A series of 180° RF rephasing pulses and their corresponding echoes for a fast or turbo spin echo pulse sequence.

See Fast Spin Echo and Turbo Spin Echo Turbo Factor.

(FE) Echo produced by reversing the direction of the magnetic field gradient to cancel out the position-dependent phase shifts that have accumulated due to the gradient.

See also Gradient Echo Sequence.

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.

A measurement technique for double contrast sequences, whereat echoes that determines the image resolution are used in both raw data matrices.

Echo spacing is the distance in time between the echoes in multiple echo sequences like, e.g. echo planar imaging, fast spin echo. A short echo space produces compact sequence timing and less image artifacts. The shorter the rise time, the faster the gradients and therefore the echo spacing. Gradients with a shorter echo spacing will have a better resolution and more slices per TR.

See also Fast Spin Echo.