Radiologists specialize in diagnosing and treating illnesses using medical imaging. Radiologists work with MRIs, CT scans, X-rays, and PET scans. They can decide what tests to run, oversee the tests, and review them to make a diagnosis. Radiologists often work with other care providers; for example, if you came into the ER with a head injury, you would see an emergency doctor, a radiologist, and possible others depending on the diagnosis and extent of the injury. Radiologists specialize in the types of diseases they diagnose, such as radiation oncology. They can also specialize in interventional or diagnostic radiology, and can help provide diagnoses and treatment plans depending on their specializations.