Peter Saparin

Structural Adaptation of Trabecular Bone Revealed by Position Resolved Analysis of Proximal Femora of Different Primates

The anisotropic arrangement of trabeculae in the proximal femur of humans and primates is seen as striking evidence for the functional adaptation of trabecular bone architecture. Quantitative evidence to demonstrate this adaptation for trabecular bone is still scarce, because experimental design of controlled load change is difficult. In this work, we use the natural variation of loading caused by a different main locomotor behavior of primates. Using high‐resolution computed tomography and advanced image analysis techniques, we analyze the heterogeneity of the architecture in four proximal femora of four primate species. Although the small sample number does not allow an interspecies comparison, the very differently loaded bones are well suited to search for common structural features as a result of adaptation. A cubic volume of interest of size (5 mm)3 was moved through the proximal femur and a morphometric analysis including local anisotropy was performed on 209 positions on average. The correlation of bone volume fraction (BV/TV) with trabecular number (Tb.N) and trabecular thickness (Tb.Th) leads to the suggestion of two different mechanisms of trabecular bone adaptation. Higher values of BV/TV in highly loaded regions of the proximal femur are due to a thickening of the trabeculae, whereas Tb.N does not change. In less loaded regions, however, lower values of BV/TV are found, caused by a reduction of the number of the trabeculae, whereas Tb.Th remains constant. This reduction in Tb.N goes along with an increase in the degree of anisotropy, indicating an adaptive selection of trabeculae. Anat Rec, 2010.

Segmentation of bone CT images and assessment of bone structure using measures of complexity

A nondestructive and noninvasive method for numeric characterization (quantification) of the structural composition of human bone tissue has been developed and tested. In order to quantify and to compare the structural composition of bones from 2D computed tomography (CT) images acquired at different skeletal locations, a series of robust, versatile, and adjustable image segmentation and structure assessment algorithms were developed. The segmentation technique facilitates separation from cortical bone and standardizes the region of interest. The segmented images were symbol-encoded and different aspects of the bone structural composition were quantified using six different measures of complexity. These structural examinations were performed on CT images of bone specimens obtained at the distal radius, humeral mid-diaphysis, vertebral body, femoral head, femoral neck, proximal tibia, and calcaneus. In addition, the ability of the noninvasive and nondestructive measures of complexity to quantify trabecular bone structure was verified by comparing them to conventional static histomorphometry performed on human fourth lumbar vertebral bodies. Strong correlations were established between the measures of complexity and the histomorphometric parameters except for measures expressing trabecular thickness. Furthermore, the ability of the measures of complexity to predict vertebral bone strength was investigated by comparing the outcome of the complexity analysis of the CT images with the results of a biomechanical compression test of the third lumbar vertebral bodies from the same population as used for histomorphometry. A multiple regression analysis using the proposed measures including structure complexity index, structure disorder index, trabecular network index, index of a global ensemble, maximal L-block, and entropy of x-ray attenuation distribution revealed an excellent relationship (r=0.959, r2=0.92) between the measures of complexity and compressive bone strength. In conclusion, the image segmentation techniques and the assessment of bone architecture by measures of complexity have been successfully applied to analyze high-resolution peripheral quantitative computed tomography (pQCT) and CT images obtained from the distal radius, humeral mid-diaphysis, third and fourth lumbar vertebral bodies, proximal femur, proximal tibia, and calcaneus. The proposed approach is of broad interest as it can be applied for the quantification of structures and textures originating from different imaging modalities in other fields of science.

Bone architecture assessment with measures of complexity.

Architectural changes in trabecular bone by osteoporosis were utilized as a model for the changes which probably occur in human bone while exposed to microgravity conditions. Although there are many concerns about microgravity-induced bone loss, little is known about the impact of microgravity on the three-dimensional architecture of the skeleton. 50 (level L3) and 57 (level L4) vertebral bones harvested from human cadavers were investigated by computed tomography (CT) and quantified in terms of bone mineral density (BMD). Based on the symbol-encoded transformed CT-images, five measures of complexity were developed which quantify the structural composition of the trabecular bone. This quantification determines the bone architecture as a whole. Depending on the specific measure of complexity and its relation to BMD, a 5-10% change of BMD is related to a 5-90% change in structural composition. The method requires a non-invasive CT-procedure of the lumbar spine resulting in a radiation exposure of about 30 microSv effective dose. The technique is useful for the evaluation of the bone status of space-flying, personnel as well as for patients on ground. Grant numbers: BMH1-CT92-0296.

QUANTIFYING CHANGES IN THE SPATIAL STRUCTURE OF TRABECULAR BONE

We apply recently introduced measures of complexity for the structural quantification of distal tibial bone. For the first time, we are able to investigate the temporal structural alteration of trabecular bone. Based on four patients, we show how the bone may alter due to temporal immobilization.

Bones And Nonlinear Dynamics — The Quantification Of Architecture

In order to quantify the internal architecture of a bone in a holistic manner based on radiological images, the methodology of nonlinear dynamics was applied. Image processing algorithms, an expansion of symbolic dynamics, and five measures of complexity were introduced to quantify the trabecular part of human lumbar vertebral bodies. Healthy vertebral bones have a complex and ordered architecture with a high degree of spatiodynamics. Pathology changes the architecture significantly and can be quantified by measures of complexity.

The complexity of bone architecture: A tool to differentiate bone diseases

We introduce a generalization of symbolic dynamics to analyze two-dimensional objects and propose measures of complexity to quantify the structure of symbol encoded images. This technique is applied to evaluate the architecture of human cancellous bone by analyzing computed tomography images of vertebrae acquired from specimens and in vivo. The pixels of the preprocessed images are encoded using a mixture of static and dynamic encoding. The architecture of encoded cancellous bone is evaluated as a whole using measures of complexity. A set of new parameters are introduced to quantify the different aspects of structure: complexity and degree of disorder of the architecture as a whole, or spatial arrangements of hard or soft elements of the bone separately. It is found that the complexity of the bone structure relates to its density exponentially. Normal bone has a complex ordered structure, while the architecture during the initial stage of bone loss is characterized by lower complexity and a maximal level ...