  The vacuum polarisation effects from the nucleon sector lead to large medium
modifications of the vector meson masses in the Walecka model. With a quantum
hadrodynamic framework including the quantum effects, and using a quasiparticle
description for quark gluon plasma(QGP), the dilepton emission rate from the
hot and dense matter resulting from relativistic nuclear collisions is
calculated. Using a model for the fireball evolution which has been shown to
reproduce other observables such as charmonium suppression, photon emission and
the abundance of hadronic species, we compare with the dilepton invariant mass
spectrum measured by the CERES collaboration at CERN SPS. We also compare the
results to a previous calculation where the spectral function of a virtual
photon (a key ingredient for the emission rate) has been calculated in a chiral
SU(3) model.
