Cascaded statistical shape model based segmentation of the full lower limb in CT

Abstract

Image segmentation has become an important tool in orthopedic and biomechanical research. However, it greatly remains a time-consuming and laborious task. In this manuscript, we propose a fully automatic model-based segmentation pipeline for the full lower limb in computed tomography (CT) images. The method relies on prior shape model fitting, followed by a gradient-defined free from deformation. The technique allows for the generation of anatomically corresponding surface meshes, which can subsequently be applied in anatomical and mechanical simulation studies. Starting from an initial, small (n ≤ 10) sample of manual segmentations, the model is continuously updated and refined with newly segmented training samples. Validation of the segmentation pipeline was performed by comparing the automatic segmentations against corresponding manual segmentations. Convergence of the segmentation pipeline was obtained in 250 cases and failed in three samples. The average distance error ranged from 0.53 to 0.76 mm and maximal error ranged from 2.0 to 7.8 mm for the 7 different osteological structures that were investigated. The accuracy of the shape model-based segmentation gradually increased as the number of training shapes in the updated population also increased. When optimized with the free form deformation, however, average segmentation accuracy rapidly plateaued from already as little as 20 training samples on. The maximum segmentation error plateaued from 100 training samples on.

Keywords:

• Image segmentation
• lower limb
• computed tomography
• statistical shape model

Disclosure statement

The authors declare that they have no competing interests that could inappropriately influence this work.

Additional information

Funding

Jan Van Houcke was financially supported by PhD grant 11V2215N from the Research Foundation Flanders. Emmanuel Audenaert was financially supported by a senior clinical research fellowship from the Research Foundation Flanders. Diogo F Almeida was financially supported by a VLAIO (FWO Flanders) innovation grant.

Notes on contributors

Jan Van Houcke

EA designed the algorithms. JVH implemented the algorithms and assisted the segmental statistical shape model building. DV and GS checked the implementation of the algorithms. DA, MP and LP performed manual segmentation required for validation and helped to polish the manuscript. All authors read and approved the final manuscript.