A psychiatrist is a physician who specializes in psychiatry and is certified in treating mental disorders. All psychiatrists are trained in diagnostic evaluation and in psychotherapy. And, as part of their evaluation of the patient, psychiatrists are one of only a few mental health professionals who may prescribe psychiatric medication, conduct physical examinations, order and interpret laboratory tests and electroencephalograms, and may order brain imaging studies such as computed tomography or computed axial tomography, magnetic resonance imaging, and positron emission tomography scanning.