DICOM PS3.17 2020a - Explanatory Information

XXX.3.8.2 Encoding Outline (Current)
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#### XXX.3.8.2 Encoding Outline

To create a Planar MPR view which shows the colorized PET data blended with the grayscale CT data the Planar MPR VPS IOD instance defines via the Volumetric Presentation State Display Module a volumetric pipeline with 2 inputs.

Figure XXX.3.8-2. Planar MPR VPS Pipeline for PET/CT Blending

The first input to the Volumetric Presentation State (VPS) Display pipeline provides the MPR view of the anatomy in the display, which will be left as grayscale in the VPS Display pipeline. This will provide the backdrop to the colorized PET input to be subsequently overlaid in the second stage of the VPS pipeline.

Since PET and CT datasets usually have different resolutions and are not aligned (even if they reference the same Frame of Reference IOD instance) the datasets are spatially registered to the Volumetric Presentation State RCS. From these registered volumes grayscale Planar MPRs are generated using the same MPR geometry.

The Volume Presentation State Display pipeline then blends the MPRs into one view (see Section FF.2.3.2.1 “Classification Component Components” in PS3.4).

In the Volumetric Presentation State Display Module the Presentation State Classification Component Sequence (0070,1801) defines classification components for mapping the MPRs to RGBA.

The first MPR (CT) view is mapped to grayscale RGBA by an EQUAL_RGB RGB LUT Transfer Function (0028,140F). Alpha LUT Transfer Function (0028,1410) is set to NONE, since the anatomy will be rendered as completely opaque background.

For the second MPR (functional, PET) view an RGBA transfer function maps the tracer intensity values to a color range. Alpha-2 is set to 0 for black pixels, making them completely transparent. Alpha-2 for all other pixels is set to a single value between 0 and 1, depending on the intended transparency of the functional data.

It is envisioned that display applications provide mechanisms to the user for manipulating the Alpha-2 value which has been set in the Presentation State, thereby allowing the user to control the visibility of the anatomy vs. the functional data.

The RGB Compositor then performs "Partially Transparent A over B" compositing as described in Section XXX.5.2 by passing through Alpha-2 as Weight-2 and (1- Alpha-2) as Weight-1

Figure XXX.3.8-3 shows details of the classification and compositing for the blended PET/CT Planar MPR.

Figure XXX.3.8-3. PET/CT Classification and Compositing Details

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DICOM PS3.17 2020a - Explanatory Information