PET stands for positron emission tomography. It involves an isotope that is injected and emits some radiation, a ring of detectors which detects this radiation, and the conversion of this detected radiation into an image. The PET scanner consists of the bed, which is not the most comfortable bed. And this bed is slowly moved through a ring of detectors. Basically, it looks very similar to a CAT scan. The CAT scan would send radiation from outside through the body while we inject isotopes that send radiation from inside the body outside to the detectors.
I tell the patients that they have to be aware of two things. One, the bed is quite uncomfortable, and two, it’s kind of boring to be in the scanner. At the time of the radioisotope injection, the patient might feel a little bit of a metallic taste in his mouth. Then there is an uptake period. We wait until the radioisotope really accumulates in the tissue that we want to look at. And after these 40 minutes, the patient is moved into the scanner, during which time the images are being taken.
When the patient is in the scanner, you accumulate data over, let’s say, a five- or six-minute period and convert it into a gray scale. The impulses are digitized. Usually when you see color displays, normally, it’s indicated in red or yellow. So if you have a 16-grade color scale, each of the colors would represent a six percent change in radioisotope activity. The scanner actually acquires 63 image planes at the same time in this given field of view, which is about 15 centimeters. You can, in fact, label any compound that you have in mind with a positron emitter and image the process that you’re interested in imaging.