Magnetic resonance imaging (MRI) is a non-destructive imaging technique that works on the basis of nuclear magnetic resonance (NMR). This noninvasive imaging method is used for the observation of anatomic structures, physiological functions, and molecular composition of tissues. Raymond Vahan Damadian (an American physician) performed a full-body scan of a human being for the first time, in 1977. The basis of MRI is that certain atomic nuclei, typically those of hydrogen, in the tissue, become magnetized when placed in an external magnetic field. This produces, in the tissue, a net magnetization, M, that is initially aligned with the direction of the main magnetic field, B₀. This imaging technique is remarkable because of high spatial resolution, strong soft tissue contrast and specificity, and good depth penetration. However, MR imaging of hard tissues, such as bone and teeth, remains challenging due to low proton content in such tissues as well as to very short transverse relaxation times.
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