Creation of images of objects such as the body by use of the nuclear magnetic resonance phenomenon. The immediate practical application involves imaging the distribution of hydrogen nuclei (protons) in the body. The image brightness in a given region depends on the spin density and the relaxation times, with their relative importance determined by the particular imaging technique employed. Image brightness is also affected by motion such as blood flow.

See also Zeugmatography and Magnetic Resonance Imaging MRI.

The core or center part of an atom, which contains protons having a positive charge and neutrons having no electrical charge, except in the common isotope of hydrogen, where the nucleus is a single proton.

When a magnetic moment (e.g. hydrogen nuclei) is placed within an external magnetic field (e.g. B0), it begins to oscillate about the direction of the field; this motion is called precession. The frequency of the precession (Larmor frequency) of the nuclide depends on this particular field strength. A higher field strength results in a higher frequency of the precession.

See also Precession.

Precession is a wobbling motion that occurs when a spinning object is the subject of an external force. Relevant to MRI, the proton of a hydrogen nucleus spins around its axis giving it an angular moment (quantum mechanics). Through the protons positive charge and its spin it generates a magnetic field and gets a magnetic dipole moment (MDM) parallel to the rotation axis. If placed in a magnetic field the magnetic dipole moment will precess about the direction of the magnetic field with an angular frequency (Larmor frequency). The Larmor equation dictates that the frequency of the precession at higher field strengths is higher.

Standard compound used as a standard reference spectral line for defining chemical shifts for a given nucleus. As recommended by the ASTM, for 1H it is tetramethylsilane (TMS) and for 31P it is phosphoric acid, although for practical biological applications water and PCr have been used as secondary references for hydrogen and phosphorus spectroscopy, respectively. The reference compound can be in a capsule outside of the subject (external) or can be in the subject (internal); internal references are generally preferable where possible, as external references may be subject to different conditions.