sim_rf

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sim_rf#

pypulseqpp.sim_rf()[source]#

Simulate an RF pulse versus off-resonance without relaxation.

Follows MATLAB Pulseq’s simRf: a hard-pulse approximation with no selection gradient, so frequency maps to position only for a constant selection gradient.

Parameters:

  • rf (SimpleNamespace or RfEvent) – Its freq_ppm and phase_ppm are converted with the default system’s gamma and B0, with a warning.

  • rephase_factor (float, default=None) – Free precession after the pulse, as a signed fraction of its duration. Defaults to zero when rf.use == "refocusing" and to -(shape_dur - center) / shape_dur, the slice-select rephaser, otherwise.

  • prephase_factor (float, default=0.0) – The same, before the pulse.

  • df (float, default=1.0) – In Hz: the axis holds round(bandwidth / df) points, so their spacing is about bandwidth_multiplier * df.

  • bandwidth_multiplier (float, default=4.0) – Width of the frequency axis, in bandwidths. The bandwidth is calc_rf_bandwidth() at half maximum plus |freq_offset|; the axis is centred on freq_offset.

  • dt (float, default=None) – Simulation raster, in s. Chosen from the bandwidth when omitted.

Returns:

  • mz_z (numpy.ndarray) – Mz after the pulse, starting from +z.

  • mz_xy (numpy.ndarray) – Mx + i My after the pulse, starting from +z.

  • f (numpy.ndarray) – The frequency axis, in Hz.

  • ref_eff (numpy.ndarray) – Complex refocusing efficiency: its magnitude is the refocused fraction and its phase twice the azimuth of the refocusing axis.

  • mx_xy, my_xy (numpy.ndarray) – Mx + i My starting from +x and from +y.

Warns:

UserWarning – If the pulse carries a ppm offset, which is read against the gamma and B0 of the default system.

Examples

>>> import numpy as np
>>> import pypulseqpp as pp

A hard 90 takes +z into the transverse plane, on resonance:

>>> rf = pp.make_block_pulse(np.pi / 2, duration=0.5e-3)
>>> mz_z, mz_xy, f = pp.sim_rf(rf)[:3]
>>> on_resonance = int(np.argmin(abs(f)))
>>> bool(abs(mz_z[on_resonance]) < 0.15), bool(abs(mz_xy[on_resonance]) > 0.85)
(True, True)

A hard 180 inverts it:

>>> mz_z, _, f = pp.sim_rf(pp.make_block_pulse(np.pi, duration=0.7e-3))[:3]
>>> bool(mz_z[int(np.argmin(abs(f)))] < -0.85)
True

See also

calc_rf_bandwidth

the width alone, from the envelope’s transform.

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