Biomedical subjects

D Newitt

Publications and source records attributed to D Newitt.

24 records · Page 2Linked to original sources

PubMed1998

In vivo high resolution MRI of the calcaneus: differences in trabecular structure in osteoporosis patients.

The purpose of this study was to use high resolution (HR) magnetic resonance (MR) images of the calcaneus to investigate the trabecular structure of patients with and without osteoporotic hip fractures and to compare these techniques with bone mineral density (BMD) in differentiating fracture and nonfracture patients. Axial and sagittal HR MR images of the calcaneus were obtained in 50 female (23 postmenopausal patients with osteoporotic hip fractures and 27 postmenopausal controls). A three-dimensional gradient-echo sequence was used with a slice thickness of 500 micron and in plane resolution of 195 x 195 micron. Texture analysis was performed using morphological features, analogous to standard histomorphometry and fractal dimension. Additionally, BMd measurements of the hip (dual-energy X-ray absorptiometry) were obtained in all patients. Significant differences between both patient groups were obtained using morphological parameters and fractal dimension as well as hip BMD (p < 0.05). Odds ratios for the texture parameters apparent (app.) bone volume/total volume and app. trabecular separation were higher than for hip BMD. Receiver operator characteristic values of texture measures and hip BMD were comparable. In conclusion, trabecular structure measures derived from HR MR images of the calcaneus can differentiate between postmenopausal women with and without osteoporotic hip fractures.

Absorptiometry, Photon↗

PubMed1997

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.

Adult↗

PubMed1996

Magnetic resonance imaging of trabecular bone structure in the distal radius: relationship with X-ray tomographic microscopy and biomechanics.

The contribution of trabecular bone structure to bone strength is of considerable interest in the study of osteoporosis and other disorders characterized by changes in the skeletal system. Magnetic resonance (MR) imaging of trabecular bone has emerged as a promising technique for assessing trabecular bone structure. In this in vitro study we compare the measures of trabecular structure obtained using MR imaging and higher-resolution X-ray tomographic microscopy (XTM) imaging of cubes from human distal radii. The XTM image resolution is similar to that obtained from histomorphometric sections (18 microns isotropic), while the MR images are obtained at a resolution comparable to that achievable in vivo (156 x 156 x 300 microns). Standard histomorphometric measures, such as trabecular bone area fraction (synonymous with BV/TV), trabecular width, trabecular spacing and trabecular number, texture-related measures and three-dimensional connectivity (first Betti number/volume) of the trabecular network have been derived from these images. The variation in these parameters as a function of resolution, and the relationship between the structural parameters, bone mineral density and the elastic modulus are also examined. In MR images, because the resolution is comparable to the trabecular dimensions, partial volume effects occur, which complicate the segmentation of the image into bone and marrow phases. Using a standardized thresholding criterion for all images we find that there is an overestimation of trabecular bone area fraction (approximately 3 times), trabecular width (approximately 3 times), fractal dimension (approximately 1.4 times) and first Betti number/ volume (approximately 10 times), and an underestimation of trabecular spacing (approximately 1.6 times) in the MR images compared with the 18-microns XTM images. However, even for a factor of 9 difference in spatial resolution, the differences in the morphological trabecular structure measures ranged from a factor of 1.4 to 3.0. We have found that trabecular width, area fraction, number, fractal dimension and Betti number/volume measured from the XTM and MR images increases, while trabecular spacing decreases, as the bone mineral density and elastic modulus increase. A preliminary bivariate analysis showed that in addition to bone mineral density alone, the Betti number, trabecular number and spacing contributed to the prediction of the elastic modulus. This preliminary study indicates that measures of trabecular bone structure using MR imaging may play a role in the study of osteoporosis.

Absorptiometry, Photon↗

PubMed1996

Distal radius: in vivo assessment with quantitative MR imaging, peripheral quantitative CT, and dual X-ray absorptiometry.

PURPOSE: To evaluate in vivo the relationship between magnetic resonance (MR) imaging relaxation time and bone mineral density (BMD) at the distal radius. MATERIALS AND METHODS: The 1/T2* MR imaging relaxation rates and dual X-ray absorptiometry (DXA) measurements were evaluated in the trabecular bone of the distal 5 cm of the radius in 14 healthy premenopausal women and 11 healthy postmenopausal women and in 11 women with osteoporosis. Trabecular and total BMD were measured with peripheral quantitative computed tomography (CT). RESULTS: In healthy women, 1/T2* values and trabecular BMD at peripheral quantitative CT were significantly correlated but 1/T2* and total BMD were not. Statistically significant (P = .03) correlations between 1/T2* and DXA were found only in the most distal area covered with DXA. The 1/T2* values were more closely correlated with age and showed higher relative annual decreases (0.47%-0.81%) than peripheral quantitative CT (0.20%-0.59%) or DXA (0.10%-0.39%). Pre- and postmenopausal healthy subjects could be distinguished only with MR imaging, and postmenopausal healthy and osteoporotic subjects only with CT and DXA. CONCLUSION: MR imaging relaxation rates correlate well with trabecular BMD in vivo.

Absorptiometry, Photon↗

PubMed1995

Evaluation of technical factors affecting the quantification of trabecular bone structure using magnetic resonance imaging.

High resolution magnetic resonance (MR) techniques combined with standard techniques of stereology and texture analysis have been used to quantify trabecular structure. Using dried excised specimens from the tibia (n = 10) and radius (n = 2) we evaluate the impact of using volumetric gradient-echo (GE) and spin-echo (SE) MR imaging sequences, the relative importance of echo time in gradient-echo MR imaging, and the impact of different threshold values to segment the bone and bone marrow on the estimation of trabecular bone structure. We also investigate the inter-relationships between the different structural parameters derived from MR images. Images were obtained using fast gradient-echo and spin-echo imaging sequences, with TE values ranging from 7 to 17 ms using 4.7 and 1.5 Tesla imaging systems. In-plane image resolution ranged from 128 to 156 microns, and slice thickness ranged from 128 to 1000 microns. We derived stereological measures such as the mean intercept length, trabecular width, fractional area of trabecular bone, trabecular number, and trabecular spacing, the fractal dimension as a texture-related parameter and the Euler number as a measure of connectivity from these images. We found that the mean intercept length as a function of angle traced an ellipse with the orientation of the principal axis of the ellipse, a measure of trabecular orientation, identical when measured from the spin-echo or gradient-echo MR images. Absolute measures such as the fractional area, trabecular width, trabecular number, and fractal dimension as measured from gradient echo images were 28%, 30%, 1.3%, and 0.6% greater, respectively, than those calculated from spin-echo images, while the trabecular spacing was 14% less when calculated from gradient-echo images compared to spin-echo images. The structural parameters also depended on the echo time used to obtain the MR image. The choice of the threshold used to segment the high resolution images also affected the estimated structural parameters significantly. Our results indicate that MR may be used to visualize and quantify trabecular bone architecture; however, the different technical factors that could affect the appearance of MR images must be understood and considered in the data analysis and interpretation.

Absorptiometry, Photon↗

PubMedDate not supplied

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.

Adult↗