Studying High Energy Final State Interactions by N / D Method

We discuss the final state interaction effects at high energies via a multi-channel N/D method. We find that a 2 by 2 charge-exchange final state rescattering typically contributes an enhancement factor of a few times 10^-2 in the B meson decay amplitude, for both the real and the imaginary parts. We also make some discussions on the elastic rescattering effects.