Xiaolong Ouyang

A Comparative Study of Trabecular Bone Properties in the Spine and Femur Using High Resolution MRI and CT

The purpose of this study was to use high resolution (HR) magnetic resonance (MR) and computed tomography (CT) images combined with texture analysis to investigate the trabecular structure of human vertebral and femoral specimens and to compare these techniques with bone mineral density (BMD) in the prediction of bone strength. Twenty‐nine bone cubes were harvested from 12 proximal femur cadaver specimens and 29 from 8 spines. HR MR and CT images were obtained, and texture analysis techniques were used to assess trabecular structure. Additionally, BMD, elastic modulus (EM), and maximum compressive strength were determined. R2 for EM versus texture measures computed in the MR images was higher (R2 = 0.27–0.64, p < 0.01) in the spine than in the femur specimens (R2 = 0.12–0.22, p < 0.05). R2 values were similar in the CT images. R2 for EM versus BMD was 0.66 (p < 0.01) in the spine and 0.61 (p < 0.01) in the femur specimens. In the MR images, texture measures combined with BMD in a multivariate‐regression model significantly increased R2, while improvement was less significant in the CT images. Thus, texture analysis may provide additional information needed to analyze bone strength and quality.

Fractal analysis of radiographs: Assessment of trabecular bone structure and prediction of elastic modulus and strength

The purpose of this study was to determine whether fractal dimension of radiographs provide measures of trabecular bone structure which correlate with bone mineral density (BMD) and bone biomechanics, and whether these relationships depend on the technique used to calculate the fractal dimension. Eighty seven cubic specimen of human trabecular bone were obtained from the vertebrae and femur. The cubes were radiographed along all three orientations--superior-inferior (SI), medial-lateral (ML), and anterior-posterior (AP), digitized, corrected for background variations, and fractal based techniques were applied to quantify trabecular structure. Three different techniques namely, semivariance, surface area, and power spectral methods were used. The specimens were tested in compression along three orientations and the Youngs modulus (YM) was determined. Compressive strength was measured along the SI direction. Quantitative computed tomography was used to measure trabecular BMD. High-resolution magnetic-resonance images were used to obtain three-dimensional measures of trabecular architecture such as the apparent bone volume fraction, trabecular thickness, spacing, and number. The measures of trabecular structure computed in the different directions showed significant differences (p<0.05). The correlation between BMD, YM, strength, and the fractal dimension were direction and technique dependent. The trends of variation of the fractal dimension with BMD and biomechanical properties also depended on the technique and the range of resolutions over which the data was analyzed. The fractal dimension showed varying trends with bone mineral density changes, and these trends also depended on the range of frequencies over which the fractal dimension was measured. For example, using the power spectral method the fractal dimension increased with BMD when computed over a lower range of spatial frequencies and decreased for higher ranges. However, for the surface area technique the fractal dimension increased with increasing BMD. Fractal measures showed better correlation with trabecular spacing and number, compared to trabecular thickness. In a multivariate regression model inclusion of some of the fractal measures in addition to BMD improved the prediction of strength and elastic modulus. Thus, fractal based texture analysis of radiographs are technique dependent, but may be used to quantify trabecular structure and have a potentially valuable impact in the study of osteoporosis.

Trabecular Bone Mineral and Calculated Structure of Human Bone Specimens Scanned by Peripheral Quantitative Computed Tomography: Relation to Biomechanical Properties

The relationship of cortical bone mineral density (BMD), and geometry to bone strength has been well documented. In this study, we used peripheral quantitative computerized tomography (pQCT) to acquire trabecular BMD and high‐resolution images of trabeculae from specimens to determine their relationship with biomechanical properties. Fifty‐eight human cubic trabecular bone specimens, including 26 from the vertebral bodies, were scanned in water and air. Trabecular structure was quantitated using software developed with Advanced Visual Systems interfaced on a Sun/Sparc Workstation. BMD was also obtained using a whole‐body computerized tomography scanner (QCT). Nondestructive testing of the specimens was performed to assess their elastic modulus. QCT and pQCT measurements of BMD of specimens in water were strongly correlated (r2 = 0.95, p < 0.0001), with a slope (0.96) statistically not significantly different from 1. Strong correlations were found between pQCT measurements of specimens in water and in air, for BMD (r2 = 0.96, p < 0.0001), and for apparent trabecular structural parameters (r2 = 0.89–0.93, p < 0.0001). Correlations were moderate between BMD and apparent trabecular structural parameters (r2 = 0.37–0.64, p < 0.0001). Precision as coefficient of variation (CV) and standardized coefficient of variation (SCV) for these measurements was < 5%. For the vertebral specimens, the correlation was higher between elastic modulus and BMD (r2 = 0.76, p < 0.0001) than between elastic modulus and apparent trabecular structural parameters (r2 = 0.58–0.72, p < 0.0001), while the addition of apparent trabecular nodes and branches to BMD in a multivariate regression model significantly increased the correlation with the elastic modulus (r2 = 0.86, p < 0.01). Thus, pQCT can comparably and reproducibly measure trabecular bone mineral in water or air, and trabecular structure can be quantitated from pQCT images. The combination of volumetric BMD with trabecular structural parameters rather than either alone improves the prediction of biomechanical properties. Such a noninvasive approach may be useful for the preclinical study of osteoporosis.

Noninvasive Assessment of Bone Density and Structure Using Computed Tomography and Magnetic Resonance

For several reasons, including low cost and radiation dose, simplicity, and the ability to image several skeletal sites, dual X-ray absoptiometry (DXA) is the most widely employed technique for diagnostic and serial assessment of integral bone mass in osteoporosis and other metabolic bone diseases. However, three-dimensional imaging modalities such as quantitative computed tomography (QCT) and magnetic resonance (MR) imaging offer the ability to separately examine different factors that may play independent and important roles in osteoporosis. These factors include the density of the trabecular and cortical compartments as well as the pattern of trabecular microarchitecture. New developments in QCT include volumetric approaches for precise compartmental assessment of the spine and proximal femur as well as thin-slice tomography of the vertebral body for assessment of trabecular texture. In addition, ultrahigh resolution CT scanners (spatial resolution ë50-150(i)i) have been developed for imaging of trabecular structure in specimens and in some cases for the peripheral skeleton (distal radius and phalanges). High resolution MR measurements may be employed for assessment of the trabecular texture at a range of peripheral sites, including the calcaneus, distal radius, and phalanges.

High resolution magnetic resonance imaging of the calcaneus: age-related changes in trabecular structure and comparison with dual X-ray absorptiometry measurements

Abstract. A high-resolution magnetic resonance imaging (MRI) protocol, together with specialized image processing techniques, was applied to the quantitative measurement of age-related changes in calcaneal trabecular structure. The reproducibility of the technique was assessed and the annual rates of change for several trabecular structure parameters were measured. The MR-derived trabecular parameters were compared with calcaneal bone mineral density (BMD), measured by dual X-ray absorptiometry (DXA) in the same subjects. Sagittal MR images were acquired at 1.5 T in 23 healthy women (mean age: 49.3 ± 16.6 [SD]), using a three-dimensional gradient echo sequence. Image analysis procedures included internal gray-scale calibration, bone and marrow segmentation, and run-length methods. Three trabecular structure parameters, apparent bone volume (ABV/TV), intercept thickness (I.Th), and intercept separation (I.Sp) were calculated from the MR images. The short- and long-term precision errors (mean %CV) of these measured parameters were in the ranges 1–2% and 3–6%, respectively. Linear regression of the trabecular structure parameters vs. age showed significant correlation: ABV/TV (r2= 33.7%, P < 0.0037), I.Th (r2= 26.6%, P < 0.0118), I.Sp (r2= 28.9%, P < 0.0081). These trends with age were also expressed as annual rates of change: ABV/TV (− 0.52%/year), I.Th (−0.33%/year), and I.Sp (0.59%/year). Linear regression analysis also showed significant correlation between the MR-derived trabecular structure parameters and calcaneal BMD values. Although a larger group of subjects is needed to better define the age-related changes in trabecular structure parameters and their relation to BMD, these preliminary results demonstrate that high-resolution MRI may potentially be useful for the quantitative assessment of trabecular structure.

Assessment of Trabecular Structure Using High Resolution Ct Images and Texture Analysis

PURPOSE Our goal was to use high resolution (HR) CT images combined with texture analysis to investigate the trabecular structure of human vertebral specimens and to compare these techniques with bone mineral density (BMD) in the prediction of bone strength. METHOD HR CT images with a slice thickness of 1 mm were obtained of 28 bone cubes. Four different groups of texture analysis techniques were used to assess these images. In addition, quantitative CT (QCT) was performed and elastic modulus (EM) was determined biomechanically. RESULTS R2 between EM and BMD was 0.78 (p < 0.01). R2 values for EM versus most of the texture measures were also significant. Texture measures in addition to measures of BMD in a multivariate regression model significantly increased R2 up to 0.87. CONCLUSION In an experimental setting, texture parameters calculated using HR CT images correlated significantly with EM. Combining texture measures with BMD improved the prediction of EM significantly.

Morphometric texture analysis of spinal trabecular bone structure assessed using orthogonal radiographic projections

The measurement of bone microstructure as well as bone mineral density may improve the estimation of bone strength. Cubic specimens (N = 26, 12 mm X 12 mm X 12 mm) of human cadaver vertebrae were cut along three orthogonal anatomic orientations, i.e., superior-inferior (SI), medial-lateral (ML), and anterior-posterior (AP). Contact radiographs of the bone cubes along all three orientations were obtained and then digitized by a laser scanner with pixel size of 50 microns x 50 microns. The specimens were tested in compression along the 3 orthogonal orientations and the Youngs modulus (YM) was calculated for each direction. Quantitative computed tomography (QCT) was used to obtain a measure of trabecular bone mineral density (BMD). Global gray level thresholding and local thresholding algorithms were used to extract the trabecular bone network. Apparent trabecular bone fraction (ABV/TV), mean intercept length (I.TH), mean intercept separation (I.SP), and number of nodes (N.ND) were measured from the extracted trabecular network. Fractal dimension (Fr.D) of the trabecular bone texture was also measured. Paired t-tests showed that the mean values of each texture parameter (except ABV/TV) and of YM along the SI direction were significantly different (p < 0.05) from those along the ML and AP direction. However, the mean values along the ML and AP directions were not significantly different. Multivariate regression of YM as a function of the texture parameters and BMD showed that without adjusting for the effect of BMD, YM was significantly explained by all the texture parameters (R2 = 0.2-0.6). When BMD was included in the regression, although the variations in YM of ML, AP, and SI orientations could be explained by BMD alone, some of the texture parameters did improve the overall prediction of the biomechanical properties, while, some parameters such as ABV/TV and Fr.D in the ML orientation showed a more significant overall effect in explaining mechanical strength than did BMD. In conclusion, trabecular texture parameters correlated significantly with BMD and YM. Trabecular texture parameters from projectional radiographs reflect the anisotropy of trabecular structure. Quantitative radiographic assessment of trabecular structure using fine-detail radiography can potentially improve the estimation of bone strength.

Texture analysis of direct magnification radiographs of vertebral specimens: Correlation with bone mineral density and biomechanical properties

RATIONALE AND OBJECTIVES The authors used direct magnification radiographs, combines with texture analysis, to investigate the trabecular structure of human vertebral specimens and compared these techniques with measurement of bone mineral density (BMD) by using quantitative computed tomography to predict bone strength. METHODS Direct magnification radiographs and BMD measurements were obtained from 38 motion segments from the thoracolumbar spines of 11 female human cadavers. Maximum compressive strength (MCS) was determined with a materials testing machine. Morphologic parameters, digital skeletons, and fractal dimension were obtained from the radiographs in three different regions of interest. RESULTS Correlations between BMD and MCS were statistically significant (r = .81, P < .01). With morphologic parameters, correlation coefficients of up to .64 (P < .01) were obtained. Use of multivariate regression analysis with one morphologic parameter (the width of the black pixels, or thicknessB) in addition to BMD improved correlations versus MCS (P < .01). CONCLUSION In an experimental setting, BMD showed statistically significant correlation with bone strength, whereas the structural parameters demonstrated only modest correlations. BMD together with one of these measures (thicknessB), however, showed the highest correlation.

A New Trabecular Region of Interest for Femoral Dual X‐Ray Absorptiometry: Short‐Term Precision, Age‐Related Bone Loss, and Fracture Discrimination Compared with Current Femoral Regions of Interest

We defined a new region of interest (ROI) for femoral Wards triangle, centered on the femoral neck axis including comparatively trabecular‐rich bone. Forty‐seven premenopausal, 39 healthy postmenopausal, and 35 osteoporotic postmenopausal women with vertebral fractures were evaluated comparing the new with the standard femoral ROIs, using a Hologic QDR‐2000. Additionally, spinal dual X‐ray absorptiometry (DXA) was performed. The short‐term precision error of the new ROI expressed as the root mean square of the coefficient of variations was 1.34% for premenopausal women, 1.69% for healthy postmenopausal women, and 2.46% for osteoporotic postmenopausal women. Bone mineral density (BMD) values of the new ROI correlated highly with those of the standard femoral ROIs (r = 0.91 − 0.96) and the spinal BMD (r = 0.74). Age‐related bone loss of the new ROI was 0.75% per year (r = 0.66) in healthy women, which was approximately 1.5 times higher than the bone loss of the standard femoral ROIs, except for Wards triangle. Regarding the intergroup discrimination, the t‐value of the new ROI was similar to the t‐value of Wards triangle, and the intergroup percent decrements in BMD of the new ROI approximated those of Wards triangle. For discriminating women with vertebral fractures, the new ROI demonstrated odds ratios of 1.6 similar to most ROIs but lower than that of the trochanteric region. The new, substantially trabecular ROI appears to be an alternative to the Wards ROI traditionally used in femoral DXA having improved short‐term precision and comparable sensitivity.

Structural Analysis of High Resolution In Vitro MR Images Compared to Stained Grindings

The recent advancement of high resolution magnetic resonance imaging has opened up new avenues for the determination of structural characteristics of the trabecular network, which may significantly improve the diagnosis of osteoporosis. An analysis of the calcaneus in healthy women has shown similar age-related changes when comparing structural parameters in high resolution MR images and BMD as measured by DXA [1]. Here we undertook an in vitro study to further compare structural measurements in MR images with those from stained grindings. A 3D gradient echo sequence on a 1.5 T scanner was used to obtain four contiguous sagittal MR images with a slice thickness of 1 mm and an in plane pixel size of 195 microns. Twenty-one stained grindings with a slice thickness of 1 micron each were obtained from a 3 mm thick slab of the same volume investigated by MR. The stack of stained grindings was also used to simulate the influence of variations in slice thickness and in plane resolution. Results for structural parameters derived from the high resolution MR images differed considerably from those derived from the stained grindings because the MR images are heavily influenced by partial volume artifacts. This finding was supported by simulations which also revealed that even at a slice thickness of 500 microns and an in plane pixel size of 13 microns, accurate results could not be obtained when a histomorphometric type analysis was applied. Results also depended strongly on the segmentation method. However, contrary to the stained grindings, images averaged over several slices reveal the three-dimensional network character of the trabecular structure. New efforts should be undertaken to develop analysis strategies that are more adequate for in vivo high resolution images instead of using analysis techniques applied in classical histomorphometry.