PET Scans

What is a PET/CT Scan?

A PET/CT (Positron Emission Tomography/Computed Tomography) measures blood flow, oxygen use and glucose metabolism, which helps doctors identify abnormal from normal functioning organs and tissues. The scan also can be used to evaluate the effectiveness of a patient's treatment plan.

What Problems Can a PET/CT Scan Detect?

PET/CT scans are commonly used to detect cancer, heart problems (including coronary artery disease), brain disorders and other central nervous system disorders.

Understanding How PET/CT Scans Detect Cancer

Cancer cells grow at a very fast rate. Growing cells use glucose as a primary source of energy. The faster the cells grow, the more glucose is consumed.

A form of glucose called FDG, which emits particles called positrons, is injected in the patient as part of a PET/CT scan. The FDG molecules are consumed more in fast-growing cancer cells than in normal cells; resulting in concentrations of the FDG and positrons in areas of cancer. A PET/CT scan detects where positrons are being emitted from within the patient and provides images that map the locations. PET FDG mapping is combined with a CT image's structural detail in order to identify both the presence of the disease and its precise location.

How Does a PET/CT Scan Work?

The test involves injecting a very small dose of a radioactive chemical (a radiotracer) into a vein of your arm. The tracer travels through the body and is absorbed by the organs and tissues being studied. Next, you will lie on a flat examination table that is moved into the center of a PET scanner (a doughnut-shaped machine that detects and records energy given off by the tracer). With the aid of a computer, this energy is converted into 3D pictures. A physician can then look at cross-sectional images of the organ from any angle to detect any functional problems.

How to Prepare for Your PET/CT Scan

A PET/CT scan usually is performed as an outpatient procedure. Your doctors will give you detailed instructions on preparation before the test. Here are some general instructions to keep in mind when preparing for your PET/CT scan:

  • For six hours before your test, do not eat, drink (except water), or even chew gum.
  • Your last meal before the scan should be high in protein and low in carbohydrates. For example: You can eat steak, baked chicken, fish, cheese, asparagus, broccoli or mushrooms for dinner or eggs, bacon or sausage for breakfast. No pasta, potatoes, rice or bread. You should not eat breakfast if you have an appointment before noon.
  • Continue to take any medication prescribed by your physician. If you have been advised to take your medications with food then eat nothing more than a few soda crackers four to eight hours before your exam.
  • Avoid caffeine, sugar, tobacco and heavy exercise for 24 hours before your exam.
  • If you have diabetes, discuss this with your physician and call the radiology staff 48 hours before your exam.
  • If you are, or think, you may be pregnant, discuss this with your physician. Generally, PET/CT is not performed on pregnant women.

What To Expect After a PET/CT Scan 

Most individuals can resume normal activities immediately. Over the next few hours and days, the remaining radiotracer will exit your body through your urine or stool. Drinking lots of fluids, especially water, will help remove the radiotracer from your body. In rare cases, some individuals experience an allergic reaction. There are no long-term side effects. A radiologist or other specialist with nuclear medicine training will review the results of your PET/CT scan and contact your doctor with their conclusions. We recommend that you schedule an appointment with your primary care physician to go over the test results.