[Insight-users] Demons Registration

[Ganesh Narayanasamy]

Thanks for the reply Tom.
When I increase the # iterations to say, -i 1000x500x100x50, I am giving 4 multi-resolutions steps.. Is the image scaling factor assumed to be 1/8, 1/4, 1/2 and 1 uniformly for all 3 axes? Can we set different scaling factors for the 3 axes knowing that the out-of-plane resolution is typically worse than the in-plane resolution in a standard clinical image.
Can you provide some more details about the utility of the 2 parameters: Deformation field sigma, Update field sigma.

Thanks again,
Ganesh

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"What the mind of man can conceive and believe, It can achieve" - Napolean Hill

-Ganesh 
Narayanasamy,Ph.D., PostDoc-University of Kentucky Cancer Center

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> From: tom.vercauteren at m4x.org
> Date: Thu, 24 Feb 2011 08:47:01 +0100
> Subject: Re: [Insight-users] Demons Registration
> To: nganesh76 at hotmail.com
> CC: insight-users at itk.org
> 
> Hi Ganesh,
> 
> On Wed, Feb 23, 2011 at 19:04, Ganesh Narayanasamy
> <nganesh76 at hotmail.com> wrote:
> >
> > When I run DemonsRegistration using the options as given in the command line
> > below, I can get a few output files like final image, deformation field etc.
> > How would I get the rest of the output like "True field file"?
> 
>  The "true field" is an input not an output. It may be used for
> synthetic experiments where the actual deformation is known.
> DemonsRegistration then compares at each iteration its result against
> this ground truth (but of course it does not use it to drive the
> registration).
> 
> 
> > As the image was not deforming enough, I had opted to reduce sigma from the
> > default value of 1.5 to 0.8.. is this the correct approach?
> 
> This entirely depends on your use case... That being said, I would
> first try to use more iterations and then reduce the sigma.
> 
> 
> > Size of the fixed and moving images are 384x384x64 pixels each. I would like
> > to register using the multi-resolution approach starting with 1/4th number
> > of pixels in all 3 axes (i.e, 96x96x16), going to 1/2 (ie., 192x192x32
> > pixels) and finally to the full image. How will I do this?
> 
> It is already done, see the number of multiresolution levels and
> number of iterations per level:
> >   Number of multiresolution levels: 3
> >   Number of demons iterations: [ 15 10 5 ]
> 
> Hope this helps,
> Tom
> 
> 
> > Command:
> >>DemonsRegistration.exe -f CBCT1.mha -m CBCT4.mha -o Final.mha -O DefFld.mha
> >> -s 0.8 -d 1
> >
> > Starting demons registration with the following arguments:
> > Arguments structure:
> >   Fixed image file: CBCT1.mha
> >   Moving image file: CBCT4.mha
> >   Input field file:
> >   Input transform file:
> >   Output image file: Final.mha
> >   Output field file: DefFld.mha
> >   True field file:
> >   Number of multiresolution levels: 3
> >   Number of demons iterations: [ 15 10 5 ]
> >   Deformation field sigma: 0.8
> >   Update field sigma: 0
> >   Maximum update step length: 2
> >   Update rule: exponentialize and compose (Diffeomorphic)
> >   Type of gradient: symmetrized (ESM for diffeomorphic and compositive)
> >   Use histogram matching: false
> >   Algorithm verbosity (debug level): 1
> >
> > Thanks,
> > Ganesh
 		 	   		  
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