how to calculate the Haunsfield Unit data value!

[msn123321]

hi ,all!
I have problems to calculate the Haunsfield Unit data value(ct-value),I have read some codes about the dcmtk sdk;and i wrote the codes as follows, but the result seems to be not right.

So,I need your help!

//get the Haunsfield Unit data value

int GetHounsField(CPoint ptImage)
{
int iPos = ptImage.x * ptImage.y;
long slope = 0, intercept = 0;
OFString str;

//get the slope
if ((m_dcmfile.getDataset())->findAndGetOFString(DCM_RescaleSlope,str).bad())
{
return;
}
slope = atol(str.data());

//get the intercept
if (m_dcmfile.getDataset()->findAndGetOFString(DCM_RescaleIntercept,str).bad())
{
return;
}
intercept = atol(str.data());

//m_dcmfile is a object of DcmFileFormat ;
DicomImage diImag(m_dcmfile.getDataset(),EXS_Unknown);
const DiPixel *dmp = NULL;
dmp = diImag.getInterData ();
if (NULL == dmp)
{
return 0;
}
void *pixelData = NULL ;

pixelData = (void *)dmp->getData();

if (NULL == pixelData)
{
return 0;
}
EP_Representation er_rep = dmp->getRepresentation();
int result = 0;
switch(er_rep)
{
case EPR_Sint16:
{
Sint16 *pixelNew1 = ((Sint16*)pixelData+iPos);
result = (((*pixelNew1) * slope)+intercept);
break;
}

case EPR_Uint16:
{
Uint16 *pixelNew2 = ((Uint16*)pixelData+iPos);
result = (((*pixelNew2) * slope)+intercept);
break;
}

default:
{
Sint8 *pixelNew3 = ((Sint8*)pixelData+iPos);
result = (((*pixelNew3) * slope)+intercept);
break;
}

}
return result;
}
Thank you !

[Jörg Riesmeier]

As you can read in the documentation, the modality transformation is already applied to the "intermediate representation".

[msn123321]

Dear Jörg,

Thanks for the reply.


In the debug mode,
it goes into the lines of case EPR_Sint16: ,
and intercept = -1024, the value of slope is 1 ;
the value of result is -2021,

And I test it with other software ,but the result is different,
Maybe there is somethings wrong with my codes !

Thanks and regards!

[Jörg Riesmeier]

What I wanted to say in my last posting: You are applying the modality transformation twice (since it is already applied by the DicomImage constructor)!

[alwittta]

Dear Jörg,

I would like to know , if the DicomImage class object contains the object with already applied Window width and level, then without applying the modality transformation, the above calculation for Haunsfield Unit is correct?

Thanks and regards
Alvin

[Horex]

Hi, I have seen your code and this funktion will be very interesting for me! Unfotunately I'am not knowing, what's the two parameters which are needed to commit the funktion. Could you please tell me, how I could manage this?

Thanks a lot
Horex