What is a PET scan?
Positron emission tomography (PET) is a high-resolution diagnostic test that captures images of the cells of the body as they work. A standard breast PET combines a breast computed tomography (CT) scan with a PET scan (PET-CT scan), although a PET scan may be done alone as well. It is a technique to diagnose breast cancers.
A PET scan is also used for the diagnosis of various conditions such as heart disease and Alzheimer’s disease but is especially important in cancer detection. The PET scan can detect “suspicious” areas in the body even before a person develops a mass or lump. Another advantage is that the doctor can study the distant spread of the tumor (metastasis) as well. It can also detect cancer cells in an area that has extensive scarring that makes it a superior choice in many cases compared with sonography or X-rays.
A CT scan is a high-resolution X-ray that gives us a detailed structure of the breast tissue. Breast PET combines the principles of PET and CT scans to arrive at a better diagnosis. It is also called the PET-CT scan.
What are PET scans used for?
Despite high sensitivity in detecting early-stage cancers, it is not to be used for routine screening of breast cancer. This is due to higher radiation exposure involved in the study compared to other modalities such as mammography. The PET scan also requires a sophisticated setup and expertise to perform, which may be available only in limited setups.
A specific type of PET scan of the breast known as positron emission mammography (PEM) requires the PET camera to be configured like a mammography machine. Here, the PEM cameras use two movable, flat detectors or cameras. These are pressed directly against the breast to obtain the image. PEM has a sensitivity and specificity of over 90% in detecting primary breast cancer. Camera technology used by PEM is more sensitive than whole-body PET/CT imaging in detecting breast tumors. The total exposure to radioactive substances in these scans is also low.
Following are the indications for breast PET:
- When other imaging scan results such as X-ray mammography or CT mammography are indeterminate
- During presurgical planning in breast cancer
- When monitoring the response to cancer therapy
- In case of suspected tumor recurrence
- During breast cancer staging
- When guiding breast biopsies, especially in cases of recurred tumors
Sometimes, the doctor will order breast PET or a PEM scan to determine how far the cancer has spread and assess whether distantly spread (metastatic) breast cancer is responding to ongoing treatment.
What Happens During the PET Scan Procedure?
- You will need about two hours for this outpatient procedure.
- You will be taken to the setup where a CT scan will be done first.
- You will then be injected with a small amount of a radioactive sugar called fluorodeoxyglucose-18 (radioactive glucose or a tracer) in your veins.
- The absorption of this tracer in your body requires 30-60 minutes. The PET scan will be done after the requisite time has passed.
How does PET detect cancer?
- All the cells in your body absorb sugar.
- Because the cancer cells are hyperactive and fast multiplying, they use more energy than healthy cells.
- Hence, the cancerous cells pick up more sugar.
- A camera takes the pictures of your body from various angles and feeds it to a computer.
- The computer combines PET and CT images and constructs detailed three-dimensional (3D) images of anything abnormal, including tumors.
- The scan highlights the areas of cancer cells because of the excess intake of radioactive sugar. These “bright spots” where the radioactive tracer is collected prompt your doctor regarding the further course of management.
After the procedure, you can resume your daily activity unless your doctor instructs you otherwise. You will need to drink plenty of fluids to help flush the tracer from your body.
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