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make_trap_pulse.py
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Mon, Sep 23, 03:15

make_trap_pulse.py
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import math
from types import SimpleNamespace
import numpy as np
from pypulseq.opts import Opts
def make_trapezoid(channel: str, amplitude: float = 0, area: float = None, delay: float = 0, duration: float = 0,
flat_area: float = 0, flat_time: float = -1, max_grad: float = 0, max_slew: float = 0,
rise_time: float = 0, system: Opts = Opts()) -> SimpleNamespace:
"""
Creates a trapezoidal gradient event.
Parameters
----------
channel : str, optional
Orientation of trapezoidal gradient event. Must be one of `x`, `y` or `z`.
amplitude : float, optional, default=0
Amplitude.
area : float, optional, default=None
Area.
delay : float, optional, default=0
Delay in milliseconds (ms).
duration : float, optional, default=0
Duration in milliseconds (ms).
flat_area : float, optional, default=0
Flat area.
flat_time : float, optional, default=-1
Flat duration in milliseconds (ms). Default is -1 to account for triangular pulses.
max_grad : float, optional, default=0
Maximum gradient strength.
max_slew : float, optional, default=0
Maximum slew rate.
rise_time : float, optional, default=0
Rise time in milliseconds (ms).
system : Opts, optional, default=Opts()
System limits.
Returns
-------
grad : SimpleNamespace
Trapezoidal gradient event created based on the supplied parameters.
Raises
------
ValueError
If none of `area`, `flat_area` and `amplitude` are passed
If requested area is too large for this gradient
If `flat_time`, `duration` and `area` are not supplied.
Amplitude violation
"""
if channel not in ['x', 'y', 'z']:
raise ValueError(f"Invalid channel. Must be one of `x`, `y` or `z`. Passed: {channel}")
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 == 0 and amplitude == 0:
raise ValueError("Must supply either 'area', 'flat_area' or 'amplitude'.")
if flat_time != -1:
if amplitude != 0:
amplitude2 = amplitude
else:
amplitude2 = flat_area / flat_time
if rise_time == 0:
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 == 0:
if rise_time == 0:
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 == 0:
rise_time = math.ceil(
abs(amplitude2) / max_slew / system.grad_raster_time) * system.grad_raster_time
if rise_time == 0:
rise_time = system.grad_raster_time
fall_time = rise_time
flat_time = duration - rise_time - fall_time
if amplitude == 0:
amplitude2 = area / (rise_time / 2 + fall_time / 2 + flat_time)
else:
if area == 0:
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 = np.divide(area, rise_time) # To handle nan
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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