I am using the DTITK tool to align diffusion tensor image, but I am not getting an registration field at the same resolution as the original tensor image, how do I ensure that the resolution of the alignment field is the same as the resolution of the original Tensor Is it possible to trilinearly interpolate the registration field directly?

Your question is out of scope for the Surfice forum. I suggest you contact the DTITK forum  https://groups.google.com/g/dtitk