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This method is limited to landmarks that are part of the convex hull. For the first method, the face of the convex hull of the pelvis with the vertices with minimal distance to the iliac and pubic regions defines the APP. During this segmentation process, the pelvis is subdivided into regions such as the iliac and pubic bones. ![]() All methods are based on a previous SSM-based segmentation and a graph-based optimized reconstruction of the subject’s pelvis from CT data. evaluated one convex hull-based method and two statistical shape model (SSM)-based methods 15. The APP is usually constructed by the anterior superior iliac spines (ASISs) and the pubic tubercles (PTs) or the pubic symphysis (PS). compared three methods for the identification of the landmarks of the anterior pelvic plane (APP). #PDF IMAGE EXTRACTOR LICENSE KEY 2.5.0.0 MANUAL#Moreover, the limited number of seven subjects and the missing comparison to a manual landmark identification impede the assessment of Ehrhardt’s method. The gray value-based initialization of the atlas is error-prone due to large anatomical variations between subjects. However, a manually labeled atlas and CT data of the subject are necessary for this approach. #PDF IMAGE EXTRACTOR LICENSE KEY 2.5.0.0 REGISTRATION#Afterwards, the atlas and the subject mesh are locally cut out within a certain radius for each landmark and the registration of each cut-out is refined by a combination of an affine and a non-linear registration algorithm taking the Euclidean distance, the normals and the curvature of the surfaces into account. Initially, the atlas is non-rigidly registered to the computed tomography (CT) data of the subject using the gray value data. The atlas consists of gray value data and a surface model of the pelvis with labeled anatomical areas and landmarks. proposed an atlas-based approach with a curvature-based refinement of the landmarks 1. While the hip joint, with the acetabulum being part of the pelvis, is one of the most investigated joints of the human body, only a few methods for fully automatic identification of pelvic landmarks on surface models have been published so far.Ī list of all abbreviations used in this paper can be found as Supplementary Table S1.Įhrhardt et al. Automatic methods for landmark identification should provide reproducible results, be invariant against the orientation and position of the bone and robust against the large inter-subject variability of the bones. Manual identification of landmarks is time-consuming 1, 12, requires medical training, is subject to intra- and inter-observer variability 13, 14 and is not suitable for the analysis of large data sets with many subjects. The landmarks are used to construct subject-specific anatomical reference frames 10, 11 and to quantitatively determine the morphology of bones. Fields of application are for instance patient-specific preoperative planning 1 and intraoperative navigation 2, 3, subject-specific scaling of musculoskeletal models 4, 5 or the statistical analysis of the bony morphology 6– 9. The identification of bony landmarks is an essential procedure in patient-specific orthopedics, subject-specific biomechanics or morphometrics. There were no significant differences for the orientation of the SISP coordinate system recommended by the International Society of Biomechanics. Whether these differences are acceptable, has to be evaluated for each specific use case. A comparison to a manual identification was performed that showed minor but significant (p < 0.05) median differences below 3 mm for the position of the landmarks and below 1° for the orientation of the APP coordinate system. The ITP method proved to be robust against the initial alignment of the pelvis in space. ![]() The method includes the landmarks to construct the two most established anatomical reference frames of the pelvis: the anterior pelvic plane (APP) coordinate system and superior inferior spine plane (SISP) coordinate system. In this paper, a new approach, called the iterative tangential plane (ITP) method, for fully automatic identification of landmarks on surface models of the pelvis is introduced. A fully automatic detection is preferable to a subjective and time-consuming manual identification. The recognition of bony landmarks of the pelvis is a required operation in patient-specific orthopedics, subject-specific biomechanics or morphometrics. ![]()
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