Heart Images: What They Are and What They Mean
Cardiovascular imaging techniques give cardiologists and radiologists faster and clearer views of the heart and cardiovascular structures. Here is an overview of some techniques and their roles in detecting and diagnosing heart diseases and conditions.
Echocardiography (Echo) uses sound waves or ultrasound beams to view the heart and is useful to assess heart muscle and valve function. With a transthoracic echocardiogram (TTE), the ultrasound probe is placed on the chest. For a transesophageal echo (TEE), the probe is passed down the throat and into the esophagus. Studies may occur at rest or after stress (patients undergo exercise or receive intravenous infusion of medications that raise the heart rate).
- Pros – No ionizing radiation. Portable and can be performed in a doctor’s office. TTE is noninvasive and easy for the patient. Stress imaging can identify regions of the heart muscle that may not be receiving enough blood supply.
- Cons – TEE requires light sedation. Unable to identify asymptomatic coronary artery disease (CAD) that may require preventive therapy.
Cardiac Computed Tomography (CT) uses X-rays and CT technology to produce high resolution images of the heart and the coronary arteries – the blood vessels supplying oxygen to the heart muscle. Cardiac CT can visualize small amounts of CAD that other tests may not find. This is particularly true when it is performed as a cardiac CT angiogram where iodinated contrast (a dye that allows blood vessels to be seen) is given at the time of the exam. Cardiac CT can also be performed without iodinated contrast. This technique is called “calcium scoring,” and it is used to quantify the amount of calcium present in coronary arteries. The presence of calcium in coronary arteries confirms CAD in a patient but cannot determine its severity. Cardiac CT also sees structures adjacent to the heart and within the chest that may be a source of symptoms or affect (if needed) surgery.
- Pros – Noninvasive. Can detect small amounts of CAD that other tests may not identify, so earlier medical treatment can be started.
- Cons – Ionizing radiation localized to the chest. Unable to determine if a given coronary artery narrowing is a cause of symptoms. Although rare, patients may have allergic reaction to the iodinated contrast.
Cardiac Magnetic Resonance Imaging (MRI) uses powerful magnetic fields to image the heart. This is the best method available to help determine if there is swelling (edema), inflammation, limited blood flow (ischemia), or scarring from old heart attacks (myocardial infarctions or MIs). Cardiac MRIs look at overall cardiac function and measure blood flow through the heart and the large blood vessels associated with it.
- Pros – Noninvasive. Able to identify regions of heart muscle with limited blood flow, which suggests the presence of a coronary artery narrowing in the vessel feeding the region. Able to identify scarring from a previous heart attack. Able to predict which areas of the heart muscle may respond to bypass surgery or angioplasty.
- Cons – Cannot be performed with implantable devices such as pacemakers. Unable to identify asymptomatic CAD. Confined space in scanner may be difficult for patients with claustrophobia.
Coronary Angiography (Heart Catheterization) involves placement of a catheter directly into the coronary arteries and injection of contrast dye into the catheter. This test looks for the presence of coronary artery blockages. If a blockage is identified at the time of the procedure, it can be opened by placing a stent in the artery.
- Pros – The only imaging procedure in which immediate treatment can occur if a blockage is identified.
- Cons – Invasive procedure that requires puncturing the artery and carries a less than 1% risk of significant complications. Ionizing radiation. Administration of iodinated contrast. Unable to identify asymptomatic CAD.
Nuclear Medicine includes various tests where a small amount of radiolabeled medication (drug that has a radioactive molecule attached to it) is injected into the bloodstream. Cameras then identify patterns of radiation emitted in order to visualize the heart.
- Pros – Noninvasive. Able to assess blood flow in the heart muscle, identify scars from old heart attacks, and identify portions of heart muscle that may benefit from either bypass surgery or angioplasty.
- Cons – Ionizing radiation goes through the entire body. Unable to identify asymptomatic CAD. Selecting the test appropriate for you is best achieved after consulting with your doctor. If you have known heart disease, your doctor may use these tests to determine if your current symptoms are directly caused by your heart.