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PET CT

What is PET?Pet-ct-scan-mg

PET stands for Positron Emission Tomography. In a PET Scan, a physician injects a patient with a liquid called a contrast agent with a very low level of radioactive content. After a waiting period and a series of chemical events in body tissues, the contrast agent turns into a photon or light particle that can be seen and translated into an image by the scanner.

The advantages of doing a PET are

High sensitivity: PET scans can pick up cancer sites other imaging tests like CT or MRI sometimes cannot.
Differentiating tumor and fibrosis: Some cancer treatments, especially radiation therapy, can cause tumor areas to fibrose. Conventional imaging techniques cannot differentiate tumor from fibrosis, whereas PET can.

Evaluating treatment effectiveness: Change in a tumor’s metabolic activity occurs much before change in its size and hence can demonstrate response to treatment much more effectively. PET enables doctors to see these changes better than other imaging methods. Also, patients shown to be responding to treatment on PET have a much better prognosis than those who don’t.

Why is CT done along with PET?

In addition to PET, the latest machines have a built-in CT scanner. CT scanners emit a series of very narrow beams though the body in an arc-shaped path, unlike an X-ray machine with uses just a single beam. As a result, CT scanners produce a final picture far more detailed than basic X-ray machines.
The addition of CT scanner has the following advantages:

  1. It helps make the PET images more accurate
  2. The PET images can be superimposed on to the CT images, so doctors can localize the site of PET abnormality correctly.
  3. Fusion of PET and CT images gives more information about tumor characteristics and metabolism.

Can PET/CT detect all tumors?

Ability to detect the tumors depends on their size, metabolic characteristics and location. PET can detect tumors of 1 cm or more with very high accuracy. Tumors between 5mm to 1cm fall in the grey zone and can sometimes be missed. Tumors less than 5 mm and microscopic disease cannot be picked on PET, or in other imaging procedures, for that matter.

What is Open Gantry PET/CT?

The Open View gantry design improves patient comfort by reducing the claustrophobic effect associated with a long tunnel and also allows for easier patient access.

What is 4D PET?

4D PET technology, which is available at Mahatma Gandhi Cancer Hospital & Research Institute, is a sophisticated technique of acquiring a PET scan that compensates for organ motion during breathing, which can make images of abnormalities look hazy. For cancer patients this advanced technique helps doctors visualize tumors, especially in the lungs, better and guide radiation therapy far more precisely than without it allowing them to target the treatment only to the tumor itself, not surrounding healthy tissue.

What are the required preparations?

  1. Pregnant women should not have PET scan. Similarly, women who are breast feeding may need to stop for at least 8 – 10 hours.
  2. Patients undergoing a Glucose PET scan must fast for at least 4 hours prior to the study. Also, they should not consume beverages such as coffee, tea, juice or other drinks that contain sugar. Drinking water is OK.
  3. Diabetic patients need to control their blood glucose before the test. It should be at a level of <150mg/dl. The physician conducting the PET scan can give you more details.
  4. Apart from diabetic medications, other medications can generally be continued. Patients should consult their physicians for details.

What happens to the radioactivity that is injected?

After emitting the radiation these elements convert into more stable forms. This process of conversion from a radioactive state to a stable state is called decay. Radioactive elements decay naturally, becoming less and less radioactive as time passes. The rate at which they decay is measured in terms of half-life. One half-life is the time required for half of the radioactive material to decay. After 4 half-lives, approximately 95% of the activity is decayed. And your body excretes some of the radioactive materials, too, so the amount of radiation decreases with time.

What are side effects of PET/CT scan?

Side-effects to nuclear medicine agents are extremely rare. The amount of radioactive substance injected is an incredibly tiny fraction of a gram. Very rarely side-effects can occur either from the organ specific agent or preparation agents used, but they generally do is less than one in 50,000 cases.

Can I Have a PET scan even if I do not have cancer?

PET scan can also be done for conditions other than cancer such as:

  1. Unexplained fever
  2. Inflammatory diseases such as arthritis
  3. Chronic infective diseases
  4. Brain disorders such as dementia, memory loss, movement disorders or epilepsy.
  5. Cardiac abnormalities.