High-resolution computed tomography for clinical imaging of bone microarchitecture

Abstract

Background: The role of bone structure, one component of bone quality, has emerged as a contributor to bone strength. The application of high-resolution imaging in evaluating bone structure has evolved from an in vitro technology for small specimens to an emerging clinical research tool for in vivo studies in humans. However, many technical and practical challenges remain to translate these techniques into established clinical outcomes.

Questions/purposes: We reviewed use of high-resolution CT for evaluating trabecular microarchitecture and cortical ultrastructure of bone specimens ex vivo, extension of these techniques to in vivo human imaging studies, and recent studies involving application of high-resolution CT to characterize bone structure in the context of skeletal disease.

Methods: We performed the literature review using PubMed and Google Scholar. Keywords included CT, MDCT, micro-CT, high-resolution peripheral CT, bone microarchitecture, and bone quality.

Results: Specimens can be imaged by micro-CT at a resolution starting at 1 μm, but in vivo human imaging is restricted to a voxel size of 82 μm (with actual spatial resolution of ~ 130 μm) due to technical limitations and radiation dose considerations. Presently, this mode is limited to peripheral skeletal regions, such as the wrist and tibia. In contrast, multidetector CT can assess the central skeleton but incurs a higher radiation burden on the subject and provides lower resolution (200-500 μm).

Conclusions: CT currently provides quantitative measures of bone structure and may be used for estimating bone strength mathematically. The techniques may provide clinically relevant information by enhancing our understanding of fracture risk and establishing the efficacy of antifracture for osteoporosis and other bone metabolic disorders.

Fig. 1A–B

Three-dimensional micro-CT images (16-μm isotropic voxel size) show (A) the spatial distribution of thickness and (B) the spatial distribution of the diameters of the intertrabecular marrow space in two specimens of human trabecular bone calculated by the direct three-dimensional distance transformation method of Hildebrand and Ruegsegger [65].

Fig. 2

A micro-CT image shows the distribution of stresses in a human vertebral trabecular bone specimen under a simulated 1% compressive strain by micro-FEA. Red areas correspond to the locations of highest stress and blue to the areas of low stress. FEA = finite element analysis.

Fig. 3A–D

In vivo MDCT images of the vertebral body show three-dimensional reconstructions (A) pre- and (B) postteriparatide therapy for 6 months, (C) 12 months, and (D) 24 months. Images provided by and printed with permission of Claus C. Glüer, Medizinische Physik, Klinik für Diagnostische Radiologie, Universitätsklinikum Schleswig Holstein–Campus Kiel, Kiel, Germany. MDCT = multidetector CT.

Fig. 4A–B

Scout acquisition is used to define the HR-pQCT scan region for (A) the distal radius and (B) the distal tibia. The solid green region corresponds to the imaging location and consists of 110 slices spanning 9.02 mm longitudinally. In the radius the scan region is fixed 9.5 mm proximal from the midjoint line, while in the tibia the scan region is 22.5 mm proximal from the tibial plafond. HR-pQCT = high-resolution peripheral quantitative CT.

Fig. 5A–D

(A, B) Cross-sectional HR-pQCT images through the distal radius show two individuals with identical areal BMD by DXA at the ultradistal radius but substantial differences in trabecular and cortical structure. (C, D) Three-dimensional renderings of the cortical and trabecular bone compartments and intracortical porosity (highlighted in red) were segmented using software described by Burghardt et al. [19]. HR-pQCT = high-resolution peripheral quantitative CT; BMD = bone mineral density; DXA = dual-energy xray absorptiometry.