[Insight-users] Wrong reading of spacing in "z" axis by GE low-dose CT?

[Bc. Michal Srna]

Thanks for clarification,

But there are only two values x/y  in header file of those low-dose CT data
on tag Pixel Spacing (0028,0030).

In link, you sent me:

"Indeed the value for the spacing of the image could be coming from:

   1. Imager Pixel Spacing (0018,1164)
   2. Nominal Scanned Pixel Spacing (0018,2010)
   3. Pixel Spacing (0028,0030)
   4. Pixel Aspect Ratio (0028,0034)

1. and 2. and 4. are not present in those low-dose CT, so where does it take
spacing for "z", when in Pixel Spacing tag, there are only two values, which
ITK read as spacing in x,y?

Does it mean, that spacing in "z" for those low-dose CT data readed by ITK
is correct?

I am just asking, because I don't know, where did it take that value
spacing[2] = 4.41962, when there is nothing like that in DICOM header of
those data.

Firstly I assumed that pixel spacing in "z" is the same as Slice Thickness,
because in other data set from other imaging system is Slice Thickness equal
to spacing in "z" when readed by ITK.

Maybe it's just coincidence, when you say, that those two are completely
different aspects.


2011/4/13 Mathieu Malaterre <mathieu.malaterre at gmail.com>

> FYI have a look at:
>
>
> https://sourceforge.net/apps/mediawiki/gdcm/index.php?title=Using_GDCM_API#Where_is_the_value_of_gdcm.Image.Spacing_coming_from_.3F
>
> Slice Thickness does not means physical spacing, where did you read
> that ? It means the tickness of slice during acquisition time. I know
> some broken DICOM implementation uses it but this is is incorrect.
>
> On Wed, Apr 13, 2011 at 2:50 PM, Bc. Michal Srna <michal at srna.info> wrote:
> > Hello GDCM/ITK developers,
> >
> > I just discovered, that ITKv4 (also ITK 3.20) reads probably wrong value
> of
> > DICOM tag "0018,050 Slice Thickness" from low-dose CT data provided by
> > SPECT/low-doseCT multimodal imaging system (manufacturer GE, model
> INFINIA)
> > .
> >
> > If I am not wrong - when reading CT data ITK takes as value of spacing in
> > "z" axis value from tag "0018,050 Slice Thickness". In my original
> low-dose
> > CT data it is set to 6.1, but ITK reads spacing in "z" as 4.41962 and
> when I
> > save those data via ITK, it writes that incorrect value into that tag
> > "0018,050 Slice Thickness" and also into tag "0018,088 Spacing between
> > Slices".
> >
> > So I am asking, if it's not bug, where does ITK take that value 4.41962,
> > when "0018,050 Slice Thickness" in original data is 6.1?
> >
> > If it could help developers, I can provide example of those data, which
> are
> > affected by this problem.
> >
> > Thanks for help!
> >
> > --
> > S pozdravem Bc. Michal Srna
> >
> > Fotografické portfolio:
> > http://michalsrna.cz
> >
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>
>
>
> --
> Mathieu
>



-- 
S pozdravem Bc. Michal Srna

Fotografické portfolio:
http://michalsrna.cz
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