A psychiatrist is a physician who specializes in psychiatry. A psychiatrist specializes in the diagnosis and treatment of mental disorders. Psychiatrists are medical doctors who must evaluate patients to determine whether or not their symptoms are the result of a medical illness, a combination of medical and mental, or a strictly mental one. In order to do this, they may employ the psychiatric examination itself, a physical exam, brain imaging (computerized tomography or CT/CAT scan), magnetic resonance imaging (MRI), and positron emission tomography (PET) scanning), and blood laboratories.