Magnetic Resonance Imaging or MRI consists of a hollow machine that uses a powerful magnetic field and radio waves to produce pictures of the internal structure of the body, in this case, knee. Knee MRI scan helps determine pain, weakness, swelling or inflammation in and around the knee joint. MRI scanners do not use ionizing radiation and help to determine if you require surgery. Preparing for Knee MRI Scan The doctors might require you to wear a gown or they may allow you to wear loose clothing during the scanning exam which does not contain any metal fasteners. Some MRI procedures require you to receive contrast medications intravenously that will help MRI scanner to get detailed images of the internal structure of the knee. Your radiologist or technologist might ask you if you have allergies of any kind before fixing a dosage. For people allergic to iodine, gadolinium might be used as a contrast medication. Patient consent is therefore required in such cases. Working of an MRI scanner The machine uses radio frequency pulses to realign hydrogen atoms present in our body while you are in the scanner. It does not cause any chemical changes in the body. The hydrogen atoms emit different levels of energy that vary according to the different type of body tissue.