USING TEMPORAL TRENDS OF 3D BONE MICRO-ARCHITECTURE TO PREDICT BONE QUALITY

Abstract

In vivo measurements of trabecular bone architecture provide insight into the process of bone remodeling for quantification of important components of bone quality, including morphology and mechanical integrity. In longitudinal studies, three-dimensional (3D) bone images are acquired at sequential time points essentially resulting in four-dimensional (4D) data for an individual. Based on the 4D data, we propose to calculate temporal trends and project these trends to estimate future bone architecture. The method consists of calculating deformation fields between subsequent time points utilizing Demons deformable image registration. Multiple consecutive deformation fields were extrapolated on a voxel-by-voxel basis, and five different extrapolation strategies were tested. Test data were from in vivo μCT scans of the proximal tibia of Wistar rats that were either ovariectomized (OVX; N=5) or sham operated (SHAM; N=6), and measurements were performed at baseline, 4, 8 and 12 weeks. The first three measurements for each animal were the basis to predict the 12 week data, and validation included a qualitative (3D rendering) and quantitative (geometry, morphology and micro-FE) comparison with actual 12 week data (see Fig. 1). The results demonstrated that the temporal trends could be used to predict 3D bone structure, and indicated a voxel-based linear extrapolation scheme yielded mean geometric errors that were smaller than the voxel size of 15μm. Key morphological parameters that were estimated included bone volume ratio (BV/TV; mean error 0.4%, maximum error 9%), trabecular thickness (Tb.Th; -1.1%, 11%), connectivity density (Conn.D; 9.0%, 18.5%) and the apparent Young's modulus (E1; 6.0%, 32%). These data demonstrated a promising and novel approach for quantitatively capturing in vivo bone dynamics at the local trabecular level. The method does not require an a priori understanding of the diseases state, and can provide information about the trends of the bone remodeling process that may be used for better monitoring and treatment of diseases such as osteoporosis.