Surface-Weighted Star Volume
Use Surface Weighted Star Volume to estimate tissue volume as observed from the boundary-surface of the volume.
This probe is used for complex, non-convex volumes such as volumes in lung tissue (alveoli as observed from the gas exchange surface) or bone tissue (marrow space as observed from the space's boundary surface)
Surface-weighted star volume is the average of the star volumes (un-obscured volumes) calculated from points on the phase interface (surface of the material of interest).
An array of cycloids that interacts isotropically with the tissue is used to sample the surface. At each sampled point, a ray is drawn in an isotropic direction from the surface intersection along the short axis of the cycloid. Mark where the ray intersects the next (and only the next) interface of the phase.
Prerequisites
- Isotropic sections
- Systematic random sampling
Procedure
- Click Probes>All probes>Volume/Area>Surface Weighted Star Volume.
- In the Surface Star Volume window:
- Enter the desired Cycloid Width.
- Use the Randomize Angle button to ensure an isotropic interaction. If the angle was already randomized with another method, enter the angle value in the Angle of cycloids from vertical field.
- The test grid of cycloids appears. Click to mark a point where the surface of the phase of interest intersects with the cycloids.
The program hides the cycloids and draws a line parallel to the short axis of the cycloid.
- Click the line once to indicate the distance across the phase (and sample the un-obscured volume).
The program displays the cycloids again, with a shorter line indicating the marked distance across the phase. If two intercept direction are possible, choose one at random (cf. Reed & Howard, 1998, Fig. 4).
- Repeat steps 3 and 4 until all phases are marked.
- Right-click and select Exit Surface Weighted Star Volume to end the probe. The results are immediately displayed in the Sampling Results window.