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Principles of magnetic resonance imaging

Daniel Chernoff, MD, PhD
Paul Stark, MD
Section Editor
Nestor L Muller, MD, PhD
Deputy Editor
Susan B Yeon, MD, JD, FACC


Magnetic resonance (MR) imaging is an important tool in the diagnosis and evaluation of diseases [1]. In the early 1970s, Paul Lauterbur and Raymond Damadian applied nuclear magnetic resonance (NMR) technology to the imaging of living organisms, generating images referred to as zeugmatographs [2-5]. Subsequent refinements in image acquisition and processing, developed by Sir Peter Mansfield and others, allowed improved visualization of anatomic detail and broader clinical application of MR imaging [1,6-8]. Lauterbur and Mansfield were awarded the 2003 Nobel Prize in Medicine and Physiology for their contributions to medical imaging.

This topic will review the principles of magnetic resonance imaging. Clinical applications of MR are discussed in individual topic reviews.


Atoms are characterized by mass, electrical charge, and a magnetic property called spin. Atomic nuclei that contain an odd number of protons or neutrons possess a magnetic moment, which describes the strength and direction of a microscopic magnetic field surrounding the nucleus. In the presence of a strong, constant external magnetic field, such as that produced inside an imaging magnet, a small excess fraction of nuclei, on average, align themselves with the magnetic field, producing a macroscopic, measurable magnetic moment (figure 1) [9-11].

In addition, the interaction between the magnetic moment of the nucleus and the external field causes each spinning nucleus to precess (ie, change the orientation of the rotation axis of the spinning nucleus). Each nucleus precesses at a characteristic (resonant) frequency that is proportional to the strength of the external field. The resonant frequency can be calculated with the Larmor equation:

Resonant frequency F = B0 x Larmor constant


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Literature review current through: Sep 2016. | This topic last updated: Mar 2, 2016.
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