Courtesy of Intermountain Medical Imaging, Boise, Idaho.

A bone scan is a test that uses a radioactive tracer to look at the bones of the body. Areas that absorb little or no amount of tracer appear as dark or "cold" spots. Areas of fast bone growth or repair absorb more tracer and show up as bright or "hot" spots in the pictures.

Figure 1 shows a normal whole-body scan. Figure 2 shows cancer of the prostate that has spread to the spine.