3D Cartesian multi-echo gradient echo

A slab-selective spoiled excitation is followed by several gradient echoes of one Cartesian (line, partition) view. Gradient and RF spoiling suppress residual transverse coherence between repetitions. The multiple echo times sample T2* decay; TR and flip angle determine the T1 weighting. Applications include high-resolution structural imaging, R2* mapping, and QSM.

Fully sampled acquisition

Four echoes per excitation, over every (line, partition) view inside the ellipse inscribed in the phase-encode plane.

import pypulseqpp as pp
from pypulseqpp.sequences import gre_multiecho3D_sequence

baseline = gre_multiecho3D_sequence(
    n_x=160, n_y=160, n_z=32, n_echoes=4, tr=None, n_dummy=0
)
print(f"{baseline.num_blocks} blocks, {baseline.duration()[0]:.2f} s")

39950 blocks, 52.89 s

Sequence diagram

baseline.paper_plot()

Sampling order

Colour encodes acquisition order in the phase-encode plane.

pp.plot.plot_kspace(baseline, color_by="order", plane="yz", show_trajectory=False)

Acceleration on both encoded axes

Subsampling both phase-encode axes reduces the number of repetitions. The complete echo train remains within each retained repetition.

alternative = gre_multiecho3D_sequence(
    n_x=160, n_y=160, n_z=32, n_echoes=4, ry=2, rz=2, tr=None, n_dummy=0
)

                   blocks  duration (s)  acquisitions
full                39950         52.89         15980
2 x 2               12790         16.93          5116

pp.plot.plot_kspace(alternative, color_by="order", plane="yz", show_trajectory=False)