A CT scan is a radiological imaging test that creates detailed images of the body, according to Medline Plus. It may be used to diagnose an infection, guide a surgeon to the correct area throughout a biopsy, identify masses or tumors within the body, or examine blood vessels. CT scans are performed by a CT scanner, according to Medline Plus. This imaging machine rotates around patients while shooting X-ray beams toward them. A computer that is connected to the machine then creates separate slices, or images, of the body. A doctor can thread the slices together to examine the different structures of the body.