[Insight-users] Registration (itk Plugin for volview)

[Luis Ibanez]

Hi Robert,


What version of InsightApplications are you using ?


At some point this Image Registgration VolViewPlugin
was using the QuaternionRigidTransform. The current
version is using the VersorRigid3DTransform.

In both cases they were using a customized optimizer
designed to ensure that no scaling was applied into
the transform.

I will suggest you to double check your hypothesis of
scaling taking place, by simply using the linear
measurement tool that you will find in VolView in
the menu


    View--->>  Annotations--->> VolumeAnnotations
                    ---->> Display distance measurement


A line will appear in the 3D window and you will be able
to move the end points. The length of the line will be
displayed on the bottom of the Volume window.

Select two anatomical landmarks in your data set before
registration. Measure their linear separation, and repeat
the operation in the registered data set.  We expect those
two distances to be the same *when measured in millimeters*
(not pixels).

Please let us know if you find any difference in such
distances.


--

If you implement your own registration application using
the QuaternionRigidTransform you *MUST* use the
QuaternionRigidTransformGradientDescentOptimizer:
http://www.itk.org/Insight/Doxygen/html/classitk_1_1QuaternionRigidTransformGradientDescentOptimizer.html

This is the *ONLY* optimizer that will take care of maintaining
the Quaternion inside the surface of a unit sphere and therefore
prevent any scaling effects.

If you use the VersorRigid3DTransform the you *MUST* use the
custom optimizer:
http://www.itk.org/Insight/Doxygen/html/classitk_1_1VersorRigid3DTransformOptimizer.html

which will compute increments in the space of versors as oppossed
to a naive gradient descent that will attempt to treat versors as
if they formed a vector space (which they don't).


Please let us know what you find from your measurements,


   Thanks



     Luis


------------------------
Atwood, Robert C wrote:
> 
> I have tried the registration (ITK) 'plugin' for Volview, and there is
> something I don't quite understand ... Since my lack of understanding
> extends to the underlying ITK algorithm perhaps I can ask on this list
> ...
> 
> 
> First, I tried rotating a sample volume (with my own code) and then
> registering with the original. That worked perfectly. 
> 
> Then, I tried an 'erosion' on one of the images and tried registering
> again. In this case, of course it was not quite as good, but the puzzle
> is that it appears that one of the voumes is magnified , instead of only
> rotated and translated. 
> 
> Since my aim is to measure the difference in size between the same
> object imaged before and after some experments, I would rather not  use
> the image size as one of the variable parameters. 
> 
> I read over the ITK: Quaternion Rigid Transform section of Registration
> in the ITK software guide, the final paragraph of 8.7.9 implies that the
> transformation is renormalized to avoid scaling, and I was under the
> impression from the dialog box that this is the transform used by the
> plug in. 
> 
> Is the scaling behaviour in the volview plugin intentional? 
> 
> 
> 
> If I implement a (3-d) registration using ITK  will the rigid quaternion
> transform avoid any changing of scale ? Or, should Versor Rigid 3d
> transform be used? 
> 
> Robert
> 
> 
> 
> 
> 
> 
> 
> 
> 
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