How to Read Pet Scan Images for Cancer

PET Scan (Positron Emission Tomography)

A PET Scan (or Positron Emission Tomography) is a non-invasive, diagnostic exam that finds information about the activity of different parts of the torso. Those parts of the body that are the most active need free energy, and the energy that it uses is sugar (also called glucose). A PET scan uses a particularly created substance that the body thinks is saccharide, and takes up into the cells. This substance is called a 'tracer', and it is almost exactly like saccharide, but has a modest radioactive part fastened to it. The images are based on the detection of radiation from the emission of positrons (positively charged electrons) from this radioactive tracer. The subsequent images created are used to evaluate a diverseness of diseases, with the most mutual use being whole body imaging of cancer.

How Does a PET Browse Work?

PET scans work to identify the cellular changes that occur in the body during disease. During a PET scan, the patient is given a substance chosen a tracer, typically a chemic found in the torso (oxygen, glucose, nitrogen, fluorine) which has been tagged with a radioactive atom that breaks down quickly to release positrons. The most common tracer has a complicated name, but is by and large known equally FDG (which stands for ii-[18F]fluoro-two-deoxy-D-glucose). FDG is very similar to glucose (sugar). One time in the torso FDG travels to the surface area of the body that is using a lot of carbohydrate and breaks downwardly. In breaking downwards, it releases a positron. This combines with an electron from the patient sending out radioactive waves. These waves can be detected past the PET Scanner that converts the waves into electrical signals that can be analysed by a computer. The computer can and then create images of the targeted tissue's function, in either a colour code, or in black and white. Different colours or degrees of effulgence on a PET image represent different levels of tissue or organ role. In the PET epitome to the correct, darker areas represent those that are using more saccharide, and then have more of the radioactive substance in them. For example, because healthy tissue uses glucose for energy, it accumulates some of the tagged glucose, which volition bear witness upwardly on the PET images. Nevertheless, cancerous tissue, which uses more glucose than normal tissue because it is growing much faster, will accrue more of the substance and announced brighter than normal tissue on the PET images. Therefore PET scans are commonly used to detect cancer, as the browse will find biochemical changes in the body associated with cancer as well as the extent of spread and the possible effective treatment. PET scans are oftentimes used to determine blood menstruation to the heart tissue in association with coronary middle disease and myocardial infarctions. Functions of the encephalon may likewise be examined in association with patients with memory loss, suspected or known brain tumours or seizure disorders.

During a PET Browse

PET scans are generally done in an outpatient setting and preparation is usually ready by your doctor. The scan does require the patient to lie still for a catamenia of time upwards to two hours, so if you feel you lot may have a trouble with this, delight talk to your doctor. Women who suspect they may exist pregnant or are pregnant demand to notify their medico as this is a radioactive procedure and could have effects on an unborn foetus. The PET scanner is a donut-ring shaped appliance with an attached table that moves into the scanning ring. Initial scans may be washed earlier you are taken into a special injection room where the tracer is administered, unremarkably intravenously. Information technology volition then take 30-90 minutes for the substance to travel through your trunk and accumulate. During this fourth dimension you may exist asked to rest quietly to allow the substance to travel through the body. Y'all will and so be asked to lie still on the scanner tabular array and it will motility in through the scanner ring. During the scan, which can take from 30 minutes to two hours, you must lay very nevertheless to allow for clarity of the images. After the browse in that location are no restrictions to daily action, just it is recommended you potable plenty of water to flush your arrangement of the tracer.

Benefits of a PET Browse

PET scans are beneficial as they demonstrate the biochemical changes in the body, whereas a CT or MRI scan identifies anatomical changes. A PET Scan therefore helps to place issues at the level of their activity and function, which might modify long before whatsoever changes in trunk structure (such as a tumour) go apparent. This allows for earlier diagnosis and more effective treatment of diseases such as cancer, and besides more than detailed imaging of other conditions. There is little risk involved with the intravenous assistants of the radioactive "tracer" equally the tracer has a short decay fourth dimension of merely a few hours and is apace removed from the body.

Risks of a PET Scan

The risks associated with a PET browse are very small, and are due to reactions to the radioactive "tracer" injected. The level of tracer given to a patient is very tiny, and the chances of a reaction occurring are incredibly low.

Limitations of a PET Scan

• PET scans can sometimes show upwardly areas of loftier activity which may exist mistaken for cancers. Inflammatory weather condition similar rheumatoid arthritis or tuberculosis absorb a lot of the tracer, and then can cause disruptive results.
• A PET scan is less accurate in certain situations:
  1. Wearisome-growing, less active tumors may not absorb much tracer.
  2. Small tumors (less than 7mm) may non exist detectable.
  3. High levels of blood saccharide tin can cause the cells to blot this normal sugar rather than the radioactive, injected kind. Patients are normally fasted for four hours before a PET scan, and blood sugar levels measured to lower the chances of this happening.
• The radioactive substance has a very short decay and therefore appointments must run on schedule.
• PET scans are a very expensive class of imaging, and are not readily available. They often accompany other scans such equally CT and MRI in order to be diagnostically effective.

Results of a PET Scan

After a PET scan, the doctor will receive an image of the patient displaying the different amounts of action nowadays in different parts of the body. An instance of this is given to the right, where areas of high activity in the brain are white, and depression activity are bluish. If there is a cancer somewhere in the body, this surface area will announced more than active and then PET scans are often used to see if a cancer has spread to other parts of the body or to encounter how advanced a cancer is. A PET scan is non every bit accurate for very small cancers however, so very early scans may not prove anything.

References

1. Positron Emission Tomography: Assessment Report. Medicare Services Advisory Committee, 2000. Commonwealth of Australia.
2. Soben P, Udelson KE. 'Thoracic Assessment of myocardial viability by nuclear imaging in coronary heart disease' [online], UpToDate, 2006. Bachelor at URL: http://www.uptodate.com (terminal accessed 13/07/06)
3. Stark P. 'Thoracic positron emission tomography' [online], UpToDate, 2006. Available at URL: http://www.uptodate.com (last accessed 13/07/06)

Dates

Posted On: thirty August, 2005

Modified On: 17 August, 2017

Reviewed On: 13 July, 2006

Tags

Endocrinology, Gastroenterology, Haematology, Neurology, Oncology, Orthopaedics, Paediatrics, Psychiatry, Renal, Respiratory, Rheumatology, Urology

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Source: https://www.myvmc.com/investigations/pet-scan-positron-emission-tomography/

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