The use case of two-step review (item 2a in the use case hierarchy) is addressed by the use of separate SOP Classes for 2D and 3D data representations. A review may initially be performed on the Ultrasound Image and Ultrasound Multi-frame Image instances created during the study. If additional operations on the 3D volume data are desired, the Enhanced US Volume instance referenced in the Source Image Sequence of the derived object may be individually retrieved and operated upon by an appropriate application.

The 3D volume data spatially relates individual frames of the image to each other using the Transducer Frame of Reference defined in Section C.8.24.2 in PS3.3 (items 2b in the use case hierarchy). This permits alignment of frames with each other in the common situation where a hand-held ultrasound transducer is used without an external frame of reference. However, the Transducer Frame of Reference may in turn be related to an external Frame of Reference through the Transducer Gantry Position and Transducer Gantry Orientation Attributes. This would permit the creation of optional Image Position and Orientation values relative to the Patient when this information is available. In addition to these frames of reference, the spatial registration, fiducials, segmentation, and deformation objects available for other Enhanced objects may also be used with the Enhanced US Volume instances.

The Key Object Selection Document SOP Class may be used to identify specific Enhanced US Volume instances of particular interest (item 2d in the use case hierarchy).