There is only one type of SPECT scan and it is a nuclear test. However, there are two types of stress tests that use SPECT scans. The first is the nuclear stress test. A nuclear stress test takes very clear, three-dimensional pictures of the heart when the person is at rest and shortly after physical stress. By measuring the rate of absorption of the radioactive tracer before and after exercise, these pictures show contrasts between light and dark spots, which can indicate areas of damage or reduced blood flow that are present before, during and after exercise.

If the person is unable to exercise, the physician may choose to do a type of nuclear stress test called the pharmacological stress test. Also known as a chemical stress test, this type of diagnostic tool is used with patients who are unable to perform physical activity or in cases where the chemical stress test would be more accurate. This might include patients who cannot walk because of arthritis or another limb infirmity, or due to the presence of asthma or emphysema that would hinder their ability to exercise. Finally, chemical stress tests may be ordered for patients who have an abnormal electrocardiogram (EKG) or pacemaker.

A chemical stress test measures the reaction of the heart under chemically induced stress to assess the blood supply and motion of the heart muscle. This test relies on the injection of another drug, in addition to the tracer, that causes the heart to react as if the person were exercising even though they are actually at rest. Drugs that may be used to produce the pharmacological stress include:

Another type of cardiac SPECT scan is the gated SPECT scan, which includes the multi-gated acquisition scan (MUGA). This type of scan uses an electrocardiogram (EKG) to time exactly when the gamma camera takes pictures of the heart’s functions and structures. In this way, physicians can obtain images of the heart when it is contracting (systole) and relaxing (diastole). The gated SPECT scan provides a much more complete picture of how a heart is functioning and dramatically improves the accuracy of the diagnosis. The images obtained with gated SPECT scans have the additional advantage of being highly reproducible and consistent.