Transformation of an image subvolume using imwarp.

Dear Matlab community:

I have the transformation parameters (3D rotation matrix and offset) obtained from a registration of two images with different spatial resolutions. Using imwarp I am mapping the low resolution (lowres) image to the other one without problems. However, this process is time consuming and I could be better off by only mapping one subvolume from the lowres to the other image.

Is this feasible at all? I've tried modifying the offset to account for the different positions in the image center of lowres image and its subvolume. But, does imwarp transform the image, in this case using an affine3d, relative to the image center or relative to the image origin?

Thanks