The full physical extent of the whole slide image target volume is described in the attributes Imaged Volume Width (0048,0001), Imaged Volume Height (0048,0002), and Imaged Volume Depth (0048,0003). These values reflect the maximum extent in these dimensions. There is no requirement that this entire extent is actually encoded in frames of the Image SOP Instance.
The value of Imaged Volume Depth (0048,0003) shall not be 0. If only a single focal plane is imaged, the Imaged Volume Depth may be the optical depth of field as encoded in the Slice Thickness (0018,0050) attribute of the Pixel Measures Functional Group (see C.184.108.40.206.1.1).