PET/CT stands for Positron Emission Tomography/Computed Tomography and is a type of nuclear medicine imaging. An integrated PET/CT scan combines the images from a PET scan and a CT scan, performed at the same time on the same machine. PET/CT allows for early detection of cancer recurrence and can improve chances for treatment success.
About PET/CT scans
- Combining PET and CT technologies creates a more comprehensive image than each could produce alone.
- PET scans take pictures of the function of the organs and tissues using nuclear medicine technology, while CTs create a 3D physical image using X-rays.
- A PET/CT scan is used often to image the heart, brain, liver or other organs. It is one of the most effective ways to study cancer.
What is a PET/CT scan?
PET captures functional images of very small changes in the body’s metabolism caused by the growth of abnormal cells. CT images simultaneously allow physicians to measure the physical size, shape and precise location of the diseased tissue or tumor. When the results of the scans are fused together, they provide more complete information than either test alone.
During the CT scan, a thin beam of X-rays is focused on a specific part of the body. The X-ray tube moves rapidly around this site, enabling multiple images to be made from different angles to create a cross-sectional picture. During a PET scan, a ring of detectors picks up radiation signals from the patient’s body coming from previously injected radiopharmaceuticals. The computer analyzes the information and constructs an image.
During some PET/CT scans, a contrast medium may be used to outline blood vessels or highlight organs to be more visible.
What can a PET/CT scan tell my doctor?
PET/CT is used to help diagnose a number of different diseases, including:
- Brain abnormalities, such as tumors, memory disorders, seizures and other central nervous system disorders.
- Cancer: Diagnosing, staging, evaluating of current therapies and monitoring of reoccurrence of the disease.
- Coronary heart disease, heart attacks and their effects on the heart.
- Areas of the heart muscle that would benefit from angioplasty or coronary artery bypass surgery.
PET/CT is also used to conduct the following:
- Bone imaging for cancer metastases.
- Mapping normal human brain and heart function.
How do I prepare for my exam?
Depending on the type of radiopharmaceutical used during your PET/CT scan, your doctor will probably ask you not to eat or drink anything, except for water, for four to six hours before the exam. In addition, you may be asked not to take certain medications for a certain period of time prior to your exam.
Patients should inform the doctor of medicine they are currently taking, drug allergies (especially iodine allergies) and whether they are breastfeeding or pregnant.
Please arrive 15-30 minutes before the scan to fill out paperwork. The tracer that will be injected is ordered specifically for you. Since it’s radioactive, it will decay away. If you are more than 30 minutes late, the scan will have to be rescheduled.
If you have any anxiety or a history of claustrophobia, it might be wise to ask your referring physician to prescribe a sedative or muscle relaxer. Please remember to fill the prescription and take it prior to coming to the appointment.
How is the test performed?
Patients may be asked to drink a cup of CT contrast at the PET/CT scan. A tech will obtain a small blood sample to check your blood sugar (glucose) level. Elevated glucose levels (over 200) will necessitate canceling the scan, as it can provide false results.
The tech will then start an IV line. The patient will be given an injection of a small amount of radioactive sugar (FDG) through the IV line. It is safe for diabetic patients. Patients will be asked to rest quietly for about one hour as the tracer is distributed throughout your body. The IV line will be removed.
A staff member will escort you to the restroom to empty your bladder and ask you to remove any metal or possibly change into a hospital gown. The tech will position you on the scanning bed as comfortably as possible. The CT will be done first and then you will be moved into the machine very slowly as the PET portion is acquired.
It is important that you lie still during this process to prevent blurred images. The scan takes 30 minutes to an hour, but plan on being at the PET/CT center for two to three hours.
Are there risks?
Because the doses of radiotracer administered are small, diagnostic nuclear medicine procedures result in low radiation exposure, acceptable for diagnostic exams. As a result, the radiation risk is very low compared with the potential benefits. Nuclear medicine has been used for more than five decades, and there are no known long-term adverse effects from such low-dose exposure.
To be on the safe side, talk to your doctor about how long you should wait before getting too close to an infant, or anyone who's pregnant.
How will I find out the results?
If your physician has ordered a diagnostic PET/CT, a radiologist with specialized training in interpreting PET/CT exams will report the findings to your referring physician.
Read more about nuclear medicine at Sentara.