writeSelectiveRf

Calculate timing (TE=20ms, TR=500ms)
Write to file

seq=mr.Sequence();              % Create a new sequence object
fov=220e-3; Nx=256; Ny=256;     % Define FOV and resolution

foe=200e-3;             % Field of excitation
targetWidth=22.5e-3;    % Diameter of target excitation pattern
n=8;                    % Number of spiral turns
T=8e-3;                 % Pulse duration

% Set system limits
lims = mr.opts('MaxGrad',32,'GradUnit','mT/m',...
    'MaxSlew',130,'SlewUnit','T/m/s',...
    'rfRingdownTime', 30e-6, 'rfDeadtime', 100e-6);

% Define spiral k-space trajectory
kMax=(2*n)/foe/2;       % Units of 1/m (not rad/m)
tk=0:seq.gradRasterTime:T-seq.gradRasterTime;
kx=kMax*(1-tk/T).*cos(2*pi*n*tk/T);
ky=kMax*(1-tk/T).*sin(2*pi*n*tk/T);

% Define RF pulse
tr=0:seq.rfRasterTime:T-seq.rfRasterTime;
kxRf=interp1(tk,kx,tr,'linear','extrap');
kyRf=interp1(tk,ky,tr,'linear','extrap');
beta=2*pi*kMax*targetWidth/2/sqrt(2);  % Gaussian width in k-space
signal0 = exp(-beta.^2.*(1-tr/T).^2).*sqrt((2*pi*n*(1-tr/T)).^2+1);
signal = signal0.*(1 + exp(-1j.*2*pi*5e-2*(kxRf + kyRf)));

% Add gradient ramps
[kx,ky,signal]=mr.addRamps({kx,ky},'rf',signal);

rf = mr.makeArbitraryRf(signal,20*pi/180,'system',lims);
gxRf = mr.makeArbitraryGrad('x',mr.traj2grad(kx));
gyRf = mr.makeArbitraryGrad('y',mr.traj2grad(ky));

% Define other gradients and ADC events
deltak=1/fov;
gx = mr.makeTrapezoid('x','FlatArea',Nx*deltak,'FlatTime',6.4e-3);
adc = mr.makeAdc(Nx,'Duration',gx.flatTime,'Delay',gx.riseTime);
gxPre = mr.makeTrapezoid('x','Area',-gx.area/2,'Duration',2e-3);
phaseAreas = ((0:Ny-1)-Ny/2)*deltak;

% Refocusing pulse and spoiling gradients
%[rf180, gz] = mr.makeBlockPulse(pi,'Duration',1e-3,'SliceThickness',5e-3);
[rf180, gz] = mr.makeSincPulse(pi,'system',lims,'Duration',3e-3,...
    'SliceThickness',5e-3,'apodization',0.5,'timeBwProduct',4);

gzSpoil = mr.makeTrapezoid('z','Area',gx.area,'Duration',2e-3);

Calculate timing (TE=20ms, TR=500ms)

delayTE1=ceil((20e-3/2 - mr.calcDuration(gzSpoil) - mr.calcDuration(rf180)/2)/seq.gradRasterTime)*seq.gradRasterTime;
delayTE2=delayTE1 - mr.calcDuration(gxPre) - mr.calcDuration(gx)/2;
delayTR=500e-3 - 20e-3 - mr.calcDuration(rf) - mr.calcDuration(gx)/2;

% Loop over phase encodes and define sequence blocks
for i=1:Ny
    seq.addBlock(rf,gxRf,gyRf);
    seq.addBlock(mr.makeDelay(delayTE1));
    seq.addBlock(gzSpoil);
    seq.addBlock(rf180,gz);
    seq.addBlock(gzSpoil);
    seq.addBlock(mr.makeDelay(delayTE2));
    gyPre = mr.makeTrapezoid('y','Area',phaseAreas(i),'Duration',2e-3);
    seq.addBlock(gxPre,gyPre);
    seq.addBlock(gx,adc);
    seq.addBlock(mr.makeDelay(delayTR));
end

seq.setDefinition('Name', 'se_selRF');

seq.write('selectiveRf.seq');   % Write to pulseq file
seq.plot();

return

Write to file

The sequence is written to file in compressed form according to the file format specification using the write method.

%seq.setDefinition('Scan_ID',2068);
%seq.setDefinition('Recon_Mode',1);
%seq.write('external.seq')

%seq.plot

Contents

Calculate timing (TE=20ms, TR=500ms)

Write to file