Cardiac imaging
Cardiac imaging, also called cardiovascular imaging, can be performed by computed tomography (CT), echocardiography (cardiac ultrasound) magnetic resonance imaging (MRI), angiography or nuclear imaging.
Nuclear imaging, also referred to as molecular imaging, is used as a gold standard for myocardial perfusion imaging (MPI). MPI, also called a nuclear stress test, is a noninvasive imaging test that depicts how well blood flows through the heart muscle (perfusion).
MPI can show the function of the heart muscle by showing radiotracer uptake by the cardiac muscle cells and blood flow through the heart. MPI with single-photon emission computed tomography (SPECT) is the most frequently performed study in nuclear cardiology. The scan provides three-dimensional imaging, displaying perfusion. A less common exam type used positron emission tomography (PET), which uses a much shorter scan time.
A myocardial perfusion scan uses a minute amount of radioactive substance (usually thalium or technetium-99m) called a radioactive tracer. The tracer travel through the bloodstream and ultimately gets absorbed by healthy heart muscle.
After the radioactive tracer is injected, a special type of camera (gamma camera) is used to detect the radioactive energy from outside of the body. The camera will take images of the heart. On the scan, the areas where tracer has been absorbed will appear different from areas that do not absorb the tracer. Areas in the heart that are damaged or that do not have good blood flow will not absorb the tracer. These areas are often referred to as “cold spots.”
A stress myocardial perfusion scan may also be performed assessing the blood flow to the heart muscle when it is stressed, such as during exercise. Images are taken of the heart during stress and compared to images of the heart at rest in order to make a diagnosis of damaged heart muscle.
Cardiac CT angiography (CTA or CCTA) uses a series of X-ray imagines of the patient's heart to reconstruct an image dataset.This can be sliced on any axis or used to create 3D renderings on the heart's anatomy to look for perfusion defects, structural heart defects and plaque inside the coronary arteries.
Echocardiography uses sound wave image returns (similar to sonar) to create an image. Ultrasound does not use any X-ray radiation. It is one of the most prescribed cardiac medical imaging tests. Echo is used to evaluate heart valve function and overall cardiac function by assessing ejection fraction (EF). Newer systems also can measure wall motion or speckle tracking to assess loss of movement due to changes in the heart caused by ischemia, infarct or heart failure.
Cardiac MRI is complex, time consuming, and has imaging exam times that are longer that other imaging modalities. For this reason, it has not seen wide spread use for cardiac imaging. However, MRI offers excellent soft tissue delineation and does not use radiation to create the images. Recent advances in MRI systems might make MRI a more attractive option for wider spread use in cardiac imaging in the future
The images produced are used in conjunction with a CT scan, MRI or PET scan, in order to make a clinical diagnosis.
The goal of cardiac imaging is to diagnose cardiovascular problems. Preventative health can aid in reducing heart disease. Read the article Understanding How to Reduce the Risk for Heart Attack.
Learn more about cardio PET scan and cardiac CT.