What Is the Difference Between PET Scanners and CT Scanners?

The difference between positron emission tomography scanners and computed tomography scanners is that PET scanners detect early metabolic changes that occur at the cellular level of tissue or organs, according to Cleveland Clinic. CT scanners detect disease-related structural changes in tissue or organs, which occur later. Cellular changes are frequently early signs of disease development. Having the ability to observe changes in cell function in the body is a significant element in diagnosing and treating diseases.

Doctors differentiate between normal and abnormal tissue and organ functioning by using PET scans, which measure oxygen use, blood flow and glucose metabolism, explains Cleveland Clinic. As of 2015, physicians use PET scans to detect cancer, seizures and brain tumors, coronary artery disease, heart damage after a heart attack, and other central nervous system problems. Physicians also use the doughnut-shaped machine to determine whether a patient's treatment plan is effective or needs adjusting.

Physicians typically perform the test on an outpatient basis, notes Cleveland Clinic. To conduct a PET scan, a physician injects a patient's arm with a tiny dose of a radiotracer, which is a radioactive chemical. Organs and tissues absorb the chemical as it travels through the body. The patient then lies down on an examination table, and the physician moves the table into the center of the scanner. The scanner detects and records energy from the radioactive substance. Using a computer, the doctor converts the results into three-dimensional pictures.