[Insight-users] GDCM orientation issue....

[Mathieu Malaterre]

Neil,

	This is entirely possible.
	Could you please run:

./bin/DicomImageReadPrintTags filename | grep Position

	It should return like:

Image Position Patient = ...

	If not then you have either a broken DICOMv3 file or a good old 
ACR/NEMA file. Anyway in both case gdcm fail back to the following 
mechanism: When the ordering can not be done based on IPP, it then looks 
for Image Number, and if Image Number cannot be found it fails back on a 
simple filename ordering.

Mathieu
Ps: Feel free to privately send me one of your DICOM file so that I can 
examine it.

Neil Weisenfeld wrote:
> Ah, makes perfect sense. I need to dig a bit deeper to see what is going 
> on.  It's possible that the ImagePositionPatient based sorting is 
> failing and it silently falls back to filename ordering.
> 
> Neil
> 
> 
> 
> Simon Warfield wrote:
> 
>> My understanding is DICOM guarantees the coordinate system is right 
>> handed and that the 'unencoded' direction cosine is the cross-product 
>> of the other two.
>> This tells you about the axes of the coordinate system.
>> ftp://medical.nema.org/medical/dicom/2004/printed/04_03pu3.pdf  page 
>> 275 guarantees the coordinate system is right handed.
>>
>> See also the discussion on Patient Orientation here:
>> http://www.faqs.org/faqs/medical-image-faq/part2/
>>
>>
>> There is not an obvious way to determine what constitutes 
>> 'consecutive' slices or the first and last slices other than from the 
>> Image Position (Patient) tag. For example, I don't believe you can 
>> infer 'consecutive' from the file name or part of the file name, or 
>> from the 'instance number' (a tag with an undefined start value and an 
>> undefined ordering but which identifies each image).    All I can see 
>> you can do is to sort the slices based on the Image Position (Patient) 
>> tag and this will run from the most negative position to the most 
>> positive position along the Z axis defined by the direction cosines.
>>
>>
>>
>>
>>> I apologise if I'm adding unnecessarily to the pile.
>>>
>>>
>>>
>>> Neil
>>>
>>>
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>>
>>
>>
>>
>>
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