[Insight-users] a question about rigid + nonrigid registration

[Torsten Rohlfing]

>
> I am currently trying to register two volumes. One volume only contains part 
> of the other, so I used the larger volume as fixed image and smaller volume 
> as the moving image.  First, I performed a rigid 
> registration(VersorRigid3DTransform) and then want to fine tune the 
> rigistration by nonrigid method (BSplineDeformableTransform). However, I do 
> not know how to initialize the  BSplineDeformableTransform using the 
> existing rigid result (VersorRigid3DTransform). Maybe I can use resample 
> filter to get a new moving image based on the rigid registration. But the 
> resampled moving image has the size of the larger volume, so some voxels do 
> not have resampled value and this will cause problems in further nonrigid 
> registration. Hope I made my questions clear.
>
> Qing
>   
Hi --

Indeed, resampling the moving image after affine and before nonrigid 
registration is not a good idea, both for the reason you mentioned (loss 
of field of view boundaries) and because interpolation artifacts can 
build up from stage to stage.

What you need to do is take your rigid transformation and set it as the 
"Bulk Transform" in the B-spline transformation object. That's all. 
Please consult the online documentation for the exact name of the member 
function in BSplineDeformableTransform.

Best,
  Torsten

-- 
Torsten Rohlfing, PhD          SRI International, Neuroscience Program
 Research Scientist             333 Ravenswood Ave, Menlo Park, CA 94025
  Phone: ++1 (650) 859-3379      Fax: ++1 (650) 859-2743
   torsten at synapse.sri.com        http://www.stanford.edu/~rohlfing/

     "Though this be madness, yet there is a method in't"