2D multislice Spin echo imaging

Image matrix = 256 x 256, slice thickness = 5 mm, TR = 2400 ms, TE = 20 ms, subvoxel = 2 x 1 x 4, number of isochromats = 27,335,680, calculation time = 2234.636 s (37.2 min)

Python sequence code:

from psdk import *
import numpy as np

gamma = 42.57747892 # [MHz/T]
TR = 2400.0e+3 # [us]
TE = 20.0e+3 # [us]
NR = 256 # Number of readout points
NPE1 = 256 # Number of 1st phase encoding
fov = [256.0, 256.0, 256.0] # [mm]
dwell_time = 10.0 # [us]
slice_width = 5.0 # [mm]
gx_value = 1e+6 / (dwell_time * gamma * fov[0]) # [mT/m]
gy_value = 2e+6 / (dwell_time * gamma * fov[1]) * NPE1 / NR # [mT/m]
gz_value = 1.25 / (slice_width * 1.0e-3) / gamma # [mT/m]
gx_rise_time = 300.0 # [us]
gy_rise_time = 300.0 # [us]
gz_rise_time = 300.0 # [us]
ex_pulse_width = 2400.0 # [us]
ex_pulse_flip_angle = 90.0 # [degree]

def sinc_with_hamming(flip_angle, pulse_width, points, *, min=-2.0*np.pi, max=2.0*np.pi):
    x0 = np.arange(min, max, (max - min) / points)
    x1 = x0 + (max - min) / points
    y = (np.sinc(x0 / np.pi) + np.sinc(x1 / np.pi)) * 0.5 * np.hamming(points)
    return flip_angle * y * points / (y.sum() * pulse_width * 360.0e-6 * gamma)

with Sequence('2D multislice SpinEcho'):

    with Block('Excitation', ex_pulse_width + 2.0*gz_rise_time):
        GZ(0.0, gz_value, gz_rise_time)
        RF(gz_rise_time, sinc_with_hamming(ex_pulse_flip_angle, ex_pulse_width, 160), ex_pulse_width / 160, \
            frequency=([-15.0, -12.5, -10.0, -7.5, -5.0, -2.5, 0.0, 2.5, 5.0, 7.5, 10.0, 12.5, -13.75, -11.25, -8.75, -6.25, -3.75, -1.25,
             1.25, 3.75, 6.25, 8.75, 11.25, 13.75], ['SL']))
        GZ(ex_pulse_width + gz_rise_time, 0.0, gz_rise_time)

    with Block('Slice_refocus', ex_pulse_width * 0.5 + gz_rise_time * 2.0) :
        GZ(0.0, -gz_value, gz_rise_time)
        GZ(ex_pulse_width * 0.5 + gz_rise_time, 0.0, gz_rise_time) 

    with Block('ReadPredephasing', NR // 2 * dwell_time * 2.0 + gx_rise_time):
        GX(0.0, gx_value, gx_rise_time)
        GX(NR // 2 * dwell_time * 2.0, 0.0, gx_rise_time)         

    with Block('Refocus', ex_pulse_width + 2.0*gz_rise_time):
        GZ(0.0, gz_value, gz_rise_time)
        RF(gz_rise_time, 2.0 * sinc_with_hamming(ex_pulse_flip_angle, ex_pulse_width, 160), ex_pulse_width / 160, \
            frequency=([-15.0, -12.5, -10.0, -7.5, -5.0, -2.5, 0.0, 2.5, 5.0, 7.5, 10.0, 12.5, -13.75, -11.25, -8.75, -6.25, -3.75, -1.25, 
            1.25, 3.75, 6.25, 8.75, 11.25, 13.75], ['SL']))
        GZ(ex_pulse_width + gz_rise_time, 0.0, gz_rise_time)        

    with Block('PhaseEncoding', NR // 2 * dwell_time + gx_rise_time * 2.5):
        GY(0.0, ([gy_value * (i - NPE1 // 2) / NPE1 for i in range(NPE1)], ['PE1']), gy_rise_time)
        GY(NR // 2 * dwell_time, 0.0, gy_rise_time)

    with Block('Readout', NR * dwell_time * 2.0 + gx_rise_time):
        GX(0.0, gx_value, gx_rise_time)
        AD(NR // 2 * dwell_time + gx_rise_time * 0.5, NR, dwell_time)
        GX(NR * dwell_time * 2.0, 0, gx_rise_time)
        
    with Block('Rewinding', NR // 2 * dwell_time + gx_rise_time * 2.5):
        GY(gx_rise_time * 2.5 - gy_rise_time, ([gy_value * (NPE1 // 2 - i) / NPE1 for i in range(NPE1)], ['PE1']), gy_rise_time)
        GY(NR // 2 * dwell_time + gx_rise_time * 2.5 - gy_rise_time, 0.0, gy_rise_time)
        
    with Main():
        with Loop('PE1', NPE1):
            with Loop('SL', 24):
                BlockRef('Excitation')
                BlockRef('Slice_refocus')
                BlockRef('ReadPredephasing')
                WaitUntil(TE/2 - NR * dwell_time * 0.5)
                BlockRef('Refocus')
                BlockRef('PhaseEncoding')
                WaitUntil(TE + gz_rise_time + ex_pulse_width * 0.5 - NR * dwell_time - gx_rise_time * 0.5)
                BlockRef('Readout')
                BlockRef('Rewinding')
                WaitUntil(100.0e+3)                
            WaitUntil(TR)