3D balanced SSFP

A slab-selective low-flip-angle excitation and balanced Cartesian readout repeat with alternating RF phase and zero net gradient moment in every TR. The preserved transverse coherence establishes a high-SNR steady state governed by T2/T1 and off-resonance. A half-flip preparation reduces transient oscillation. 3D bSSFP is used for high-SNR 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 bssfp3D_sequence

baseline = bssfp3D_sequence(n_x=160, n_y=160, n_z=32, tr=None)
print(f"{baseline.num_blocks} blocks, {baseline.duration()[0]:.2f} s")

11985 blocks, 16.46 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 the line and partition axes reduces the number of repetitions. TR, flip angle, RF phase alternation and the balanced gradient moments of each repetition are unchanged, so the steady state is the same.

alternative = bssfp3D_sequence(n_x=160, n_y=160, n_z=32, ry=2, rz=2, tr=None)

                   blocks  duration (s)  acquisitions
full                11985         16.46          3995
2 x 2                3837          5.27          1279

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