[Insight-users] inverting a deformation field - problem

[Bradley Lowekamp]

Hello,

I am working on integrating displacement fields into SimpleITK right now, so in just a couple days I should be able easily demonstrate this in SimpleITK Notebooks.

To use you WarpFilter on a results a a registration, you will be resampling the fixed image onto the moving image, as the is the direction of the transform.

Have you been able to use the following example:

http://www.itk.org/Doxygen/html/Filtering_2WarpImageFilter1_8cxx-example.html#_a4

With the command line arguments as "FixedImage" DisplacementFieldImage" "OutputImage"?

Does the moving and fixed image have the same domain prior to registration or is there an additional large transformation going on with the displacement field?

Also if you could share your data or a small test case illustrating the problem this may help others more extensively help you.

Brad

On Dec 9, 2013, at 9:06 AM, Tim Bhatnagar <tim.bhatnagar at gmail.com> wrote:

> I appreciate the response, Brad.
> 
> Can you tell me how the implementation of the 'WarpImageFilter' works, such that when I input my Demons-generated displacement field, and my 'movingImage' (from Demons) as input, I get what looks like my 'fixedImage' (from Demons) as output... making me think that the displacement field is actually mapping my movingImage into my fixedImage?
> 
> Also, I use Paraview to visualize my field, and when visualized, it illustrates what you are suggesting (the mapping that would take fixed -> moving). But how then, does the WarpFilter use the SAME FIELD to warp my movingImage into a very nice estimation of my fixedImage?
> 
> Sorry if any of that is convoluted..
> 
> 
> On Mon, Dec 9, 2013 at 6:00 AM, Bradley Lowekamp <brad at lowekamp.net> wrote:
> Hello,
> 
> It not uncommon for resampling-type algorithms to have some points be mapped out side the the domain. This is why a boundary condition and extrapolators are used. If there are just a limited number of pixel being mapped out side, then the simplest way be by to just check if the pixel is within the image's region.
> 
> ITK's registration frameworks solve for a transform which maps from the "Fixed" image to the "Moving" image. This is well described int Chapter Eight of the old Software guide:
> 
> http://www.itk.org/ItkSoftwareGuide.pdf
> 
> Brad
> 
> On Dec 8, 2013, at 6:38 PM, Tim Bhatnagar <tim.bhatnagar at gmail.com> wrote:
> 
>> Hello,
>> 
>> I've created a displacement field via Demons non-rigid registration. I am now trying to create the inverse (using InverseDisplacementFieldImageFilter), but when I am using the indexes to ascribe the inverted field, my program crashes mid-way through, because it appears I am trying to call a negative index (specifically, the 3rd index parameter.. the 'z'-parameter).
>> 
>> I don't do anything to the displacement field except write it to a vtk file before i invert it.. can anyone suggest a solution? I thought I could try and specify the 'direction' of the field, but I'm not sure where in my pipeline I can set the direction of the inverted displacement field...
>> 
>> sorry if that's messy.. any thoughts would be appreciated!
>> 
>> Thanks,
>> 
>> Tim
>> 
>> -- 
>> Tim Bhatnagar
>> PhD Candidate
>> Orthopaedic Injury Biomechanics Group
>> Department of Mechanical Engineering
>> University of British Columbia
>> 
>> Rm 5000 - 818 West 10th Ave.
>> Vancouver, BC
>> Canada
>> V5Z 1M9
>> 
>> Ph: (604) 675-8845
>> Fax: (604) 675-8820
>> Web: oibg.mech.ubc.ca
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> 
> 
> 
> 
> -- 
> Tim Bhatnagar
> PhD Candidate
> Orthopaedic Injury Biomechanics Group
> Department of Mechanical Engineering
> University of British Columbia
> 
> Rm 5000 - 818 West 10th Ave.
> Vancouver, BC
> Canada
> V5Z 1M9
> 
> Ph: (604) 675-8845
> Fax: (604) 675-8820
> Web: oibg.mech.ubc.ca

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