RF coil designed to operate at more than one resonance frequency, so that NMR of more than one kind of nucleus can be observed with the same coil.

An intrinsic property of certain nuclei that gives them an associated characteristic angular momentum and magnetic moment also known as inherent spin (those with odd numbers of protons and/or neutrons in their nucleus). Nuclei that do not exhibit this characteristic will not produce a NMR signal.

A coordinate system, which uses the distance from the coordinate system center and positional angles to identify points in space rather than orthogonal independent unit vectors as in the Cartesian coordinate system. Polar and partly polar (cylindrical) coordinate systems are widely used to describe spin motion in NMR experiments.
It is important to know how to compute the coordinates of a point in the polar coordinate system when they are given in a Cartesian system and vice versa. The length of the vector r pointing from the coordinate origin to a point in 2D space is given as
r = √(x² + y²).
while the polar or phase angle f is obtained by performing the operation
f = arctan (y/x),
where the arctan function is the inverse of the tangent function.

A device that amplifies very low-level signals. A preamplifier is generally placed close to its signal source and has a very low noise figure as it is the principal determinant of electronic noise within the system. Preamplifiers used in NMR systems usually have a 50 ohm input impedance, and require a matching network to interface to the RF coil, although preamplifiers with high input impedance may be used with surface coils. Such devices typically use a field effect transistor (FET) as their input stage.

Spectrum of NMR signal whose frequency components are broadened by a magnetic field gradient. In the simplest case (negligible line width, no relaxation effects, and no effects of prior gradients), it corresponds to a one-dimensional projection of the spin density along the direction of the gradient; in this form it is used in projection reconstruction imaging.