t1 t2 mr registration

hello ı am trying to merge two mri of the same patient one is t1 weighted with good sagittal view but limited to the right side of the head and other one is t2 weighted with good axiak view but its contains the whole head. all i want is the replace overlaped t2 section with t1 section but keep the rest of the head with t2 weighted images.
With landmark registration i was succesfull for this task without even putting any landarmks, 2 mri synced perceftly but everytime i try to download to merged file its only downloading t2 mri and with general registration its the same error. i hardned the transform but that also didnt helped.

hello first of all ı mixed the names ı have t2 mri with good sagittal view and t1 mri with good axial view. i downloaded few extanstions but all they do just give the intercepted area with no other areas in the image. to repeat myself my aim is replace the t1 section with t2 images and keep the rest of the images as t1 . please for this urgent matter i will be waiting for yor responses