Cardiac Imaging: Echo, Angiography, and Noninvasive Angiography Modalities

Echocardiography: overview and purpose

The echocardiogram has been an important part of cardiology since the 1960s. It provides information about abnormalities in blood flow as well as cardiac output and ejection fractions. Echocardiograms demonstrate the function of the heart valves and the thickness and motion of the heart wall, as well as the presence and severity of coronary artery disease. It also shows the state of the pericardium. There are different types of echocardiograms, each with its own method and indications.

Transthoracic echocardiography (TTE)

Transthoracic echocardiography is the standard method. It uses sonographic images made through the chest wall, allowing noninvasive visualization of cardiac structure and function.

Transesophageal echocardiography (TEE)

Transesophageal echocardiography is accomplished by passing the transducer through the patient’s esophagus. The resulting images are clearer because the transducer is closer to the heart. This approach requires fasting and sedation prior to the examination.

Stress echocardiography

Stress echocardiography is performed before and after exercising, such as on a stationary bike or treadmill. The purpose is to compare blood flow to the heart under resting conditions and under stress, aiding assessment of functional reserve and ischemia.

Doppler echocardiography

Doppler echocardiography is used for measuring the velocity and direction of the blood flow in the heart. It provides details on flow patterns, gradients across valves, and regurgitant or stenotic lesions.

Angiography: general principles and purpose

Angiography is performed to assess blood flow using iodine-based contrast material delivered into the heart and viewed with fluoroscopy. Its primary purpose is detecting obstruction of blood flow, commonly caused by arterial stenosis. There are several angiography techniques, each with specific applications.

Digital subtraction angiography (DSA)

Digital subtraction angiography produces images by comparing images taken after injecting contrast with precontrast images. The use of contrast material ensures that only the vessels are seen and not the heart itself, enhancing visualization of vascular structures.

Coronary angiography

Coronary angiography is one of the cardiac catheterization procedures for diagnostic and interventional purposes. By delivering the contrast into the left side of the heart, it is possible to specifically evaluate the coronary arteries. The slide examples show an occlusion and the state after stent placement, illustrating how catheter-based contrast imaging guides assessment and intervention.

Pulmonary angiography

The third type is pulmonary angiography, and it is used to diagnose pulmonary embolisms. It visualizes the pulmonary vasculature to identify filling defects caused by emboli.

Ventriculography

Ventriculography is used to view the motion of the ventricular wall as well as the outflow tract, providing assessment of ventricular function and dynamics.

Noninvasive angiography: MRI/CT approaches

All of these angiographic techniques are increasingly being replaced by noninvasive angiography performed with MRI and CT scans. Conventional coronary angiography, however, remains in use for gauging the severity of obstructive coronary artery disease as well as to guide certain interventions.

CT pulmonary angiography (CTA)

CT pulmonary angiography was introduced as an alternative to ventilation-perfusion scans, as high-speed modern scanners became available. In CT angiography, contrast material is introduced through a peripheral vein, making the procedure less invasive than catheter-based angiography.

The pulmonary vessels light up and become radiodense, which makes obstructions appear darker because they do not fill with contrast. The main indication for CTA is a suspicion of a pulmonary embolism (PE).

MRI angiography (MRA) and MRI-based approaches

MRI angiography (MRA) refers to MRI pulse sequences that produce signal from blood flowing in a noninvasive manner without exposure to radiation or iodine-based contrast. This approach has been used to study the aorta, major branches, and the cerebral vascular tree. However, MRI angiography has not been as successful as CT angiography or invasive catheter-based angiography in all cases. MRA is relatively expensive and generally has a lower spatial resolution than CT angiography.

Summary of practical considerations

Conventional coronary angiography remains a standard for assessing the severity of obstructive coronary artery disease and guiding interventions, despite the emergence of noninvasive CT and MR angiography techniques. Noninvasive CT pulmonary angiography offers a rapid, less invasive option for suspected pulmonary embolism, while MRI/MRA provides a radiation-free alternative for vascular imaging at the expense of higher cost and typically lower resolution. Sedation and fasting implications apply to transesophageal echocardiography, and overall, the choice of modality balances invasiveness, radiation exposure, resolution, and clinical question.