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pypulseq/pypulseq/make_block_pulse.py
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make_block_pulse.py
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import math
from types import SimpleNamespace
from typing import Tuple, Union
import numpy as np
from pypulseq.make_trap_pulse import make_trapezoid
from pypulseq.opts import Opts
def make_block_pulse(flip_angle: float, bandwidth: float = 0, delay: float = 0, duration: float = 0,
freq_offset: float = 0, max_grad: float = 0, max_slew: float = 0, phase_offset: float = 0,
return_gz: bool = False, system: Opts = Opts(), slice_thickness: float = 0,
time_bw_product: float = 0,
use: str = str()) -> Union[SimpleNamespace, Tuple[SimpleNamespace, SimpleNamespace]]:
"""
Creates a radio-frequency block pulse event and optionally an accompanying slice select trapezoidal gradient event.
Parameters
----------
flip_angle : float
Flip angle in radians.
bandwidth : float, default=0
Bandwidth in Hertz (hz).
delay : float, default=0
Delay in milliseconds (ms) of accompanying slice select trapezoidal event.
duration : float, default=0
Duration in milliseconds (ms).
freq_offset : float, default=0
Frequency offset in Hertz (Hz).
max_grad : float, default=0
Maximum gradient strength of accompanying slice select trapezoidal event.
max_slew : float, default=0
Maximum slew rate of accompanying slice select trapezoidal event.
phase_offset : float, default=0
Phase offset Hertz (Hz).
return_gz : bool, default=False
Boolean flag to indicate if slice-selective gradient has to be returned.
slice_thickness : float, default=0
Slice thickness of accompanying slice select trapezoidal event. The slice thickness determines the area of the
slice select event.
system : Opts, default=Opts()
System limits.
time_bw_product : float, default=0
Time-bandwidth product.
use : str, default=str()
Use of radio-frequency block pulse event. Must be one of 'excitation', 'refocusing' or 'inversion'.
Returns
-------
rf : SimpleNamespace
Radio-frequency block pulse event.
gz : SimpleNamespace
Slice select trapezoidal gradient event accompanying the radio-frequency block pulse event.
Raises
------
ValueError
If invalid `use` parameter is passed. Must be one of 'excitation', 'refocusing' or 'inversion'.
If neither `bandwidth` nor `duration` are passed.
If `return_gz=True`, and `slice_thickness` is not passed.
"""
valid_use_pulses = ['excitation', 'refocusing', 'inversion']
if use is not None and use not in valid_use_pulses:
raise ValueError(
f"Invalid use parameter. Must be one of 'excitation', 'refocusing' or 'inversion'. Passed: {use}")
if duration == 0:
if time_bw_product > 0:
duration = time_bw_product / bandwidth
elif bandwidth > 0:
duration = 1 / (4 * bandwidth)
else:
raise ValueError('Either bandwidth or duration must be defined')
BW = 1 / (4 * duration)
N = round(duration / 1e-6)
t = np.arange(1, N + 1) * system.rf_raster_time
signal = flip_angle / (2 * np.pi) / duration * np.ones(len(t))
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
if return_gz:
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)
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
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))))
return rf, gz if return_gz else rf
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