[Insight-users] Optimization problem

[Bradley Lowekamp]

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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