7.16 How do T1 and T2 values vary as a function of field strength?

http://www.mri-q.com/bo-effect-on-t1--t2.html

Quick fact: for typical range of field strengths used for clinical MRI (0.3T - 3.0 T), T1 approximatly doubles, and T2 is relatively unchanged.

Some mechanisms of T2 relaxation (such as chemical exchange and molecular diffusion) may actually be more efficient at higher fields and therefore cause a reduction in T2 values.