3D Cartesian spin echo

A slab-selective excitation and 180-degree refocusing pulse form one spin echo, followed by a Cartesian (line, partition) readout. Spoilers suppress unwanted coherence before the next TR. TE and TR determine T2 and longitudinal recovery weighting. 3D spin echo supports high-resolution 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 se3D_sequence

baseline = se3D_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")

31960 blocks, 53.45 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 lines and partitions by two each reduces the number of repetitions approximately fourfold outside the calibration region. Each acquired view has the prescribed echo time.

alternative = se3D_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                31960         53.45          3995
2 x 2               10232         17.11          1279

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