Trabecular texture analysis of CT images in the relationship with spinal fracture

Sheep model for fracture treatment in osteoporotic bone: a pilot study about different induction regimens

OBJECTIVE

Various regimens to induce osteoporosis in sheep were compared to establish a large animal model for further studies of fracture healing and fracture treatment in severe osteoporosis.

DESIGN

Prospective, randomized animal study (six months' duration).

PARTICIPANTS

Eight sheep (seven to nine years old) were divided into four treatment groups of two animals each.

INTERVENTION

Group 1: Ovariectomy (OVX) + calcium/vitamin D-restricted diet (O + D); Group 2: Ovariectomy + daily injection of steroids (O + S); Group 3: Ovariectomy + daily injection of steroids + calcium/vitamin D-restricted diet (O + D + S); Group 4: Control, untreated.

MAIN OUTCOME MEASUREMENTS

Preoperatively and every 2 months, the bone mineral density (BMD) was determined by quantitative computed tomography (QCT) bilaterally at the distal tibia. Bone structural parameters were determined from iliac crest biopsy specimens using micro-CT. In vitro torsional stiffness of tibia segments was measured.

RESULTS

The control group showed a slight increase in BMD with time. The greatest decrease in BMD was seen in Group 3, with a decrease of 55 percent in cancellous bone and 7 percent in cortical bone. In the iliac crest biopsy specimens, trabecular number decreased 19 percent, trabecular thickness decreased 22 percent, and bone volume fraction decrased 37 percent during the 6 months. The torsional strength and stiffness of the tibia showed a difference of approximately 50 percent between Group 3 and the control group.

CONCLUSIONS

The induction of severe osteoporosis in sheep is best possible by combined treatment with ovariectomy, calcium/vitamin D-restricted diet, and steroids. There is a good relationship between density, structural parameters, and mechanical properties of bone.

Interferon-alpha treatment decreases serum cross-linked C-terminal telopeptide of type I collagen in haematological diseases

Interferon-alpha (IFN-alpha) is used in the treatment of many haematological diseases and it is known that IFN-alpha may affect bone turnover. The effect of IFN-alpha on bone metabolism was studied in 10 haematological patients. The mean duration of the treatment was 4 (range: 2.8-7.2) months. Besides the usual markers of bone metabolism, levels of the cross-linked C-terminal telopeptide of type I collagen (ICTP), the N-terminal propeptide of type I procollagen (PINP) and the bone-specific alkaline phosphatase were measured. The bone mineral density was measured by computed tomography. During IFN-alpha treatment, serum ICTP decreased from a mean of 5.4 (range: 1.8-12.4) to 3.6 (range: 1.4-8.8) microg/l (P = 0.017). All other variables reflecting bone metabolism remained unaltered during IFN-alpha treatment. The bone mineral density remained unchanged. It was concluded that the observed decrease in ICTP may be an indicator of a beneficial therapeutic effect of IFN-alpha on bone turnover, resulting in decreased bone resorption. However, it is possible that elevated pretreatment ICTP values reflected disease of the bone marrow.

Does high-resolution computed tomography image analysis of the distal radius provide information independent of bone mass?

This study aimed to investigate the usefulness of computed tomography (CT) image analysis of the distal radius for comparing two groups of postmenopausal women matched for age and bone mineral density at both the lumbar spine and femoral neck. The first one consisted of 16 women with at least one vertebral fracture and the second consisted also of 16 women without disease affecting bone mass or bone metabolism. Eight slices were selected in each patient: four consecutive coronal slices and four consecutive axial slices. Bone texture analysis was performed using structural methods leading to the measurement of 24 features. Most of the structural variables derived from histomorphometric parameters and were measured after segmentation from a binary or a skeletonized image. Nine variables were significantly different between the two groups on axial slices: valley number, valley surface area, apparent bone volume/tissue volume (BV/TV), apparent trabecular separation, apparent trabecular number, trabecular bone pattern factor, trabecular skeletal length, node count, and node-to-node strut count. Also four variables were significantly different between osteoporotic women and controls on coronal slices: apparent BV/TV, trabecular partition, node-to-node strut count, and terminus-to-terminus strut count. In conclusion this study suggests that bone texture analysis could yield additional data on bone mass for explaining bone strength and therefore could be used for improving the prediction of fracture risk.

In vivo comparison between computed tomography and magnetic resonance image analysis of the distal radius in the assessment of osteoporosis

In a prospective case-control cross-sectional study, we investigated the usefulness of both computed tomography (CT) and magnetic resonance (MR) image analysis of the distal radius for distinguishing a small sample of fractured osteoporotic women from control women regardless of bone mineral density. The study population included 12 subjects who were divided into two groups according to their bone status. The first group consisted of six women with at least one vertebral fracture occurring in the absence of high-energy trauma, and the second group consisted of six women without disease affecting bone mass or bone metabolism. Cross-sectional and coronal slices were obtained from both CT and MR systems. For CT images, the slice thickness was 1000 jim and the plane resolution was approx 200 jim x 200 jim. MR images were obtained from a 1.5-T imager with a two-dimensional spin-echo Ti-weighted sequence leading to a slice thickness of 2000 jim and a plane resolution of 195 jim x 195 jim. Bone texture analysis was performed using fractal and structural methods leading to the measurement of 23 features. Most of the structural variables derived from histomorphometric parameters and were measured after segmentation from a binary or a skeletonized image. Bone densitometry was measured by dual-energy X-ray absorptiometry both at the lumbar spine and the nondominant femoral neck. On cross-sectional slices, 12 variables, mainly obtained from structural analysis, were significantly different between the two groups for CT images (p < 0.05) against two variables only for MR images (p < 0.05). The number of variables statistically different between the two groups was significantly higher for CT images compared with MR images (p = 0.003). In the same way, odds ratios for fracture per 1 control group standard deviation decrease were significant for 10 variables on CT images, whereas, in contrast, none of the variables measured on MRI images led to significant odds ratios. The results obtained for the two methods on coronal slices were poorer without a difference between either CT or MR images in terms of discrimination between fracture and nonfracture subjects. In conclusion, this study suggests that bone texture analysis obtained from CT compared with MRI offers a best discrimination between controls and osteoporotic patients, probably the result to the spatial resolution. which is better for CT than for MR images.

Alterations of the trabecular pattern of the jaws in patients with osteoporosis

OBJECTIVE

The purpose of this study was to determine whether the morphologic features of the trabecular bones of the maxilla and mandible differ between patients with osteoporosis and normal controls.

STUDY DESIGN

Periapical radiographs, obtained from dentists of 11 patients with osteoporosis and 12 control subjects, were digitized at 600 dpi. A custom computer program measured morphologic features of the trabecular architecture. The mean values for each feature were determined for the osteoporotic and control groups and compared by anatomic site.

RESULTS

Twenty-four morphologic features of the trabeculae and marrow regions were examined in each anatomical site. A principal components analysis summarized these predictors to four. The Hotelling T (2) test found that patients with osteoporosis had significantly altered morphologic pattern in the anterior maxilla (P =.019) and the posterior mandible (P =.013) in comparison with the controls. A classification tree analysis separated all subjects into 2 groups with 92% accuracy.

CONCLUSIONS

The data support the hypothesis that patients with osteoporosis have an altered trabecular pattern in the jaws in comparison with normal subjects.

Computerized analysis of gray-value profiles in spongy and cortical bone. Clinical experience

RATIONALE AND OBJECTIVES

Osteoporosis is characterized by a loss of bone mineral density and deterioration of structure. The authors present a structural parameter for the quantitative assessment of osteoporotic changes in vertebral bone.

METHODS

In 40 patients without or with known osteoporotic fractures, spongiosa and cortical bone mineral density was measured in lumbar vertebrae 1 to 3 by quantitative CT. Additional axial high-resolution CT slices were obtained for the structural analysis. In the spongiosa, the gray-value profile along a horizontal line in the CT slice was used, whereas in the cortical shell a profile was obtained from the cortical ridge. Both profiles were intersected with a horizontal line of variable position, and the maximum number of intersections was determined.

RESULTS

The maximum number of intersections is significantly higher in cases with fractures (spongiosa 48.6, cortical shell 77.3) than in cases without fractures (spongiosa 42.1, cortical shell 62.4). It also correlates with bone mineral density and age.

CONCLUSIONS

The presented method shows significantly different numeric results for patients with and without osteoporotic fractures. The analysis is easy to perform and provides additional information on the bone structure that may be used in combination with bone mineral density measurements.

Slice simulation from a model of the parenchymous vascularization to evaluate texture features: work in progress

RATIONALE AND OBJECTIVES

To demonstrate the usefulness of a model of the parenchymous vascularization to evaluate texture analysis methods.

METHODS

Slices with thickness varying from 1 to 4 mm were reformatted from a 3D vascular model corresponding to either normal tissue perfusion or local hypervascularization. Parameters of statistical methods were measured on 16128x128 regions of interest, and mean values and standard deviation were calculated. For each parameter, the performances (discrimination power and stability) were evaluated.

RESULTS

Among 11 calculated statistical parameters, three (homogeneity, entropy, mean of gradients) were found to have a good discriminating power to differentiate normal perfusion from hypervascularization, but only the gradient mean was found to have a good stability with respect to the thickness. Five parameters (run percentage, run length distribution, long run emphasis, contrast, and gray level distribution) were found to have intermediate results. In the remaining three, curtosis and correlation was found to have little discrimination power, skewness none.

CONCLUSION

This 3D vascular model, which allows the generation of various examples of vascular textures, is a powerful tool to assess the performance of texture analysis methods. This improves our knowledge of the methods and should contribute to their a priori choice when designing clinical studies.

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.

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.

Instrumental diagnosis of osteoporosis

Considerable progress in the development of methods for assessing the skeleton now makes it possible to detect osteoporosis non-invasively and early. There is a variety of techniques available at present: single-photon (SPA) and single X-ray absorptiometry (SXA), dual-photon (DPA) and dual X-ray absorptiometry (DXA), quantitative computed tomography (QCT), radiographic absorptiometry (RA), and quantitative ultrasound (QUS), and their development has certainly been driven by the need to overcome the inherent shortcomings of plain radiography for this purpose. Both SPA and SXA methods make a quantitative assessment of the bone mineral content (BMC) or density (BMD) at peripheral sites of the skeleton possible. Single energy measurements are not possible at sites with variable soft tissue thickness and composition, i.e., the axial skeleton. For these purposes, DPA and DXA techniques were introduced. The main advantages of an X-ray system over a radionuclide system are shortened examination time, greater accuracy and precision limited to higher resolution, and removal of errors due to source decay correction. Low radiation dose, availability, capacity to evaluate multiple sites, and ease of use have made DXA the most widely used technique for measuring bone mineral density. QCT can determine the true volumetric density of trabecular or cortical bone in three dimensions at any skeletal site. Recently developed new computer-assisted methods have improved RA precision, thus providing a simple and inexpensive technique for screening of bone mineral status of large populations. QUS was reported to provide information regarding the structural characteristics of bone, which may be relevant to the appearance of osteoporotic fractures; indeed, some studies suggest a relationship between QUS and bone strength beyond that which can be explained by BMD. Recent experimental studies suggested that magnetic resonance might also constitute a promising tool for assessing osteoporosis.

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.

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.

Bone density determination

Bone mineral density determination is an integral part of the diagnosis, therapeutic planning, and monitoring of a patient with osteoporosis. Although the utility of measuring bone density seems intuitive, decisions must be made regarding whom to test, when to test, which technique to use, and which body site to evaluate. Once a determination has been made, consideration has to be given to what to do with the results. Each patient must be individually considered, incorporating genetic, nutritional, lifestyle, pharmacologic, and endocrine risk factors. Other diseases that may be associated with a reduced bone mass must be excluded.

Evaluation of the cortical structure in high resolution CT images of lumbar vertebrae by analysing low bone mineral density clusters and cortical profiles

The structural classification of trabecular bone is of considerable clinical importance for the diagnosis of osteoporosis. Assessment of the cortical bone mineral density (BMD) and analysis of cortical structure is necessary because the cortex is also affected by osteoporosis. We describe a method for the automatic classification of the cortex from its structure on high resolution (HR) CT images. The method is based on the distribution of areas with low BMD in the cortex. Two different approaches are presented; one uses the grey scale profile of the cortical ridge, and the other one evaluates the distribution of connected regions (clusters) of low BMD. i.e. areas that lie below a certain threshold value. In HRCT images from 22 lumbar vertebrae, the number of intersections of the cortical intensity profile with a horizontal line was determined at various positions of this threshold line. At a certain position, there was a local maximum in the number of intersections which was 38% higher in the osteoporotic cases. The maximum shows a moderate correlation with the cortical BMD of rni = -0.72 (p < 0.0001). The number nc of connected regions (clusters) with pixel values below a certain threshold value was determined in relation to the threshold value T. The resulting function nc(T) shows a relative maximum slightly below the average grey scale value of the respective image. The curve depends on the degree of osteoporosis: the height of the maximum (i.e. the maximal number of clusters ncmax) allows distinction to be made between different degrees of osteoporosis, and ncmax shows a correlation with the cortical BMD of rnc = -0.84 (p < 0.0001).

Correlation of trabecular bone structure with age, bone mineral density, and osteoporotic status: in vivo studies in the distal radius using high resolution magnetic resonance imaging

High resolution magnetic resonance (MR) images of the distal radius were obtained at 1.5 Tesla in premenopausal normal, postmenopausal normal, and postmenopausal osteoporotic women. The image resolution was 156 microm in plane and 700 microm in the slice direction; the total imaging time was approximately 16 minutes. An intensity-based thresholding technique was used to segment the images into trabecular bone and marrow, respectively. Extensions of standard stereological techniques were used to derive measures of trabecular bone structure from these segmented images. The parameters calculated included apparent measures of trabecular bone volume fraction, trabecular thickness, trabecular spacing, and trabecular number. Fractal-based texture parameters, such as the box-counting dimension, were also derived. Trabecular bone mineral density (BMD) and cortical bone mineral content (BMC) were measured in the distal radius using peripheral quantitative computed tomography (pQCT). In a subset of patients, spinal trabecular BMD was measured using quantitative computed tomography (QCT). Correlations between the indices of trabecular bone structure measured from these high-resolution MR images, age, BMD, and osteoporotic fracture status were examined. Cortical BMC and trabecular BMD at the distal radius, spinal BMD, trabecular bone volume fraction, trabecular thickness, trabecular number, and fractal dimension all decreased with age. Trabecular spacing showed the greatest percentage change and increased with age. In addition, significant differences were evident in spinal BMD, radial trabecular BMD, trabecular bone volume fraction, trabecular spacing, and trabecular number between the postmenopausal nonfracture and the postmenopausal osteoporotic subjects. Trabecular spacing and trabecular number showed moderate correlation with radial trabecular BMD but correlated poorly with radial cortical BMC. High resolution MR imaging, a potentially useful tool for quantifying trabecular structure in vivo, may have applications for understanding and evaluating skeletal changes related to age and osteoporosis.

Usefulness of panoramic radiography in the diagnosis of postmenopausal osteoporosis in women. Width and morphology of inferior cortex of the mandible

OBJECTIVES

To evaluate the usefulness of width and morphology of the inferior cortex of the mandible on panoramic radiographs in the diagnosis of postmenopausal osteoporosis.

METHODS

The width and morphology of the mandibular inferior cortex on panoramic radiographs were compared with trabecular bone mineral density (TBMD) of the 3rd lumbar vertebrae (L3) measured by dual energy quantitative computed tomography in 29 premenopausal and 95 postmenopausal women.

RESULTS

There was a significant negative correlation between the width (Kendall's tau = -0.36, p < 0.001) and morphology (Kendall's tau = -0.49, p < 0.001) of the mandibular inferior cortex and the L3 TBMD. Regression analysis showed that significant linear relationships were observed between the L3 TBMD and age (p < 0.001), cortical width (p < 0.05), morphology (p < 0.05), controlling body mass index, number of teeth present and menopausal status (R2 = 0.42).

CONCLUSION

Our results suggest that panoramic radiography could be reliable in screening for osteoporosis.

Advances in the noninvasive assessment of bone density, quality, and structure

Recent advances in the development of methods to assess the skeleton noninvasively have contributed to screening for risk of osteoporosis, early detection of the disease, and effective monitoring of its progression and response to therapy. The capability now exists to evaluate the peripheral, central, or entire skeleton as well as the trabecular bone or cortical bone envelopes accurately and precisely, with the capacity to determine bone strength and predict fracture risk. In this article we examine the current and future capabilities of quantitative computed tomography (QCT), quantitative ultrasound (QUS), and magnetic resonance microscopy (muMR) to assess architectural and densitometric properties of the skeleton to enhance the prediction of fracture risk.