[Insight-users] Dicom Series Read Series Write: change in intensity values

[Bill Lorensen]

Matthieu,

I'm not sure if this is relevant to the current discussion.

I think that PET data often rescales each pixel with a different rescale
value. The results should be a floating point value.

Bill

On Nov 26, 2007 4:44 PM, Mathieu Malaterre <mathieu.malaterre at gmail.com>
wrote:

> Hi Matthias,
>
> On Nov 26, 2007 8:37 PM, Matthias Schabel <mschabel at ucair.med.utah.edu>
> wrote:
> > I may not fully understand this issue, so apologies in advance if I'm
> > missing something, but if the support for rescaleSlope/
> > rescaleIntercept was removed from the ITK GDCM in ITK 3.4, this change
> > breaks my code in a way that makes it very difficult to fix...
>
> Here is what happen in between ITK 3.2 and 3.4, ITK-GDCM was simply
> passing all DICOM element from the reader to the writer. This is a bad
> idea since ITK is also at the same time decompressing (applying the
> rescale+slope) to the Stored Pixel. Therefore whenever you would
> read-write-read-write the linear transform would be applied multiple
> time... yup this is a bug indeed !
>
> Now, to answer your question: I did not break any kind of backward
> compatibility since -and it's been on my TODO list for a while- there
> is no support for floating point image in ITK-GDCM.
> So if you are using some kind of low-level script (at gdcm level), you
> should still be able to use it. Simply completely by-pass any check
> done at ITK-GDCM level (ie. do not pass the meta data dictionary from
> reader to writer).
>
> > In
> > particular, I have code that performs pharmacokinetic modeling on
> > dynamically acquired MRI data to generate quantitative maps of
> > parameters (such as Ktrans, kep, Vp...) that take on floating point
> > values in the approximate range of 0.0-2.0.
>
> 2.0 ? That's pretty high for Ktrans/kep/ve, isn't it :)
>
> > These maps are then
> > exported as DICOM, with appropriate rescale factors and offsets to
> > minimize truncation error in conversion from float to short. Since the
> > latest release of the ITK libraries appears to strip rescaleSlope and
> > rescaleIntercept on DICOM write, I can no longer specify correct
> > scaling to the visualization program I'm using (OsiriX). I don't
> > understand the rationale behind this change - it makes it essentially
> > impossible to deal with small floating point numbers in DICOM if you
> > can't specify these scaling values...
>
> Please send your custom script, and I'll help you get it to work again.
> Thanks.
>
> >
> > PS The crashing problem in OSX 10.5 appears to only occur with
> > dynamically linked versions of the ITK libraries - static linkage
> > works fine.
>
> Great, thanks for the notice !
>
> --
> Mathieu
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