MRI adapts nuclear magnetic resonance (NMR) for medical imaging by measuring the spin of hydrogen nuclei in the body. Under a strong static magnetic field, these nuclei resonate with faint radio waves, and the responses are detected by antenna coils. Lauterbur showed that adding slight gradient magnetic fields in space makes it possible to determine where the signal originates. Mansfield improved signal read-out and mathematical reconstruction, creating echo-planar imaging (EPI) that produces high-resolution cross-sections within minutes. The invention greatly enhanced diagnosis of brain tumors, herniated disks and more, providing a radiation-free and therefore safer test that has spread worldwide. Today the technology has expanded to fMRI and DTI, essential for brain-function studies and regenerative-medicine research.

Originally, NMR served mainly analytical chemistry, but in 1973 Lauterbur introduced spatially selective gradient fields and demonstrated how slice-specific spectra could be acquired. Fourier transformation then reconstructs data from k-space to image space, visualizing both position and proton density. Mansfield invented echo-planar imaging, performing phase and frequency encoding within milliseconds and thus minimizing motion artefacts while enabling real-time observation. Differences in T1 and T2 relaxation times provide intrinsic contrast, and gadolinium-based contrast agents allow perfusion studies; these features underpin a wide array of clinical protocols. Modern 3- to 7-tesla systems explore neuronal connectivity and tumor microenvironments, establishing an interdisciplinary platform linking physics, biochemistry, and clinical medicine.

Lauterbur proposed projection-reconstruction using linear gradient fields, demonstrating positional encoding via radial k-space sampling. Mansfield optimized multi-channel resonators and gradient pulse trains, implementing EPI that acquires a complete k-space line set within ~20 ms, enabling dynamic contrast studies and BOLD fMRI. Their work seeded subsequent sequence families such as fast spin-echo, RARE and SS-FSE. The theory clarified engineering challenges in gradient coil design, eddy-current suppression and SAR management, and stimulated research on B0 uniformity and susceptibility artefact reduction in high-field scanners. Modern parallel imaging techniques (SENSE, GRAPPA) and multiband EPI algorithms fundamentally rely on their spatial encoding concepts.