Quantitative computed tomography (QCT) of the forearm using general purpose spiral whole-body CT scanners: accuracy, precision and comparison with dual-energy X-ray absorptiometry (DXA).

BACKGROUND: Dual-energy X-ray absorptiometry (DXA) allows clinically relevant measurement of bone mineral density (BMD) at central and appendicular skeletal sites, but DXA has a limited ability to assess bone geometry and cannot distinguish between the cortical and trabecular bone compartments. Quantitative computed tomography (QCT) can supplement DXA by enabling geometric and compartmental bone assessments. Whole-body spiral CT scanners are widely available and require only seconds per scan, in contrast to peripheral QCT scanners, which have restricted availability, limited spatial resolution, and require several minutes of scanning time. This study evaluated the accuracy and precision of whole-body spiral CT scanners for quantitatively assessing the distal radius, a common site of non-vertebral osteoporosis-related fractures, and compared the CT-measured densitometric values with those obtained from dual-energy-X-ray absorptiometry. SUBJECTS AND METHODS: A total of 161 postmenopausal women with baseline lumbar spine BMD T-scores between -1.0 and -2.5 underwent left forearm QCT using whole-body spiral CT scanners twice, 1 month apart. QCT volumes of interest were defined and analyzed at 3 specific radial regions: the ultradistal region by using slices at 8, 9, and 10 mm proximal to the ulnar styloid tip; the distal region by a slice 20 mm proximal; and the middle region by a slice 40 mm proximal. BMD, bone mineral content (BMC), volume, and average cortical thickness and circumference were measured. We evaluated QCT accuracy and precision and also report correlations between QCT and DXA for BMD and BMC. RESULTS: Overall accuracy and precision errors for BMD, BMC and volume were consistent with known skeletal QCT technology precision and were generally less than 3%. BMD and BMC assessed by QCT and DXA were correlated (r=0.55 to 0.80). DISCUSSION: Whole-body spiral CT scanners allow densitometric evaluations of the distal radius with good accuracy and very good precision. This original and convenient method provides a tool to further investigate cortical and trabecular bone variables in the peripheral skeleton in osteoporotic patients. These assessments, coupled with evaluation of the effects on cortical and trabecular bone measured in response to therapies for osteoporosis, may advance our understanding of the contributors to non-vertebral fracture occurrence.

Characterization of the integrity of three-dimensional trabecular bone microstructure by connectivity and shape analysis using high-resolution magnetic resonance imaging in vivo.

Bone mineral density and bone structure are the main determinants of bone strength in osteoporosis. In this study we used high-resolution magnetic resonance imaging to visualize the bone microstructure in the finger phalanges in vivo and to assess the topological three-dimensional connectivity of the trabecular network and the shape of the trabeculae as measures of bone quality. We visualized the phalanges of young and elderly healthy volunteers in vivo with a spatial resolution of 152 microm x 152 microm x 280 microm. Image processing software to quantify three measures of connectedness was developed and tested: connectivity, global connectivity density, and local connectivity density. Global three-dimensional connectivity ranged from 904 to 1,607 connections. Global connectivity density ranged from 2.9 to 4.7 connections per mm with large intersubject differences. We found a decrease of local connectivity density with growing distance from the joint ranging from 5.1 to 0.2 connections per mm. These preliminary results represent a quantitative description of the well-known rarefication of the trabecular network when moving from epiphysis to the diaphysis. Three-dimensional visualization showed a dense network consisting mostly of rod-like trabeculae at the epiphysis changing to a less dense network of a few plate-like structures near the medullary canal. An algorithm for the quantitative classification of trabecular architecture with regard to plate or rod-like shape was tested for feasibility. We conclude that in vivo assessment of three-dimensional properties of the trabecular network is possible in human phalanges. Determination of connectivity and shape will allow quantification of structural aspects of osteoporotic changes and may improve assessment of fracture risk.