Of the four major clinical imaging modalities, magnetic resonance imaging (MRI) is the one developed most recently. The first images were acquired in 1973 by Paul Lauterbur, who shared the Nobel Prize for Medicine in 2003 with Peter Mansfield for their shared contribution to the invention and development of MRI. Over 10 million MRI scans are prescribed ever year, and there are more than 4000 scanners currently operational in 2010.
MRI provides a spatial map of the hydrogen nuclei (water and lipid) in different tissues. The image intensity depends upon the number of protons in any spatial location, as well as physical properties of the tissue such as viscosity, stiffness and protein content. In comparison to other imaging modalities, the main advantages of MRI are: (i) no ionizing radiation is required, (ii) the images can be acquired in any two- or three-dimensional plane, (iii) there is excellent soft-tissue contrast, (iv) a spatial resolution of the order of 1 mm or less can be readily achieved, and (v) images are produced with negligible penetration effects. Pathologies in all parts of the body can be diagnosed, with neurological, cardiological, hepatic, nephrological and musculoskeletal applications all being widely used in the clinic. In addition to anatomical information, MR images can be made sensitive to blood flow (angiography) and blood perfusion, water diffusion, and localized functional brain activation.