3D stack-of-stars gradient echo

A slab-selective spoiled excitation is followed by one radial spoke with Cartesian partition encoding. Gradient and RF spoiling suppress residual transverse coherence between repetitions. TR and flip angle primarily determine T1 weighting. Stack-of-stars SPGR is used for motion-robust 3D structural and dynamic imaging.

Nyquist angular sampling

The Nyquist set of spoke angles at every partition. With the default partition_angle_shift='none', every partition uses the same angles.

import pypulseqpp as pp
from pypulseqpp.sequences import gre_stack_of_stars3D_sequence

baseline = gre_stack_of_stars3D_sequence(n=96, n_z=8, tr=None, n_dummy=0)
print(f"{baseline.num_blocks} blocks, {baseline.duration()[0]:.2f} s")

4832 blocks, 8.84 s

Sequence diagram

baseline.paper_plot()

Sampling order

The spokes of every partition, over the three k-space axes.

pp.plot.plot_kspace(baseline, color_by="shot")

Angular undersampling

Retaining one spoke angle in four reduces the number of repetitions fourfold. Every acquired spoke samples the origin of its partition.

alternative = gre_stack_of_stars3D_sequence(n=96, n_z=8, ry=4, tr=None, n_dummy=0)

                   blocks  duration (s)  acquisitions
Nyquist              4832          8.84          1208
ry = 4               1216          2.23           304

pp.plot.plot_kspace(alternative, color_by="shot")