PET also known as Positron Emission Tomography is a medical imaging procedure or technique which is widely used in clinical research. It is a type of nuclear medicine imaging. Nuclear imaging is a specialized area of medical imaging in which the severity of diseases or treating them is determined with the use of radioactive material. Nuclear medicine procedures are non invasive with intravenous injection as an exception which is usually painless.
PET scanners are used to produce 3-dimensional image of functional process of the human body. This helps to reveal the functioning of tissues and organs. The scanner detects pairs of gamma radiation which is emitted by the radioactive tracer given to the patient. The images will then be reconstructed by computer analysis. The radioactive tracer may be injected in the body, swallowed or inhaled as a gas depending on the area or the organ in the body to be examined. Eventually this radioactive material will get accumulated in the body organ to be scanned. Radioactive material will accumulate more in the area that has high level of chemical activity. In many clinical or imaging part of clinical trials PET images may be superimposed with CT – Computed Tomography to produce special views, it’s a practice known as image fusion. In this case, positron emission tomography will produce the functional aspect of the body (for example blood flow, use of oxygen, metabolism of glucose) while the computed tomography will produce the structural aspect of the body organs (for example lungs, liver, stomach, pelvis, and many more). Combined use of positron emission tomography and computed tomography helps as the fused images produced by this technique can pinpoint the anatomic location of any abnormal metabolic activity in the body.
A PET scan can evaluate various neurological conditions, heart problems and cancer. The radioactive tracers that accumulate in organs with high chemical activity corresponds to areas of disease and the PET scans show them as brighter spots also called as Hot Spots. A biologically active material is used for positron emission tomography. An analogue of glucose called as FDG or Fluorodeoxyglucose is injected to the subject before they are scanned. FDG is a radioactive material that is used in medical imaging and it is used only for PET scanning. The PET scanner forms images of the distribution of FDG in the body. This glucose analogue is used as it will be taken up by cells that use high glucose for examples organs like brain, kidney and also cancer cells. Cells in brain or kidney will release the glucose but cancer cells do not release the glucose once absorbed phosphorylation takes place as the metabolic activity is very high. FDG-PET helps to determine the extent/spread of certain cancers, its response to treatment and its recurrence. The types of cancer that can be detected by positron emission tomography technique are Brain, Breast, Cervical, colon, thyroid, pancreas, lung, and lymphoma. In case of heart disease PET scan can detect the blood flow to find out the possible benefits after conducting angioplasty or coronary artery bypass surgery. PET scans helps to determine the activity of brain during different tasks and further helps to determine seizures, memory disorders, epilepsy, Alzheimer’s or tumors.
To prepare for a PET scan, patients are asked to fast for 4 – 6 hours prior to scanning procedures, but are asked to consume plenty of water. Then the radiotracer will be injected into the arm or swallowed or inhaled which may take about 30 – 90 minutes to reach the target cells. For this duration the patient will be asked to rest and not move or talk. After this the patient will be scanned. Once the necessary part of the body is scanned the patient is again asked to consume plenty of water so as to flush the radioactive tracers out of the body more quickly. It may take about 3 – 4 hours for the radioactive tracers to completely leave the body system. It’s not recommended for pregnant women to undergo PET scanning as there is a risk for the baby.
PET – Positron Emission Tomography is used in the imaging part of a clinical trial in studies on Hodgkin’s or non-Hodgkin's lymphoma, colorectal, lung, breast cancer and melanoma. It is also used in pre-clinical studies in animals in order to facilitate repeat investigation in the same subject, thus helping in oncology research studies leading to an increase in statistical quality of the data and substantially decreasing the number of animals required for any given study. Thus using PET scanner for clinical trials is a valuable technique.
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