During a magnetic resonance (MR) scan, three orthogonal sets of gradient coils are activated in sequence. Explain why these gradient coils are essential for constructing a multi-dimensional image of the patient’s body.

Once the external radiofrequency (RF) pulse is switched off, the excited hydrogen nuclei (protons) undergo relaxation. Explain how the differences in relaxation times between water-rich tissues and lipid-rich tissues are exploited to produce high-contrast clinical images.