What Is the Difference Between a PET Scan & a CT Scan?

PET Scan

A positron emission tomography (PET) scan is a nuclear medical imaging scan measuring bodily functions such as oxygen use, blood flow and glucose metabolism. Nuclear medical imaging is the practice of using small amounts of radioactive material to help diagnose medical problems. Depending on what kind of exam is being performed, the radioactive materials, called radiopharmaceuticals or radiotracers, are either injected, swallowed or inhaled. The substance accumulates in a part of your body, and the energy is detected with a gamma camera.

CT Scan

A computed tomography (CT) scan uses special X-ray equipment to take multiple pictures of the inside of your body. These images are compounded and studied by a CT technician, who can see problems in the body's anatomy. A CT scan is similar to an X-ray but can provide a more detailed look at internal organs, blood vessels, bones and soft tissue.


The difference between a PET scan and a CT scan is the method in which the diagnostic testing is done. With a PET scan, the radioactive materials are ingested, then the specific body part is examined after the materials are in the body. A CT scan uses X-ray images to take a picture of the body from the inside out.

Combined PET and CT Scan

Often, PET scans and CT scans are done together, on machines that are actually combination PET and CT scanners. Physicians have found it very beneficial to have both types of imaging at their disposal when they are trying to diagnose conditions and pinpoint problems.

Who Needs a Scan?

PET and CT scans can help doctors properly diagnose, pinpoint, examine and treat conditions such as cancer, heart disease, brain or spinal disorders, lung issues (pneumonia and emphysema), reproductive issues or problems with the liver, kidneys or other internal organs. If your doctor feels you may have an internal issue and would like to look into it more, they will order a PET or CT scan for you. Doctors can determine in several ways what is going on inside your body, and whether it is normal, or if you need further medical treatment. Some conditions require exploratory surgery, but other conditions can be monitored with body scans, like a PET scan or a CT scan.