What is PET scan? Overview:
Positron Emission Tomography or the familiar PET scan is an imaging test where a radioactive drug (tracer) is used to reveal how the tissues and organs are functioning in the body.
Cancer being a widespread problem of the world now, with a high number of people being affected, tests like PET scan are of enormous help to mankind to learn the status, progress and recovery of the disease.
PET scan, although is useful to diagnose various other problems like heart related diseases, brain disorders including the problems in the Central Nervous System, it is most widely used for cancer diagnosis.
PET scan images give more detailed and fine results as compared to other imaging scans like CT (Computerized Tomography) scan or MRI (Magnetic Resonance Imaging). Sometimes it becomes necessary to combine the results to create a better view and understand the disease in a detailed manner.
PET scan is not painful, but patients should not consume any food for at least 4 to 6 hours before a scan. Hence usually this test is conducted during morning hours. They should drink plenty of water before the scan.
It is an outpatient procedure and you will be done with the entire procedure in a matter of 2-3 hours.
Role of PET scan in cancer diagnosis:
How a PET scan helps in cancer diagnosis?
The PET scan is generally done using a special dye containing radioactive tracers.
A machine is used here that detects radiation which is emitted by a radiotracer. A radiotracer consists of a radioactive material tagged to a natural chemical, such as glucose.
These tracers are either swallowed, inhaled, or injected into a vein in your arm depending on the organ under analysis. This tracer travels to the cells which utilise glucose for energy.
It is then absorbed by the organs and tissues of higher chemical activity which becomes helpful, as cancerous cells will have higher metabolic activity than non-cancerous cells. Images start appearing on the computer once the absorption starts.
Bright spots are observed on scanning in such affected areas indicating the disease. Doctors understand the functioning of an organ or tissue with the help of the PET scan images.
An example of a glucose-based radiotracer is fluorodeoxyglucose (FDG). FDG is the radiotracer most commonly used today.
Success of Cancer diagnosis with PET scan:
PET scan is a boon to cancer related treatments as it detects diseases at a cellular level before it shows up on other imaging tests. Not only diagnosis but PET scan is also helpful to know –
- If cancer has spread to any other organs.
- If the tumor has reduced in size, as in, to know if the cancer treatment is working effectively on the patient.
- Helps in checking if the cancer has re-occurred in the affected area.
- PET scan measures the blood flow and oxygen use of a particular tissue or organ
- It also helps inspect how the sugar is absorbed by the body, how it is used by the body.
- Helps doctors to understand the functioning, metabolism of your organs and tissues.
- It gives the best view of complex diseases.
A radiologist plays an important role in detecting the findings of the PET scan and analysing the images as, at times, a non-cancerous condition might look like a cancerous condition on a scan.
Solid tumors like the following ones are shown very clearly in a PET scan –
- Head and neck
Disadvantages of PET scan in Cancer diagnosis:
Yes!! PET scan though gives a detailed picture of the underlying problem, at times it can fail too!
Adenomas, bronchioloalveolar carcinomas, carcinoid tumors, low grade lymphomas and small sized tumors that have low glycolytic activity have proven a failure on PET scan.
Fluorodeoxyglucose (FDG), the radioactive tracer used in PET scan is not a cancer-specific agent, and false positive findings in benign diseases have been reported in active inflammation or infection.
Radiologists have a common problem in differentiating between a benign and malignant pulmonary nodule.
For this reason, at times images from different imaging techniques like CT scan or MRI scans are combined to get a detailed outlook of the disease.
Despite the above problem, PET scan still remains the most common scan conducted worldwide to diagnose cancer, plan the treatment and to know more about the effect of the treatment on cancer patients!