The NMR signal can be calculated from the equation
$$S = KH ({1 -e^{-TR/T1}}) {e^{-TE/T2}} $$
Reference
If we alter the TR of a sequence and keep the T2, let the resultant signals be
$$S1 = KH ({1 -e^{-TR1/T1}}) {e^{-TE/T2}} $$ and
$$S2 = KH ({1 -e^{-TR2/T1}}) {e^{-TE/T2}} $$
So, $$ S1/S2 = \frac{1 -e^{-TR1/T1}} {1-e^{-TR2/T1}} $$
S1, S2, TR1 and TR2 are known.
Is there any way find T1 from this ?