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Implementation of ImageType (0008,0008) tag
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Nick Hobson
May 19, 2022, 10:21:21 AM5/19/22
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Hi all, I'm looking for more details on the way the ImageType (0008,0008) tag is typically used in PACS implementations.
We take CT images for patient-specific pedicle screw guide design, so require certain specs on those images for quality. One spec we currently reject is this Image Type being anything other than ‘Original\Primary’ due to uncertainty about whether pixel values have changed. I have a sense that ‘Original\Secondary’ images should be usable in at least most if not all cases, since this is most often just going to reflect a pull from PACS rather than direct from scanner, and any post-processing or pixel value changes should change this tag to 'Derived\Secondary', but need a way to determine this with certainty.
Is there anything within the DICOM header that would allow me to make this determination? Or, barring that, something within the documentation of specific PACS implementations?
We take CT images for patient-specific pedicle screw guide design, so require certain specs on those images for quality. One spec we currently reject is this Image Type being anything other than ‘Original\Primary’ due to uncertainty about whether pixel values have changed. I have a sense that ‘Original\Secondary’ images should be usable in at least most if not all cases, since this is most often just going to reflect a pull from PACS rather than direct from scanner, and any post-processing or pixel value changes should change this tag to 'Derived\Secondary', but need a way to determine this with certainty.
Is there anything within the DICOM header that would allow me to make this determination? Or, barring that, something within the documentation of specific PACS implementations?
David Gobbi
May 20, 2022, 9:53:20 AM5/20/22
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On Thursday, 19 May 2022 at 08:21:21 UTC-6, Nick Hobson wrote:
> I have a sense that ‘Original\Secondary’ images should be usable in at least most if not all cases, since this is most often just going to reflect a pull from PACS rather than direct from scanner, and any post-processing or pixel value changes should change this tag to 'Derived\Secondary'
My understanding is that 'Original\Secondary' usually indicates secondary capture, such as film scans or screen captures of the original. In any case, the ImageType will never change simply because an image is pushed to or pulled from a PACS.
> I have a sense that ‘Original\Secondary’ images should be usable in at least most if not all cases, since this is most often just going to reflect a pull from PACS rather than direct from scanner, and any post-processing or pixel value changes should change this tag to 'Derived\Secondary'
Can you provide additional information about any 'Original\Secondary' images you have encountered? In general, only 'Original\Primary' guarantees that you are getting the original pixel values. Images that are 'Original\Secondary' might have distorted values, additional noise, or lower quality. That doesn't mean they are unsuitable, but it does mean that the primary image is preferable if available.
David Gobbi
May 20, 2022, 10:25:51 AM5/20/22
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Additionally, your 'Original\Secondary' CTs might be MPRs, resampled from the primary.
Nick Hobson
May 20, 2022, 1:05:18 PM5/20/22
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My interpretation of the Value 1 'Pixel Characteristics' of this tag was that any pixel value change would be covered by 'Derived' and that the definition for 'Original' (- is the image an ORIGINAL Image; an image whose pixel values are based on original or source data) meant that the pixel values are directly transferred from the original, but I suppose the phrase 'based on' makes this suspect.
As far as I can tell, these are not secondary captures (none of the associated tags present, e.g. Conversion Type or Secondary Capture Device ID) nor MPRs (no relevant tags present there either).
The most consistent thing I'm noticing is that these images usually have been written to physical media (e.g. CD/DVD) - but it doesn't seem to be the case that this always causes the Secondary type either, so maybe I'm wrong in thinking that could be a cause.
Maybe I need to just catch one of these as it comes in and track down the radiology center and try to follow their whole process to see what's causing the change?
robertv...@gmail.com
May 21, 2022, 2:22:51 AM5/21/22
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our Canon CT default transversal images are: 0008,0008 ImageType DERIVED\PRIMARY\MPR
so rejecting everything other than ‘Original\Primary’ could lead to rejecting too much.
so rejecting everything other than ‘Original\Primary’ could lead to rejecting too much.
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