Modality LUT & VOI LUT - DICOM

This is a discussion on Modality LUT & VOI LUT - DICOM ; Hi, I need a clarification on the following topics: When an image is loaded into a viewer, then if the image has VOI LUT present then the parameters pertaining to VOI LUT is used for presenting the image. If the ...

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Thread: Modality LUT & VOI LUT

  1. Modality LUT & VOI LUT

    Hi,

    I need a clarification on the following topics:

    When an image is loaded into a viewer, then if the image has VOI LUT
    present then the parameters pertaining to VOI LUT is used for
    presenting the image. If the VOI LUT is not present the Window Level/
    Window Width is used for presenting the image on the viewer. Supposing
    that the above is correct, then for an Image with VOI LUT, if the end
    user applies Window level on the image, he should experience a sudden
    change in the image pattern. This is due to the difference between the
    VOI LUT values and the Window Center/Window Level values. Is this
    correct observation?

    Now for the same image when I am applying the Window Level/Window
    width, then what would be the parameters that would control the image
    display? Should it be the difference in the Maximum and minimum PIXEL
    value or the difference between the maximum and minimum CO-ORDINATE
    values? I believe that that it should be the difference in the PIXEL
    values. Is it so? If yes, does this conform to the DICOM standards?

    Supposing that it is the difference in the PIXEL values, then would
    this cause a drastic change in the image display, say for a small
    change in the cursor position, there would be a drastic change in the
    brightness/contrast values for the image. Is this correct? But this
    would not be what the end-user would prefer. He would expect a gradual
    change in the image characteristics for small movement of the cursor.
    But then this would mean that the implementation is Non dicom
    compliant,

    Which option should we go for? Should we prefer to go with DICOM
    standards or shou we give importance to the User preference? Kindly
    suggest the possible solution for this,

    Thirdly where do we need to use the SIGMOID Function? Sorry for this
    long post

    Thanks

    JK

    Tha

  2. Re: Modality LUT & VOI LUT

    Hi

    We have tried to explain this in the IHE Radiology Technical
    Framework Volume 2, when we were adding in the Mammo profile.

    Specifically:

    "4.16.4.2.2.1 Display of Digital X-Ray, Mammo and Intra-Oral Images

    For the “For Presentation” variant of the Digital X-Ray Image,
    the Digital Mammography Image, and the Digital Intra-oral
    X-Ray Image, the Image Display or Imaging Document Consumer actor
    shall have both the capability to apply all the transformations
    specified by the VOI LUT Sequence (0028,3010) and the capability
    to apply all the transformations specified by the Window Width
    (0028,1051)/Window Center (0028,1050)/VOI LUT Function (0028,1056)
    attributes in the DX Image Module as selected by the user from
    the choices available (e.g., guided by Window Center/Width
    Explanation (0028,1055) or LUT Explanation(0028,3003).

    If VOI LUT Function (0028,1056) is absent, then Window Width
    (0028,1051)/Window Center (0028,1050) shall be assumed to be
    the parameters of a linear window operation. VOI LUT
    Function (0028,1056) values of “SIGMOID” and “LINEAR” shall be
    supported.

    The Image Display or Imaging Document Consumer shall support
    the application of LUT Data (0028,3006) in items of the VOI
    LUT Sequence (0028,3010) regardless of the Value Representation
    (i.e., the DICOM standard allows either OW or US Value Representation).

    The Image Display or Imaging Document Consumer actor must also
    support pixel rendering according to the Grayscale Standard
    Display Function (GSDF) defined in DICOM 2007 PS 3.14, because
    the output values of these images are always P-Values.

    If the DICOM image is referenced by other DICOM composite objects,
    such as Grayscale Softcopy Presentation States, it is optional
    for the Image Display or Imaging Document Consumer to actually
    retrieve and display/apply these objects."

    and

    "4.16.4.2.2.1.1.4 Image Contrast Adjustment

    As described in 4.16.4.2.2.1 Display of Digital X-Ray, Mammography
    and Intra-Oral Images, the Image Display shall provide the user with
    the ability to select amongst the available window and VOI LUT
    choices available in the image object.

    Subsequent to the initial application of the chosen contrast
    transformation, the Image Display actor shall allow the user to
    adjust the contrast without reverting to a purely linear
    transformation:

    - If the chosen contrast transformation is a lookup table, then
    the Image Display shall allow the input value of the lookup table to
    be stretched and translated so as to give the affect of adjusting
    contrast and brightness whilst applying the same general shape as
    the curve encoded in the lookup table. To provide feedback to the
    user, the “window width” can be reported as the adjusted range of
    input values to the LUT, and the “window center” can be reported
    as the center value of that range.

    - If the chosen contrast transformation is a sigmoid shaped VOI
    LUT Function parameterized by the window center and width, then
    the Image Display shall allow the window center and width values
    to be adjusted and a sigmoid function reapplied.

    If a Pixel Padding Value (0028,0120) only is present in the image
    then image contrast manipulations shall be not be applied to those
    pixels with the value specified in Pixel Padding Value (0028,0120).

    If both Pixel Padding Value (0028,0120) and Pixel Padding Range
    Limit (0028,0121) are present in the image then image contrast
    manipulations shall not be applied to those pixels with values
    in the range between the values of Pixel Padding Value (0028,0120)
    and Pixel Padding Range Limit (0028,0121), inclusive."

    David

    Jayakrishnan M wrote:
    > Hi,
    >
    > I need a clarification on the following topics:
    >
    > When an image is loaded into a viewer, then if the image has VOI LUT
    > present then the parameters pertaining to VOI LUT is used for
    > presenting the image. If the VOI LUT is not present the Window Level/
    > Window Width is used for presenting the image on the viewer. Supposing
    > that the above is correct, then for an Image with VOI LUT, if the end
    > user applies Window level on the image, he should experience a sudden
    > change in the image pattern. This is due to the difference between the
    > VOI LUT values and the Window Center/Window Level values. Is this
    > correct observation?
    >
    > Now for the same image when I am applying the Window Level/Window
    > width, then what would be the parameters that would control the image
    > display? Should it be the difference in the Maximum and minimum PIXEL
    > value or the difference between the maximum and minimum CO-ORDINATE
    > values? I believe that that it should be the difference in the PIXEL
    > values. Is it so? If yes, does this conform to the DICOM standards?
    >
    > Supposing that it is the difference in the PIXEL values, then would
    > this cause a drastic change in the image display, say for a small
    > change in the cursor position, there would be a drastic change in the
    > brightness/contrast values for the image. Is this correct? But this
    > would not be what the end-user would prefer. He would expect a gradual
    > change in the image characteristics for small movement of the cursor.
    > But then this would mean that the implementation is Non dicom
    > compliant,
    >
    > Which option should we go for? Should we prefer to go with DICOM
    > standards or shou we give importance to the User preference? Kindly
    > suggest the possible solution for this,
    >
    > Thirdly where do we need to use the SIGMOID Function? Sorry for this
    > long post
    >
    > Thanks
    >
    > JK
    >
    > Tha


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