A surface coil placed over a region of interest will have an effective selectivity for a volume approximately subtended by the coil circumference and one radius deep from the coil center. Such a coil can be used for simple localization of sites for measurement of chemical shift spectra, especially of phosphorus, and blood flow studies. Some additional spatial selectivity can be achieved with magnetic field gradients.

(LMR) A particular technique for obtaining NMR spectra, for example, of phosphorus, from a limited region by creating a sensitive volume with inhomogeneous applied gradient magnetic fields, which may be enhanced with the use of surface coils.

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.