Osteoporosis is a disease characterized by bone volume loss and architectural deterioration. The majority of work aimed at evaluating the structural implications of the disease has been performed based on stereologic analysis of histomorphometric sections. Only recently noninvasive imaging methods have emerged that provide sufficient resolution to resolve individual trabeculae. In this article, we apply digital topological analysis (DTA) to magnetic resonance microimages (-MRI) of the radius obtained at 137 ؋ 137 ؋ 350 m 3 voxel size in a cohort of 79 women of widely varying bone mineral density (BMD) and vertebral deformity status. DTA is a new method that allows unambiguous determination of the three-dimensional (3D) topology of each voxel in a trabecular bone network. The analysis involves generation of a bone volume fraction map, which is subjected to subvoxel processing to alleviate partial volume blurring, followed by thresholding and skeletonization. The skeletonized images contain only surfaces, profiles, curves, and their mutual junctions as the remnants of trabecular plates and rods after skeletonization. DTA parameters were compared with integral BMD in the lumbar spine and femur as well as MR-derived bone volume fraction (BV/TV). Vertebral deformities were determined based on sagittal MRIs of the spine with a semiautomatic method and the number of deformities counted after threshold setting. DTA structural indices were found the strongest discriminators of subjects with deformities from those without deformities. Subjects with deformities (n ؍ 29) had lower topological surface (SURF) density (p < 0.0005) and surface-to-curve ratio (SCR; a measure of the ratio of platelike to rodlike trabeculae; p < 0.0005) than those without. Profile interior (PI) density, a measure of intact trabecular rods, was also lower in the deformity group (p < 0.0001). These data provide the first in vivo evidence for the structural implications inherent in postmenopausal osteoporosis accompanying bone loss, that is, the conversion of trabecular plates to rods and disruption of rods due to repeated osteoclastic resorption. (J Bone Miner Res 2001;16:1520 -1531)
ABSTRACT:We evaluated the effect of testosterone treatment on trabecular architecture by µMRI in 10 untreated severely hypogonadal men. After 2 years, µMRI parameters of trabecular connectivity improved significantly, suggesting the possibility that testosterone improves trabecular architecture.Introduction: Osteoporosis, characterized by low BMD and diminished bone quality, is a significant public health problem in men. Hypogonadal men have decreased BMD and deteriorated trabecular architecture compared with eugonadal men, and testosterone treatment improves their BMD. We tested the hypothesis that testosterone replacement in hypogonadal men would also improve their trabecular architecture. Materials and Methods: We selected 10 untreated severely hypogonadal men and treated them with a testosterone gel for 24 months to maintain their serum testosterone concentrations within the normal range. Each subject was assessed before and after 6, 12, and 24 months of testosterone treatment by magnetic resonance microimaging (MRI) of the distal tibia and by DXA of the spine and hip. The MRI parameters reflect the integrity of the trabecular network and include the ratio of all surface voxels (representing plates) to curve voxels (representing rods) and the topological erosion index, a ratio of topological parameters expected to increase on trabecular deterioration to those expected to decrease. The higher the surface-to-curve ratio and the lower the topological erosion index, the more intact the trabecular network. Results: Serum testosterone concentrations increased to midnormal after 3 months of treatment and remained normal thereafter. After 24 months of testosterone treatment, BMD of the spine increased 7.4% (p < 0.001), and of the total hip increased 3.8% (p ס 0.008). Architectural parameters assessed by MRI also changed: the surface-to-curve ratio increased 11% (p ס 0.004) and the topological erosion index decreased 7.5% (p ס 0.004). Conclusions: These results suggest the possibility that testosterone replacement of hypogonadal men improves trabecular architecture.
Cancellous bone consists of a network of bony struts and plates that provide mechanical strength to much of the skeleton at minimum weight. It has been shown that loss in bone mass is accompanied by architectural changes that relate to both scale and topology of the network. In this paper, the concept of three‐dimensional (3D) digital topology is presented for characterizing the local topology of each bone voxel after skeletonization of the binary bone images. This method allows us to identify each voxel as belonging to a surface, curve, or junction structure in the trabecular bone network. The method has been quantitatively validated on synthetic images demonstrating its relative immunity to partial volume blurring and noise. Parameters introduced to characterize network topology include surface‐to‐curve ratio and erosion index. Finally, the technique is shown to quantify the architecture of human trabecular bone in magnetic resonance micro‐images acquired from cadavers and in vivo.© 2000 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 11, 81–90, 2000
Bone strength depends on trabecular architecture, characterized by interconnected plates and rods. In osteoporosis, the plates become fenestrated, resulting in more rods that deteriorate and become disconnected. In men, hypogonadism is a common cause of osteoporosis. To determine whether male hypogonadism affects trabecular architecture, we selected 10 men with severe, untreated hypogonadism, and for each hypogonadal man, we selected a eugonadal man matched for race and age. Trabecular architecture in the distal tibia was assessed by magnetic resonance microimaging. Two composite topological indices were determined: the ratio of surface voxels (representing plates) to curve voxels (representing rods), which is higher when architecture is more intact; and the erosion index, a ratio of parameters expected to increase upon architectural deterioration to those expected to decrease, which is higher when deterioration is greater. The surface/curve ratio was 36% lower (P = 0.004), and the erosion index was 36% higher (P = 0.003) in the hypogonadal men than in the eugonadal men. In contrast, bone mineral density of the spine and hip were not significantly different between the two groups. We conclude that male hypogonadism is associated with marked deterioration of trabecular architecture and to a greater degree than bone densitometry of the spine and hip suggests.
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