Statistical multi-level shape models for scalable modeling of multi-organ anatomies.

Statistical shape modeling is an indispensable tool in the quantitative analysis of anatomies. Particle-based shape modeling (PSM) is a state-of-the-art approach that enables the learning of population-level shape representation from medical imaging data (e.g., CT, MRI) and the associated 3D models of anatomy generated from them. PSM optimizes the placement of a dense set of landmarks (i.e., correspondence points) on a given shape cohort. PSM supports multi-organ modeling as a particular case of the conventional single-organ framework via a global statistical model, where multi-structure anatomy is considered as a single structure. However, global multi-organ models are not scalable for many organs, induce anatomical inconsistencies, and result in entangled shape statistics where modes of shape variation reflect both within- and between-organ variations. Hence, there is a need for an efficient modeling approach that can capture the inter-organ relations (i.e., pose variations) of the complex anatomy while simultaneously optimizing the morphological changes of each organ and capturing the population-level statistics. This paper leverages the PSM approach and proposes a new approach for correspondence-point optimization of multiple organs that overcomes these limitations. The central idea of multilevel component analysis, is that the shape statistics consists of two mutually orthogonal subspaces: the within-organ subspace and the between-organ subspace. We formulate the correspondence optimization objective using this generative model. We evaluate the proposed method using synthetic shape data and clinical data for articulated joint structures of the spine, foot and ankle, and hip joint.

Virtual Scoliosis Surgery Using a 3D-Printed Model Based on Biplanar Radiographs.

The aim of this paper is to describe a protocol that simulates the spinal surgery undergone by adolescents with idiopathic scoliosis (AIS) by using a 3D-printed spine model. Patients with AIS underwent pre- and postoperative bi-planar low-dose X-rays from which a numerical 3D model of their spine was generated. The preoperative numerical spine model was subsequently 3D printed to virtually reproduce the spine surgery. Special consideration was given to the printing materials for the 3D-printed elements in order to reflect the radiopaque and mechanical properties of typical bones most accurately. Two patients with AIS were recruited and operated. During the virtual surgery, both pre- and postoperative images of the 3D-printed spine model were acquired. The proposed 3D-printing workflow used to create a realistic 3D-printed spine suitable for virtual surgery appears to be feasible and reliable. This method could be used for virtual-reality scoliosis surgery training incorporating 3D-printed models, and to test surgical instruments and implants.

Combined Beneficial Effect of Voluntary Physical Exercise and Vitamin D Supplementation in Diet-induced Obese C57BL/6J Mice.

PURPOSE: Physical exercise (PE) combined with nutritional approaches has beneficial effects that are widely advocated to improve metabolic health. Here we used voluntary PE together with vitamin D (VD) supplementation, which has already shown beneficial effects in primary and tertiary prevention in obese mice models, to study their combined additive effects on body weight management, glucose homeostasis, metabolic inflammation, and liver steatosis as key markers of metabolic health. METHODS: Ten-week-old male C57BL/6J mice were fed a high-fat/sucrose (HFS) diet for 10 wk, then assigned to a 15-wk intervention period with PE, VD supplementation, or both PE and VD supplementation. Morphological, histological, and molecular phenotype data were characterized. RESULTS: The HFS-induced increases in body mass, adiposity, and adipocyte hypertrophy were improved by PE but not by VD supplementation. The HFS-induced inflammation (highlighted by chemokines mRNA levels) in inguinal adipose tissue was decreased by PE and/or VD supplementation. Furthermore, the intervention combining PE and VD showed additive effects on restoring insulin sensitivity and improving hepatic steatosis, as demonstrated through a normalization of size and number of hepatic lipid droplets and triglyceride content and a significant molecular-level decrease in the expression of genes coding for key enzymes in hepatic de novo lipogenesis. CONCLUSIONS: Taken together, our data show beneficial effects of combining PE and VD supplementation on obesity-associated comorbidities such as insulin resistance and hepatic disease in mice. This combined exercise-nutritional support strategy could prove valuable in obesity management programs.

Evaluation of a Patient-Specific Finite-Element Model to Simulate Conservative Treatment in Adolescent Idiopathic Scoliosis.

STUDY DESIGN: Retrospective validation study. OBJECTIVES: To propose a method to evaluate, from a clinical standpoint, the ability of a finite-element model (FEM) of the trunk to simulate orthotic correction of spinal deformity and to apply it to validate a previously described FEM. SUMMARY OF BACKGROUND DATA: Several FEMs of the scoliotic spine have been described in the literature. These models can prove useful in understanding the mechanisms of scoliosis progression and in optimizing its treatment, but their validation has often been lacking or incomplete. METHODS: Three-dimensional (3D) geometries of 10 patients before and during conservative treatment were reconstructed from biplanar radiographs. The effect of bracing was simulated by modeling displacements induced by the brace pads. Simulated clinical indices (Cobb angle, T1-T12 and T4-T12 kyphosis, L1-L5 lordosis, apical vertebral rotation, torsion, rib hump) and vertebral orientations and positions were compared to those measured in the patients' 3D geometries. RESULTS: Errors in clinical indices were of the same order of magnitude as the uncertainties due to 3D reconstruction; for instance, Cobb angle was simulated with a root mean square error of 5.7°, and rib hump error was 5.6°. Vertebral orientation was simulated with a root mean square error of 4.8° and vertebral position with an error of 2.5 mm. CONCLUSIONS: The methodology proposed here allowed in-depth evaluation of subject-specific simulations, confirming that FEMs of the trunk have the potential to accurately simulate brace action. These promising results provide a basis for ongoing 3D model development, toward the design of more efficient orthoses.

Evaluation of a Three-Dimensional Reconstruction Method of the Rib Cage of Mild Scoliotic Patients.

STUDY DESIGN: Validation study. OBJECTIVE: To evaluate a method of 3-dimensional (3D) reconstruction of the rib cage in a population of scoliotic patients. SUMMARY OF BACKGROUND DATA: Evaluation of the thoracic cage clinical parameters would be helpful in the management of spinal deformities. METHODS: Biplanar X-rays were performed using the EOS system and the rib cage was reconstructed using a previously developed semi-automated method. Thoracic parameters were calculated from the 3D reconstructions: volume, frontal and sagittal diameters, 3D spinal penetration index (SPI), thoracic index, and rib hump. To test accuracy, the authors constructed biplanar projections from 3 computed tomography scans and then used these projected X-rays as material for stereoradiographic reconstructions. The models were then compared with volumetric objects reconstructed from these 3 computed tomography scans. To test intra-observer and interobserver reproducibility, 22 chests (mean Cobb angle, 28° [range, 17° to 45°]) were reconstructed twice by 3 operators. The 95% confidence interval was calculated for the study parameters. RESULTS: The mean signed point to surface distance was -1.6 mm. Interobserver reproducibility was 9 mm for maximum anteroposterior and lateral diameters, <0.8% for SPI, 5° for rib hump, .02 for thoracic index, and 450 cm3 for volume. CONCLUSIONS: The results of the reproducibility study were satisfactory. The 95% confidence interval was <6% for the transverse diameters and <10% for volume and SPI. The reported method of 3D reconstruction of the rib cage provides accurate and reproducible determinations of the investigated thoracic parameters in scoliotic patients.