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pypulseq/pulseq/pulse_sequence_demos/spiral_2d_nshot.py
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spiral_2d_nshot.py
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"""
This is starter code to demonstrate a working example of a 2D Spiral (N-shots) as a pure Python implementation.
"""
from math import pi
import numpy as np
from pulseq.core.Sequence.sequence import Sequence
from pulseq.core.calc_duration import calc_duration
from pulseq.core.make_adc import makeadc
from pulseq.core.make_delay import make_delay
from pulseq.core.make_sinc import make_sinc_pulse
from pulseq.core.make_trap import make_trapezoid
from pulseq.core.makearbitrary_grad import makearbitrary_grad
from pulseq.core.opts import Opts
from pulseq.core.utils.vds_2d import vds_2d
kwargs_for_opts = {"max_grad": 32, "grad_unit": "mT/m", "max_slew": 130, "slew_unit": "T/m/s", "grad_dead_time": 10e-6}
system = Opts(kwargs_for_opts)
seq = Sequence(system)
fov = 256e-3
Nx = 128
Ny = 256
slice_thickness = 5e-3
dx = fov / Nx
TR = 25e-3
TE = 5e-3
n_shots = 16
alpha = 9
[ktraj, G, lamda] = vds_2d(fov, Nx, n_shots, alpha, system)
ktraj = ktraj * 1e-3
ktrajs = np.zeros((np.size(ktraj, 0), np.size(ktraj, 1), 2))
ktrajs[:, :, 0] = np.real(ktraj)
ktrajs[:, :, 1] = np.imag(ktraj)
flip = 15 * pi / 180
kwargs_for_sinc = {"flip_angle": flip, "system": system, "duration": 1.5e-3, "slice_thickness": slice_thickness,
"apodization": 0.5, "time_bw_product": 4}
rf, gz = make_sinc_pulse(kwargs_for_sinc, 2)
kwargs_for_adc = {"num_samples": max(G.shape), "dwell": system.grad_raster_time}
adc = makeadc(kwargs_for_adc)
n_slices = 3
deltaz = n_slices * slice_thickness
z = np.linspace(-(deltaz / 2), (deltaz / 2), deltaz / slice_thickness + 1)
pre_time = 8e-4
kwargs_for_gz_reph = {"channel": 'z', "system": system, "area": -gz.area / 2, "duration": 1e-3}
gz_reph = make_trapezoid(kwargs_for_gz_reph)
kwargs_for_gz_spoil = {"channel": 'z', "system": system, "area": gz.area * 2, "duration": 3 * pre_time}
gz_spoil = make_trapezoid(kwargs_for_gz_spoil)
kwargs_for_arb_gx = {"channel": 'x', "system": system, "waveform": np.squeeze(np.real(G[:, 0]))}
gx = makearbitrary_grad(kwargs_for_arb_gx)
delayTE = TE - calc_duration(gz_reph) - (calc_duration(rf) / 2)
delayTR = TR - calc_duration(gz_reph) - calc_duration(rf) - calc_duration(gx) - calc_duration(gz_spoil)
delay1 = make_delay(delayTE)
delay2 = make_delay(delayTR)
for s in range(n_slices): w
freq_offset = gz.amplitude * z[s]
rf.freq_offset = freq_offset
for ns in range(n_shots):
seq.add_block(rf, gz)
seq.add_block(gz_reph)
kwargs_for_arb_gx = {"channel": 'x', 'system': system, 'waveform': np.squeeze(np.real(G[:, ns]))}
gx = makearbitrary_grad(kwargs_for_arb_gx)
kwargs_for_arb_gy = {"channel": 'y', 'system': system, 'waveform': np.squeeze(np.imag(G[:, ns]))}
gy = makearbitrary_grad(kwargs_for_arb_gy)
seq.add_block(delay1)
seq.add_block(gx, gy, adc)
seq.add_block(gz_spoil)
seq.add_block(delay2)
# Display entire plot
seq.plot()
# The .seq file will be available inside the /gpi/<user>/imr_framework folder
seq.write('spiral_2d_256_9_3_16_python.seq')
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