[Insight-users] Optimization problem

[Fischer, Sven]

Hi Brad,

 

Thank you very much for your reply. I tried to use the
ExhaustiveOptimizer, but it did not iterate over my first parameter. Is
there some bug in the ExhaustiveOptimizer? I found on the Kitware public
wiki-page "ITK Adopt A Bug Program" an entry for the
ExhaustiveOptimizer. What is the bug mentioned there about? Thank you in
advance.

 

Cheers

Sven

 

________________________________

Von: Bradley Lowekamp [mailto:blowekamp at mail.nih.gov] 
Gesendet: Dienstag, 16. September 2008 17:55
An: Fischer, Sven
Betreff: Re: [Insight-users] Optimization problem

 

Hello,

 

I know it's not the fastest, but I have found using the
ExhaustiveOptimizer at the coarsest resolution can be useful of finding
a good starting point. If you are able to get the right resolution (or
coarse feature) and the right grid size it should give you a reasonable
starting place for iterative methods.

 

Brad

 

 

 

On Sep 16, 2008, at 5:26 AM, Fischer, Sven wrote:





Hi all,

 

I'm doing a 2D 3D registration between fluoroscopic images and CT
images, creating a DRR. Since I have several local optima I use a multi
resolution approach. I scale the images by a factor of two and do
Gaussian blurring. So I scale in 4 steps. First I register the images
with one eighth of the original size, than with one fourth, with the
half size and finally with the original size. But I have local optima in
the first step. So it leads me to misregistration when my starting point
is too far away from the final point when my images are correct
registered. I can avoid this problem with using a different step size
for the Powell optimizer. But when I find a good step size for one
starting point it often is useless for other starting points.

My images are cardiac images, where the aorta and the spine can be seen
very clearly. I use the Gradient Difference Metric ( not exactly the
ITK-Implementation, I changed it a bit, and it worked very well in
several tests ).

Do you have an idea how I could find good starting points or how to
choose the step size for the Optimizer, depending on the information the
image gives me? Or should I use another Optimizer? What is your
experience? I'm looking forward to your answers.

 

Regards

Sven

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========================================================

Bradley Lowekamp  

Lockheed Martin Contractor for

Office of High Performance Computing and Communications

National Library of Medicine 

blowekamp at mail.nih.gov





 

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