[Insight-users] Using deformation fields when testing registration quality?

[Luis Ibanez]

Hi Motes,

The direction of the Transform that is computed
by the ITK Image Registration framework is
explained in the ITK Software Guide:

      http://www.itk.org/ItkSoftwareGuide.pdf

in Section:

     8.3.1 "Direction of the Transform Mapping"

in pdf-pages :

                          358 - 359.

Please pay special attention to

           Figure 8.7  in pdf-page 358.


In short:

    The Transform is such that it maps points
     from the coordinate system of the Fixed image
     to the coordinate system of the Moving image.




      Regards,


             Luis


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On Mon, Oct 26, 2009 at 8:00 PM, motes motes <mort.motes at gmail.com> wrote:
> Ok so the deformation field returned from the registration is actually
> a set of coefficients that transforms the fixed image into the moving
> image space?
>
> I thought that the result of the image registration was the parameters
> that transformed the moving image into the fixed image space and not
> the other way around.
>
>
>
> On Mon, Oct 26, 2009 at 6:32 PM, Luis Ibanez <luis.ibanez at kitware.com> wrote:
>> Hi Motes,
>>
>> I would suggest that you subtract the Known deformation field
>> from the deformation field that results from the registration. This
>> will give you a "residual" deformation field. Then you could
>> compute the Average Magnitude of all the vectors in these
>> residual deformation field.
>>
>> It may also be worth to report the "largest magnitude" of that
>> residual deformation field.
>>
>> For subtracting two deformation fields, the itkSubtractImageFilter
>> should do the trick (although I have not tried this filter with images
>> of vectors).
>>
>> The computation of the average and maximum magnitude may
>> require you to write a customized while-loop with Iterators.
>>
>> It should take about 30~40   lines of code....  :-)
>>
>>
>> Please let us know if you find any problem,
>>
>>
>>     Thanks
>>
>>
>>         Luis
>>
>>
>> -----------------------------------------------------------------------------------------
>> On Mon, Oct 26, 2009 at 12:11 PM, motes motes <mort.motes at gmail.com> wrote:
>>> I would like to measure the quality of my modfied BSplineDeformable
>>> transform. I have used one of the ITK examples to create a known
>>> deformation of the fixed image that I use as the moving image.
>>>
>>> But how do I use this known deformation in the quality measure? Since
>>> the deformation field is applied to the fixed image and the result is
>>> the moving image I don't see what benefit it does when measuring the
>>> quality of the registration?
>>>
>>> How are deformation fields used in this context?
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>>
>