Contents
seq=mr.Sequence();
fov=256e-3; Nx=256; Ny=256;
alpha=10;
sliceThickness=3e-3;
TE=4.3e-3;
TR=10e-3;
rfSpoilingInc=117;
sys = mr.opts('MaxGrad', 28, 'GradUnit', 'mT/m', ...
'MaxSlew', 150, 'SlewUnit', 'T/m/s', 'rfRingdownTime', 20e-6, ...
'rfDeadTime', 100e-6, 'adcDeadTime', 10e-6);
[rf, gz] = mr.makeSincPulse(alpha*pi/180,'Duration',3e-3,...
'SliceThickness',sliceThickness,'apodization',0.5,'timeBwProduct',4,'system',sys);
deltak=1/fov;
gx = mr.makeTrapezoid('x','FlatArea',Nx*deltak,'FlatTime',3.2e-3,'system',sys);
adc = mr.makeAdc(Nx,'Duration',gx.flatTime,'Delay',gx.riseTime,'system',sys);
gxPre = mr.makeTrapezoid('x','Area',-gx.area/2,'Duration',1e-3,'system',sys);
gzReph = mr.makeTrapezoid('z','Area',-gz.area/2,'Duration',1e-3,'system',sys);
phaseAreas = ((0:Ny-1)-Ny/2)*deltak;
gxSpoil=mr.makeTrapezoid('x','Area',2*Nx*deltak,'system',sys);
gzSpoil=mr.makeTrapezoid('z','Area',4/sliceThickness,'system',sys);
delayTE=ceil((TE - mr.calcDuration(gxPre) - gz.fallTime - gz.flatTime/2 ...
- mr.calcDuration(gx)/2)/seq.gradRasterTime)*seq.gradRasterTime;
delayTR=ceil((TR - mr.calcDuration(gz) - mr.calcDuration(gxPre) ...
- mr.calcDuration(gx) - delayTE)/seq.gradRasterTime)*seq.gradRasterTime;
assert(all(delayTE>=0));
assert(all(delayTR>=mr.calcDuration(gxSpoil,gzSpoil)));
rf_phase=0;
rf_inc=0;
for i=1:Ny
for c=1:length(TE)
rf.phaseOffset=rf_phase/180*pi;
adc.phaseOffset=rf_phase/180*pi;
rf_inc=mod(rf_inc+rfSpoilingInc, 360.0);
rf_phase=mod(rf_phase+rf_inc, 360.0);
seq.addBlock(rf,gz);
gyPre = mr.makeTrapezoid('y','Area',phaseAreas(i),'Duration',mr.calcDuration(gxPre),'system',sys);
seq.addBlock(gxPre,gyPre,gzReph);
seq.addBlock(mr.makeDelay(delayTE(c)));
seq.addBlock(gx,adc);
gyPre.amplitude=-gyPre.amplitude;
seq.addBlock(mr.makeDelay(delayTR(c)),gxSpoil,gyPre,gzSpoil)
end
end
check whether the timing of the sequence is correct
[ok, error_report]=seq.checkTiming;
if (ok)
fprintf('Timing check passed successfully\n');
else
fprintf('Timing check failed! Error listing follows:\n');
fprintf([error_report{:}]);
fprintf('\n');
end
Timing check passed successfully
prepare sequence export
seq.setDefinition('FOV', [fov fov sliceThickness]);
seq.setDefinition('Name', 'gre');
seq.write('gre.seq')
plot sequence and k-space diagrams
seq.plot('timeRange', [0 5]*TR);
[ktraj_adc, ktraj, t_excitation, t_refocusing, t_adc] = seq.calculateKspace();
time_axis=(1:(size(ktraj,2)))*sys.gradRasterTime;
figure; plot(time_axis, ktraj');
hold; plot(t_adc,ktraj_adc(1,:),'.');
figure; plot(ktraj(1,:),ktraj(2,:),'b');
axis('equal');
hold;plot(ktraj_adc(1,:),ktraj_adc(2,:),'r.');
Current plot held
Current plot held
very optional slow step, but useful for testing during development e.g. for the real TE, TR or for staying within slewrate limits
rep = seq.testReport;
fprintf([rep{:}]);
Number of blocks: 1280
Number of events:
RF: 256
Gx: 768
Gy: 512
Gz: 768
ADC: 256
Delay: 512
Sequence duration: 2.560000s
TE: 0.004306s
TR: 0.010000s
Flip angle: 10.00°
Unique k-space positions (a.k.a. columns, rows, etc): 256
Unique k-space positions (a.k.a. columns, rows, etc): 256
Dimensions: 2
Spatial resolution: 1.00 mm
Spatial resolution: 1.00 mm
Repetitions/slices/contrasts: 1 range: [1 1]
Cartesian encoding trajectory detected
Block timing check passed successfully
Max. Gradient: 1190476 Hz/m == 27.96 mT/m
Max. Gradient: 549451 Hz/m == 12.91 mT/m
Max. Gradient: 1190476 Hz/m == 27.96 mT/m
Max. Slew Rate: 6.26566e+09 Hz/m/s == 147.16 T/m/s
Max. Slew Rate: 6.37755e+09 Hz/m/s == 149.79 T/m/s
Max. Slew Rate: 6.34921e+09 Hz/m/s == 149.13 T/m/s
Max. Absolute Gradient: 1770978 Hz/m == 41.60 mT/m
Max. Absolute Slew Rate: 1.09174e+10 Hz/m/s == 256.42 T/m/s