[ITK-users] [ITK] Evaluate results of registration

[Andras Lasso]

Hi Matias,

Checkerboard pattern image is easy to generate but conveys very limited information while taking up a lot of space. The main issue is that you can only see displacement (residual registration error) along gridlines, but only at those points where a linear image feature (for example, an organ contour) crosses a gridline. So, in an entire image you can estimate the displacement only at a couple of relevant points. Using a more dense grid does not help much, because it makes image features harder to recognize.

I would suggest the following representation instead:

1. Show only the fixed image with the following information overlaid (in one or more images)
- contours segmented on the moving image with/without registration: this allows evaluation of displacement along the entire segmented contour, not just at a few points; the segmentation can be also used for quantitative evaluation (e.g., Hausdorff distance)
- vector field of the registration transform (shown as arrows, distorted grid, etc.): this is important because very often registration at the contours look perfect but in areas where the image gradients are smaller the registration transform may become very irregular

2. Visualize the vector field of the transformation (with arrows or distorted grid) in 3D: this allows the evaluation of how realistic the computed displacements are

These visual representations have not been very easy to generate in the past but since we added full support of real-time visualization of non-linear transforms to 3D Slicer, this should not be a problem anymore. Slicer can read ITK transforms (even composite transforms), concatenate them, invert them, and apply them to any 3D volume, surface mesh, point cloud, etc. and visualize them in 2D and 3D. See some example visualizations here: http://www.slicer.org/slicerWiki/index.php/Documentation/Nightly/Modules/Transforms. 

Andras

-----Original Message-----
From: Community [mailto:community-bounces at itk.org] On Behalf Of Matt McCormick
Sent: Friday, February 13, 2015 3:31 PM
To: Matias Montroull
Cc: insight-users at itk.org Users
Subject: Re: [ITK] [ITK-users] Evaluate results of registration

Hi Matias,

Yes, it is possible to get the intensities on similar scales with the RescaleIntensityImageFilter [1] or the IntensityWindowingImageFilter [2] before passing into the CheckerBoardImageFilter.

HTH,
Matt

[1] http://www.itk.org/Doxygen/html/classitk_1_1RescaleIntensityImageFilter.html

[2] http://www.itk.org/Doxygen316/html/classitk_1_1RescaleIntensityImageFilter.htmlhttp://www.itk.org/Doxygen316/html/classitk_1_1RescaleIntensityImageFilter.html

On Fri, Feb 13, 2015 at 7:33 AM, Matias Montroull <matimontg at gmail.com> wrote:
> Hi,
>
> I'm using a check-board output (CheckerBoardImageFilter) to evaluate 
> the results of a CT/RM registration, now I would like to write 
> something where I could change the WL WC of the 2 images independently 
> to really make sure the registration is right; I guess is not possible 
> with ITK itself and I need to write some code for visualizing the CT 
> and the RM and then change window levels independently, am I right?
>
> Thank you,
>
> Matias.
>
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