How Nuclear Medicine Works

SPECT, Cardiovascular Imaging and Bone Scanning

­SPECT is a technique similar to PET. But the radioactive substances used in SPECT (Xenon-133, Technetium-99, Iodine-123) have longer decay times than those used in PET, and emit single instead of double gamma rays. SPECT can provide information about blood flow and the distribution of radioactive substances in the body. Its images have less sensitivity and are less detailed than PET images, but the SPECT technique is less expensive than PET. Also, SPECT centers are more accessible than PET centers because they do not have to be located near a particle accelerator.

Cardiovascular imaging techniques use radioactive substances to chart the flow of blood through the heart and blood vessels. One example of a cardiovascular imaging technique is a stress thallium test, in which the patient is injected with a radioactive thallium compound, exercised on a treadmill, and imaged with a gamma ray camera. After a period of rest, the study is repeated without the exercise. The images before and after exercising are compared to reveal changes in blood flow to the working heart. These techniques are useful in detecting blocked arteries or arterioles in the heart and other tissues.

Bone scanning detects radiation from a radioactive substance (technetium-pp methyldiphosphate) that, when injected into the body, collects in bone tissue, as bone tissue is good at accumulating phosphorus compounds. The substance accumulates in areas of high metabolic activity, and so the image produced shows "bright spots" of high activity and "dark spots" of low activity. Bone scanning is useful for detecting tumors, which generally have high metabolic activity.