In MR, saturation is a nonequilibrium state with no net magnetization. The same amount of nuclear spins is aligned against and with the magnetic field. Saturation methods like FatSat, SPIR etc., work with a frequency selective saturation pulse for a specific chemical shift applied before the actual sequence starts. This saturation pulse adjusts the magnetization from tissue components to zero. The hydrogen nuclei of fat and water resonate at different frequencies, which makes it possible to excite just the fat with repeatedly applying RF pulses at the Larmor frequency with interpulse times compared to T1. The resulting signal is then destroyed with a gradient pulse (Spoiler Gradient Pulse). Fat is the chemical compound to be saturated at a fat saturation sequence. When the actual sequence follows, (e.g., a spin echo sequence) the unwanted suppressed component will not resonate.

See also Saturation Recovery.

Sequence of RF (and gradient) pulses designed to produce saturation, typically in a selected region or set of regions, most often by the use of selective excitation followed by a spoiler pulse. Similar to some spectral suppression techniques. Can be used to reduce signal from flowing blood by saturating regions upstream from region being imaged.

(SR) Particular type of partial saturation pulse sequence in which the preceding pulses leave the spins in a state of saturation, so that recovery at the time of the next pulse has taken place from an initial condition of no magnetization. A rare used MRI pulse sequence that generates a predominantly proton density dependent signal, basically employing a 90° RF excitation pulse, with a very long repetition time. With this technique T1 times can be measured faster than with inversion recovery pulse sequences.
This saturation recovery sequence consists of multiple 90° radio frequency (RF) pulses with a short repetition time. A spoiler gradient pulse dephases the longitudinal magnetization that remains after the first 90° radio frequency pulse. A repetition time interval after the application of this spoiling gradient turns an additional 90° pulse the new developed longitudinal magnetization into the transverse plane, followed by recording a gradient echo.

Nuclei can retain their magnetic orientation through a chemical reaction. Thus, if RF radiation is supplied to the spins at a frequency corresponding to the chemical shift of the nuclei in one chemical state so as to produce saturation or inversion, and chemical reactions transform the nuclei into another chemical state with a different chemical shift in a time short compared to the relaxation time, the NMR spectrum may show the effects of the saturation or inversion on the corresponding, unirradiated line in the spectrum. This technique can be used to study reaction kinetics of suitable molecules.

A quantity or measurement, having only magnitude.