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.

Manganese chloride (MnCl2) is used as an oral contrast agent (LumenHance®) for MRI of the abdomen and/or pelvis. MnCl2 has also been used in magnetic resonance imaging of animals to maximize the contrast of different tissues e.g. in mice and crayfish with different injection methods. Caused by the hepatic uptake, manganese chloride has potential as a hepatobiliary contrast agent.
Manganese chloride is produced by the reaction of hydrochloric acid with manganese oxide or manganese carbonate. In an aqueous solution, manganese chloride can serve as phantom fluid, used for e.g. the daily quality assurance.

See also Classifications, Characteristics, etc.

Quantification relies on inflow effects or on spin phase effects and therefore on quantifying the phase shifts of moving tissues relative to stationary tissues.
With properly designed pulse sequences (see phase contrast sequence) the pixel by pixel phase represents a map of the velocities measured in the imaging plane. Spin phase effect-based flow quantification schemes use pulse sequences specifically designed so that the phase angle in a pixel obtained upon measuring the signal is proportional to the velocity. As the relation of the phase angle to the velocity is defined by the gradient amplitudes and the gradient switch-on times, which are known, velocity can be determined quantitatively on a pixel-by-pixel basis. Once, this velocity is known, the flow in a vessel can be determined by multiplying the pixel area with the pixel velocity. Summing this quantity for all pixels inside a vessel results in a flow volume, which is measured, e.g. in ml/sec.
Flow related enhancement-based flow quantification techniques (entry phenomena) work because spins in a section perpendicular to the vessel of interest are labeled with some radio frequency RF pulse. Positional readout of the tagged spins some time T later will show the distance D they have traveled.
For constant flow, the velocity v is obtained by dividing the distance D by the time T : v = D/T. Variations of this basic principle have been proposed to measure flow, but the standard methods to measure velocity and flow use the spin phase effect.
Cardiac MRI sequences are used to encode images with velocity information. These pulse sequences permit quantification of flow-related physiologic data, such as blood flow in the aorta or pulmonary arteries and the peak velocity across stenotic valves.

The mapping of the magnetic field by measuring or imaging the spatial distribution of magnetic field strength, can be performed by scanning with a probe and handles a large range of field strengths, but is slow and tedious. Accurate field maps can be made by measuring the Larmor frequency as a function of position.
The field must be homogeneous enough to allow MR imaging to be performed, than the magnetic field can be mapped by different methods.
1. The adaptation of chemical shift imaging.
2. The faster one measures the change in signal phase in an image obtained with a gradient echo pulse sequence resulting from a change in echo time TE, which is proportional to the local field strength.
Also useful is a spin echo pulse sequence with data collection from two time locations of the readout gradient and the data acquisition interval, where each having a known shift of the acquisition center away from the spin echo.