Advanced GRE Sequences

This flashcard set covers the basic features, formulas, acronyms, and types of Advanced Gradient Recalled Echo sequences, including Steady State, Coherent, Spoiled, Balanced, and Hybrid techniques.

Gradient Recalled Echo (GRE) Sequence

A sequence characterized by an excitation pulse of $90^{\circ}$ or less ($\alpha$), no $180^{\circ}$ re-phasing RF pulse, and the use of an extra lobe of the FEG to de-phase and re-phase spins.

3D Scan Time Formula

$$TR \times Ny \times Nz \times NEX$$

Nz

The extra phase encoding gradient along the Z axis, also referred to as 'slab thickness'.

Steady State

A condition created when TR < T2 < T1, resulting in a continuous amount of transverse magnetization in the XY plane.

Ernst Angle

The optimal flip angle that provides the best signal and desired image contrast in a GRE sequence; commonly $30 - 45^{\circ}$ in Steady State GRE.

Steady State Free Precession (SSFP)

A standard steady state sequence where stimulated echoes are created due to extremely short TRs, the TE is longer than the TR (almost double), and FIDs are not sampled.

PSIF

The Siemens acronym for Fast Imaging with Steady State Free Precession, which is related to FISP.

Rewinder

An additional phase encoding gradient (PEG) with reversed polarity applied after the echo is read and before the next TR to rephase spins within the XY plane.

Coherent (Unspoiled) Steady State GRE

A sequence that uses a rewinder to provide $T2^*$ weighted image contrast where both the FID and stimulated echoes provide signal; known by acronyms like GRASS and FISP.

Balanced Gradient Echo

A variation on SSFP or Coherent GRE that utilizes flow compensation through three additional FEG lobes (negative, positive, and negative) to correct phase errors from motion.

FIESTA

The GE acronym for Fast Imaging Employing Steady State Acquisition, a type of Balanced Gradient Echo.

True FISP

The Siemens acronym for True Fast Imaging with Steady State Free Precession.

Spoiled (Incoherent) Gradient Echo

A steady state GRE sequence where spins are purposely de-phased between TRs using RF or gradient 'spoilers' to remove residual transverse magnetization and produce T1 weighting.

SPGR

The GE acronym for Spoiled Gradient Recalled Echo.

LAVA / VIBE

Dynamic fast 3D sequences associated with GE (LAVA) and Siemens (VIBE) platforms.

Fast Gradient Echo Techniques

Methods to decrease scan time including Fractional Echoes, Fractional RF Pulses, Fractional NEX (Partial Fourier), and increased rBW.

IR Prepared

Inversion Recovery prepared; a $180^{\circ}$ RF inversion pulse used before the GRE sequence to increase T1 contrast or allow for tissue suppression.

DE Prepared

Driven Equilibrium prepared; a triplet of $90-180-90^{\circ}$ RF pulses used before the GRE sequence flip angle to increase T2 image contrast.

GRASE

Gradient and Spin Echo; a hybrid non-steady state sequence that combines FSE with gradient echoes to reduce scan time compared to traditional FSE.