initial conditions and the freeze-out prescription and another where the EoS was fixed and the treatment of the freeze-out was changed. We presented a systematic investigation of these effects on the HBT radii. It was found that the latent heat influences the emission of particles visibly and hence the HBT radii of the pion source. While the final rescatterings result in an independence of the calculated HBT-parameters from the transition criterion, they do not improve the quantitative agreement with the experimental data. The details of the hydro-freeze-out prescription do not affect the HBT radii as well as the $R_O/R_S$ ratio as long as the HR in the subsequent hadronic transport model were taken into account. Overall, the HBT data seem to favor a stiff EoS [@Bekele:2007ee], but one should also keep in mind that viscosity effects are neglected during the hydrodynamic stage and that the particle emission from the early stages should be handled more carefully.

In the future, bulk and shear viscosity will be further considered for the hydrodynamic phase, and the non-equilibrated particle emission should be treated more precisely.

Acknowledgments {#acknowledgments .unnumbered}
===============

We thank S. Pratt for providing the CRAB program and thank D.H. Rischke for providing 