Population Average Methodology

David F. Wiley

The following steps are used to create a population average from a set of input specimen based on 3D volumetric data. In the example below,
3D anatomic landmark points placed on three input specimen guide the process to create a population average.

This is the method used in Stratovan Checkpoint's Population Average capability. Click here for more information on How to Create a Population Average using our Checkpoint software.

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Step 1Input specimen. Volume data (CT, MRI, etc.)
with surfaces and a homologous set of
3D landmark points are placed on
each specimen. Landmark points should
be concentrated around features of
Step 2The 3D landmark point sets are used to
represent the population. Orientation and
scale may be different among specimen.
Step 3Specimen landmark point sets undergo rigid alignment
to remove orientation differences. Scale differences
can be maintained or removed as desired.
Step 4Average pointset is computed using
Generalized Procrustes Alignment (GPA) to
remove scale (if desired). Resulting in the
target average pointset (orange dots).
Step 5Each scan volume is warped to the average pointset
using Thin-Plate Spline (TPS) warping. All deformed
volumes are then merged together.
Step 6The resulting population average volume can
be manipulated just as any of the original specimen
volumes. Surfaces can be extracted, analyzed,
and rendered from this average volume.

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