loading window level preset - DICOM

This is a discussion on loading window level preset - DICOM ; Hello all, The issue i am facing is .. I see that in case of CT images: level - width/2 ; is always negative .. (however this is not the case with mr images) I am working on a preset ...

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Thread: loading window level preset

  1. loading window level preset

    Hello all,

    The issue i am facing is ..

    I see that in case of CT images:
    level - width/2 ; is always negative .. (however this is not the case
    with mr images)

    I am working on a preset (for window width/level setting) loading
    facility for an image viewer ..

    In that context I have to calculate 'displaymin' & 'displaymax' values
    and set the window level .. I have to read preset window width/level
    values from a predefined location (eg bone -2500/480 ; brain - 80/40
    .... etc) .. and set displayMin and displayMax values ..

    How can I calculate the above values from given 'window width' and
    'window level' (for CT/mr/us etc images) .. is there a genaric solution
    to this ?


  2. Negative window values, was Re: loading window level preset

    sando wrote:

    > The issue i am facing is ..
    >
    > I see that in case of CT images:
    > level - width/2 ; is always negative .. (however this is not the case
    > with mr images)


    This should not be surprising ... CT image pixel values are
    often negative because they are in Hounsfield Units, which
    are defined such that air is -1000 and water is 0. See
    "http://en.wikipedia.org/wiki/Hounsfield_units". CT window
    values are always specified in Hounsfield Units.

    So, even if the stored pixel value (7FE0,0010) range does not
    include negative values, it will once the Rescale Slope
    and Intercept are applied to transform them into HU, which
    is required before applying the Window Center and Width values

    For other modalities the same is also true if the Rescale
    attributes are specified in the IOD for that modality, PET
    being the one exception, since all vendors have consistently
    erred in not following the standard, and not applying Rescale
    Slope prior to the specified window values.

    > I am working on a preset (for window width/level setting) loading
    > facility for an image viewer ..
    >
    > In that context I have to calculate 'displaymin' & 'displaymax' values
    > and set the window level .. I have to read preset window width/level
    > values from a predefined location (eg bone -2500/480 ; brain - 80/40
    > ... etc) .. and set displayMin and displayMax values ..
    >
    > How can I calculate the above values from given 'window width' and
    > 'window level' (for CT/mr/us etc images) .. is there a genaric solution
    > to this ?


    See DICOM PS 3.3 C.11.2.1.2 for definitions and examples.

    David

  3. Re: Negative window values, was Re: loading window level preset

    Thanks David ..

    But I still cannot be sure about the calculations ..

    Can you please provide a sample calculation for getting display and
    displayMax values..

    say for example .. window width = 400 ; window level = 0 ; rescale
    slope = 1.0 ; rescale intercept = 0.0

    How to proceed with the above information ?


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