Biomedical subjects

Zbisław Tabor

Publications and source records attributed to Zbisław Tabor.

9 recordsLinked to original sources

PubMed2006

Quantifying anisotropy of trabecular bone from gray-level images.

In this study, a gray-level image-based approach to quantifying structural anisotropy is described. The secant modulus was estimated for thirty L(3) vertebral bodies using nondestructive testing. The vertebral bodies were imaged with a clinical CT scanner. QCT measurements of BMD were also performed for trabecular regions. Structural anisotropy in trabecular regions was quantified from binarized images using the mean intercept length (MIL) method and from gray-level images using the gray-level structure tensor (GST) method. BMD alone explained 28% of the variation of the secant modulus. Multivariable regression models combining BMD and measures of anisotropy, as proposed by the relations formulated by Cowin, revealed significant improvement in the prediction of the secant modulus. Combining a principal value of the fabric tensor, as computed by either MIL or GST methods, with BMD resulted in increased correlation with the secant modulus. The highest correlation (R(2)=0.81) was achieved with a combination of BMD and the third principal value of the GST. Adding a term proportional to the minimal cross-sectional area of the vertebral body explained 86% of the variation of the secant modulus.

Adult↗

PubMed2006

Quantifying deterioration of bone tissue from grey-level images.

Quantification of the severity of the deterioration in bone tissue is an important diagnostic problem involving the assessment of connectedness of the tissue from its grey-level images. In this study a fuzzy parameter was introduced for quantifying the severity of discontinuities of network-like structures. For each two pixels of an analyzed image, the fuzzy parameter was derived from the grey-level intensity along the brightest path connecting them. The performance of this parameter was tested on images of continuous and discontinuous samples of vertebral trabecular bone, matched for mean gray-level intensity. It was shown that the values of the parameter were significantly different (P-value<10(-6)) in both groups and equal to 0.02+/-0.11 and 0.46+/-0.22 for discontinuous and continuous samples, respectively. The decrease in the fuzzy parameter could be interpreted as the result of either an increasing gap size in discontinuous structures or a decreasing thickness of structure elements in continuous structures. A possible application of the method for use in quantifying severity of discontinuities within the vertebral cortical rim was described.

Adult↗

PubMed2006

Optimal response function in networks of excitatory elements.

In this paper the problem of signal propagation in networks of excitatory elements is studied. It is found that the geometry of signal transmission paths depends crucially on how an excitatory element responds to a stimulus. Two types of responses are defined: fast and slow. In the slow response case the signal transmission paths are in the same universality class as optimal paths in the limit of strong disorder. The signal transmission paths formed in the fast response case constitute possibly a new universality class.

Action Potentials↗

PubMed2006

Optimal cut of trabecular network.

It has been shown recently that failure of mechanically tested trabecular bone samples can be localized within a part of the volume of the samples. Bone volume fraction BV/TV of failure regions was found to be a better determinant of the mechanical competence of the specimens and was smaller than BV/TV of the whole samples. These results suggest that localization of a failure within a part of an inhomogeneous trabecular network can be related to the presence of a surface of minimal cut-a surface separating the analyzed trabecular sample into two disjoint parts in such a way, that the separation requires removal of minimal possible amount of bone material. Thus, to properly address the problem of mechanical competence of a trabecular bone sample, one must be able to detect and describe the surface of minimal cut. In this paper an algorithm localizing surfaces of minimal cut within 3D trabecular structures is introduced.

Algorithms↗

PubMed2006

Estimating structural properties of trabecular bone from gray-level low-resolution images.

In this paper the relationship between three-dimensional histomorphometric parameters derived from microCT and MRI images of distal radius trabecular bone samples is studied. microFE analysis of the trabecular samples is performed and Young's modulus for cranio-caudal direction is calculated. Most of the MRI and microCT parameters correlate significantly with, respectively, MRI and microCT estimates of bone volume fraction. For some of the parameters strong correlation between microCT and MRI results is also observed. However, in these cases there simultaneously exists correlation between: microCT parameter and microCT bone volume fraction; microCT and MRI bone volume fraction; MRI bone volume fraction and MRI parameter. It is found that, comparing to bone volume fraction, histomorphometric information derived from binarized MRI images does not improve estimation of the Young's modulus of trabecular bone samples (calculated for "gold standard" microCT data). Thus a novel method of "optimal paths" analysis of gray-level MRI images is introduced. "Optimal paths" parameters improve estimation of the Young's modulus of trabecular bone samples. They also provide surrogate, gray-level image-based measure of trabecular thickness.

Aged↗

PubMed2005

Novel algorithm detecting trabecular termini in muCT and MRI images.

In this paper, a novel algorithm detecting trabecular termini in three-dimensional images of trabecular bone is introduced. The algorithm is applied to the analysis of muCT and MRI images of distal radius trabecular bone samples. In muCT images, the volume of the trabecular termini constitutes at most 2.1% of the bone volume fraction BV/TV and is typically smaller than 1% of BV/TV. Isolated trabeculae are not observed in the interior of the trabecular bone samples. Trabecular bone structure assessed with muCT appears thus highly optimized. The volume and the number of the trabecular termini do not correlate with BV/TV. These quantities do not correlate also with apparent Young's modulus of the samples. In contrast in MRI images, segmented with the dual reference limit method, the volume of the trabecular termini and the volume of isolated parts constitute even up to 14% of the apparent bone volume fraction App.BV/TV. For MRI images, the volume of the trabecular termini increases significantly with decreasing App.BV/TV. The volume and the number of the trabecular termini, derived from MRI images do not correlate with Young's modulus. There is also no correlation between the number and the volume of the trabecular termini, estimated from MRI and muCT images. The volume of the trabecular termini is overestimated 15 times in MRI images. App.BV/TV correlates strongly with BV/TV. Young's modulus derived from MRI images correlates strongly with Young's modulus found for muCT data. It is shown that the diagnostic significance of latter result is highly limited.

Aged↗

PubMed2004

Influence of 50 Hz magnetic field on human heart rate variability: linear and nonlinear analysis.

This study investigated the problem of the influence of 50 Hz magnetic field (MF) on human heart rate variability (HRV). The exposure system was a commercial device for magnetotherapy, generating field of the strength of 500 microT at the center of the coil, 150-200 microT at the position of human subjects' heart and 20-30 microT at the position of subjects' head. The exposure protocols, applied randomly, were either "half hour MF-off/half hour MF-on" or "half hour MF-off/half hour MF-off." The phonocardiographic (PhCG) signal of 15 volunteers were obtained during exposure and used for calculation of time-domain HRV parameters (mean time between heart beats (N-N), standard deviation of time between heart beats (SDNN), and the number of differences of successive beat-to-beat intervals greater than 50 ms, divided by the total number of beat-to-beat intervals (pNN50)) and nonlinear HRV measures (approximate entropy (ApEn), detrended fluctuation scaling exponents). The protocol MF-off/MF-on was applied in nine subjects. Repeated measures ANOVA (RMANOVA) performed for Mf-off/MF-off protocol indicated no statistical difference among four 15 min intervals of HRV data (P value >20% for all parameters except for N-N, where P = 3.7%). RMANOVA followed by the post hoc Tukey test performed for Mf-off/MF-on protocol indicated a statistically significant difference during MF on for N-N (8% increase, P <.1%), SDNN (40% increase, P = 1.1%), and pNN50 (110% increase, P <.1%). The results of the analysis indicate that the changes of these parameters could be associated with the influence of MF.

Adult↗

PubMed2003

Simulated aging--a novel method for estimating the risk of fracture of trabecular bone.

In the study we show how the methods of percolation theory could be used in the description of age-related changes of mechanical competence of trabecular bone. A previously introduced stochastic model of remodeling of trabecular bone is applied to the simulated aging of pairs of 2D sections of trabecular bone matched for apparent density, structural anisotropy, and the age of the donors. The critical density of the structures--defined here as the density below which percolating bone cluster disappears, i.e., the structure is fractured--is estimated for each structure. It is shown that structures belonging to pairs matched for density (clinically used as the principal determinant of fracture risk) lose mechanical competence at a different rate, depending on the value of critical density. Thus it is hypothesized that the risk of fracture must depend not only on the density of the structure but also on its critical density.

Adult↗

PubMed2002

Origin of the pattern of trabecular bone: an experiment and a model.

As a result of an experiment in which the development of a mineral phase in the rabbit embryo was observed, a model is proposed to explain the mechanism that controls the place of precipitation of crystals in mineralizing tissue. The reaction-diffusion equations for the specified compounds are formulated and solved. Among a variety of compounds the concentrations of carbon dioxide, oxygen, HCO-3 ions, H+ ions, calcium, and inorganic phosphorus are evaluated. CO2, HCO-3 ions, and H+ ions, are distinguished due to their key role in the maintenance of the pH value. The local concentration of oxygen is the pivot factor that controls the metabolic rate, i.e., production of CO2. Next the supersaturation was estimated on the basis of the calculated values of pH and the concentrations of calcium and inorganic phosphorus. It is assumed that the synthesis of the organic matrix breaks the metastable equilibrium with respect to spontaneous precipitation and leads to the deposition of minerals. It was found that the geometry of the vasculature determines the shape of primitive trabecular bone (woven bone) while the value of the diffusion coefficient may be the key factor indicating the possibility of mineralization under the control of a living organism.

Animals↗