  Within the Matsubara formalism we derive expressions for the pion self-energy
and the two-pion propagator in a hot pion gas. These quantities are used to
selfconsistently calculate the in-medium $\pi\pi$ amplitude beyond the
quasiparticle approximation (QPA). The results are shown to differ
significantly from QPA-based calculations. We also examine the impact of chiral
constraints on the $\pi\pi$ interaction in a chirally improved version of the
J\"ulich $\pi\pi$ model.
