chinese woman holding an x-ray image by Allen Penton from Fotolia.com

PET and CT scans both involve the use of high-tech imaging equipment to examine the body’s internal structures. However, a PET scan can reveal changes on a cellular level, while the CT scan reveals changes in the overall structure of organs or tissue. A PET scan can detect diseases at an earlier stage than a regular CT scan.

PET Scans

PET stands for "positron emission tomography." This scan uses a small amount of radioactive material that is injected into a vein, inhaled or swallowed. The PET scan reveals where the radioactive material accumulates and can detect problems with blood flow, oxygen use and metabolism.

CT Scans

CT, short for "computerized tomography" (sometimes called a CAT scan), combines a series of X-ray views and provides cross-sectional images. These images can be viewed individually, likes slices of bread, or combined to produce a three-dimensional view.


According to the Radiological Society of North America, PET scans can detect cancer and whether it has spread, identify heart problems and examine brain and nervous system disorders. CT scans can quickly identify internal injuries from accidents and other trauma, provide follow-up for surgeries and chemotherapy and also detect cancer and vascular diseases.


While both PET and CT procedures have been used for decades and in most cases have minimal side effects, they do involve the use of radiation. CT scans may slightly increase the risk of developing cancer. Mayo Clinic radiologist Brian J. Bartholmai, M.D., states that “this small risk is vastly outweighed by the crucial usefulness obtained by CT scans.” Bartholmai adds that CT scans should be used only when medically necessary. Women who are pregnant or breastfeeding should inform their doctors before undergoing PET or CT scans.


In 2009, the U.S. Food and Drug Administration began investigating instances of excessive radiation exposure linked to CT scans. According to the FDA, overexposure may go undetected during the scan, which puts patients at increased risk for long-term radiation effects. The FDA provided a list of recommendations for medical facilities to help prevent excess radiation exposure.

Combination Scans

Many PET scans are performed using a combination of PET and CT scanners, which makes it easier to diagnose and treat diseases.