(DE - dual / double echo) Dual echo sequences include images with different weightings and / or echo times and are used to obtain both, proton density and T2 weighted images or in phase and out of phase gradient echo images, simultaneously without increasing the measurement time.

(DESS) This sequence was originally known as FADE. It combines both the gradient echoes acquired in FISP and PSIF sequences in separate acquisition periods during a single interpulse interval. Phase encoding gradients are balanced to maintain the transverse steady state signals. The frequency encoding gradient is left on for the period of both the echoes, and is incompletely balanced to avoid dark banding artifacts otherwise associated with long TR fully balanced steady state sequences. The contrast of DESS is quite unique, true T2 or T1 contrast weighting is not possible. There is a strong fluid signal but fat is bright and other soft tissues appear similar to the short TR FISP image.
Used for, e.g. the joints, cartilage and the prostate.

See Steady State Free Precession and Dual Echo Sequence.

Fast gradient echo sequences are used to study dynamic processes with time periods on the order of a second and allow continuous monitoring of most physiologic motions. A common use of dynamic scanning is the investigation of the time course of tissue contrast after injection of a paramagnetic contrast agent.

Echo offset is the time setting of spin echo and gradient echo to be not coincident and to generate phase differences between different spectral line signals (e.g., water and fat). The echo offset is the product of the frequency line difference and the time difference (TD) in the echo times and is equal to the magnitude of the result of the phase difference between two spectral lines. Phases may not change linearly with echo offset time in the presence of a large field inhomogeneity. An echo offset excitation pulse sequence can be used in the magnetic field mapping method, to generate maps from which the standard deviation of the phase difference can be calculated.

(EPI Factor) The imaging speed in Echo Planar Imaging (EPI) depends on many factors. Single shot EPI should provide images within 100 ms or less. Because of this limitations, a multi shot EPI approach is in most cases preferred. The parameter 'EPI Factor' is used to specify the number of k-space profiles collected per excitation.
The EPI factor 64 means a measurement time 64 times faster than a normal gradient echo sequence. See also Echo Planar Imaging.