A system for performing a model-based segmentation of an anatomical structure in a medical image, the system comprising: - an input for obtaining image data of the medical image; - a data storage comprising model data defining a deformable model for segmenting a type of anatomical structure, the deformable model comprising parts to be fitted to corresponding parts of the anatomical structure; and - a processor configured for performing a model-based segmentation of the anatomical structure by applying the deformable model to the image data; - wherein the data storage further comprises definition data defining a geometric relation between a first part and a second part of the deformable model of which a corresponding first part of the anatomical structure is presumed to be better visible in the image data than a corresponding second part of the anatomical structure, wherein the geometric relation is defined by at least one of the group of: a distance, a range of distances, a direction, and a range of directions, from the first part of the deformable model to the second part of the deformable model; - wherein the processor is further configured to apply the deformable model to the image data to fit the first part of the deformable model to the first part of the anatomical structure, wherein the processor is configured for, after said applying: i) using the definition data to locate an image feature in the image data which matches the geometric relation with the first part of the deformable model; and ii) adjusting a fit of the second part of the deformable model based on a location of the image feature so as to better fit the second part of the deformable model to the second part of the anatomical structure; wherein said using the definition data to locate an image feature comprises: using the geometrical relation between the first part of the deformable model and the second part of the deformable model if correctly applied to the image data; locating the image feature by searching for the image feature in an intensity profile of the image data using the geometric relation as search parameter, and wherein the intensity profile sets out intensity values as a function of position in a specific direction, wherein the processor is configured to establish the intensity profile orthogonally to the first part of the deformable model - an input for obtaining image data of the medical image; - a data storage comprising model data defining a deformable model for segmenting a type of anatomical structure, the deformable model comprising parts to be fitted to corresponding parts of the anatomical structure; and - a processor configured for performing a model-based segmentation of the anatomical structure by applying the deformable model to the image data; - wherein the data storage further comprises definition data defining a geometric relation between a first part and a second part of the deformable model of which a corresponding first part of the anatomical structure is presumed to be better visible in the image data than a corresponding second part of the anatomical structure, wherein the geometric relation is defined by at least one of the group of: a distance, a range of distances, a direction, and a range of directions, from the first part of the deformable model to the second part of the deformable model; - wherein the processor is further configured to apply the deformable model to the image data to fit the first part of the deformable model to the first part of the anatomical structure, wherein the processor is configured for, after said applying: i) using the definition data to locate an image feature in the image data which matches the geometric relation with the first part of the deformable model; and ii) adjusting a fit of the second part of the deformable model based on a location of the image feature so as to better fit the second part of the deformable model to the second part of the anatomical structure; wherein said using the definition data to locate an image feature comprises: using the geometrical relation between the first part of the deformable model and the second part of the deformable model if correctly applied to the image data; locating the image feature by searching for the image feature in an intensity profile of the image data using the geometric relation as search parameter, and wherein the intensity profile sets out intensity values as a function of position in a specific direction, wherein the processor is configured to establish the intensity profile orthogonally to the first part of the deformable model i) using the definition data to locate an image feature in the image data which matches the geometric relation with the first part of the deformable model; and ii) adjusting a fit of the second part of the deformable model based on a location of the image feature so as to better fit the second part of the deformable model to the second part of the anatomical structure; using the geometrical relation between the first part of the deformable model and the second part of the deformable model if correctly applied to the image data; locating the image feature by searching for the image feature in an intensity profile of the image data using the geometric relation as search parameter, and wherein the intensity profile sets out intensity values as a function of position in a specific direction, wherein the processor is configured to establish the intensity profile orthogonally to the first part of the deformable model