This approach , termed `` 3D T2prep-GRE , '' was implemented at 7 Tesla ( T ) with a typical spatial ( 2.52.52.5 mm ( 3 ) ) and temporal ( TR = 2.3 s ) resolution for functional MRI ( fMRI ) and whole-brain coverage ( 55 slices ) , and compared with the widely used 2D spin-echo EPI sequence .