Volume data may be presented through a variety of display algorithms, such as frame-by-frame viewing, multi-planar reconstruction, surface rendering and volume rendering. The Volumetric Source Information consists of one or more volumes (3D or 4D) used to form the presentation. When a volume Presentation View is created through the use of a Display Algorithm, it typically requires a set of Display Parameters that determine the specific presentation to be obtained from the volume data. Persistent storage of the Display Parameters used by a Display Algorithm to obtain a presentation from a set of volume-related data is called a Volumetric Presentation State (VPS):
Each Volumetric Presentation State describes a single view with optional animation parameters. A Volumetric Presentation State may also indicate that a particular view is intended to be displayed alongside the views from other Volumetric Presentation States. However, descriptions of how multiple views should be presented are not part of a Volumetric Presentation State and should be specified by a Structured Display, a Hanging Protocol or by another means.
The result of application of a Volumetric Presentation State is not expected to be exactly reproducible on different systems. It is difficult to describe the rendering algorithms in enough detail in an interoperable manner, such that a presentation produced at a later time is indistinguishable from that of the original presentation. While Volumetric Presentation States use established DICOM concepts of grayscale and color matching (GSDF and ICC color profiles) and provides a generic description of the different types of display algorithms possible, variations in algorithm implementations within display devices are inevitable and an exact match of volume presentation on multiple devices cannot be guaranteed. Nevertheless, reasonable consistency is provided by specification of inputs, geometric descriptions of spatial views, type of processing to be used, color mapping and blending, input fusion, and many generic rendering parameters, producing what is expected to be a clinically acceptable result.
A Volumetric Presentation State is different from Softcopy Presentation States in several ways:
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Unlike Softcopy Presentation States, a Volumetric Presentation State describes the process of creating a new image rather than parameters for displaying an existing one
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Volumetric Presentation State may not be displayed exactly the same way by all display systems due to differences in the implementations of rendering algorithms.
While both Volumetric Presentation States and Softcopy Presentation States reference source images, a display application applying a Volumetric Presentation State will not directly display the source images. Instead, it will use the source data to construct a volume and then create a new view of the volume data to be displayed. Depending on the specific Volumetric Presentation State parameters, it is possible that some portion of the inputs may not contribute to the generated view.
Some types of volumetric views may be significantly influenced by the hardware and software used to create them, and the industry has not yet standardized the volume rendering pipelines to any great extent.
While volume geometry is consistent, other display characteristics such as color, tissue opacity and lighting may vary slightly between display systems.
The use of the Rendered Image Reference Sequence (0070,1104) to associate the Volumetric Presentation State with a static rendering of the same view is encouraged to facilitate the assessment of the view consistency (see Section XXX.2.3).