Volumetric DXA (VXA): A new method to extract 3D information from multiple in vivo DXA images

Abstract

Three-dimensional geometric and structural measurements of the proximal femur are of considerable interest in understanding the strength of the femur and its susceptibility to fracture. Quantitative computed tomography (QCT) with a small voxel size ( 1 mm per side) is the current ''gold standard'' to examine the macrostructure of the femur, but it has a high effective radiation dose (approximately 2 to 5 mSv) and cost. Volumetric dual-energy X-ray absorptiometry (VXA) uses a commercially available DXA system (Hologic Discovery A) to reconstruct the proximal femur from four DXA scans delivering an effective radiation dose of 0.04 mSv. VXA was compared with QCT (voxel size of 0.29 Â 0.29 Â 1 mm) in 41 elderly women (age 82 AE 2.4 years) at slices located at the femoral neck and trochanteric regions of interest. For parameters of shape, the femoral neck axis length (FNAL) and the cross-sectional slice area (SA), accuracy and strong linear correlations (r ¼ 0.84 to 0.98) were demonstrated. Similar correlations (r ¼ 0.81 to 0.97) were observed for the density parameters, the cross-sectional bone area (CSA) and volumetric bone mineral density (vBMD). VXA also demonstrated strong correlations (r ¼ 0.76 to 0.99) for the engineering parameters of the minimum, maximum, and polar cross-sectional moments of inertia (CSMIs) and the section modulus (Z). We conclude that VXA is capable of generating a variety of 3D geometric and structural measurements that are highly correlated with QCT in elderly subjects in vivo. Moreover, the VXA measurements can be made with a commercially available DXA device at a very low radiation dose. ß

Differences in structural geometrical outcomes at the neck of the proximal femur using two-dimensional DXA-derived projection (APEX) and three-dimensional QCT-derived (BIT QCT) techniques

“…This was achieved by using the results of a three-dimensional reconstruction of the hip using four DXA images. By using an iterative technique, the 3D DXA image was co-registered to the 3D QCT image [12]. This allowed selection of a QCT plane that closely replicated the routine DXA plane.…”

Calcium intake and bone mineral density as an example of non-linearity and threshold analysis

“…In addition, BMD at different femoral sites show similar associations with fracture risk, further justifying the restriction to one site in the present work [40]. Only areal measurements of bone mineral density were available for the present study, and future studies should preferably employ volumetric assessments less prone to distortions by bone volume and body size [1]. Other limitations are the crosssectional design and the assessment of calcium intake by 24-h recall, though the reliability of the data source used has been demonstrated time and again [2].…”

2D-3D regularized deformable b-spline registration: Application to the proximal femur

“…The reported techniques for 2D-3D registration can be split into two main categories [1]: feature-based methods [3] and intensity-based methods [2,4,5]. The methods belonging to the former category typically require an implicit or explicit image segmentation which is error-prone and hard to achieve automatically.…”

“…While intensity-based rigid 2D-3D registration is regarded as a solved problem [1], intensity-based non-rigid registration is still an active research field [2,4,5].Most of these solutions require construction of shape-intensity statistical models.…”

“…The applications of 2D-3D registration of a set of 2D C-arm images with a 3D volumetric intensity data are pervasive, ranging from patients pose determination in image-guided interventions [1] to estimation of 3D bone mineral density (BMD) distribution in orthopaedic biomechanics [2]. The reported techniques for 2D-3D registration can be split into two main categories [1]: feature-based methods [3] and intensity-based methods [2,4,5].…”