Efficiency characteristic of the device or material itself.

Form of the Fourier transformation that reverses the process, e.g. if the Fourier transformation is used to analyze a function of time into its equivalent frequency components, the inverse Fourier transformation will synthesize that function of time from these frequency components.

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.

(IR-EPI) Inversion recovery sequence with echo planar imaging.

See Inversion Recovery and Echo Planar Imaging.