Magnetic Resonance Imaging, or MRI is used for the purpose of seeing in detail structures within the body. It works on the principle that the nuclei of the atoms within the body can be aligned using a magnetic field. Next, this alignment is altered using radio frequency magnetic fields. A scanner is needed to detect the rotating field and an image is then produced of the area of the body being tested. This device is useful to image soft tissues and it can be used to detect cancer. Various muscles including the heart as well as the nervous tissue of the brain can be imaged with this technology. MRI is a valuable tool to visualize what is happening within the body, without surgery.