solution to this problem, as VSS are an artificial construct. However, the VSS should be smooth to avoid the introduction of visual artifacts. In our case we use *Inverse Distance Weighting* [@shepard1968two] which is smooth and has a control parameter to adjust the influence of samples depending on their distance to the target point (see Equations \[eq:isd\]). Other spatial interpolation techniques such as *Green Coordinates* [@lipman2008green], *Poisson Image Editing* [@perez2003poisson], or *Kriging Interpolation* [@oliver1990kriging] might also be useable to fill the empty areas between vascular structures. However, *Inverse Distance Weighting* has the advantages that it is easy to implement and each pixel can be calculated in parallel which makes it perfectly suitable to achieve interactive frame rates through a GPU implementation. Thus, we synthesize the depth values as follows:

$$\begin{aligned}
    \begin{split}
        z'(x_0) &= \frac{\sum_{i=1}^{N} w(x_i) \cdot z(x_i)}{\sum_{i=1}^{N} w(x_i)} \\
        w(x_i) &= \frac{1}{d(x_0, x_i)^p}
    \end{split}
    \label{eq:isd}\end{aligned}$$

whereby $z'$ is the depth at an interpolated point $x_0$ and $z$ denote the sample depth at an interpolating point $x_i$ with $N$ being the total number of points. The weight $w$ consists of the inverse of a given distance metric $d$ from $x_0$ to $x_i$. The so called power parameter $p$ controls the amount 