[Insight-users] Error in Registration results

[Luis Ibanez]

Hi Emma,



        mm... it is hard to explain indeed.


Your intuition is correct regarding the fact that the
default pixel value "shouldn't" appear in the middle slices.

That being said, it is not "impossible" for the value to
appear there.  The fact that it is appearing, is an indication
that one of the nodes in the BSplineGrid has a deformation so
large that it sends the point outside of the image physical
extent. In other words, the registration failed largely.

The extreme deformation that the two sliced display are also
a bad indication of the results of the registration. For
example, the first slice in your email has the lungs collapsed
towards the medial plane.

You should probably rerun the registration by using different
parameters for the optimizer. In particular you probably should
set the Bound values for the parameters of the Transform.


BTW:

1) How many iterations did the algorithm *actually* ran ?

2) Where the two images of the same modality ?

    The metric used in this example is MeanSquares,
    so it pretty much assumes that the images are of
    the same modality and with a very close distribution
    of intensity values.



  Regards,



      Luis



-----------------
Emma Ryan wrote:
> Hi,
> 
>   I am trying to register 2 volumes.  I use ITK example - 
> DeformableRegistration7.cxx to do so. The default pixel values is 100. 
> So any empty space is filled with this grey value.  So it is 
> understandable if the first  slice shows this grey region since they are 
> tyring to align along the 'Z' direction. Also, if this grey value 
> appears along the boundary of the images, it makes sense.
> 
>   But how does one explain the appearance of the default grey value 
> (100) in the center slices.  I have attached some images and labelled 
> them with thier corresponding slice number.
> 
>   I thought the problem was with resampling, but that part of the code 
> seems correct, besides I have used the example cpp file as is.
> 
>  I see some of these 'artifacts' in the center slices as well.
> Any clue ?
> 
> Emma
> 
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