in Myocardial Infarction (TIMI) score can help select appropriate patients for CT. [12]
Computed tomography angiography (CTA), an imaging methodology using a ring-shaped machine with an X-ray source spinning around the circular path so as to bathe the inner circle with a uniform and known X-ray density. Cardiology uses are growing with the incredible developments in CT technology. Currently, multidetector CT, specially the 64 detector-CT are allowing to make cardiac studies in just a few seconds (less than 10 seconds, depending on the equipment and protocol used). These images are reconstructed using algorithms and software.
Cardiac CT (CCT) is a modified form of the traditional chest CT due to the difficulty of imaging the complex, moving heart. [16] This is achieved through the use of thin slices and high-resolution scanning, as well as the addition of electrocardiogram (ECG) gating or triggering to capture a motion-free image. Standard CT scans are acquired in either Axial or Helical modes, while CCT adds the ECG gating dimension to these modes to capture images of the heart. [16] These modifications are necessary to obtain the required data from the planar slice images, which are reconstructed from back-projected transmitted data obtained by radial excursion of the X-ray tube and detector. [16]
A coronary CT calcium scan is a computed tomography (CT) scan of the heart for the assessment of severity of coronary artery disease. Specifically, it looks for calcium deposits in the coronary arteries that can narrow arteries and increase the risk of heart attack. [17] This severity can be presented as Agatston score or Coronary Artery Calcium (CAC) score. The CAC score is an independent marker of risk for cardiac events, cardiac mortality, and all-cause mortality. [18] In addition, it provides additional prognostic information to other cardiovascular risk markers. [18] A typical coronary CT calcium scan is done without the use of radiocontrast dye, but it can possibly be done from contrast-enhanced images as well, such as in coronary CT angiography. [19]
Positron emission tomography (PET) is a nuclear medicine imaging methodology that tracks positron emitting radioisotopes. [20] PET enables visual image analysis of multiple different metabolic chemical processes and is thus one of the most flexible imaging technologies. Cardiology uses are growing very slowly due to technical and relative cost difficulties. Most uses are for research, not clinical purposes. Appropriate radioisotopes of elements within chemical compounds of the metabolic pathway being examined are used to make the location of the chemical compounds of interest visible in a PET image.
PET tracers emit positrons, which are nearly identical to negatively charged electrons, but have the opposite charge and are considered antimatter. When a positron and an electron come close together, they annihilate each other, producing two gamma rays that travel in opposite directions. [21] PET scanners detect these gamma rays to produce images showing the location of the positrons and the metabolic processes in the body. [21] The accuracy of the image depends on the initial speed of the emitted positron, which affects the ability of the scanner to define the position of radioactive atoms in the body. [21]
Most new PET scanners are combined with a CT scanner, a type of X-ray machine. Using the CT scan instead of the traditional rotating rod source transmission scan reduces the scan time and produces almost noise-free images. [22] The two scanners are located in the same machine, but they do not perform scans at the same time. A CT scan is typically done first, followed by a PET scan. [22] For cardiac scans, combining CT cardiac data with PET metabolic or perfusion data from PET/CT machines may be of clinical value. While there are unresolved issues with using a high-speed CT scan for attenuation correction of cardiac images, many new CT scanners are marketed with PET scanners and can be used to measure myocardial thickening, which is a useful adjunct to PET physiological imaging. [22]
PET/MRI systems combine the capabilities of positron emission tomography (PET) and magnetic resonance imaging (MRI) to provide both functional and morphological information in various clinical applications. [22] Cardiac MRI can produce complementary data to increase accuracy and reproducibility to PET scans, especially in systemic diseases, inflammatory processes, assessing risk of atherosclerotic plaque rupture, and stem cell tracking. [22] PET/MRI systems come in two types: tandem, in-line systems where two imagers share a patient transport system for sequential acquisitions, and integrated systems where both scanners operate simultaneously. The latter has some performance limitations, but it may be essential in some applications, such as cardiac perfusion and metabolism. [22] PET/MRI is still in its early stages, and more work is needed to establish it as a widespread and cost-effective clinical tool for cardiac imaging. [22]
Single photon emission computed tomography (SPECT), a nuclear medicine imaging methodology using gamma rays emitted by a radioactive tracer injected into the blood stream, which ultimately distributes into the heart. SPECT provides information about blood flow to the heart and how well the heart is functioning. It is commonly used to evaluate patients who have, or are suspected to have, coronary artery disease and is additionally used for myocardial perfusion imaging. [23] The accuracy of the test depends on the technical quality of the study, and interpreting the results requires knowledge of the physics and technical aspects of the procedure.
Coronary catheterization uses pressure monitoring and blood sampling through a catheter inserted into the heart through blood vessels in the leg or wrist to determine the functioning of the heart, and, following injections of radiocontrast dye, uses X-ray fluoroscopy, typically at 30 frames per second, to visualize the position and volume of blood within the heart chambers and arteries. Coronary angiography is performed during a cardiac catheterization and used to determine the patency and configuration of the coronary artery lumens.
Intravascular ultrasound , also known as a percutaneous echocardiogram is an imaging methodology using specially designed, long, thin, complex manufactured catheters attached to computerized ultrasound equipment to visualize the lumen and the interior wall of blood vessels.
Fractional flow reserve (FFR) examines the pressure drop across the stenosis in suspected ischemic coronary artery that may require percutaneous coronary intervention (PCI) or coronary artery bypass surgery.
Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to reveal internal structures hidden by the skin and bones, as well as to diagnose and treat disease. Medical imaging also establishes a database of normal anatomy and physiology to make it possible to identify abnormalities. Although imaging of removed organs and tissues can be performed for medical reasons, such procedures are usually considered part of pathology instead of medical imaging.
Single-photon emission computed tomography is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera, but is able to provide true 3D information. This information is typically presented as cross-sectional slices through the patient, but can be freely reformatted or manipulated as required.
A cardiac stress test is a cardiological test that measures the heart's ability to respond to external stress in a controlled clinical environment. The stress response is induced by exercise, intravenous pharmacological (drug) stimulation, or in some cases, a combination of both.
An atheroma, or atheromatous plaque, is an abnormal accumulation of material in the inner layer of an arterial wall.
Electron beam computed tomography (EBCT) is a specific form of computed tomography (CT) in which the X-ray tube is not mechanically spun in order to rotate the source of X-ray photons. This different design was explicitly developed to better image heart structures that never stop moving, performing a complete cycle of movement with each heartbeat.
Perfusion is the passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, usually referring to the delivery of blood to a capillary bed in tissue. Perfusion may also refer to fixation via perfusion, used in histological studies. Perfusion is measured as the rate at which blood is delivered to tissue, or volume of blood per unit time per unit tissue mass. The SI unit is m3/(s·kg), although for human organs perfusion is typically reported in ml/min/g. The word is derived from the French verb "perfuser" meaning to "pour over or through". All animal tissues require an adequate blood supply for health and life. Poor perfusion (malperfusion), that is, ischemia, causes health problems, as seen in cardiovascular disease, including coronary artery disease, cerebrovascular disease, peripheral artery disease, and many other conditions.
Neuroimaging is the use of quantitative (computational) techniques to study the structure and function of the central nervous system, developed as an objective way of scientifically studying the healthy human brain in a non-invasive manner. Increasingly it is also being used for quantitative research studies of brain disease and psychiatric illness. Neuroimaging is highly multidisciplinary involving neuroscience, computer science, psychology and statistics, and is not a medical specialty. Neuroimaging is sometimes confused with neuroradiology.
Myocardial perfusion imaging or scanning is a nuclear medicine procedure that illustrates the function of the heart muscle (myocardium).
Computed tomography angiography is a computed tomography technique used for angiography—the visualization of arteries and veins—throughout the human body. Using contrast injected into the blood vessels, images are created to look for blockages, aneurysms, dissections, and stenosis. CTA can be used to visualize the vessels of the heart, the aorta and other large blood vessels, the lungs, the kidneys, the head and neck, and the arms and legs. CTA can also be used to localise arterial or venous bleed of the gastrointestinal system.
Cardiac magnetic resonance imaging, also known as cardiovascular MRI, is a magnetic resonance imaging (MRI) technology used for non-invasive assessment of the function and structure of the cardiovascular system. Conditions in which it is performed include congenital heart disease, cardiomyopathies and valvular heart disease, diseases of the aorta such as dissection, aneurysm and coarctation, coronary heart disease. It can also be used to look at pulmonary veins. Patient information may be found here.
Coronary artery aneurysm is an abnormal dilatation of part of the coronary artery. This rare disorder occurs in about 0.3–4.9% of patients who undergo coronary angiography.
Anomalous left coronary artery from the pulmonary artery is a rare congenital anomaly occurring in approximately 1 in 300,000 liveborn children. The diagnosis comprises between 0.24 and 0.46% of all cases of congenital heart disease. The anomalous left coronary artery (LCA) usually arises from the pulmonary artery instead of the aortic sinus. In fetal life, the high pressure in the pulmonic artery and the fetal shunts enable oxygen-rich blood to flow in the LCA. By the time of birth, the pressure will decrease in the pulmonic artery and the child will have a postnatal circulation. The myocardium which is supplied by the LCA, will therefore be dependent on collateral blood flow from the other coronary arteries, mainly the RCA. Because the pressure in RCA exceeds the pressure in LCA a collateral circulation will increase. This situation ultimately can lead to blood flowing from the RCA into the LCA retrograde and into the pulmonary artery, thus forming a left-to-right shunt.
A myocardial bridge (MB) is a congenital heart defect in which one of the coronary arteries tunnels through the heart muscle itself (myocardium). In normal patients, the coronary arteries rest on top of the heart muscle and feed blood down into smaller vessels which then take blood into the heart muscle itself. However, if a band of muscle forms around one of the coronary arteries during the fetal stage of development, then a myocardial bridge is formed – a "bridge" of heart muscle over the artery. Each time the heart squeezes to pump blood, the band of muscle exerts pressure and constricts the artery, reducing blood flow to the heart. This defect is present from birth. It is important to note that even a very thin ex. <1 mm and/or short ex. 20 mm MB can cause significant symptoms. MBs can range from a few mm in length to 10 cm or more. The overall prevalence of myocardial bridge is 19%, although its prevalence found by autopsy is much higher (42%).
Cardiac PET is a form of diagnostic imaging in which the presence of heart disease is evaluated using a PET scanner. Intravenous injection of a radiotracer is performed as part of the scan. Commonly used radiotracers are Rubidium-82, Nitrogen-13 ammonia and Oxygen-15 water.
In the fields of cardiology and medical imaging, speckle tracking echocardiography (STE) is an echocardiographic imaging technique. It analyzes the motion of tissues in the heart by using the naturally occurring speckle pattern in the myocardium.
A diagnosis of myocardial infarction is created by integrating the history of the presenting illness and physical examination with electrocardiogram findings and cardiac markers. A coronary angiogram allows visualization of narrowings or obstructions on the heart vessels, and therapeutic measures can follow immediately. At autopsy, a pathologist can diagnose a myocardial infarction based on anatomopathological findings.
Cardiac magnetic resonance imaging perfusion, also known as stress CMR perfusion, is a clinical magnetic resonance imaging test performed on patients with known or suspected coronary artery disease to determine if there are perfusion defects in the myocardium of the left ventricle that are caused by narrowing of one or more of the coronary arteries.
Coronary CT angiography is the use of computed tomography (CT) angiography to assess the coronary arteries of the heart. The patient receives an intravenous injection of radiocontrast and then the heart is scanned using a high speed CT scanner, allowing physicians to assess the extent of occlusion in the coronary arteries, usually in order to diagnose coronary artery disease.
A hybrid cardiac surgical procedure in a narrow sense is defined as a procedure that combines a conventional, more invasive surgical part with an interventional part, using some sort of catheter-based procedure guided by fluoroscopy imaging in a hybrid operating room (OR) without interruption. The hybrid technique has a reduced risk of surgical complications and has shown decreased recovery time. It can be used to treat numerous heart diseases and conditions and with the increasing complexity of each case, the hybrid surgical technique is becoming more common.
Michelle Claire Williams is a Scottish physician and professor at the University of Edinburgh. She is president elect of the British Society of Cardiovascular Imaging. Her research makes use of medical imaging and machine learning to understand cardiovascular disease.
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