Display of CAD results via BSPS - DICOM

This is a discussion on Display of CAD results via BSPS - DICOM ; Suppose a CAD algorithm analyzes contrast enhanced MRI and creates a value at each pixel in the range [0-25]; the higher the value, the more suspicious the pixel is for cancer. Blending Softcopy Presentation State (BSPS) has the ability to ...

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Thread: Display of CAD results via BSPS

  1. Display of CAD results via BSPS

    Suppose a CAD algorithm analyzes contrast enhanced MRI and creates a
    value at each pixel in the range [0-25]; the higher the value, the
    more suspicious the pixel is for cancer.

    Blending Softcopy Presentation State (BSPS) has the ability to present
    fused displays consisting of the original grayscale underlying image
    and the CAD results as a pseudo color overlay image. This sounds like
    what we want.

    The pallete color LUT Module within BSPS describes the color mapping
    to be used for the superimposed image set.

    Suppose we want to start the mapping at index "7", e.g.,

    Index Color
    -------------------
    7-10 YELLOW
    11-25 RED

    The standard allows us to set the first pixel value mapped ("7" in
    this case). However, it says (PS 3.3 2008, C.7.6.3.1.5):

    "All image pixel values less than the first value mapped are also
    mapped to the first entry in the LUT..."

    Hmmm. I interpret that to mean that pixel values [0-6] would then be
    mapped to YELLOW, which is not what we want. Moreover, since all
    pixels have values in the range [0-25], it follows that every pixel
    should be mapped to some color in the LUT.

    Seems what I want instead is to start the mapping at index "0", e.g.,

    Index Color
    -------------------
    0-6 TRANSPARENT
    7-10 YELLOW
    11-25 RED

    However, the LUT does not provide an alpha channel, except globally
    via Relative Opacity (0070,0403).

    Thus, I am stuck. I don't see how we can indicate transparent (non-
    colored) areas in the overlay.

    Scott

  2. Re: Display of CAD results via BSPS

    Hi Scott

    Will not black do what you want?

    R=G=B=0 results in no change to the underlying pixel except scaling
    of the luminance by the relative opacity.

    See the equation in PS 3.4 N.2.4.3.

    David

    PS. I presume you are storing your CAD array of probability of malignancy
    values in a Segmentation Storage SOP Instance ? You should be, since that
    is what it is intended for.

    Scott Thompson wrote:
    > Suppose a CAD algorithm analyzes contrast enhanced MRI and creates a
    > value at each pixel in the range [0-25]; the higher the value, the
    > more suspicious the pixel is for cancer.
    >
    > Blending Softcopy Presentation State (BSPS) has the ability to present
    > fused displays consisting of the original grayscale underlying image
    > and the CAD results as a pseudo color overlay image. This sounds like
    > what we want.
    >
    > The pallets color LUT Module within BSPS describes the color mapping
    > to be used for the superimposed image set.
    >
    > Suppose we want to start the mapping at index "7", e.g.,
    >
    > Index Color
    > -------------------
    > 7-10 YELLOW
    > 11-25 RED
    >
    > The standard allows us to set the first pixel value mapped ("7" in
    > this case). However, it says (PS 3.3 2008, C.7.6.3.1.5):
    >
    > "All image pixel values less than the first value mapped are also
    > mapped to the first entry in the LUT..."
    >
    > Hmmm. I interpret that to mean that pixel values [0-6] would then be
    > mapped to YELLOW, which is not what we want. Moreover, since all
    > pixels have values in the range [0-25], it follows that every pixel
    > should be mapped to some color in the LUT.
    >
    > Seems what I want instead is to start the mapping at index "0", e.g.,
    >
    > Index Color
    > -------------------
    > 0-6 TRANSPARENT
    > 7-10 YELLOW
    > 11-25 RED
    >
    > However, the LUT does not provide an alpha channel, except globally
    > via Relative Opacity (0070,0403).
    >
    > Thus, I am stuck. I don't see how we can indicate transparent (non-
    > colored) areas in the overlay.
    >
    > Scott


  3. Re: Display of CAD results via BSPS

    David:

    Thanks for your reply. It provided the clarification I needed.

    The blending equation in PS 3.4 N.2.4.3 for each color component, c,
    is:

    c_out = c_super * A + c_under * (1-A).

    This makes it clear to me that BSPS is limited to "blending," as the
    name implies. I was thinking that it might have additional
    capabilities, i.e., general compositing in the sense of Porter and
    Duff.

    In a general compositing framework, in addition to the color at each
    pixel, there is an alpha value (). So for two images A & B, we have
    color and alpha: c_A, _A, c_B, _B. Furthermore, fractions f_A and
    f_B denote the fractional amount that each pixel contributes to the
    composited pixel. The resultant color and alpha are then:

    c = f_A * c_A + f_B * c_B
    = f_A * _A + f_B * _B

    So in addition to blending, many effects are possible within this
    framework.

    For example, my goal was to display the underlying grayscale image (A)
    unless the CAD probability of malignancy (image B) was above some
    threshold, in which case an appropriate opaque color would overwrite
    the pixel. In the composite framework, I could be achieved by
    assigning transparent black (R,G,B,=0) for low probability pixels in
    image B, and opaque colors for those pixels I wanted to show up. Then
    by setting the fractions f_A = (1-_B), f_B=1, the resulting color and
    alpha values gives the desired effect:

    c = (1-_B) * c_A + c_B
    = (1-_B) * _A + _B

    Do you know of some other way to achieve this?

    Are you looking for someone to write up "CSPS: Compositing Softcopy
    Presentation State"? ha, ha.

    Regards,
    Scott

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