A novel method of anatomical landmark selection for rib cage 3D reconstruction from biplanar radiography

Methods to reconstruct anatomical structures in 3D are gaining interest in medicine because they give access to quantitative information on the patient's geometry. However, these methods are user-dependent and require a trained operator, which is time consuming and a source of error and unreliability. The aim of this work was to validate a novel method of landmark selection to perform the 3D reconstruction of the rib cage from biplanar calibrated radiographies. The method uses digital painting for digitisation of anatomical landmarks (eight ribs midlines, posterior extrema, sternum) to build a first estimate of the 3D ribcage geometry. Totally, 20 scoliotic patients were included (Cobb angle: 43 degrees +/- 11 degrees) and their ribcage was reconstructed twice with the proposed method by four trained operators. Measurement reproducibility was similar to previously validated methods. Uncertainty (95% CI) was 2.3 degrees for the rib hump measurement, 9.7 mm and 3.8 mm for maximal antero-posterior and lateral diameter, 395 cm3 for ribcage volume. The method was qualitatively considered more user-friendly than previous versions, although it still requires a trained operator, and it took approximately 2 min of manual digitisation. The new method should facilitate diffusion of 3D quantitative analysis of ribcage in clinical routine.