Positron Emission Tomography (PET)

Positron Emission Tomography (PET) scanning is a form of medical diagnosis that falls in the region of Nuclear Medicine. Although the word nuclear has a number of negative suggestions, nuclear medicine is just the name given to a medical procedure of diagnosis that simply utilizes radioactive substances (that are not hazardous to the human body) as an instrument to images the body and treats disease.

Nuclear medical techniques allow doctors to examine the insides of the human body in a non-invasive manner, i.e. without exploratory surgery. Nuclear medical techniques gain information from both the physiology (function) of the body as well as the body’s anatomy to establish both a diagnosis and the appropriate treatment.

As nuclear medical technology advanced in the last half-century, it paved the way for a number of new medical technological procedures that are rooted in nuclear medical practices.

Positron Emission Tomography, or PET imaging or PET scan as it is also referred to, is a non-invasive diagnostic imaging procedure that allows physicians to examine organs such as the heart and brain.

Originally used solely as a research tool, it was not until 1975 that the first primarily used commercial PET scanner was introduced. With technological advances made in the nuclear medicine field, the PET scan procedure moved from low tech to producing 3-D images in the 1980s. Despite these innovations, Positron Emission Tomography was predominantly used in research. However, in the early 1990s, the use of PET expanded into clinical use. Hospitals, diagnostic clinics, mobile systems and physician practices began to understand the promise of PET and began to master its use.

The PET scan procedure differentiates itself as an imaging procedure from other procedures like x-rays, computed tomography (CT), and magnetic resonance imaging (MRI) as it produces images that are able to detail the chemical function of the targeted organ or tissue. MRI, CT and X-rays can are only able to detail body structure.

This pronounced difference is important, as PET imaging is able to make the distinction between benign (alive tissue) and malignant (dead tissue) disorders, where as MRI, CT and X-rays can only confirm the presence of a suspect mass.

Consequently PET is a valuable tool for physicians who require information about the chemical function of such vital organs as the heart and brain in recommending a medical course of action.

PET scans are now a vital part of the medical diagnosis arsenal and as such has a range of different medical uses. A PET scan allows physicians to measure the body's abnormal molecular cell activity. This function means that PET scans are generally used in three areas of medicine:

Cancer

  • Breast cancer
  • Lung cancer
  • Colorectal cancer
  • Lymphoma
  • Melanoma
  • Other skin cancers

Brain Disorders

  • Alzheimer's Disease
  • Parkinson's Disease
  • Epilepsy
  • Stroke
  • Tumors

Heart Disease

  • Coronary artery disease
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Positron Emission Tomography (PET) Scanning

How Positron Emission Tomography is able to produce the images it produces is rooted in the basis of nuclear medicine. A PET scans give information about the body's chemistry that is not available with other imaging techniques, revealing metabolic information (as opposed to anatomical information), providing the physician with extra insight.

If a person is considering undergoing a PET scan, it is usually because their physician has recommended this procedure. Many people when they learn that they have to undergo a Positron Emission Tomography (PET) scan are often concerned due to the use of radiation in this medical procedure. However this reaction is not necessary as Positron Emission Tomography (PET) is extremely safe

The Positron Emission Tomography procedure works like a camera that produces detailed images of biological functions from inside the human body.

The Positron Emission Tomography scan is a unique, non-invasive diagnostic imaging tool that is a metabolic imaging tool. What this means is that a PET scan produces images detailing the biochemical functioning of an organ or tissue. In essence The PET scan visualizes biochemical changes caused by disease.

A PET scan usually takes place in a major medical center that contains a small cyclotron. A cyclotron is a highly advanced nuclear medical machine that is used to produce radioisotopes: an ingredient that is used to synthesize the radioactive tracer that is used to help visualize metabolic changes in the body, due to disorders.

In the PET scan procedure, a patient is given a substance that is usually tagged with a radio pharmaceutical that has a short half-life (the time it takes for the radioactive nuclei in the radioisotope to reduce to half of its previous value).

A radioactive isotope with a short half-life means that the radiation only last for a very short period of time, before which the isotope decays to become a stable element. The period is so brief that the radiation does no damage to the body, but can be used in helping to locate tumours

Radio pharmaceuticals are given to a patient predominantly through injection, but can also be given through an existing intravenous line or inhaled as a gas. Once the radiopharmaceutical is inside the body, it travels to its targeted source.

The most common injection used in a PET scan is one that consists of a glucose-based radiopharmaceutical called FDG. FDG travels through the body, eventually traveling to the organs and tissues targeted for examination.

In the scan the patient lies flat on a bed or table that moves steadily through the PET scanner. The scanner has cameras that detect the gamma rays emitted from the patient, and turns these emissions into electrical signals.

A computer to generate the medical images processes the gamma ray signals that are collected by the scanner. The bed/table moves a few inches again, and the process is repeated.

This finite procedure produces clear digital images, which are assembled by the computer into a 3-D image of the patient's body. If an area is cancerous, the signals will be stronger there than in surrounding tissue as more of the radiopharmaceutical (FDG) is being absorbed in those areas



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