[Insight-users] Inconsistent registration result.

[lien lee]

Hi all,

Just experienced the case of inconsistent registration results, which I
could not explain.

I have a registration pipeline with three steps: rigid transform + affine
transform + BSpline transform. Each step was a three-level multi-resolution
image registration.  Mattes mutual information metric was used for all the
three. I applied the itk::ImageMaskSpatialObject for both the moving image
and the fixed image.  Unfortunately, I observed that the final registration
results were quite different from one run to another on the same computer.

I printed out Metric->GetNumberOfPixelsCounted() for each iteration, and I
noticed that for the runs with better results, that number were usually
larger than those with bad results.  I googled, and found a webpage
mentioning that ImageMaskSpatialObject.ValueAt() method may reject some
sample points when the mask is very thin.  However, my
ImageMaskSpatialObject is in 3D and definetely NOT a thin or small object.
 I also tried to set FixedImageRegion to be just the bounding box of the
ImageMaskSpatialObject, but it could not solve the problem.

I used itk v3 with the itk version 4.2.

Anyone experienced similar issue? I appreciate any sort of comments or
advice.

Thanks!

Lien.
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