[Insight-users] Control of deformation field generation via landmarks?

[Ruben Schilling]

Hi,

I am trying to evaluate some particular elastic and large  
deformations using landmarks. I have assigned a modest number of  
landmarks (about 30) sitting in image volumes of size 400 x 400 x  
250. Considering the particular type of (elastic) deformation I am  
facing the landmarks seem to cover the deformation pretty well.
I have built a prototype program around the example  
LandmarkWarping2.cxx, which I have modified for 3D and additional  
optional large (sigma ~ 50) gaussian regularization of the  
deformation field from the spline. I am using a reciprocal elastic  
body kernel (without stiffness).


I am having two kinds of trouble though:
(1) Scanning through the image slices, it seems that they are  
shifting from right to left (which is also the main direction of my  
landmark positions)
(2) The biggest portion of the moving image is cut off (about 60 out  
of 250 slices remaining), primarily about 20 slices before and after  
the slice-block with the landmarks stay in the game

Since my landmarks do not cover the whole image depth I would have  
expected parts not covered by landmarks to be moved via spline  
regularization estimated from the sparse deformation field of the 30  
landmarks.


Is there a way to increase the radius of regularization (e.g. some  
linear weigth of distance to next landmark) or any control of the  
regularization at all?
My guess is, that my gaussian regularization looses too much strength  
over distance. Is there another (maybe direct?) way to control the  
deformation field interpolation with the kernel transforms?

I would be grateful for advice on this matter.

Best,
Ruben