A medical device is any instrument, apparatus, implant, in vitro reagent, or similar or related article that is used to diagnose, prevent, or treat disease or other conditions. The most common medical devices are stents, x-rays, catheters, and CAT scanners. A stent is a small tube-shaped device that is inserted into an artery to keep it open and allow for better blood flow. An x-ray is a type of radiation used to create images of the inside of the body. A catheter is a thin tube that is inserted into a vein or artery to allow for the administration of medication or fluids. A CAT scanner is a type of imaging device that uses computer-aided tomography to create detailed 3D images of the inside of the body.