[Insight-users] Re: Is there a way to validate results of 3D registrations?

[Luis Ibanez]

Hi Eve,



   1) What image Metric are you using ?

   2) What optimizer are you using ?



It is normal for some metrics and some optimizers to report
different registration results at different runs. This is
mainly due to the fact that part of their processing use
random number generators.



This is the case for:

  a) MattesMutualInformationImageToImageMetric
  b) MutualInformationImageToImageMetric (Viola-Wells)
  c) OnePlusOneOptimizer



The variations on the results are probably not related to the
Transform but to the use of one of the metrics or optimizers
described above.


Image Registration is a *"satisfaction"* kind of problem, meaning
that there is *NO* correct answer for a registration problem. What
you can hope to get, are answers that are *"Good Enough"* for solving
the problem at hand at a particular cost (in computation time and
time invested in tunning parameters).


The idea of "Validating" a registration is un-realistic and
impractical. It is only good for publishing papers in Decadent
Reputation-Based Journals.


In the real world, what makes sense is to define your requirements:


1) How much precision do your require for your clinical problem ?
    1mm ?, 0.1 microns ? in translation; 0.1 degrees of rotation ?

2) How much time can you allow for your registration to compute ?

3) How much of your time can you allow for fine tunning the
    parameters of your registration.


By defining the answers to these questions you will be able to
determine when a registration is "good enough" for your application.


A visual comparison of the numerical values of the Rigid3DTransform
is far from ideal for comparing the registration results. The best
way is to resample the moving image using these transforms and to
visualize the fixed image and resampled moving image together.  You
can do this by using VTK filters such as blending, or contouring,
as well as by using the checker board 3D widget and the Rectilinear
Wipe widget.



     Regards,


        Luis


----------------
Eve Heyes wrote:
> Hello ITK-users,
>  
> I'm currently performing 3D registrations using the 
> Versor3DRigidTransform. The following results are generated from 5 
> separate registrations. While the output image of each registration 
> appears to be registered, the transforms used are very different. Can 
> anyone suggest the reason for this? Or, is there a more appropriate way 
> to validate registration results?
>  
> Center of rotation used: [249.057, 227.131, 162.8]
> 
> 1/
> Total iterations: 161
> finalParameters:[0.00540255, 0.00608688, 0.0391753, -4.9541, 17.0141, 
> -2.08383]R
> esult =
> Matrix =
> 0.996856 -0.0782221 0.0125873
> 0.0783537 0.996872 -0.0103195
> -0.0117407 0.0112733 0.999868
> Offset =
> [11.5463, -0.110014, -1.69868]
> 
> 2/
> finalParameters:[0.0143756, 0.00588364, 0.0542648, -4.32434, 19.0096, 
> -1.87543]
> Result =
> Matrix =
> 0.994041 -0.108187 0.0133087
> 0.108526 0.993697 -0.0280668
> -0.0101883 0.0293439 0.999517
> Offset =
> [19.5658, -2.01871, -5.92431]
> 
> 3/
> finalParameters:[0.00947486, 0.00226582, 0.0538679, -4.69318, 17.5486, 
> -2.53202]
> Result =
> Matrix =
> 0.994186 -0.107531 0.00554563
> 0.107617 0.994017 -0.0186772
> -0.00350407 0.0191654 0.99981
> Offset =
> [20.2757, -4.85468, -5.98147]
>  
> 4/
> Result =
>  versor X      = 0.0173336
>  versor Y      = 0.00266175
>  versor Z      = 0.0355604
>  Translation X = -5.71732
>  Translation Y = 10.6958
>  Translation Z = -12.211
>  Iterations    = 168
>  Metric value  = -0.0675146
> Matrix =
> 0.997457 -0.0709726 0.0065521
> 0.0711572 0.99687 -0.0344506
> -0.00408654 0.0348292 0.999385
> Offset =
> [9.96952, -0.706962, -19.0038]
>  
> 5/
> Result =
>  versor X      = -0.0481644
>  versor Y      = -0.00675409
>  versor Z      = 0.00144871
>  Translation X = 4.41412
>  Translation Y = 10.6494
>  Translation Z = -33.1111
>  Iterations    = 62
>  Metric value  = -0.0728881
> Matrix =
> 0.999905 -0.00224338 -0.0136317
> 0.0035446 0.995356 0.0961951
> 0.0133526 -0.0962342 0.995269
> Offset =
> [7.16668, -4.83927, -13.8086]
>  
>  
> Thanks in advance for your help.
>  
> Eve
> 
>  
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