Purpose: Accurate quantification of bone microstructure plays a significant role in understanding bone mechanics and response to disease or treatment. High‐resolution peripheral quantitative computed tomography (HR‐pQCT) allows for the quantification of trabecular and cortical structurein vivo, with the capability of generating images at multiple voxel sizes (41, 82, and 123 μm). The aim of this study was to characterize the effect of voxel size on structural measures of trabecular and cortical bone and to determine accuracy in reference to micro‐CT (µCT), the gold standard for bone microstructure quantification. Methods: Seventeen radii from human cadaver specimens were imaged at each HR‐pQCT voxel size and subsequently imaged using µCT. Bone density and microstructural assessment was performed in both the trabecular and cortical compartments, including cortical porosity quantification. Two distinct analysis techniques were applied to the 41 μm HR‐pQCT data: the standard clinical indirect analysis and a direct analysis requiring no density or structural model assumptions. Analysis parameters were adjusted to enable segmentation and structure extraction at each voxel size. Results: For trabecular microstructural measures, the 41 μm HR‐pQCT data displayed the strongest correlations and smallest errors compared to µCT data. The direct analysis technique applied to the 41 μm data yielded an additional improvement in accuracy, especially for measures of trabecular thickness. The 123 μm data performed poorly, with all microstructural measures either having moderate or nonsignificant correlations with µCT data. Trabecular densitometric measures showed strong correlations to µCT data across all voxel sizes. Cortical thickness was strongly correlated with µCT values across all HR‐pQCT voxel sizes. The accuracy of cortical porosity parameters was highly dependent on voxel size; again, the 41 μm data was most strongly correlated. Measures of cortical density and pore diameter at all HR‐pQCT voxel sizes had either weak or nonsignificant correlations. Conclusions: This study demonstrates the effect of voxel size on the accuracy of HR‐pQCT measurements of trabecular and cortical microstructure and presents parameters for HR‐pQCT analysis at nonstandard resolutions. For all parameters measured, correlations were strongest at 41 μm. Weak correlations for porosity measures indicate that a better understanding of pore structure and resolution dependence is needed.

Numerous clinical cohorts are exposed to reduced skeletal loading and associated bone loss, including surgical patients, stroke and spinal cord injury victims, and women on bed rest during pregnancy. In this context, understanding disuse-related bone loss is critical to developing interventions to prevent fractures and the associated morbidity, mortality, and cost to the health care system. The aim of this pilot study was to use high-resolution peripheral QCT (HR-pQCT) to examine changes in trabecular and cortical microstructure and biomechanics during a period of non weight bearing (WB) and during recovery following return to normal WB. Surgical patients requiring a 6-week non-WB period (n = 12, 34.8 ± 7.7 yrs) were scanned at the affected and contralateral tibia prior to surgery, after the 6-week non-WB period, and 6 and 13 weeks after returning to full-WB. At the affected ultradistal tibia, integral vBMD (including both trabecular and cortical compartments) decreased with respect to baseline (−1.2%), trabecular number increased (+5.6%), while trabecular thickness (−5.4%), separation (−4.6%), and heterogeneity (−7.2%) decreased (all p<0.05). Six weeks after return to full-WB, trabecular structure measures reverted to baseline levels. In contrast, integral vBMD continued to decrease after 6 (−2.0%, p < 0.05) and 13 weeks (−2.5%, p = 0.07) of full-WB. At the affected distal site, the disuse period resulted in increased porosity (+16.1%, p < 0.005), which remained elevated after 6 weeks (+16.8%, p < 0.01) and after 13 weeks (+16.2%, p < 0.05). A novel topological analysis applied to the distal tibia cortex demonstrated increased number of canals with surface topology (“slabs” +21.7%, p < 0.01) and curve topology (“tubes” +15.0%, p < 0.05) as well as increased number of canal junctions (+21.4%, p < 0.05) following the disuse period. Porosity increased uniformly through increases in both pore size and number. Finite element analysis at the ultradistal tibia showed decreased stiffness and failure load (−2.8% and −2.4%, p < 0.01) following non-WB. These biomechanical predictions remained depressed following 6 and 13 weeks of full-WB. Finite element analysis at the distal site followed similar trends. Our results suggest that detectable microstructural and biomechanical degradation occurs – particularly within the cortical compartment – as a result of non-WB and persists following return to normal loading. A better understanding of these microstructural changes and their short- and long-term influence on biomechanics may have clinical relevance in the context of disuse-related fracture prevention.

Purpose:The investigation of cortical porosity is an important aspect of understanding biological, pathoetiological, and biomechanical processes occurring within the skeleton. With the emergence of HR-pQCT as a noninvasive tool suitable for clinical use, cortical porosity at appendicular sites can be directly visualized in vivo. The aim of this study was to introduce a novel topological analysis of the cortical pore network for HR-pQCT data and determine the influence of resolution on measures of cortical pore network microstructure and topology. Methods: Cadaveric radii were scanned using HR-pQCT at two different voxel sizes (41 and 82 μm) and also using μCT at a voxel size of 18 μm. HR-pQCT and μCT image sets were spatially coregistered. Segmentation and quantification of cortical porosity (Ct.Po) and mean pore diameter (Ct.Po.Dm) were achieved using an established extended cortical analysis technique. Topological classification of individual pores was performed using topology-preserving skeletonization and multicolor dilation algorithms. Based on the pore skeleton topological classification, the following parameters were quantified: total number of planar surface-skeleton canals (N.Slabs), tubular curve-skeleton canals (N.Tubes), and junction elements (N.Junctions), mean slab volume (Slab.Vol), mean tube volume (Tube.Vol), mean slab orientation (Slab.θ ), mean tube orientation (Tube.θ ), N.Slabs/N.Tubes, and integral (total) slab volume/integral tube volume (iSlab.Vol/iTube.Vol). An in vivo reproducibility study was also conducted to assess short-term precision of the topology parameters. Precision error was characterized using root mean square coefficient of variation (RMSCV%). , though proportional bias was evident in these correlations. Weak correlations were seen for iSlab.Vol/iTube.Vol at both voxel sizes (41: r 2 = 0.52, p < 0.01; 82: r 2 = 0.39, p < 0.05). Slab.Vol was significantly correlated to μCT data at 41 μm (r 2 = 0.60, p < 0.01) but not at 82 μm, while Tube.Vol was significantly correlated at both voxel sizes (41: r 2 = 0.79, p < 0.001; 82: r 2 = 0.68, p < 0.01). In vivo precision error for these parameters ranged from 2.31 to 9.68 RMSCV%. Conclusions: Strong correlations between μCT-and HR-pQCT-derived measurements were found, particularly in HR-pQCT images obtained at 41 μm. These data are in agreement with our previous study investigating the effect of voxel size on standard HR-pQCT metrics of trabecular and cortical microstructure, and extend our previous findings to include topological descriptors of the cortical pore network.

No abstract

Although the tibia can serve as the location for relatively common benign and malignant bone tumors, there are several more uncommon entities that occur almost exclusively in the tibia. For example, rare lesions such as adamantinoma, osteofibrous dysplasia, and chondromyxoid fibroma are seen predominantly in the tibia with infrequent involvement of other bones in the appendicular skeleton. This article reviews the imaging features of common and uncommon tibial tumors and provides a framework for formulating a differential diagnosis based on imaging and patient characteristics.

The abdomen and pelvis contain a complex network of systemic and portomesenteric veins. Disease processes (including occlusion or narrowing of these vessels) may create pathologic changes that may be compensated by collateral venous formation or alterations in physiology. This article reviews the imaging features of a variety of venous conditions within the abdomen and pelvis.