The present invention relates to an apparatus (26) and a method for determining a fractional flow reserve. For this purpose, a new personalized hyperemic boundary condition model is provided. The personalized hyperemic boundary condition model is used to condition a parametric model for a simulation of a blood flow in a coronary tree (34) of a human subject. As a basis for the personalized hyperemic boundary condition 5 model, a predefined hyperemic boundary condition model is used, which represents empirical derived hyperemic boundary condition parameters. However, these empirical hyperemic boundary condition parameters are not specific for a human subject under examination. In order to achieve a specification of the respective predefined hyperemic boundary condition model, specific human subject features are derived from a volumetric image of the coronary 10 tree of the human subject. These features are used to adjust the predefined hyperemic boundary condition model resulting in a personalized hyperemic boundary condition model. As an effect, a flow simulation using the parametric model conditioned by the personalized hyperemic boundary condition model. As an effect, a flow simulation using the parametric model conditioned by the personalized hypefcmtc boundary condition model improves the performance of flow simulation in order to determine an enhanced fractional flow reserve. 15
