All three scans are types of diagnostic imaging. The main difference is that MRI does not use radiation, while X-rays and CT scans do. Instead, MRI (which stands for Magnetic Resonance Imaging) machines use a strong magnetic field and pulses of radio frequency to create detailed images of the human body.   Many physicians prescribe MRI scans because of their unique ability to detect certain diseases earlier than other diagnostic imaging techniques can, specifically in soft tissue structures such as muscle, fat, organs, and ligaments.