Center For Positron Emission Tomography (CPET)

Positron Emission Tomography (PET)

Positron Emission Tomography
(PET) is a non invasive, diagnostic imaging technique for measuring the metabolic activity of cells in the human body. It is useful clinically in patients with certain conditions affecting the brain and the heart as well as in patients with certain types of cancer. The field of PET has been emerging into clinical diagnostic medicine and is approved by many insurance carriers for coverage.
PET is unique because it produces images of the body's basic biochemistry or function. Traditional diagnostic techniques, such as x-rays, CT scans or MRI, produce images of the body's anatomy or structure. The premise with these techniques is that the change in structure or anatomy that occurs with disease can be seen. Biochemical processes are also altered with disease and may occur before there is a change in gross anatomy. PET is an imaging technique that is used to visualize some of these processes that change. Even in diseases, such as Alzheimer's disease, where there is no gross structural abnormality, PET is able to show a biochemical change. PET is a very useful addition to the clinician's diagnostic toolbox, providing significant advances to traditional diagnostic methods.
 
A PET Scan is a simple procedure. It involves the use of a small amount of a radioactive material, similar to what is used in other nuclear medicine procedures. The radioactivity is attached or tagged to a compound that is familiar to your body. Compounds similar to glucose, water, ammonia, and certain drugs may be used. The radioactive drug is administered to the patient, usually by injection, and a specially designed PET scanner images how the body processes the drug. PET has been in clinical use since the early 1990s.
 
Explore our website to learn more about the equipment used in PET, including the cyclotron or generators to produce the PET drugs or the cameras that produce the images.
 
PET has been shown to be useful to physicians in the care of patients with many types of diseases. Specifically, PET is useful in the diagnosis and management of patients cancer, with certain neurologic disorders, and with heart disease.
 
There is considerable information about PET and its clinical applications throughout this web site.

Labeling

Chemical compounds we'd like to follow through the body are labeled with radioactive atoms that decay by emitting positrons. Labeling is a process of attaching some kind of identifying tag to the compound you want to follow which will later let you identify where the compound has gone. In PET the compounds that can be labeled are limited only by the imagination of the investigators and the physical half-life of the positron emitting label. One of the big advantages of PET is that the atoms which can be labeled (turned into positron emitters) are the same atoms which naturally comprise the organic molecules utilized in the body. These atoms include oxygen, carbon and nitrogen to name a few. Since these atoms occur naturally in organic compounds, replacing the naturally occurring atoms in a compound with a labeled atom leaves you a compound that is chemically and biologically identical to the original (so it will behave in a manner identical to its unlabeled sibling) and that is traceable. In addition to naturally occurring compounds such as neurotransmitters, sugars, etc., it is also possible to label synthesized compounds (such as drugs) and follow them as well.

 

Tracers

A second important attribute of PET is that it can follow labeled compounds in trace quantities. This means that the labeled compounds can be introduced into the body without affecting the normal processes of the body. For example, labeling a pound of sugar and ingesting that sugar would be a good example of a non-trace quantity of labeled compound. At these quantities, blood chemistry would be altered (e.g. insulin produced in response to rising blood sugar levels). Often you want to follow the time course of a compound in the body by introducing trace quantities of a compound that will behave the same as the unlabeled compound without altering the ongoing physiological state of chemical processes of the body. PET is sensitive enough to detect trace amounts of labeled compound and so is well suited to this kind of investigation.

 

Steps in the PET process

  • production of positron emitting isotope in a cyclotron
  • chemistry of labeling compound with positron emitter and preparing compound in a form suitable for administration in humans
  • transport of labeled compound from chemistry group to camera group
  • administration (injection) of tracer compound & data acquisition with PET camera
  • processing of data from PET camera to extract information related to the tracer's kinetics in the body
  • interpretation of result