MRI is a non-invasive imaging technique that uses magnetic fields and radio waves to produce detailed images of soft tissues in the body. It does not use radiation and has a low risk of allergic reaction to contrast agents compared to other imaging methods. While MRI is able to create hundreds of high quality images covering large areas of the body and can detect cancer spread, it is also expensive and cannot replace all other imaging techniques due to limitations such as inability to find all cancers or distinguish between benign or malignant tumors in some cases.