The manual step in semi-automatic segmentation of medical volume images typically involves initialization procedures such as placement of seed-points or positioning of surface models inside the object to be segmented. The initialization is then used as input to an automatic algorithm. We investigate how such initialization tasks can be facilitated by using haptic feedback. This paper describes a haptic interaction technique based on gradient vector flow (GVF) that allows a user to stay centered inside the object while still feeling the object boundaries. Our method is not limited to elongated structures, which is a common restriction for other approaches. Initial tests of the method shows encouraging results for differently shaped objects.