weight.c File Reference

Functions for setting weight factors based on SIF. More...

#include "libtpcimgio.h"

Go to the source code of this file.

Functions
void	sifWeight (SIF *data, double halflife)
	Calculate weights for frames in SIF data based on true counts. Weights are normalized to have an average of 1.0.
void	sifWeightByFrames (SIF *data, double halflife)
	Calculate weights for frames in SIF data based on frame lengths. Weights are normalized to have an average of 1.0.
void	sifWeightNorm (SIF *d)
void	sifModerateTrues (SIF *sif, double limit)
void	sifModerateWeights (SIF *sif, double limit)
int	sifExistentCounts (SIF *sif)

Detailed Description

Functions for setting weight factors based on SIF.

Author

Vesa Oikonen

Definition in file weight.c.

Function Documentation

sifExistentCounts()

int sifExistentCounts

(

SIF *

sif

)

Verify that SIF contains prompts and randoms.

Returns

Returns 0 if neither prompts or randoms can be found, 1 or 2 if prompts or randoms can be found, and 3 if both prompts and randoms are there.

See also

sifInit, sifRead, sifWeight

Parameters

sif	Pointer to SIF struct

Definition at line 207 of file weight.c.

  {
  int fi, p=0, r=0;
  double v1, v2;
  if(sif==NULL || sif->frameNr<1) return 0;
  /* If just one frame, then value > 0 is fine */
  if(sif->frameNr==1) {
    if(sif->prompts[0]>0.00000001) p=1;
    if(sif->randoms[0]>0.00000001) r=2;
    return(p+r);
  }
  /* Otherwise, check also that frames have different count level */
  for(fi=1; fi<sif->frameNr; fi++) {
    v1=sif->prompts[fi]-sif->prompts[fi-1]; if(fabs(v1)>0.001) p=1;
    v2=sif->randoms[fi]-sif->randoms[fi-1]; if(fabs(v2)>0.001) r=2;
    if((p+r)>2) break;
  }
  return(p+r);
}

sifModerateTrues()

void sifModerateTrues	(	SIF *	sif,
		double	limit )

Moderate the trues in SIF.

True values in SIF are used to calculate weight factors for time frames. If trues are very low in certain frames, the weight factors in other frames may become very low. This function finds the maximum trues, and adds max/limit to each trues value, if min trues < max trues / limit. Negative trues are always eliminated.

See also

sifWeight, sifModerateWeights, sifRead, sifWrite, sifWeightNorm

Parameters

sif	Pointer to SIF in which the trues are moderated
limit	Max trues / limit is added to all trues values; 100.0 might be good

Definition at line 131 of file weight.c.

  {
  if(SIF_TEST) printf("sifModerateTrues(*sif, %g)\n", limit);
 
  if(sif==NULL || sif->frameNr<2) return;
  if(limit<=1.0) return;
 
  int fi;
  double w, f;
  for(w=f=sif->trues[0], fi=1; fi<sif->frameNr; fi++) {
    if(sif->trues[fi]>w) w=sif->trues[fi];
    else if(sif->trues[fi]<f) f=sif->trues[fi];
  }
  if(f*limit<w) {
    for(w/=limit, fi=0; fi<sif->frameNr; fi++)
      if(sif->trues[fi]>0.0) sif->trues[fi]+=w; else sif->trues[fi]=w;
  } else {
    for(fi=0; fi<sif->frameNr; fi++)
      if(sif->trues[fi]<0.0) sif->trues[fi]=0.0;
  }
}

Referenced by imgSetWeights().

sifModerateWeights()

void sifModerateWeights	(	SIF *	sif,
		double	limit )

Moderate the weights in SIF.

This function finds the maximum weight, and adds max/limit to each weight value (except if weight is 0), if min weight < max/limit. Negative weights are set to zero.

See also

sifWeight, sifModerateTrues, sifRead, sifWrite, sifWeightNorm

Parameters

sif	Pointer to SIF in which the weights are moderated
limit	Max weight / limit is added to all weights; 100.0 might be good

Definition at line 167 of file weight.c.

  {
  if(SIF_TEST) printf("sifModerateWeights(*sif, %g)\n", limit);
 
  if(sif==NULL || sif->frameNr<2) return;
  if(limit<=1.0) return;
 
  int fi;
  double w, f;
  w=f=nan("");
  for(fi=0; fi<sif->frameNr; fi++) {
    if(isnan(sif->weights[fi])) continue;
    if(sif->weights[fi]<=0.0) {sif->weights[fi]=0.0; continue;}
    if(isnan(w)) w=sif->weights[fi];
    if(isnan(f)) f=sif->weights[fi];
    if(sif->weights[fi]>w) w=sif->weights[fi];
    if(sif->weights[fi]<f) f=sif->weights[fi];
  }
  if(isnan(w) || isnan(f)) return;
 
  if(f*limit<w) {
    for(w/=limit, fi=0; fi<sif->frameNr; fi++)
      if(sif->weights[fi]>0.0) sif->weights[fi]+=w;
  }
}

sifWeight()

void sifWeight	(	SIF *	data,
		double	halflife )

Calculate weights for frames in SIF data based on true counts. Weights are normalized to have an average of 1.0.

Weights are calculated from formula weight=(frame duration)^2 / (trues in a frame). Before calling this routine, trues must be calculated as total counts - randoms. Counts in SIF are not corrected for physical decay. Therefore, isotope halflife must be known, if weights are to be calculated for decay corrected TACs. Isotope halflife must be set to 0, if weights are used for TACs that are not corrected for decay.

Reference: Mazoyer BM, Huesman RH, Budinger TF, Knittel BL. Dynamic PET data analysis. J Comput Assist Tomogr 1986; 10:645-653.

See also

sifInit, sifRead, sifWrite, sifEmpty, sifModerateTrues, sifModerateWeights, sifExistentCounts, sifWeightByFrames, dftWeightByFreq, dftDecayCorrection

Parameters

data	Pointer to SIF data.
halflife	Halflife (in seconds) of the isotope; If halflife is 0, the weights are calculated for non-decay corrected data. If halflife is >0, the weights are calculated using decay corrected trues, but trues data in SIF are not changed.

Definition at line 28 of file weight.c.

  {
  int i;
  double f, d;
 
  if(SIF_TEST) printf("sifWeight(*sif, %g)\n", halflife);
  /* Calculate weights */
  for(i=0; i<data->frameNr; i++) {
    if(data->trues[i]<1.0) data->trues[i]=1.0;
    f=data->x2[i]-data->x1[i]; if(f<=0.0) f=1.0;
    if(halflife<=1.0E-8) 
      d=1.0;
    else
      d=exp( ((data->x1[i]+data->x2[i])/2.0)*0.693147/halflife );
    data->weights[i]=(f*f)/(d*data->trues[i]);
    /*printf("%3d %g %g\n", i, data->trues[i], data->weights[i]);*/
  }
 
  /* Scale weights so that average weight is 1.0 */
  sifWeightNorm(data);
 
  return;
}

Referenced by imgSetWeights().

sifWeightByFrames()

void sifWeightByFrames	(	SIF *	data,
		double	halflife )

Calculate weights for frames in SIF data based on frame lengths. Weights are normalized to have an average of 1.0.

Weights are calculated from the simple formula weight=(frame duration), if isotope halflife is set to 0, and using formula weight=(frame duration)*exp(-t*ln(2)/halflife), if isotope halflife is given (less weight for late frames, which may be more suitable for PET data that is corrected for physical decay).

See also

sifInit, sifRead, sifWrite, sifEmpty, sifWeight, dftWeightByFreq

Parameters

data	Pointer to SIF data.
halflife	Halflife (in seconds) of the isotope; If halflife is >0, the late frames are given less weight.

Definition at line 72 of file weight.c.

  {
  int i;
  double f, d;
 
  if(SIF_TEST) printf("sifWeightByFrames(*sif, %g)\n", halflife);
  /* Calculate weights */
  for(i=0; i<data->frameNr; i++) {
    f=data->x2[i]-data->x1[i]; if(f<=0.0) f=1.0;
    if(halflife<=1.0E-8) 
      d=1.0;
    else
      d=exp( -((data->x1[i]+data->x2[i])/2.0)*0.693147/halflife );
    data->weights[i]=f*d;
  }
 
  /* Scale weights so that average weight is 1.0 */
  sifWeightNorm(data);
 
  return;
}

sifWeightNorm()

void sifWeightNorm

(

SIF *

d

)

Scale weights in SIF data so that average weight is 1.0, and the sum of weights equals the nr of frames.

See also

sifInit, sifRead, sifWrite, sifEmpty, sifWeight, sifWeightByFrames

Parameters

d	Pointer to SIF data.

Definition at line 105 of file weight.c.

  {
  if(SIF_TEST) printf("sifWeightNorm(*sif)\n");
  int i;
  double f=0.0;
  for(i=0; i<d->frameNr; i++) f+=d->weights[i];
  f/=(double)d->frameNr;
  for(i=0; i<d->frameNr; i++) d->weights[i]/=f;
  return;
}

Referenced by sifWeight(), and sifWeightByFrames().