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pypulseq/pypulseq/make_trap_pulse.py
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make_trap_pulse.py
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import math
from types import SimpleNamespace
from pypulseq.opts import Opts
def make_trapezoid(channel='z', system=Opts(), duration=0, area=-1, flat_time=None, flat_area=None, amplitude=None,
max_grad=0, max_slew=0, rise_time=0, delay=0):
"""
Creates a trapezoidal gradient event.
Parameters
----------
channel : str, optional
Orientation of trapezoidal gradient event. Must be one of `x`, `y` or `z`.
system : Opts, optional
System limits. Default is a system limits object initialised to default values.
duration : float, optional
Duration in milliseconds (ms). Default is 0.
area : float, optional
Area. Default is -1.
flat_time : float, optional
Flat duration in milliseconds (ms). Default is `None`.
flat_area : float, optional
Flat area. Default is `None`.
amplitude : float, optional
Amplitude. Default is `None`.
max_grad : float, optional
Maximum gradient strength. Default is 0.
max_slew : float, optional
Maximum slew rate. Default is 0.
rise_time : float, optional
Rise time in milliseconds (ms). Default is 0.
delay : float, optional
Delay in milliseconds (ms). Default is 0.
Returns
-------
grad : SimpleNamespace
Trapezoidal gradient event created based on the supplied parameters.
"""
if channel not in ['x', 'y', 'z']:
raise ValueError()
if max_grad <= 0:
max_grad = system.max_grad
if max_slew <= 0:
max_slew = system.max_slew
if rise_time <= 0:
rise_time = system.rise_time
if area is None and flat_area is None and amplitude is None:
raise ValueError('Must supply either \'area\', \'flat_area\' or \'amplitude\'')
if flat_time is not None:
if amplitude is not None:
amplitude2 = amplitude
else:
amplitude2 = flat_area / flat_time
if rise_time is None:
rise_time = abs(amplitude2) / max_slew
rise_time = math.ceil(rise_time / system.grad_raster_time) * system.grad_raster_time
fall_time, flat_time = rise_time, flat_time
elif duration > 0:
amplitude2 = amplitude
if amplitude is None:
if rise_time is None:
dC = 1 / abs(2 * max_slew) + 1 / abs(2 * max_slew)
possible = duration ** 2 > 4 * abs(area) * dC
amplitude2 = (duration - math.sqrt(duration ** 2 - 4 * abs(area) * dC)) / (2 * dC)
else:
amplitude2 = area / (duration - rise_time)
possible = duration > 2 * rise_time and abs(amplitude2) < max_grad
if not possible:
raise ValueError('Requested area is too large for this gradient')
if rise_time is None:
rise_time = math.ceil(
abs(amplitude2) / max_slew / system.grad_raster_time) * system.grad_raster_time
fall_time = rise_time
flat_time = duration - rise_time - fall_time
if amplitude is None:
amplitude2 = area / (rise_time / 2 + fall_time / 2 + flat_time)
else:
if area is None:
raise ValueError('Must supply a duration')
else:
rise_time = math.ceil(math.sqrt(abs(area) / max_slew) / system.grad_raster_time) * system.grad_raster_time
amplitude2 = area / rise_time
t_eff = rise_time
if abs(amplitude2) > max_grad:
t_eff = math.ceil(abs(area) / max_grad / system.grad_raster_time) * system.grad_raster_time
amplitude2 = area / t_eff
rise_time = math.ceil(
abs(amplitude2) / max_slew / system.grad_raster_time) * system.grad_raster_time
flat_time = t_eff - rise_time
fall_time = rise_time
if abs(amplitude2) > max_grad:
raise ValueError("Amplitude violation")
grad = SimpleNamespace()
grad.type = 'trap'
grad.channel = channel
grad.amplitude = amplitude2
grad.rise_time = rise_time
grad.flat_time = flat_time
grad.fall_time = fall_time
grad.area = amplitude2 * (flat_time + rise_time / 2 + fall_time / 2)
grad.flat_area = amplitude2 * flat_time
grad.delay = delay
grad.first = 0
grad.last = 0
return grad
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