This section maps the use case hierarchy in Section PP.2.2 to specific solutions in the DICOM Standard. As described in items 1a and 1b, there are two different types of data related to 3D image acquisition: the 3D volume data itself and 2D images derived from the volume data. See Figure PP.3-1.
The 3D volume data is conveyed via the Enhanced US Volume SOP Class, which represents individual 3D Volume Data sets or collections of temporally-related 3D Volume Data sets using the 'enhanced' multi-frame features used by Enhanced Storage SOP Classes for other modalities, including shared and per-frame functional group sequences and multi-frame dimensions. The 3D Volume Data sets represented by the Enhanced Ultrasound IOD (the striped box in Figure PP.3-1) are suitable for Multi-Planar Reconstruction (MPR) and 3D rendering operations. Note that the generation of the Cartesian volume, its relationship to spatially-related 2D frames (whether the volume was created from spatially-related frames, or spatially-related frames extracted from the Cartesian volume), and the algorithms used for MPR or 3D rendering operations are outside the scope of this Standard.
Functional Group Macros allow the storage of many parameters describing the acquisition and positioning of the image planes relative to the patient and external frame of references (such as a gantry or probe locating device). These macros may apply to the entire instance (Shared Functional Group) or may vary frame-to-frame (Per-Frame Functional Group).
Multi-frame Dimensions are used to organize the data type, spatial, and temporal variations among frames. Of particular interest is Data Type used as a dimension to relate frames of different data types (like tissue and flow) comprising each plane of an ultrasound image (item 1c in the use case hierarchy). Refer to Section C.8.24.3.3 for the use of Dimensions with the Enhanced US Volume SOP Class.
Sets of temporally-related volumes may have been acquired sequentially or acquired asynchronously and reassembled into a temporal sequence, such as through Spatial-Temporal Image Correlation (STIC). Regardless of how the temporal volume sequence was acquired, frames in the resultant volumes are marked with a temporal position value, such as Temporal Position Time Offset (0020,930D) indicating the temporal position of the resultant volumes independent of the time sequence of the acquisition prior to reassembly into volumes.