Radiology is a medical specialty that uses imaging to diagnose and treat diseases seen within the body. Radiologists use a variety of imaging techniques such as X-ray radiography, ultrasound, computed tomography (CT), nuclear medicine including positron emission tomography (PET), and magnetic resonance imaging (MRI) to diagnose and/or treat diseases. Interventional radiology is the performance of (usually minimally invasive) medical procedures with the guidance of imaging technologies.