[Insight-users] A quick question on combining displacement fields

[Anja Ende]

Hello,

I have a set of three images (say A, B and C) and my registration
process is as follows:

A (moving image) is registered to B (fixed image) rigidly. I take the
transformation and generate a displacement or position field using the
grid of the fixed image (B).

B (moving image) is registered to C (fixed image) using non-rigid
transformation. I can generate a similar displacement or position
field using the grid of fixed image (C).

Now, what I want to do is combine these two displacement or position
fields and generate a composite field that I can use to resample A
using the composite transformation in the space of C.

However, I am not clear on how I should combine these displacement or
position fields as the grid sizes of B and C may not be the same.

One simple solution is to do two resampling: first one to resample A
into the space of B and then resample the result using the second
transformation into the space of C. However, I would like to avoid
this multiple resampling, if possible.

Does anyone have any idea on how I can go about this?

I would really appreciate your help and comments.

Thanks,

Anja