About Positron Emission Tomography and Computed Tomography

Positron emission tomography (PET) is a nuclear medicine technology that determines the metabolic activity of cells in human tissues. Nuclear medicine is a technique that involves the use of a trace quantity of a radioactive chemical. Referred to as a radiopharmaceutical (radionuclide or radioactive tracer), it aids in the inspection of the tissue under investigation.

PET is a technique that combines nuclear medicine and biochemistry. Oncologists often use positron emission tomography to detect and evaluate a patient’s cancer and aid in staging the disease. The stage is a term used to indicate the location of cancer, whether it has spread, and how it may impact your body’s processes. Understanding the stage of cancer enables you and your doctor to select the most effective treatment. Additionally, it assists your physician in predicting your likelihood of recovery.

How does a PET scan detect cancer?

PET enables visualization of biochemical changes occurring within the body, such as the heart muscle’s metabolism (the process by which cells convert food into energy) after it has been digested and absorbed into the circulation).

PET is distinguished from conventional nuclear medicine tests because it measures metabolic activity within bodily tissues. In comparison, other nuclear medicine tests determine the quantity of radioactive material accumulated in bodily tissue at a specific region to assess the tissue’s function.

Cancer cells metabolize at a faster pace than noncancerous cells. Due to their high level of chemical activity, cancer cells appear as bright spots on PET scans. As a result, PET scans are beneficial for identifying cancer and determining whether the disease has spread.

Specifically, PET examinations analyze the metabolism of a particular organ or tissue to get information about the organ or tissue’s physiology (functionality) and anatomy (structure) and its biochemical features. PET can detect metabolic changes in an organ or tissue that indicate the initiation of a disease process before the appearance of morphological abnormalities associated with the disease.

PET-CT scan

A PET scan may also be performed along with a CT scan. If so, doctors call it a PET-CT scan. Nevertheless, you might also hear it is just called a PET scan. Is a PET scan and CT scan performed on the same equipment? In the past, it was not. CT imaging uses special x-ray equipment that passes x-rays through the body to create images. However, newer technology combines PET and CT into one scanner, known as PET/CT.

In addition to determining the stage of your cancer, a PET-CT scan can assist the doctor in the following ways:

  • Locate the optimal location for a biopsy
  • Determine whether your cancer therapy is effective.
  • Following the conclusion of therapy, monitor for new cancer growth.
  • Prepare for treatment

What is the procedure of a PET-CT scan?

An injection of a radiotracer called fluorodeoxyglucose-18 is given before your PET-CT scan. Fluorodeoxyglucose (FDG) is a molecule similar to glucose. This radioactive glucose, or sugar, is absorbed by the cells of your body. Areas that consume more energy absorb a greater amount of FDG. Cancer cells consume a greater amount of energy than healthy ones. PET scans determine the location of the radioactive tracer in your body.

A CT scan generates various x-ray images of your body.  An injection of a special dye may be given before the x-rays. The dye enhances the visibility of certain features. Finally, the PET and CT images are combined by a computer. Your physician receives a detailed 3-D image that reveals any abnormalities, including cancers.

Are PET-CT scans considered safe?

There is a risk of exposure to radiation associated with PET-CT scans with the x-rays and the radioactive material used. Generally, the advantages of these tests outweigh the dangers. You will be exposed to low levels of radiation during these examinations. This extremely tiny amount of radiation has not been demonstrated to be harmful. There is a slight possibility of an elevated risk of cancer in the future for children and other individuals who require frequent PET scans, CT scans, and x-rays.

Doctors might utilize lower dosage scans or scan only specific locations. Ascertain that all of your physicians are aware of the quantity and sort of imaging scans you’ve undergone. This information can assist them in determining which scans to do in the future to assist in reducing your risk. If you are concerned about your radiation exposure, speak with your doctor about other tests that utilize less radiation.

Who will perform the PET-CT scan?

PET-CT scans are administered by a technician who specializes in positron emission tomography and computed tomography. Following the test, a specialist in reviewing test findings will examine your scan. This individual is an expert in nuclear medicine or a radiologist. They will determine the significance of the findings.

Preparing for a PET-CT scan

When you make an appointment for a PET-CT scan, the staff will instruct you on how to prepare. Ensure that you carefully follow the scan operator’s directions to prevent influencing the scan findings. Discuss the following issues with the staff and ask questions about any unclear or disturbing material to you.

What to eat – You may be instructed the night before the scan to consume only clear beverages after midnight. Depending on the area of your body that will be scanned, you may need to fast for four hours before the scan. 

Your pharmaceutical regimen and medical history – Inquire about taking your regular drugs or supplements on the day of the test. Additionally, inform them if you have diabetes or any other medical condition. Diabetes, in particular, might affect your test findings, and the radioactive tracer can affect your blood sugar. Inform the personnel if you are nursing or may be pregnant. These scans may endanger the infant.

Allergies – Inform the professionals of any drug or food allergies you may have, especially any previous allergic responses to iodine.

What to avoid – Avoid vigorous exercise such as running, jogging, or weightlifting 24 hours before your exam. Exercise can impair the accuracy of your scans.

What to wear – Dress loosely and comfortably, avoiding metal zippers and buttons. You will need to remove any metal-containing clothes, as metal can interfere with the scan. Belts, jewelry, clothes with snaps or zippers, bras, and spectacles all contain metal. 

If you cannot wear your normal attire during the scan, you may use a hospital gown. Because you will be required to remove any jewelry, you may choose to leave it at home on the day of your test.

Costs, insurance, and permission – If you are concerned about the expense of your PET-CT scan, contact your insurance provider before the scan to determine what your plan will cover. Inquire as to how much of the expense you will be responsible for. When you arrive at the physician’s office or hospital, you will be asked to sign a permission form. The form certifies that you have read and understood the scan’s advantages and hazards and agree to have it.

Throughout the PET-CT scan

An IV, a tiny tube with a needle attached, will be inserted into one of your veins by a staff member. The IV has the sensation of a pinprick. Once the IV is placed, the radioactive chemical for the scan will be administered. The radioactive material will not affect you.

After the chemical has been injected, you must rest and prevent exercise, but sit comfortably in a chair. Excessive movement can cause the drug to migrate into locations that have not been investigated. Moving impairs doctors’ ability to read the scan. It takes 30 to 90 minutes for the radioactive chemical to reach the bodily areas that will be scanned.

Additionally, you may get contrast liquid via your IV. This contrast liquid aids in the clarity of the images. You will be asked to go to the restroom shortly before the test begins to empty your bladder.

This liquid may cause the region around your IV to feel hot or itching. Additionally, you may get a metallic taste on your tongue. These reactions should subside after a few minutes. If you experience a more severe response, such as difficulty breathing, speak up immediately.

When the scan is ready to begin, the technician will assist you in comfortably positioning your body on a table. While you will most likely be lying on your back, you may be required to lie on your stomach or side. Your body posture is determined by the area of your body that has to be scanned.

A PET-CT scan may be used to schedule your cancer therapy for treatment. Your body posture will be critical in this scenario. With the use of a mask or cast, the technologist places you. These items assist you in remaining completely motionless throughout the scan.

The PET-CT scanner resembles a big doughnut. When it begins, the table immediately slides through the middle slot. This assists in determining whether you are in the proper position. The table then glides back and forth slowly. A member of staff will monitor the test from an adjacent room. You can communicate with them, and they can communicate with you. The staff will do all possible to make you feel at ease.

 Is a PET-CT scan completely painless?

Certain postures may be somewhat painful or exhausting. You must remain motionless throughout the scan. Additionally, you may need to keep your arms over your head. There may be times you will be asked to hold your breath momentarily. Breathing motion might result in hazy images.

During the scan, the staff member may also elevate, lower, or tilt the table. By repositioning the table, you may capture images from a variety of perspectives. Inquire as to when the table will be moved. You may anticipate hearing the machine whirring or clicking. Certain machines generate more noise than others.

Your session will last between one and three hours. Once the radioactive material is delivered to the proper location via the IV, the scan typically takes around 30 minutes. The test may take longer if the scanner scans a broad region. A staff member can provide you with an estimate of how long it will take.

When the scan is complete, you may be asked to remain on the table while a doctor examines the photos to ensure they are not blurry. If they are not clear, another scan may be necessary.

Following the PET-CT scan

Following the scan, you can resume normal activities, including driving. The staff will instruct you to drink many glasses of water to aid in the removal of the radioactive chemical and dye from your body.




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