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

[Bc. Michal Srna]

Oah thanks, now I know, where does it tak that value :-)

2011/4/13 Bill Lorensen <bill.lorensen at gmail.com>

> The z spacing is computed from the image position and orientation between
> two consecutive  slices.
>
>
> On Wed, Apr 13, 2011 at 10:06 AM, Bc. Michal Srna <michal at srna.info>wrote:
>
>> 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
>>
>> _____________________________________
>> Powered by www.kitware.com
>>
>> Visit other Kitware open-source projects at
>> http://www.kitware.com/opensource/opensource.html
>>
>> Kitware offers ITK Training Courses, for more information visit:
>> http://www.kitware.com/products/protraining.html
>>
>> Please keep messages on-topic and check the ITK FAQ at:
>> http://www.itk.org/Wiki/ITK_FAQ
>>
>> Follow this link to subscribe/unsubscribe:
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>>
>


-- 
S pozdravem Bc. Michal Srna

Fotografické portfolio:
http://michalsrna.cz



-- 
S pozdravem Bc. Michal Srna

Fotografické portfolio:
http://michalsrna.cz
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