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make_arbitrary_grad.py
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Mon, Jun 10, 17:16

make_arbitrary_grad.py
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from types import SimpleNamespace
import numpy as np
from pypulseq.opts import Opts
def make_arbitrary_grad(channel: str, waveform: np.ndarray, system: Opts = Opts(), max_grad: float = 0,
max_slew: float = 0, delay: float = 0) -> SimpleNamespace:
"""
Creates a gradient event with arbitrary waveform.
Parameters
----------
channel : str
Orientation of gradient event of arbitrary shape. Must be one of `x`, `y` or `z`.
waveform : numpy.ndarray
Arbitrary waveform.
system : Opts, optional
System limits. Default is a system limits object initialised to default values.
max_grad : float, optional
Maximum gradient strength. Default is 0.
max_slew : float, optional
Maximum slew rate. Default is 0.
delay : float, optional
Delay in milliseconds (ms).
Returns
-------
grad : SimpleNamespace
Gradient event with arbitrary waveform.
"""
if channel not in ['x', 'y', 'z']:
raise ValueError(f'Invalid channel. Must be one of x, y or z. You passed: {channel}')
if max_grad <= 0:
max_grad = system.max_grad
if max_slew <= 0:
max_slew = system.max_slew
g = waveform
slew = np.squeeze(np.subtract(g[1:], g[:-1]) / system.grad_raster_time)
if max(abs(slew)) >= max_slew:
raise ValueError(f'Slew rate violation {max(abs(slew)) / max_slew * 100}')
if max(abs(g)) >= max_grad:
raise ValueError(f'Gradient amplitude violation {max(abs(g)) / max_grad * 100}')
grad = SimpleNamespace()
grad.type = 'grad'
grad.channel = channel
grad.waveform = g
grad.delay = delay
grad.t = np.arange(len(g)) * system.grad_raster_time
grad.first = g[0]
grad.last = g[-1]
return grad

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