A coil is an essential component of any MRI machine, and allows us to capture high end images of specific body parts. So depending on what area of the body is being imaged determines what type of coil to use.
You can think of the MRI coil as an antenna. During the scan, the machine uses a magnet and radio waves to noninvasively look inside the body. The coil receives the radio frequency signal coming out of your body and transmits that data to a computer, which then generates images.
For some exams, the MRI coil fits over the body part being scanned. Sometimes the coil is built into the MRI table, like during a spine exam, and the patient lies on top of it. A coil for an ankle or knee is smaller and fits around the body part being scanned. A coil for an abdominal scan is like a pad that lies over the body.