2D radial spin echo

A slice-selective excitation and 180-degree refocusing pulse form one spin echo, followed by a radial spoke through k-space centre. Spoilers suppress unwanted coherence before the next TR. TE controls T2 weighting and TR controls longitudinal recovery. Radial spin echo supports motion-robust structural imaging.

Nyquist angular sampling

ceil(pi / 2 * n) spokes over half a turn, which sample the outer radius at the Nyquist spacing.

import pypulseqpp as pp
from pypulseqpp.sequences import se_radial2D_sequence

baseline = se_radial2D_sequence(n=192, n_slices=1, te=None, tr=None, n_dummy=0)
print(f"{baseline.num_blocks} blocks, {baseline.duration()[0]:.2f} s")

2114 blocks, 5.90 s

Sequence diagram

baseline.paper_plot()

Sampling order

Colour encodes spoke acquisition order.

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

Angular undersampling

Retaining one spoke angle in three reduces peripheral angular sampling; every acquired spoke still crosses the k-space origin.

alternative = se_radial2D_sequence(n=192, n_slices=1, ry=3, te=None, tr=None, n_dummy=0)

                   blocks  duration (s)  acquisitions
Nyquist              2114          5.90           302
ry = 3                707          1.97           101

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