Hospitals are institutions that provide a wide variety of medical and surgical treatment for sick or injured persons. They employ a diverse group of medical staff, including doctors (MD's), registered nurses (RN's), and licensed practitioner nurses (LPN's), who are trained to treat an even wider variety of medical emergencies and relatively short term illnesses. Locations that perform diagnostic radiology specialize in developing x-rays and using them to diagnose medical problems. Clinics are similar to hospitals, except that they specialize in outpatient treatment, meaning that the patients do not stay overnight.