[Insight-users] Problems with MultiResMiRegistration

[Luis Ibanez]

Hi Jose,

Thanks for the detailed description of your problem.

When you are fine tunning the parameters of a Multi-Resolution
registration, you must solve one level at a time.

Attempting to tune the parameters of all the levels at the same
time is very time consuming and almost impossible to do right
because you will not see the intermediate results from the previous
resolution level.


The rule in multi-Resolution is quite simple:


    NEVER GO TO THE NEXT HIGHER RESOLUTION LEVEL
    UNLESS YOU HAVE COMPLETELY REGISTERED THE
    CURRENT LEVEL.


If your images at not registered at the current level,
it is very unlikely that the next higher resolution
level will do any better.



What you want to do, then is to select just one pyramid level and
define the subsample factor as the maximum that you are planning
to use for the full schedule.

In your case, you should start with the subsample factor of (4x4x1).
Use first this single resolution level and modify the parameters of
the optimiazer and the parameters scaling until you get full convergence
and you are satisfied with the registration at that level. Note for
example, that you have to make sure that the optimizer stopped because
it reached one of the convergence criteria, and not because it ran out
of iterations.


In order to fine tune the parameters you will find useful to attach a
Command/Observer to the optimizer, so you can see the trace of the
optimization process. You will find multiple examples in the ITK
Software Guide on how to add Observers to the optimizer.


Please let us know if you have further questions.


    Thanks


      Luis


-------------------------
José Ángel Tavira wrote:

> Hi everyone
>  
> I am using the MultiResMiRegistration framework in order to registrate 2 
> medical studies (a CT study and a MR study).
>  
> The InsightApplications software offers an application using these 
> components.
>  
>  * In particular, it uses the ITK registration framework with
>  * the following combination of components:
> 
>  *   - MutualInformationImageToImageMetric
>  *   - QuaternionRigidTransform
>  *   - QuaternionRigidTransformGradientDescentOptimizer
>  *   - LinearInterpolateImageFunction
>  
> This application has the next parameters to configure:
>   
>     moving image initial shrink factors
>     fixed image initial shrink factors  
>     optimizer number of iterations
>     number of multiresolution levels    
>     learning rates per level
>     translation scales
>  
> And, finally, these are the set of values I use for them:
>  
>     moving image initial shrink factors       (4,4,1)
>     fixed image initial shrink factors          (4,4,1)
>     optimizer number of iterations             (2500)
>     number of multiresolution levels          3,4 or 5
>     learning rates per level                       1e-03 1e-04 1e-05 
> 1e-06 1e-07, ...
>     translation scales                              around 320 (1 or 2 
> orders lower and higher)
>  
>     The set of studies I'm working with, has the next parameters (or 
> similar):
>  
>     CT Dimensions: 512 x 512 x 105 (x,y,number of slices)
>     CT Resolutions: 0.7 x 0.7 x 1.25 (x,y,z)
>  
>    MR Dimensions: 256 x 256 x 120 (x,y,number of slices)
>    MR Resolutions: 0.9 x 0.9 x 1.4 (x,y,z)
>  
>  
>     I have made a lot of combinatios with the registration values 
> described above but the registration still remains very, very inexact!!
>  
> Could anyone help me?  Do I have to configure any other parameters 
> inside the ITK code?
>  
>  
> Thank you very much in advance.
>  
>  
>  
> José.
>  
>  
> 
>  
> 
> 
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