3D Cartesian gradient echo

A 3D spoiled gradient-echo (SPGR) acquisition applies a low-flip-angle slab excitation before one Cartesian (line, partition) readout per TR. Gradient spoiling and quadratic RF/receiver phase cycling suppress coherent residual transverse magnetisation. TR, flip angle, and TE determine the T1 and T2* weighting. This sequence is used for high-resolution T1-weighted structural imaging.

Fully sampled acquisition

Every (line, partition) view inside the ellipse inscribed in the phase-encode plane is acquired.

import pypulseqpp as pp
from pypulseqpp.sequences import gre3D_sequence

baseline = gre3D_sequence(n_x=160, n_y=160, n_z=32, te=None, tr=None, n_dummy=0)
print(f"{baseline.num_blocks} blocks, {baseline.duration()[0]:.2f} s")
print(f"TR {baseline.get_definition('TR')[0] * 1e3:.2f} ms")

15980 blocks, 26.77 s
TR 6.70 ms

Sequence diagram

baseline.paper_plot()

Sampling order

Colour encodes acquisition order in the phase-encode plane. All lines of one partition are acquired before the next partition.

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

Acceleration on both encoded axes

ry and rz subsample the line and partition axes independently. With ry=rz=2, the phase-encode plane outside the central calibration region is acquired in approximately one quarter of the repetitions; the calibration region remains fully sampled.

alternative = gre3D_sequence(
    n_x=160, n_y=160, n_z=32, ry=2, rz=2, te=None, tr=None, n_dummy=0
)

                   blocks  duration (s)  acquisitions
full                15980         26.77          3995
2 x 2                5116          8.57          1279

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