Surfactor

Purpose

Use Surfactor to estimate the absolute surface area of particles of arbitrary shape such as cells.

Identifying where rays are emanating from the chosen point that is associated with each particle crosses the particle’s boundaries, and by adjusting tangential rays at these points the mean surface area of particles can be estimated.

All surfactor rays do not necessarily need to intersect the particle.

A ray might intersect a particle multiple times, depending on the shape of the particle and the location of the arbitrary point associated with the particle.

Requirements

Before using this probe, you need to obtain a systematic random sample of particles; use the Image Volume Fractionator or another systematic random sampling scheme for this.

  • The sections' orientation is isotropic.
  • An arbitrary point is associated with each particle; it should be consistent from particle to particle, and does not need to lie inside of the particle.
  • The use of a unique arbitrary point for each particle (e.g., nucleus of a cell) helps ensure that measurements are made at random depth along the Z-axis (measuring each cell at a depth where its largest cross-section is visible might bias the resulting volume estimates).

Procedure

  1. Start the Image Volume Fractionator workflow (from the Number section of the Probes ribbon) and work through the steps up to the Count objects step.
  2. At the Count objects step, click the Start Counting button in the workflow and identify the first particle.

  3. Click the Surfactor button from the Surface section of the Probes ribbon.

    Enter the number of rays that will be associated with each measurement.

  4. Select a marker and click a particle to be sampled. The selected number of rays is drawn, equi-angular from each other and outward from the arbitrary point.

    • Extend the length of the ray by dragging the white squares delimiting the ray.
    • If you placed the marker incorrectly, remove it by positioning the cursor over it, right-clicking and selecting Delete?.

  5. Click where each ray intersects the boundary of the particle.

    If a ray intersects the boundary multiple times, mark each intersection.

    • Stereo Investigator Cleared Tissue Edition draws a tangent line perpendicular to the ray crossing the boundary. Change the orientation of the ray by dragging the mouse when the cursor changes to a hand.
    • If you have more than 2 rays, right-click and select Mark Next Tangent to mark the tangents on the remaining rays.
  6. When you have finished marking the boundary of the current particle, right-click and select Finish Current Surfactor.
  7. Click the next particle and repeat.
  8. When you're done sampling particles, right-click and select Finish Current Surfactor and Exit.
  9. To view results, use Probe Run List.

See Surfactor formulas