Friday, May 1, 2009

Positron Emission Tomography (PET)

PET is a nuclear medicine imaging technique which produces a three-dimensional image or picture of functional processes in the body. It detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide introduced into the body on a biologically active molecule. Images of tracer concentration in 3-dimensional space within the body are then reconstructed by computer analysis. In modern scanners, this reconstruction is often accomplished with the aid of a scan using CT X-ray performed on the patient during the same session, in the same machine.It is both a medical and research tool. It is used  for clinical diagnosis of certain diffuse brain diseases such as those causing various types of dementias. It is an important research tool to map normal human brain and heart function.It is also used in pre-clinical studies using animals, where it allows repeated investigations into the same subjects. This is particularly valuable in cancer research, as it results in an increase in the statistical quality of the data..

Alternative methods of scanning include x-ray computed tomography(CT), magnetic resonance imaging(MRI), functional magnetic resonance imaging(fMRI), ultrasound and single photon emission computed tomography(SPECT). PET and SPECT are capable of molecular biology detecting areas. PET scanning is non-invasive, but it does involve exposure to ionising radiation.The total dose of radiation is small, however, usually around 7 mSv. This can be compared to average background radiation of 2.2 mSv, 0.02 mSv for a chest x-ray, up to 8 mSv for a CT scan of the chest.

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