[Insight-users] Demon's Registration Question

[Luis Ibanez]

Hi Alice,

                    Welcome to ITK !

Thanks for the detailed description of the problem.


The outcome of the Demosn registration algorithm
is and image that has the same grid as the Fixed
image, but is populated with the intensity levels
of the Moving image.

If in your case:

Fixed Image    = Cylinder  at value  5000
Moving Image = Ellipse    at value   4860

Then the outcome of the registration process
should be an at value 4860.

Is that what you observe ?

Also, please notice that the Demons registration
is based on the assumption that both images have
the same intensity distribution.  That is, in principle,
you should rescale the intensities of both  images
before you pass them as input to the Demons filter.

You may also need to blur the images a bit in order
to create ramps of intensity in the border of the objects,
to make possible for Demons to compute displacement
vectors based on the direction of the gradient.

(maybe a screenshot of your images will helpful).



      Regards,


              Luis


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On Fri, Apr 23, 2010 at 10:33 AM, calice14 <gtg102x at mail.gatech.edu> wrote:

>
> Hello all,
>
> I have a quick question about Demon's Registration.  I have successfully
> implemented an example, but the results were not what I expected. The
> simulated phantom are of ellipsoid and cylinder shape. One constrain for
> the
> two phantoms is, the total intensities of the two phantoms are the same. So
> for the cylinder phantom, the pixel value is 5000 while for ellipsoid it's
> 4860. After registration, I got the result phantom which shape can match
> the
> cylinder. The problem is, the pixel intensity of the registered images
> followed the moving phantom(ellipsoid 4860), not the fixed phantom
> (cylinder
> 5000).
> As it's assumed that Demon registration should keep the total intensity in
> the registered images, I'm wondering why my registered images don't have
> the
> correct pixel value (4860)?
>
> Is the Demon's Algorithm not implemented to keep total intensity values
> constant after registration?
>
> Please excuse me if this seems trivial.  I am a very much a newbie to the
> image registration world :)
>
> Thanks all,
>
> Alice Cheung
> --
> View this message in context:
> http://old.nabble.com/Demon%27s-Registration-Question-tp28342139p28342139.html
> Sent from the ITK - Users mailing list archive at Nabble.com.
>
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