(NEX) How many times each line of k-space data is acquired during the scan.

See also Signal Averaging.

(NSA) The average number for each phase encoding step. The NSA determine each distinct position-encoded signal to be used in image reconstruction.

See also Signal Averaging.

The phase conjugate symmetry benefits from the symmetry (see also Hermitian symmetry) of the raw data in k-space and is used to reduce the data acquisition time by acquiring only a part of k-space data.

See also Partial Fourier Technique, Partial Averaging and acronyms for 'phase conjugate symmetry' from different manufacturers.

This function is similar to partial averaging in that the complex conjugate relationship between the both halves of k-space is used to shorten the echo time in an imaging sequence.

See Partial Echo.

Refocused GRE sequences use a refocusing gradient in the phase encoding direction during the end module to maximize (refocus) remaining xy- (transverse) magnetization at the time when the next excitation is due, while the other two gradients are, in any case, balanced.
When the next excitation pulse is sent into the system with an opposed phase, it tilts the magnetization in the α direction. As a result the z-magnetization is again partly tilted into the xy-plane, while the remaining xy-magnetization is tilted partly into the z-direction.
Companies use different acronyms to describe certain techniques.

Different terms for these gradient echo pulse sequences
R-GRE Refocused Gradient Echo,
FAST Fourier Acquired Steady State,
FFE Fast Field echo,
FISP Fast Imaging with Steady State Precession,
F-SHORT SHORT Repetition Technique Based on Free Induction Decay,
GFEC Gradient Field Echo with Contrast,
GRASS Gradient Recalled Acquisition in Steady State,
ROAST Resonant Offset Averaging in the Steady State,
SSFP Steady State Free Precession.
STERF Steady State Technique with Refocused FID
In this context, 'contrast' refers to the pulse sequence, it does not mean enhancement with a contrast agent.