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make_sinc_pulse.py
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Mon, Sep 23, 13:58

make_sinc_pulse.py
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import math
from types import SimpleNamespace
import numpy as np
from pypulseq.make_trap_pulse import make_trapezoid
from pypulseq.opts import Opts
def make_sinc_pulse(flip_angle, system=Opts(), duration=0, freq_offset=0, phase_offset=0, time_bw_product=4,
apodization=0, center_pos=0.5, max_grad=0, max_slew=0, slice_thickness=0, delay=0, use=''):
"""
Makes a Holder object for an 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.
"""
BW = time_bw_product / duration
alpha = apodization
N = int(round(duration / 1e-6))
t = np.arange(1, N + 1) * system.rf_raster_time
tt = t - (duration * center_pos)
window = 1 - alpha + alpha * np.cos(2 * np.pi * tt / duration)
signal = np.multiply(window, np.sinc(BW * tt))
flip = np.sum(signal) * system.rf_raster_time * 2 * np.pi
signal = signal * flip_angle / flip
rf = SimpleNamespace()
rf.type = 'rf'
rf.signal = signal
rf.t = t
rf.freq_offset = freq_offset
rf.phase_offset = phase_offset
rf.dead_time = system.rf_dead_time
rf.ringdown_time = system.rf_ringdown_time
rf.delay = delay
if use != '':
rf.use = use
if rf.dead_time > rf.delay:
rf.delay = rf.dead_time
try:
if slice_thickness == 0:
raise ValueError('Slice thickness must be provided')
if max_grad > 0:
system.max_grad = max_grad
if max_slew > 0:
system.max_slew = max_slew
amplitude = BW / slice_thickness
area = amplitude * duration
gz = make_trapezoid(channel='z', system=system, flat_time=duration, flat_area=area)
gzr = make_trapezoid(channel='z', system=system, area=-area * (1 - center_pos) - 0.5 * (gz.area - area))
if rf.delay > gz.rise_time:
gz.delay = math.ceil((rf.delay - gz.rise_time) / system.grad_raster_time) * system.grad_raster_time
if rf.delay < (gz.rise_time + gz.delay):
rf.delay = gz.rise_time + gz.delay
except:
gz = None
gzr = None
if rf.ringdown_time > 0:
t_fill = np.arange(1, round(rf.ringdown_time / 1e-6) + 1) * 1e-6
rf.t = np.concatenate((rf.t, rf.t[-1] + t_fill))
rf.signal = np.concatenate((rf.signal, np.zeros(len(t_fill))))
# Following 2 lines of code are workarounds for numpy returning 3.14... for np.angle(-0.00...)
negative_zero_indices = np.where(rf.signal == -0.0)
rf.signal[negative_zero_indices] = 0
return rf, gz, gzr

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