communication.** Finally, it is important that vessel visualizations can be intuitively interpreted. While it is certainly possible to craft dedicated visualizations, which precisely communicate the depth of certain structures, it is not clear that such techniques are intuitively interpretable. Furthermore, it can be expected that such techniques add to the visual clutter, and might thus even result in cognitive overload. Therefore, we assume that vessel visualizations should be natural in a way that they exploit natural depth cues, which do not require additional explanations to be interpreted.

Void Space Surfaces for Vessel Visualization {#sec:vss}
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Following our guidelines discussed above, and motivated by the usually large amounts of empty space between vessel structures, we utilize this area for the enhancement of depth and shape perception. To do so, we propose void space surfaces (VSS), which allow us to completely eliminate all depth cues from the vessel surface’s color channel and shift them to regions which are usually unused. As a consequence, we take advantage of the entire screen by using the void space for depth enhancements. Thus, VSS have been designed to improve the communication of morphological structures, while at the same time allowing for mapping functional parameters onto the 