A 3D reconstruction method of the body envelope from biplanar X-rays: Evaluation of its accuracy and reliability

Abstract

The aim of this study was to propose a novel method for reconstructing the external body envelope from the low dose biplanar X-rays of a person. The 3D body envelope was obtained by deforming a template to match the surface profiles in two X-rays images in three successive steps: global morphing to adopt the position of a person and scale the template׳s body segments, followed by a gross deformation and a fine deformation using two sets of pre-defined control points. To evaluate the method, a biplanar X-ray acquisition was obtained from head to foot for 12 volunteers in a standing posture. Up to 172 radio-opaque skin markers were attached to the body surface and used as reference positions. Each envelope was reconstructed three times by three operators. Results showed a bias lower than 7mm and a confidence interval (95%) of reproducibility lower than 6mm for all body parts, comparable to other existing methods matching a template onto stereographic photographs. The proposed method offers the possibility of reconstructing body shape in addition to the skeleton using a low dose biplanar X-rays system.

Determination of a new uniform thorax density representative of the living population from 3D external body shape modeling

“…These bi-planar radiographies allow three dimensional (3D) reconstructions of the bones and human body shape using well documented models (Aubert et al, 2014;Humbert et al, 2009;Nérot et al, 2015) (Figs. 1 and 2).…”

“…Body shape reconstruction was based on the deformation of a template which had been preliminarily segmented into 15 body segments, based on reference radiographs (Nérot et al, 2015). During the envelope reconstruction process, the template was morphed to match the skin contours on the orthogonal radiographs and body segments were thereby adjusted to the anthropometry of the subject on the radiographs (by scaling using bony points, and surface deformation algorithm) (Nérot et al, 2015). The thorax was defined from templates' mesh proximal and distal limits with axilla as limits on the sides.…”

“…A new low-dose imaging system taking bi-planar radiographies (Dubousset et al, 2010) combined with 3D reconstruction technique of the external body shape (Nérot et al, 2015), spine (Humbert et al, 2009) and of rib cage (Aubert et al, 2014) allows for volume estimation. Densities for each thorax tissues and segment have been well documented in the literature (Dempster, 1955;Erdmann and Gos, 1990;Hayashi et al, 2011;Li et al, 2010).…”

Alignment of centers of mass of body segments with the gravity line

“…3D reconstruction of the external body shape was performed (Nérot et al 2015) ( Figure 1) and the following segments were obtained: head, thorax (from T1 to T12), arms, forearms, hands, abdomen, thighs, lower legs, and feet.…”

“…No study to date has provided reference values for the alignment of centers of mass (CoM) of different body segments in asymptomatic subjects. The use of a bi-planar X-ray system (Dubousset et al 2010) combined with 3D reconstruction of the external body shape (Nérot et al 2015) allows for computation of the body segments' CoM. The aim of this study was to provide baseline values for the position of each segment's CoM compared to the gravity line (GL) in the sagittal plane.…”