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pypulseq/pulseq/core/makearbitrary_rf.py
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makearbitrary_rf.py
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from math import pi
import numpy as np
from pulseq.core.holder import Holder
from pulseq.core.make_trap import make_trapezoid
from pulseq.core.opts import Opts
def make_arbitrary_rf(kwargs, nargout=1):
"""
Makes a Holder object for an arbitrary RF pulse Event.
Parameters
----------
kwargs : dict
Key value mappings of RF Event parameters_params and values.
nargout: int
Number of output arguments to be returned. Default is 1, only RF Event is returned. Passing any number greater
than 1 will return the Gz Event along with the RF Event.
Returns
-------
rf : Holder
RF Event configured based on supplied kwargs.
gz : Holder
Slice select trapezoidal gradient Event.
"""
flip_angle = kwargs.get("flip_angle")
system = kwargs.get("system", Opts())
signal = kwargs.get("signal", 0)
freq_offset = kwargs.get("freq_offset", 0)
phase_offset = kwargs.get("phase_offset", 0)
time_bw_product = kwargs.get("time_bw_product", 0)
bandwidth = kwargs.get("bandwidth", 0)
max_grad = kwargs.get("max_grad", 0)
max_slew = kwargs.get("max_slew", 0)
slice_thickness = kwargs.get("slice_thickness", 0)
signal = signal / sum(signal * system.rf_raster_time) * flip_angle / (2 * pi)
N = len(signal)
duration = N * system.rf_raster_time
t = [x * system.rfRasterTime for x in range(0, N)]
rf = Holder()
rf.type = 'rf'
rf.signal = signal
rf.t = t
rf.freq_offset = freq_offset
rf.phase_offset = phase_offset
rf.rf_dead_time = system.rf_dead_time
rf.ring_down_time = system.rf_ring_down_time
if nargout > 1:
if slice_thickness <= 0:
raise ValueError('Slice thickness must be provided')
if bandwidth <= 0:
raise ValueError('Bandwidth of pulse must be provided')
system.maxgrad = max_grad if max_grad > 0 else system.maxgrad
system.max_slew = max_slew if max_slew > 0 else system.max_slew
BW = bandwidth
if time_bw_product > 0:
BW = time_bw_product / duration
amplitude = BW / slice_thickness
area = amplitude * duration
kwargs_for_trap = {"channel": 'z', "system": system, "flat_time": duration, "flat_area": area}
gz = make_trapezoid(**kwargs_for_trap)
t_fill = np.arange(1, round(gz.rise_time / 1e-6) + 1) * 1e-6
rf.t = [t_fill, rf.t + t_fill[-1], t_fill + rf.t[-1] + t_fill[-1]]
rf.signal = [np.zeros(len(t_fill)), rf.signal, np.zeros(len(t_fill))]
if rf.ring_down_time > 0:
t_fill = np.arange(1, round(gz.rise_time / 1e-6) + 1) * 1e-6
rf.t = [rf.t, rf.t[-1] + t_fill]
rf.signal = [rf.signal, np.zeros(len(t_fill))]
return rf, gz
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