[Insight-users] Question about All points mapped outside..

[Kajetan Berlinger]

Hi,

Jonathan Wong wrote:
> Hi, I'm new to ITK and I am trying to understand how the
> MultiResMIRegistration example application works. I managed to run samples
> images from brainweb and I got decent results (They were oriented
> correctly). However, I created some of my own vtkImages from microCT scans
> of bone specimens. The specimens I was making them from had be thresholded
> so they were binary. I made one image. And then I rotated the specimen and
> made a second image. I also made a smoothed version of the original and
> rotated that to make another two images. (I did this because I read
> somewhere that when using Mattes, the moving image should be smoother) At
> first I got the following error with my specimens:
> 
> Line: 193
> Description: itk::ERROR: MutualInformationImageToImageMetric(01763328): All
> the sampled point mapped to outside of the moving image
> 
> However, after changing the number of iterations and learning rate I did 
> get
> the program to run fee from errors. However the output would hardly be
> called accurate for any combination of the 4 images I created.
> 
> So I had a a few questions.
> 
> What is a good metric to use on bone volumes?
> 
> What makes for a good metric in general?

That depends on the different types of images you want to match with.
There is monomodal registration and multimodal registration.
Monomodal means both images were acquired by the same imaging technique (CT-CT, MR-MR ...).
Here for example Correlation Coefficient or Mean Squares would be a good decision, because both are 
based on using image intensities only.

Multimodal means that you want to match images taken by different imaging techniques (CT-MR, 
CT-US...). Here for example Mutual Information would be a good choice. MI is based on Information 
Theory and uses the joint entropy for measuring the amount of combined information in two images.

For further information have a look at page 415 in:
http://www.itk.org/ItkSoftwareGuide.pdf

> 
> How does one configure the param.file for the MultiResMIRegistration 
> example
> correctly without playing a guessing game to see whether or not errors
> result? (Like how can one tell, when one will get the Line 193 Error?)

The error means that with respect to your current transformation the fixed and the moving image 
don't intersect, overlap and therefore the metric can't compute any values. Perhaps you should check 
your initial transform?
You can observe the pixels taken for computation of a metric value using 
metric->GetNumberOfPixelsCounted().

> 
> Here's a link to one of the vtkImages.
> 
> http://www.yousendit.com/transfer.php?action=download&ufid=7A676C6B77938FB4
> http://www.yousendit.com/transfer.php?action=download&ufid=E9D4EECF2A3CD065
> http://www.yousendit.com/transfer.php?action=download&ufid=BAC0A34D221379C8
> 
> Thanks
> Jonathan
> 

Hope that helps.

cu
Kaj


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