An MR scanner utilizes superconducting coils to produce a strong, uniform magnetic field, but also incorporates gradient coils. Explain how the magnetic field produced by these gradient coils allows the scanner to locate the origin of the radio frequency signals within the patient's body.

Following the termination of the radio frequency pulse, hydrogen nuclei (protons) undergo a relaxation process. Explain how differences in relaxation rates between different biological tissues are used to generate image contrast.