Cardiac SPECT (single photon computed tomography) scans are noninvasive imaging tests that can provide very accurate, three-dimensional pictures of the heart’s structures and function. This is accomplished through the use of a radionuclide tracer that is injected into the patient’s blood and travels to the heart. As it is travels through the heart, the tracer emits energy that is visible to a special camera called a gamma camera. During a SPECT test, the gamma camera rotates around the patient, taking pictures of the tracer’s progress as it is absorbed by the heart muscle. If absorbed unevenly or too slowly, a physician may suspect heart disease and order further tests or make a diagnosis.

Today, many cardiac patients undergo a SPECT scan as part of their diagnostic work-up for detection and evaluation of heart disease. Cardiac SPECT imaging is a valuable tool for:

SPECT scans are increasingly used to monitor patients following bypass surgery, in which a section of a blood vessel from another part of the body is taken and used to create a detour around a clogged coronary artery. Studies have shown that SPECT scans can be an effective tool in determining if patients remain at a high risk for heart attack or other major cardiac event. They can be used, for example, to assess patients with left bundle branch block who have had a heart attack. SPECT scans have also been used to predict potential heart problems for patients with diabetes who are unable to exercise and are at high risk for heart attack. Because SPECT scans are generally effective tools in predicting heart attack risk, they are also used in hospital emergency departments for evaluation of patients who arrive with complaints of chest pain.

Cardiac SPECT scans are particularly important in the diagnosis of heart disease in women because other tests such as the electrocardiogram (EKG) and the exercise stress test and planar scans could fail to detect heart disease in women accurately. This is because women’s thicker breast tissue can make it difficult to obtain clear images using older traditional planar imaging or diagnostic techniques. A SPECT scan gives improved image quality. SPECT scans are also being used in the diagnosis and evaluation of tumors in the breast and other areas, including the brain.

There are a number of important similarities and differences between SPECT and some other imaging techniques:

• SPECT, the standard magnetic resonance imaging (MRI) and the traditional computed tomography (CT) scan all produce an image of an organ’s anatomy. However, only SPECT provides a picture of how an organ is functioning by measuring its ability to absorb the tracer, which allows physicians to measure how quickly the heart muscle takes up blood, rather than an image of its anatomy. This information is often used to detect and monitor coronary artery disease.
  
  
• Both SPECT and a positron emission tomography (PET) are forms of nuclear imaging. However, the SPECT test differs from the PET test in that the tracers used in SPECT testing stay in the bloodstream, whereas the sensitive tracers used in PET are absorbed into the tissues themselves. In PET testing, this is accomplished by attaching radionuclide tracers to molecules such as glucose that travel into cells, thus allowing physicians to gauge the metabolic function of the organ by measuring glucose uptake patterns, for example. While PET testing may yield more detailed information, it is more expensive and requires use of radioactive particles that have an extremely short half-life and must be produced relatively near to the PET scanner. SPECT scanners, by contrast, use more stable radionuclide tracers and are more common and less expensive.
  
  
• Both SPECT and a coronary angiogram can help detect arterial stenosis (narrowing or blockage of an artery). However, SPECT is often used as an initial assessment to avoid a coronary angiogram because SPECT is noninvasive and relatively inexpensive.

There are certain conditions that could interfere with the clarity of SPECT images, making a patient ineligible for a SPECT scan. These conditions include viral infection of the heart (myocarditis) or recent lung infection. Pregnant or breastfeeding women should also avoid the SPECT scan because of its use of a radioactive tracer.