A computer implemented method for refining a model of an anatomical structure in an image, the method comprising: acquiring a model of the anatomical structure in the image, the model comprising a plurality of control points, each control point corresponding to a feature in the anatomical structure, wherein the model further comprises anatomical context information that is encoded in the model and that relates to the features to which the control points correspond, and wherein the anatomical context information sets one or more restrictions on an adjustment that can be made to a respective control point to ensure that the shape of the feature to which the respective control point corresponds is reflected in the resulting model; placing the model in the image with respect to the anatomical structure; and based on a user input received to adjust a position of at least one of the control points in the model in the image, adjusting the position of the at least one of the plurality of control points to alter a shape of the model to the anatomical structure in the image, wherein the adjustment that the user is permitted to make to the position of one or more of the at least one control points is restricted during the adjustment, based on information relating to the at least one control point; and wherein the information relating to the at least one control point comprises the anatomical context information encoded in the model relating to the anatomical feature to which the at least one control point corresponds, and wherein the information relating to the at least one control point further comprises an intensity of the anatomical structure in the image and wherein: a larger adjustment is permitted for a higher intensity feature compared to a lower intensity feature; and/or editing is not permitted in regions of the image having an absolute intensity exceeding a maximum value. acquiring a model of the anatomical structure in the image, the model comprising a plurality of control points, each control point corresponding to a feature in the anatomical structure, wherein the model further comprises anatomical context information that is encoded in the model and that relates to the features to which the control points correspond, and wherein the anatomical context information sets one or more restrictions on an adjustment that can be made to a respective control point to ensure that the shape of the feature to which the respective control point corresponds is reflected in the resulting model; placing the model in the image with respect to the anatomical structure; and based on a user input received to adjust a position of at least one of the control points in the model in the image, adjusting the position of the at least one of the plurality of control points to alter a shape of the model to the anatomical structure in the image, wherein the adjustment that the user is permitted to make to the position of one or more of the at least one control points is restricted during the adjustment, based on information relating to the at least one control point; and wherein the information relating to the at least one control point comprises the anatomical context information encoded in the model relating to the anatomical feature to which the at least one control point corresponds, and wherein the information relating to the at least one control point further comprises an intensity of the anatomical structure in the image and wherein: a larger adjustment is permitted for a higher intensity feature compared to a lower intensity feature; and/or editing is not permitted in regions of the image having an absolute intensity exceeding a maximum value. a larger adjustment is permitted for a higher intensity feature compared to a lower intensity feature; and/or editing is not permitted in regions of the image having an absolute intensity exceeding a maximum value.