void init_generic(GENERIC_GRADIENT_T *grad, char name[], double amp, double time)
{
if ((ix > 1) && !sglarray) return;
initGeneric(grad); /* initialize generic gradient with defaults */
grad->amp = amp; /* assign gradient amplitude */
grad->duration = time; /* assign gradient duration */
grad->maxGrad = gmax; /* assign maximum allowed gradient */
strcpy(grad->name,name); /* assign waveform name */
}
void trapezoid(GENERIC_GRADIENT_T *grad, char name[], double amp, double time, double moment, int write_flag)
{
/* check is input values for moment, amplitude, time are set */
if ((amp == 0) && (time == 0) && (moment == 0)) {
sgl_abort_message("ERROR gradient %s: All input values to <trapezoid> function are zero",name);
return;
}
initGeneric(grad); /* initialize generic gradient with defaults */
grad->amp = amp; /* assign amplitude */
grad->duration = time; /* assign duration */
grad->m0 = moment; /* assign moment0 */
grad->maxGrad = gmax; /* assign maximum allowed gradient */
grad->writeToDisk = write_flag; /* set writeToDisk flag */
strcpy(grad->name,name); /* assign waveform name */
/* check amplitude */
if (amp > glim*gmax) {
sgl_abort_message("ERROR gradient %s: amp too large (%f), reduced to glim*gmax (%f)",
name, amp, glim*gmax);
}
/* evaluate imputs and set correct calcFlag */
if ((amp != 0) && (time != 0) && (moment == 0)) {
grad->calcFlag = MOMENT_FROM_DURATION_AMPLITUDE;
}
else if ((amp == 0) && (time != 0) && (moment != 0)) {
grad->calcFlag = AMPLITUDE_FROM_MOMENT_DURATION;
}
else if ((amp != 0) && (time == 0) && (moment != 0)) {
grad->calcFlag = DURATION_FROM_MOMENT_AMPLITUDE;
}
calcGeneric(grad);
}
void calc_readout_rampsamp(READOUT_GRADIENT_T *grad, double *dwell, double *minskip, int *npr) {
double this_gro, skip, skip_m0, dwint, dw, dwflat;
double ramp_t, ramp_m0, flat_t, flat_m0, dwell_sum, rt;
int npro, np_ramp, np_flat;
int pt, pt2;
GENERIC_GRADIENT_T gg;
/* Calculate gradient amplitude based on FOV and sw */
this_gro = sw/grad->gamma/lro;
grad->amp = this_gro;
/* Nominal dwell time is 1/sw */
dw = granularity(1/sw,1/epi_grad.ddrsr);
dwflat = dw; /* we may later end up with different dw on flat part */
dwint = dw*grad->amp; /* Gradient Integral per point */
npro = (int) np/2;
/* Calculate the area that is skipped for phase encoding blip */
skip = *minskip;
if (skip == 0)
skip = dw + getval("aqtm")-at; /* Need at least a dwell time at the end */
skip_m0 = skip*(skip*grad->slewRate)/2; /* Area of that skipped part */
/* Calculate the ramp time */
grad->tramp = granularity(grad->amp/grad->slewRate,grad->resolution);
grad->slewRate = grad->amp/grad->tramp;
ramp_m0 = grad->tramp*grad->amp/2;
np_ramp = (int) ((ramp_m0 - skip_m0)/dwint);
/* Check that we even need points on the flat part */
if (np_ramp >= npro/2) {
np_ramp = npro/2 - 1; /* Center two points considered "flat part" */
/* We may not need to go all the way to full gradient
in order to fit all points on ramp; adjust amplitude */
ramp_m0 = np_ramp*dwint + skip_m0;
grad->tramp = granularity(sqrt(2*ramp_m0/grad->slewRate),grad->resolution);
grad->amp = grad->tramp * grad->slewRate;
/* recalculate ramp area and np_ramp */
ramp_m0 = grad->tramp*grad->amp/2;
/* Now adjust the dwell time necessary on flat part with this amplitude */
dwflat = granularity(dwint/grad->amp,1/epi_grad.ddrsr);
}
np_flat = npro - 2*np_ramp;
/* How long must the flat part be? */
grad->duration = granularity((np_flat-1)*dwflat,grad->resolution);
/* Due to rounding of gradient duration,
we may be able to fit more points on flat part */
while (grad->duration - (np_flat-1)*dwflat >= 2*dwflat) {
np_flat += 2;
np_ramp -= 1;
}
/* Now add the ramp times to the total duration */
grad->duration += 2*grad->tramp;
/* Use a generic to calculate the actual shape, ie fill in dataPoints */
initGeneric(&gg);
gg.amp = grad->amp;
gg.duration = grad->duration;
gg.tramp = grad->tramp;
gg.slewRate = grad->slewRate;
gg.calcFlag = MOMENT_FROM_DURATION_AMPLITUDE_RAMP;
gg.writeToDisk = FALSE;
calcGeneric(&gg);
if (gg.error != ERR_NO_ERROR) {
printf("Temporary generic gradient: \n");
displayGeneric(&gg);
abort_message("Problem calculating RO gradient with ramp sampling");
}
grad->m0 = gg.m0;
grad->m1 = gg.m1;
grad->m0ref = grad->m0/2;
grad->numPoints = gg.numPoints;
free(grad->dataPoints); // release original array
grad->dataPoints = gg.dataPoints;
/* Recalculate the skipped part with new gradient integral */
skip_m0 = (grad->m0 - dwint*(np/2-1))/2;
skip = sqrt(2*skip_m0/grad->slewRate);
/* Skip rampsampling if gradient is longer than necessary */
if ((grad->m0-ramp_m0*2) > npro*dwint) {
warn_message("The gradient is too long, no ramp sampling");
for (pt = 0; pt < npro; pt++) {
dwell[pt] = dwflat;
}
*minskip = grad->tramp;
return;
}
/* Calculate where we start acquisition on the ramp */
/* Do we have extra integral on flat part? */
flat_m0 = (grad->m0 - 2*ramp_m0) - ((np_flat-1)*dwflat*grad->amp);
/* if yes, then what is the duration of this? */
if (flat_m0 > 0)
flat_t = (grad->duration - 2*grad->tramp) / ((np_flat - 1)*dwflat);
else
flat_t = 0;
/* Double-check that gradient is long enough */
if (flat_m0 < -1e-9)
abort_message("Gradient integral too small %f vs %f (%f) G/cm*us",
(grad->m0-2*ramp_m0)*1e6,(np_flat-1)*dwint*1e6,flat_m0*1e9);
/* If extra integral > 2*dwint, we could move a point from each ramp up to the flat */
if (flat_m0 > 2*dwint)
warn_message("Gradient flat part longer than necessary with ramp sampling, check gradient calculation\n");
/**************************************************************************/
/* Calculate dwell times */
/**************************************************************************/
dwell_sum = 0;
/* Start at top of ramp and walk down ramp */
pt = np_ramp - 1;
rt = grad->tramp;
/* Top point on ramp first, it may use a bit of time from the flat part */
if (flat_m0 > 0) {
ramp_m0 -= (dwint - flat_m0/2); /* area at ramp at previous point */
flat_t = (grad->duration - 2*grad->tramp) - ((np_flat - 1)*dwflat); /* extra duration at top */
flat_t /= 2; /* divide evenly between both ramps */
}
else {
ramp_m0 -= dwint; /* area at ramp at previous point */
flat_t = 0;
}
ramp_t = sqrt(2*ramp_m0/grad->slewRate); /* time at ramp at previous point */
dwell[pt] = granularity(flat_t + (rt-ramp_t), 1/epi_grad.ddrsr);
dwell_sum += dwell[pt];
ramp_t = rt - (dwell[pt] - flat_t); /* correct for rounding of dwell */
/* Do all the rest of the points on the ramp */
for(pt = np_ramp-2; pt >= 0; pt--) {
rt = ramp_t; /* remember current time */
ramp_m0 -= dwint; /* total area of ramp at previous point */
if (ramp_m0 <= 0) {
if (fabs(ramp_m0) > dwint*0.01) abort_message("problem: ramp_m0 negative %f\n",ramp_m0*1000);
ramp_t = 0;
}
else ramp_t = sqrt(2*ramp_m0/grad->slewRate); /* time at previous point */
dwell[pt] = granularity(rt-ramp_t,1/epi_grad.ddrsr);
dwell_sum += dwell[pt];
ramp_t = rt - dwell[pt];
}
skip = ramp_t;
dwell_sum += skip;
for (pt = np_ramp; pt < np_ramp+np_flat-1; pt++) { /* Flat part */
dwell[pt] = dwflat;
dwell_sum += dwflat;
}
pt2 = np_ramp-1;
for (pt = np_ramp+np_flat-1; pt < np_ramp*2 + np_flat - 1; pt++) {
dwell[pt] = dwell[pt2--];
dwell_sum += dwell[pt];
}
/* Very last point, just set dwell = 1/sw */
pt = np_ramp*2 + np_flat - 1;
dwell[pt] = dw;
dwell_sum += skip;
if (fabs(dwell_sum - grad->duration) > 12.5e-9)
warn_message("Mismatch in sum of dwells (%.3fus) vs. gradient duration (%.3fus)",
dwell_sum*1e6,grad->duration*1e6);
/* Return values */
*minskip = skip;
*npr = np_ramp;
if (sgldisplay) {
printf("============== DEBUG DWELL (%d, %d, %d) ===============\n",np_ramp,np_flat,np_ramp);
dwell_sum = skip;
for (pt = 0; pt < npro-1; pt++) {
printf("[%3d] %3.6f\t%3.3f\t%3.6f\n",pt+1,dwell_sum*1e6,dwell[pt]*1e6,(dwell[pt]+dwell_sum)*1e6);
dwell_sum += dwell[pt];
}
printf("[%3d] %3.6f\t%3.3f\t%3.6f\n",(pt+1),dwell_sum*1e6,0.0,dwell_sum*1e6);pt++;
printf("[%3d] %3.6f\t%3.3f\t%3.6f\n",pt+1,dwell_sum*1e6,skip*1e6,(skip+dwell_sum)*1e6);
dwell_sum += skip;
printf("Did we get a full gradient's worth? %.6f, %.6f\n",grad->duration*1e6,dwell_sum*1e6);
printf("=======================================================\n");
}
}