[Insight-users] Problems using FEM Registration with my own mesh

[Jonathan Orban]

Hi,

I'm currently working on FEM Registration (Image is 90*90*80 and has
only pixel dimensions => the range of the image is [0->89, 0->89,
0->79]). I'm trying to use my own mesh (687 nodes for 3447 elements) to
do this. My mesh has the same range than the image [0->89, 0->89,
0->79]. Thanks to N. Tustison, I managed to transform my .vtk file in
a .fem file that looks just like the examples proposed in the
itk->Testing->Data->Input->FEM. I tried a registration based on
DeformableRegistration1.cxx with the
FiniteElementRegistrationParameters1.txt with some adaptation to use 3D
images.

The registration starts by loading everything and  applying loads on 3
different nodes (is it possible to chose these nodes?). Then it
allocates the deformation field with load sizes of [90,90,80] and image
[90,90,80] and gives me the following error:

> terminate called after throwing an instance of 'itk::fem::FEMExceptionItpackSparseMatrixSbsij'
>   what():  /export/itk/InsightToolkit-3.0.1/Code/Numerics/FEM/itkFEMItpackSparseMatrix.cxx:305:
> Error: maximumNumberOfNonZeroValuesInMatrix is too small
> Aborted (core dumped)

Does anybody know that kind of error? 

I have also another question related to the same topic. I have images 
where the body to be registered is surrounded by air. Is it possible 
to define a mesh only on this body and not on the entire image in order 
to add elastic properties only on the body and not on the air? Or do I 
have to define a mesh on the whole image and give different properties 
on the body and on the air?


Thanks for your answers,


Jonathan Orban

Communications and Remote Sensing Lab.
UCL/TELE, Belgium