A radiologist diagnoses and treats diseases utilizing radiologic imaging procedures in adults and children. Physicians practicing in the field of radiology most often specialize in diagnostic radiology, radiation oncology, or radiological physics. A diagnostic radiologist utilizes x-ray, radionuclides, ultrasound, and electromagnetic radiation to diagnose and treat disease. A radiation oncologist deals with the therapeutic applications of radiant energy and its modifiers and the study and management of disease, especially malignant tumors. A radiological physicist deals with the diagnostic and therapeutic applications of roentgen rays, gamma rays from sealed sources, ultrasonic radiation, and radio-frequency radiation, as well as the equipment associated with their production and use, including radiation safety.