In this paper implicit representations of deformable models for medica
l image enhancement and segmentation are considered. The advantage of
implicit models over classical explicit models is that their topology
can he naturally adapted to objects in the scene, A geodesic formulati
on of implicit deformable models is especially attractive since it has
the energy minimizing properties of classical models, The aim of this
pager is twofold, First, a modification to the customary geodesic def
ormable model approach is introduced by considering all the level sets
in the image as energy minimizing contours. This approach is used to
segment multiple objects simultaneously and for enhancing and segmenti
ng cardiac computed tomography (CT) and magnetic resonance images. Sec
ond, the approach is used to effectively compare implicit and explicit
models for specific tasks. This shows the complementary character of
implicit models since in case of poor contrast boundaries or gaps in b
oundaries e.g. due to partial volume effects, noise, or motion artifac
ts, they do not perform well, since the approach is completely data-dr
iven.