initialize_3D_repi

initialize_3D_repi#

mrinufft.trajectories.trajectory3D.initialize_3D_repi(Nc, Ns_readouts, Ns_transitions, nb_blades, nb_blade_revolutions=0, blade_tilt='uniform', nb_spiral_revolutions=0, spiral='archimedes', nb_trains='auto', in_out=True)[source]#

Initialize 3D REPI trajectory.

This is an implementation of the REPI (Radial Echo Planar Imaging) trajectory proposed in [RMS22] and officially inspired from TURBINE proposed in [MGM10]. It consists of multi-echo stacks of lines or spirals rotated around any axis (here \(k_z\)-axis) in a radial fashion, but each stack is also slightly shifted along the rotation axis in order to be entangled with the others without redundancy. This feature is similar to choosing skip_factor equal to nb_blades in TURBINE.

Note that our implementation also proposes to segment the planes/stacks into several shots, instead of just one. Spirals can also be customized beyond the classic Archimedean spiral.

Parameters:

  • Nc (int) – Number of shots

  • Ns_readouts (int) – Number of samples per readout

  • Ns_transitions (int) – Number of samples per transition between two readouts

  • nb_blades (int) – Number of line stacks over the kz axis

  • nb_blade_revolutions (float) – Number of revolutions over lines/spirals within a blade over the kz axis.

  • blade_tilt (str, float, optional) – Tilt between individual blades, by default “uniform”

  • nb_spiral_revolutions (float, optional) – Number of revolutions of the spirals over the readouts, by default 0

  • spiral (str, float, optional) – Spiral type, by default “archimedes”

  • nb_trains (int, str) – Number of trains dividing the readouts, such that each shot will be composed of n readouts with Nc = n * nb_trains. If “auto” then nb_trains is set to nb_blades.

  • in_out (bool, optional) – Whether the curves are going in-and-out or start from the center

Returns:

3D REPI trajectory

Return type:

array_like

References

[RMS22]

Rettenmeier, Christoph A., Danilo Maziero, and V. Andrew Stenger. “Three dimensional radial echo planar imaging for functional MRI.” Magnetic Resonance in Medicine 87, no. 1 (2022): 193-206.