ABSTRACT:Introduction: Estrogen depletion after menopause is accompanied by bone loss and architectural deterioration of trabecular bone. The hypothesis underlying this work is that the MRI-based virtual bone biopsy can capture the temporal changes of scale and topology of the trabecular network and that estrogen supplementation preserves the integrity of the trabecular network. Materials and Methods: Subjects studied were early postmenopausal women, 45-55 yr of age (N ס 65), of whom 32 were on estrogen (estradiol group), and the remainder were not (control group). Early menopause was defined by amenorrhea for 6-24 mo and elevated serum follicle-stimulating hormone (FSH) concentration. The subjects were evaluated with three imaging modalities at baseline and 12 and 24 mo to determine the temporal changes in trabecular and cortical architecture and density. MRI of the distal radius and tibia was performed at 137 × 137 × 410-m 3 voxel size. The resulting bone volume fraction maps were Fourier interpolated to a final voxel size of 45.7 × 45.7 × 136.7 m 3 , binarized, skeletonized, and subjected to 3D digital topological analysis (DTA). Skeletonization converts trabecular rods to curves and plates to surfaces. Parameters quantifying scale included BV/TV, whereas DTA parameters included the volume densities of curves (C) and surface (S)-type voxels, as well as composite parameters: the surface/curve ratio (S/C), and erosion index (EI, ratio of the sum of parameters expected to increase with osteoclastic resorption divided by the sum of those expected to decrease). For comparison, pQCT of the same peripheral locations was conducted, and trabecular density and cortical structural parameters were measured. Areal BMD of the lumbar vertebrae and hip was also measured. Results: Substantial changes in trabecular architecture of the distal tibia, in particular as they relate to topology of the network, were detected after 12 mo in the control group. S/C decreased 5.6% (p < 0.0005), and EI increased 7.1% (p < 0.0005). Most curve-and profile-type voxels (representative of trabecular struts), increased significantly (p < 0.001). Curve and profile edges resulting from disconnection of rod-like trabeculae increased by 9.8% and 5.1% (p ס 0.0001 and <0.001, respectively). Similarly, DXA BMD in the spine and hip decreased 2.6% and 1.3% (p < 0.0001 and <0.005, respectively), and pQCT cortical area decreased 3.6% (p ס 0.0001). However, neither trabecular density nor BV/TV changed. Furthermore, none of the parameters measured in the estradiol group were significantly different after 12 mo. Substantial differences in the mean changes from baseline between the estradiol treatment and control groups, in particular after 24 mo, were observed, with relative group differences as large as 13% (S/C, p ס 0.005), and the relative changes in the two groups had the opposite sign for most parameters. The observed temporal alterations in architecture are consistent with remodeling changes that involve gradual conversion of plate-like to rod-...
In postmenopausal women with a wide range of vertebral deformities, MRI-based structural measures of topology and scale at the distal radius are shown to account for as much as 30% of vertebral deformity, independent of integral vertebral BMD.Introduction: Trabecular bone architecture has been postulated to contribute to overall bone strength independent of vertebral BMD measured by DXA. However, there has thus far been only sparse in vivo evidence to support this hypothesis. Materials and Methods: Postmenopausal women, 60-80 yr of age, were screened by DXA, and those with T-scores at either the hip or spine falling within the range of −2.5 ± 1.0 were studied with the MRI-based virtual bone biopsy, along with heel broadband ultrasound absorption and pQCT of the tibia. The data from 98 subjects meeting the enrollment criteria were subjected to MRI at the distal tibia and radius, and measures of topology and scale of the trabecular bone network were computed. A spinal deformity index (SDI) was obtained from morphometric measurements in midline sagittal MR images of the thoracic and lumbar spine to evaluate associations between structure and deformity burden. Results: A number of structural indices obtained at the distal radius were correlated with the SDI. Among these were the topological surface density (a measure of trabecular plates) and trabecular bone volume fraction, which were inversely correlated with SDI (p < 0.0001). Combinations of two structural parameters accounted for up to 30% of the variation in SDI (p < 0.0001) independent of spinal BMD, which was not significantly correlated. pQCT trabecular BMD was also weakly associated, whereas broadband ultrasound absorption was not. No significant association between SDI and structural indices were found at the tibia. Conclusions: Structural measures at the distal radius obtained in vivo by MRI explained a significant portion of the variation in total spinal deformity burden in postmenopausal women independent of areal BMD.
Abstract-Geographic routing is an attractive option for large scale wireless sensor networks (WSNs) because of its low overhead and energy expenditure, but is inefficient in realistic localization conditions. Positioning systems are inevitably imprecise because of inexact range measurements and location errors lead to poor performance of geographic routing in terms of packet delivery ratio (PDR) and energy efficiency. This paper proposes a novel, low-complexity, error-resilient geographic routing method, named conditioned mean square error ratio (CMSER) routing, intended to efficiently make use of existing network information and to successfully route packets when localization is inaccurate. Next hop selection is based on the largest distance to destination (minimizing the number of forwarding hops) and on the smallest estimated error figure associated with the measured neighbor coordinates. It is found that CMSER outperforms other basic greedy forwarding techniques employed by algorithms such as most forward within range (MFR), maximum expectation progress (MEP) and least expected distance (LED). Simulation results show that the throughput for CMSER is higher than for other methods, additionally it also reduces the energy wasted on lost packets by keeping their routing paths short.
Objective-High-resolution MRI methods have been used to evaluate carotid artery atherosclerotic plaque content. The purpose of this study was to assess the performance of high-resolution MRI in evaluation of the quantity and pattern of mineral deposition in carotid endarterectomy (CEA) specimens, with quantitative micro-CT as the gold standard. Methods and Results-High-resolution MRI and CT were compared in 20 CEA specimens. Linear regression comparing mineral volumes generated from CT (V CT ) and MRI (V MRI ) data demonstrated good correlation using simple thresholding (V MRI ϭϪ0.01ϩ0.98V CT ; R 2 ϭ0.90; thresholdϭ4ϫnoise) and k-means clustering methods (V MRI ϭϪ0.005ϩ1.38V CT ; R 2 ϭ0.93). Bone mineral density (BMD) and bone mineral content (BMC [mineral mass]) were calculated for CT data and BMC verified with ash weight. Patterns of mineralization like particles, granules, and sheets were more clearly depicted on CT. Conclusions-Mineral volumes generated from MRI or CT data were highly correlated. CT provided a more detailed depiction of mineralization patterns and provided BMD and BMC in addition to mineral volume. Key Words: magnetic resonance imaging Ⅲ computed tomography Ⅲ carotid arteries Ⅲ calcium A significant fraction of all ischemic strokes is caused by carotid atherosclerosis. Degree of stenosis is a major risk factor, but factors unrelated to the extent of vascular constriction play a role in causing neurological symptoms, including the morphology and composition of the atherosclerotic plaque. 1,2 Components of plaque associated with symptoms ("vulnerable plaque") include surface ulceration, thinning of fibrous cap, presence of hemorrhage, lipid core, and inflammation and neovascularity. [3][4][5][6] Dystrophic calcification (mineralization) and even lamellar bone have been described in carotid plaques. 7,8 There is evidence for an association between plaque lipid and dystrophic mineralization. 9 Using confocal microscopy, Sarig et al 10 found that cholesterol or associated lipids may act as a nucleus for hydroxyapatite crystal formation. It is unclear to what extent carotid plaque calcification affects the risk of embolic stroke. Certain patterns of calcification may help grade lesions and provide an indicator of stability. 11 The potential role of MRI for noninvasive assessment of plaque morphology and lesion burden quantification has been addressed in several investigations ex vivo and in vivo. [12][13][14][15][16][17][18][19][20][21][22][23][24] The appearance of plaque calcification has been described as uniformly dark in signal intensity on all MRI sequences. 18,25,26 However, there are other components of atherosclerotic plaque that may show decreased signal intensity on some or all pulse sequences; for example, solid cholesterol hydrate may be present and plaque lipids may exhibit T2 shortening secondary to liquid crystal behavior, depending on the lipid composition and cholesterol content. 20,27 Induced magnetic field inhomogeneities caused by differences in diamagnetic susceptibility betw...
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