Overview

In conventional X-ray or CT examinations, the radiation comes out of a machine and then passes through the patient's body.  Nuclear medicine exams, however, use the opposite approach: a radioactive material is introduced into the patient's body (usually by injection), and is then detected by a machine called a gamma camera.

X-rays produce a structural image of an organ -- in other words, they tell us what the organ looks like.  On the other hand, nuclear scans image organ function.  That is, they can tell us what part of an organ is working properly, and what part is not.  For example, in one kind of nuclear scan called bone imaging, the bone metabolism changes caused by trauma, infection or invasion by tumor may be seen weeks or months before an abnormality is seen with X-rays.