Use of a magnetic field gradient to effectively eliminate residual transverse magnetization by producing a strong position dependence of phase within a resolution element. See Spoiler Gradient Pulse.

(ISIS) Image selected in vivo spectroscopy is used as a localization sequence to provide complete gradient controlled three-dimensional localization with a reduced number of sequence cycles, e.g. for in vivo 31P spectroscopy. The ISIS method generates three 180° pulses prior to a 90° pulse, after which the free induction decay is recorded. Specific 180° pulses (slice-selective) are combined and the FID's added or subtracted to generate a spectrum.
An advantage of the ISIS method is that the magnetization (before the final 90° pulse) is predominantly along the z-axis and so T2 effects are relatively small. This explains the value of this technique for 31P data acquisition, because some phosphorus metabolites (e.g. ATP) have short T2 values.
A disadvantage is that eight acquisitions are required to accomplish the spatial localization, therefore the sequence cannot be used for localized shimming. Another problem, because any variation between these data collections (for example, due to movement) will degrade these applications, can be solved by incorporating outer volume suppression techniques such as OSIRIS (modified ISIS).

A state of a set of spins in which the ensemble of spins in a voxel are uniformly distributed with phases between 0 and 2p reducing the transverse magnetization in a voxel to essentially zero.

A nonequilibrium state in which the macroscopic magnetization vector is oriented opposite to the magnetic field; usually produced by adiabatic fast passage or 180° RF pulses.

(IR) Inversion recovery is an MRI technique, which can be incorporated into MR imaging, wherein the nuclear magnetization is inverted at a time on the order of T1 before the regular imaging pulse-gradient sequences. The resulting partial relaxation of the spins in the different structures being imaged can be used to produce an image that depends strongly on T1. This may bring out differences in the appearance of structures with different T1 relaxation times. Note that this does not directly produce an image of T1. T1 in a given region can be calculated from the change in the MR signal from the region due to the inversion pulse compared to the signal with no inversion pulse or an inversion pulse with a different inversion time. This sequence involves successive 180° and 90° pulses. The inversion recovery sequence is specified in terms of three parameters, inversion time (TI), repetition time (TR) and echo time (TE).

See also Inversion Recovery Sequence and FLAIR.