Back-to-Back Correlations (BBC) of particle-antiparticle pairs are predicted to appear if hot and dense hadronic matter is formed in high energy nucleus-nucleus collisions. Back-to-back correlations are related to in-medium mass-modification and squeezing of the quanta involved. The formalisms are analogous in the bosonic (bBBC) and in the fermionic (fBBC) cases. Both bBBC and fBBC are positive and unlimited correlations of similar strength, thus differing from two-identical particle (bosons/fermions) correlations. For testing the survival and intensity of the effect in a more realistic situation, we study back-to-back correlations for mass-modification occurring in a finite sized, thermalized medium. For illustration, we consider a non-relativistically expanding fireball with finite emission time, and evaluate the width of the back-to-back correlation function. We show that the BBC signal indeed survives the expansion and flow effects, with sufficient magnitude to be observed at RHIC.