How to "certify" a DICOM viewer's measurements - DICOM

This is a discussion on How to "certify" a DICOM viewer's measurements - DICOM ; Hi. We are developing a DICOM viewer which has the capability of making distance, area, angle and density measurements over DICOM images. Now my question is: is there an independent way to "certify" / verify correctness and optimal working of ...

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Thread: How to "certify" a DICOM viewer's measurements

  1. How to "certify" a DICOM viewer's measurements

    Hi.

    We are developing a DICOM viewer which has the capability of making
    distance, area, angle and density measurements over DICOM images.

    Now my question is: is there an independent way to "certify" / verify
    correctness and optimal working of such measurement functionalities?
    For instance, I am thinking about sample DICOM images containing
    dummies representing given distances, or containing zones having
    different known densities... Is there something of this kind
    somewhere?

    Up to now, we have checked the correctness of the measurement tools of
    our viewer by checking the measurement results against the ones
    provided by a different well-known viewer, but I believe that
    "certification by imitation" is not a good way to follow... Can you
    suggest alternative approaches?

    Any suggestion would be greatly appreciated.

    Thank you and best regards,

    Marco.

  2. Re: How to "certify" a DICOM viewer's measurements

    Hello Marco,

    I was involved in performing offline measurement using DICOM
    ultrasound Images. We generally acquire images measurements embedded
    from the modality on the Image itself, like distance, angle, area,
    circumference(fetal abdomen, head), volume (2 images kidney, ovary),
    time (doppler), velocity (doppler), Heart rate (M Mode). Later
    calibrate with the sale available on the image. Finally compare with
    the embedded modality value.

    This was proved more efficient while comparing with different units
    (mm, cm, inches, etc...)
    Hope this helps you.

    With regards
    Ravindran Padmanabhan.


  3. Re: How to "certify" a DICOM viewer's measurements

    Dear Ravindran,

    thank you for your message.

    In practice, what you suggest is that I try to find some DICOM images
    having measurement signs already "burnt" into the image by the
    modality itself, and then comparing these measurements with the ones
    taken by the measurement tools of our DICOM viewer, am I correct?

    Well, it could be an idea, but if I find "errors" or differences
    between measurements, it could also be due to an incorrect or
    inaccurate "Pixel Spacing" data element stored by the modality. What I
    would like to ensure is that my viewer performs correct measurements
    on the basis of the calibration data available in the DICOM file.

    Also, what about densities? Are there sample images containing zones
    of known densities (for instance, HU densities for CT scans)?

    Any suggestion would be greatly appreciated.

    Best regards,

    Marco.



    "Rady" wrote in message news:<1101207574.495158.247140@z14g2000cwz.googlegroups. com>...
    > Hello Marco,
    >
    > I was involved in performing offline measurement using DICOM
    > ultrasound Images. We generally acquire images measurements embedded
    > from the modality on the Image itself, like distance, angle, area,
    > circumference(fetal abdomen, head), volume (2 images kidney, ovary),
    > time (doppler), velocity (doppler), Heart rate (M Mode). Later
    > calibrate with the sale available on the image. Finally compare with
    > the embedded modality value.
    >
    > This was proved more efficient while comparing with different units
    > (mm, cm, inches, etc...)
    > Hope this helps you.
    >
    > With regards
    > Ravindran Padmanabhan.


  4. Re: How to "certify" a DICOM viewer's measurements

    marco.sambin@poste.it (Marco) wrote in message news:...
    > Hi.
    >
    > We are developing a DICOM viewer which has the capability of making
    > distance, area, angle and density measurements over DICOM images.
    >
    > Now my question is: is there an independent way to "certify" / verify
    > correctness and optimal working of such measurement functionalities?
    > For instance, I am thinking about sample DICOM images containing
    > dummies representing given distances, or containing zones having
    > different known densities... Is there something of this kind
    > somewhere?
    >
    > Up to now, we have checked the correctness of the measurement tools of
    > our viewer by checking the measurement results against the ones
    > provided by a different well-known viewer, but I believe that
    > "certification by imitation" is not a good way to follow... Can you
    > suggest alternative approaches?


    Two ways to do this are:

    1. create synthetic DICOM images that contain objects of a specific shape
    or pixel value, and with specific attribute values like rescale slope
    and intercept and/or pixel spacing, and measure the displayed result and
    compare with the theoretical truth

    2. scan images of a phantom containing objects of known size, shape and
    density and compare the displayed result with the known values in the
    phantom

    To be robust, you need to do this in the face of differing image header
    values (especially with respect to pixel representation, bit depth and
    rescaling) and since you may not have access to a sufficient range of
    scanners, the synthesized image approach may be the best for testing
    the boundaries of your implementation.

    David

  5. Re: How to "certify" a DICOM viewer's measurements

    Biomedical maintenance personnel at imaging facilities usually have
    rulers with graduations and unit scales etched or painted on with
    lead. Images taken of these rulers can be "measured" by software using
    the dicom pixel size attributes as a basis. The software measurement
    vs visible scale in the image provides calibration verification of the
    imaging device. Many CT and MR phantoms also have embedded scale
    measurements. These are used as part of routine calibration procedure
    for the modality to ensure the spatial measurements in the images are
    properly correlated with the real objects. Clear plastic film overlay
    rulers are also used on medical displays to verify software "true
    size" displays are properly calibrated for the size of the image on
    the display.

  6. Re: How to "certify" a DICOM viewer's measurements

    Dear David,

    thanks a lot for your reply. I believe what you suggest may be an
    interesting approach, i.e., comparing the values measured by the
    software with the "theoretical" values, given the knowledge of the
    various DICOM parameters influencing the measurement (original pixel
    value, pixel representation, bit depth, rescale slope / intercept...).

    I have a question about the "density" measurement performed by a DICOM
    software measurement tool: the measurement tool should always report
    the pixel value AFTER having applied the Rescale Slope / Intercept
    transformation? For instance, HU values for a CT image are always
    given by the original pixel value modified by the Rescale Slope /
    Intercept transformation?

    Thank you for your suggestions on this point.

    Regards,

    Marco.


    dclunie@dclunie.com (David Clunie) wrote in message news:...
    > marco.sambin@poste.it (Marco) wrote in message news:...
    > > Hi.
    > >
    > > We are developing a DICOM viewer which has the capability of making
    > > distance, area, angle and density measurements over DICOM images.
    > >
    > > Now my question is: is there an independent way to "certify" / verify
    > > correctness and optimal working of such measurement functionalities?
    > > For instance, I am thinking about sample DICOM images containing
    > > dummies representing given distances, or containing zones having
    > > different known densities... Is there something of this kind
    > > somewhere?
    > >
    > > Up to now, we have checked the correctness of the measurement tools of
    > > our viewer by checking the measurement results against the ones
    > > provided by a different well-known viewer, but I believe that
    > > "certification by imitation" is not a good way to follow... Can you
    > > suggest alternative approaches?

    >
    > Two ways to do this are:
    >
    > 1. create synthetic DICOM images that contain objects of a specific shape
    > or pixel value, and with specific attribute values like rescale slope
    > and intercept and/or pixel spacing, and measure the displayed result and
    > compare with the theoretical truth
    >
    > 2. scan images of a phantom containing objects of known size, shape and
    > density and compare the displayed result with the known values in the
    > phantom
    >
    > To be robust, you need to do this in the face of differing image header
    > values (especially with respect to pixel representation, bit depth and
    > rescaling) and since you may not have access to a sufficient range of
    > scanners, the synthesized image approach may be the best for testing
    > the boundaries of your implementation.
    >
    > David


  7. Rescale output is in HU, was Re: How to "certify" a DICOM viewer's measurements

    marco.sambin@poste.it (Marco) wrote in message news:...
    >
    > I have a question about the "density" measurement performed by a DICOM
    > software measurement tool: the measurement tool should always report
    > the pixel value AFTER having applied the Rescale Slope / Intercept
    > transformation? For instance, HU values for a CT image are always
    > given by the original pixel value modified by the Rescale Slope /
    > Intercept transformation?


    Correct.

    For CT images the "units" of the output of the rescale operation are
    always HU. See C.8.2.1 CT Image Module.

    For most other IODs that include the Modality LUT Module, the "units"
    of the rescale operation are specified in the Rescale Type attribute,
    if present. See C.11.1 Modality LUT Module. The XA and XRF IODs use
    the Modality LUT module in a strange and different inverse way for
    some image types.

    In the case of the PET IOD, the "units" of the output of the rescale
    operation are defined by the Units attribute. See the description of
    Rescale Slope and Intercept in C.8.9.4 PET Image Module, though the
    text in the definition of the Units attribute in C.8.9.1.1.3 Units in
    the PET Series Module incorrectly refers to the Units as describing
    the Pixel Data.

    The enhanced CT and MR multiframe also have additional mechanisms of
    mapping to one or more different real world value units, described in
    the corresponding functional group macros.

    David

  8. Re: How to "certify" a DICOM viewer's measurements

    Hello Marco,

    Just a comment for your information - Making measurements on Ultrasound
    images (US, US-MF) requires that your viewer support the "Ultrasound
    Region Calibration" module/attributes. US images (usually) do not
    include the "pixel spacing" attribute, for example, used by other
    modalities as it is not part of the US IOD. I mention this only
    because a surprising number of contemporary DICOM viewers do not
    support Ultrasound Region Calibration and users are often surprised /
    unhappy to discover they cannot make measurements on their ultrasound
    images without resorting to manual calibration on these systems. Also,
    although most modern US systems produce images with "square" (1:1)
    pixels, some popular ultrasound systems produce images with non-square
    pixels. This fact has also 'surprised' some DICOM viewer developers
    (and users) in the past and led to measurement/calibration
    difficulties.

    Best regards,

    Bill Stewart

    Marco wrote:
    > Hi.
    >
    > We are developing a DICOM viewer which has the capability of making
    > distance, area, angle and density measurements over DICOM images...



  9. Re: How to "certify" a DICOM viewer's measurements

    As an addendum add to Bill's comments, there is a new Supplement
    that adds significant explanation about Ultrasound Region Calibration.
    See DICOM part 3 C.8.5.5.1 or see Supplement 84 at
    ftp://medical.nema.org/medical/dicom/final/sup84_ft.pdf

    - Doug


    "Bill Stewart" wrote in message
    news:1103157816.020595.72470@c13g2000cwb.googlegro ups.com...
    > Hello Marco,
    >
    > Just a comment for your information - Making measurements on Ultrasound
    > images (US, US-MF) requires that your viewer support the "Ultrasound
    > Region Calibration" module/attributes. US images (usually) do not
    > include the "pixel spacing" attribute, for example, used by other
    > modalities as it is not part of the US IOD. I mention this only
    > because a surprising number of contemporary DICOM viewers do not
    > support Ultrasound Region Calibration and users are often surprised /
    > unhappy to discover they cannot make measurements on their ultrasound
    > images without resorting to manual calibration on these systems. Also,
    > although most modern US systems produce images with "square" (1:1)
    > pixels, some popular ultrasound systems produce images with non-square
    > pixels. This fact has also 'surprised' some DICOM viewer developers
    > (and users) in the past and led to measurement/calibration
    > difficulties.
    >
    > Best regards,
    >
    > Bill Stewart
    >
    > Marco wrote:
    >> Hi.
    >>
    >> We are developing a DICOM viewer which has the capability of making
    >> distance, area, angle and density measurements over DICOM images...

    >




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