[Freesurfer] bbregister for MRA

Hi Surfers I want to use bbregister to register my MRA scans to the structural scans. The first attempts by using these parameters came out OK but not perfect:

bbregister --s <Subject_ID> --mov MRA.nii --init-fsl --reg register.dat --bold

However, there are obvious problems around frontal areas.

I have to admit that one of the reasons for this imperfect registration may be that MRA scans do not cover the whole brain. However, they still cover a large portion of it. I was wondering if there is any argument in bbregister command that may help me improve the quality. It is very fine if it increases the registration time.

Regards

P.S.: using --t2 in bbregister (instead of --bold) generated the same outcome but --t1 was completely off.