Positron Emission Tomography (PET)
Positron Emission Tomography (PET)
Definition
Positron emission tomography (PET) is a noninvasive scanning technique that utilizes small amounts of radioactive positrons (positively charged particles) to visualize body function and metabolism.
Purpose
PET is the fastest growing nuclear medicine tool in terms of increasing acceptance and applications. It is useful in the diagnosis, staging, and treatment of cancer because it provides information that cannot be obtained by other techniques such as computed tomography (CT) and magnetic resonance imaging (MRI).
PET scans are performed at medical centers equipped with a small cyclotron. Smaller cyclotrons and increasing availability of certain radiopharmaceuticals are making PET a more widely used imaging modality.
Physicians first used PET to obtain information about brain function, and to study brain activity in various neurological diseases and disorders including stroke, epilepsy, Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease; and in psychiatric disorders such as schizophrenia, depression, obsessive-compulsive disorder, attention deficit hyperactivity disorder (ADHD), and Tourette syndrome. PET is now used to evaluate patients for these cancers: head and neck, lymphoma, melanoma, lung, colorectal, breast, and esophageal. PET also is used to evaluate heart muscle function in patients with coronary artery disease or cardiomyopathy.
Description
PET involves injecting a patient with a radiopharmaceutical similar to glucose. An hour after injection of this tracer, a PET scanner images a specific metabolic function by measuring the concentration and distribution of the tracer throughout the body.
When it enters the body, the tracer courses through the bloodstream to the target organ, where it emits positrons. The positively charged positrons collide with negatively charged electrons, producing gamma rays. The gamma rays are detected by photomultiplier-scintillator combinations positioned on opposite sides of the patient. These signals are processed by the computer and images are generated.
KEY TERMS
Electron— One of the small particles that make up an atom. An electron has the same mass and amount of charge as a positron, but the electron has a negative charge.
Gamma ray— A high-energy photon emitted by radioactive substances.
Half-life— The time required for half of the atoms in a radioactive substance to disintegrate.
Photon— A light particle.
Positron— One of the small particles that make up an atom. A positron has the same mass and amount of charge as an electron, but the positron has a positive charge.
PET provides an advantage over CT and MRI because it can determine if a lesion is malignant. The two other modalities provide images of anatomical structures, but often cannot provide a determination of malignancy. CT and MRI show structure, while PET shows function. PET has been used in combination with CT and MRI to identify abnormalities with more precision and indicate areas of most active metabolism. This additional information allows for more accurate evaluation of cancer treatment and management.
Resources
BOOKS
Bares, R., and G. Lucignani. Clinical PET. Kluwer Academic Publishers, 1996.
Gulyas, Balazs, and Hans Muller-Gartner. Positron Emission Tomography: A Critical Assessment of Recent Trends. Kluwer Academic Publishers, 1996.
Kevles, Bettyann Holtzmann. Medical Imaging in the Twentieth Century. Rutgers University Press 1996.
PERIODICALS
“Brain Imaging and Psychiatry: Part 1.” Harvard Mental Health Letter 13 (Jan. 1997): 1.
“Brain Imaging and Psychiatry: Part 2.” Harvard Mental Health Letter 13 (February 1997): 1403.
Goerres, G. “Position Emission Tomography and PET CT of the Head and Neck: FDG Uptake in Normal Anatomy, in Benign Lesions, and Changes Resulting from Treatment.” American Journal of Roentgenology (November 2002): 1337.
Kostakoglu, L. “Clinical Role of FDG PET in Evaluation of Cancer Patients.” Radiographics (March-April 2003): 315
Shreve, P. “Pitfalls in Oncologic Diagnosis with FDG PET Imaging: Physiologic and Benign Variants.” Radio-graphics 62 (January/February 1999).
“Studies Argue for Wider Use of PET for Cancer Patients.” Cancer Weekly Plus 15 (December 1997): 9.
OTHER
Di Carli, M. F. “Positron Emission Tomography (PET).” 1st Virtual Congress of Cardiology. October 4, 1999. http://www.fac.org.
Madden Yee, Kate. “Start-up Enters Breast Imaging Arena with Scintimammography, PET Offerings.” Radiology News. March 14, 2001. http://www.auntminnie.com.
“Nycomed Amersham and the Medical Research Council: Major Collaboration in World Leading Imaging Technology.” Medical Research Center 2001. http://www.mrc.ac.uk/whats_new/press_releases/PR_2001/mrc_02_01.html.
Dan Harvey
Lee A. Shratter, M.D.