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Eugeniusz Rokita

Publications and source records attributed to Eugeniusz Rokita.

10 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↗
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↗
PubMed2004

Geometry corrections in a rotating 3-dimensional sonographic system.

OBJECTIVE: To devise a system for geometry corrections in a rotating 3-dimensional sonographic system. METHODS: A 3-dimensional sonographic imaging system based on a standard sonography machine was developed. The transducer mounted in a specially designed holder was rotated about its axis to acquire the spatial information. The most important postulate in rotating 3-dimensional systems is the assumption of parallelity between the rotation axis and the transducer axis. It allows the use of simple geometric relationships between 2-dimensional slices in a 3-dimensional reconstruction. The errors appearing in the 3-dimensional reconstruction when the axes are not parallel were investigated. RESULTS: A simple correction method based on phantom measurements is proposed. The phantom contains a plane, which is inclined to the rotation axis. The analysis of 2-dimensional plane images allows the geometric corrections. The construction of the phantom is described, and the formulas used in the calculations are presented. The method was tested in computer simulations and in patient investigations. CONCLUSIONS: A complete method of the geometric investigations and corrections useful in 3-dimensional sonographic systems based on rotational geometry is proposed. Both the computer simulations and the phantom measurements confirmed the usefulness, precision, and simplicity of the proposed method.

Algorithms↗
PubMed2004

[Calcific and degenerative aortic stenosis--pathogenesis and new possibilities of treatment].

Currently, degenerative changes are the most important cause of valvular aortic stenosis. Epidemiological as well as experimental studies suggest that inflammatory process induced and intensified by common atherosclerosis risk factors as age, hyperlipidemia, diabetes, hypertension, male sex and smoking, is responsible for these changes. Microscopic examination of the affected valves reveals: endothelium derangement, thickening of the subendothelial layer, intra- and extracellular lipid, lipoprotein and protein deposits, inflammatory infiltrate composed of macrophages, T lymphocytes, foam cells and intensive calcification in the zones of lipid accumulation. The method of choice in the assessment of aortic valve stenosis is echocardiography. New, more sensitive, quantitative radiological methods like Electron Beam Computed Tomography and Multislice Computed Tomography may be useful in a detection of early lesions and monitoring of their progress. As the process of aortic valve degeneration is long and progressive in nature, early introduction of effective prevention would decrease the number of patients operated on for aortic stenosis. A number of studies indicate the role of statins in slowing the progression of aortic valve degeneration. Nevertheless, no large randomized prospective study has emerged in this field and there is no strong enough evidence for the efficacy of statins in degenerative aortic valve disease.

Aortic Valve↗
PubMed2004

[Effect of the dispersion of calcium deposits on allogenic aortic valves durability. Mineralization phases].

This investigation was aimed at comparison of calcium content and calcium dispersion in allogenic aortic valve leaflets removed due to dysfunction, to establish the influence of both parameters on graft durability. Calcification was assessed histochemically (von Kossa) as well as physicochemically using atomic absorption spectroscopy (AAS). The morpho-metric data (leaflet area involved in the calcification process) were obtained by computer-assisted image analysis system. The dry weight content of leaflet calcium and phosphorus were assessed by atomic absorptive spectroscopy (AAS) and Ca/P ratio was calculated. Calcium dispersion coefficient (Dc) was established according to the formula: Dc = 1/Ca(c)/Ap, where Ca(c) = calcium dry weight concentration; Ap = percent of leaflet area involved in calcification. We found biphasic correlation between calcium concentration and area involved in calcification. The first one was characterized by rising dispersion of calcium deposits while for the second one saturation with hydroxyapatite of formerly calcified areas was predominant, negatively influencing graft durability. Allograft durability was correlated with calcium dispersion (Dc) (p<0.001), while no significant correlation was found with calcium concentration. Decreased Dc was characteristic for 93.8% of low durability grafts (<11.6 years). Our results suggest that lowered calcium dispersion decreasing allograft lifetime and is a better predictor of allograft durability than the total calcium content.

Adolescent↗
PubMed2004

[Mineralization of homograft aortic valves stored in a nutrient solution].

BACKGROUND AND AIM OF THE STUDY: Mineralization of the homograft aortic valve cusps is a complex process leading to their degeneration and decreasing durability. Factors that play a decisive role in regulation of mineralization, growth of hydroxyapatite crystals are still open questions. We studied development of mineralization in the homograft aortic valves prepared for transplantation stored in the Parker's solution with antibiotics. METHOD: The aortic valves were explanted from 12 donors <18 hours after death. All the cusps were divided into halves. One half of each cusp was stored in the Parker's solution with antibiotics for 28 days at 4 degrees C. Concentrations of several elements (P, S, Cl, K, Ca, Mn, Fe, Ni, Cu, Zn i Sr) in incubated and control samples were determined using energy dispersive X-ray fluorescence (ED-XRF). RESULTS: The study showed that the concentration of Ca and Ca/P increased during incubation that may indicate development of mineralization. CONCLUSIONS: The homograft aortic valve cusps underwent mineralization during in vitro incubation. This may aggravate mineralization in the aortic valve recipients and decrease valve durability which indicate a need for modification of storing condition.

Adult↗
PubMed2003

Mineralization and organic phase modifications as contributory factors of accelerated degeneration in homograft aortic valves.

BACKGROUND AND AIM OF THE STUDY: The study aim was to assess histological and mineralogical properties of leaflets in human, antibiotic-preserved aortic homograft valves (recovered during surgical replacement) in order to identify factors accounting for pathological changes leading to accelerated graft dysfunction. A comparison was made with aortic valves prepared for grafting, with a view to assessing morphological and mineralogical characteristics as a potential preimplantation risk factor. METHODS: Valve leaflets were examined with light and scanning electron microscopy. Mineralization was assessed histochemically, and also physicochemically by atomic absorption spectroscopy (AAS). RESULTS: All explanted homograft valve leaflets revealed prominent degenerative changes seen as decreased surface area, fibrosis, mineralization and focal thrombosis. Substantial loss of endothelium and fibroblasts, reduced collagen bundles crimping, inflammation (81%) and disappearance of layered structure (59%) was identified. The elastic elements were relatively stable, though a gradual age-dependent loss was observed in both groups. Accelerated mineralization was seen in all explanted homografts; inorganic deposits were composed mainly of hydroxyapatite. Two types of mineralization were identified: large limited nodular structures, and diffuse mineral deposits. Homografts with moderately elevated mineralization, well-preserved layered structure and sporadic infective changes proved to have the greatest durability. Homograft durability was also affected by the difference in host and donor age. CONCLUSION: Preimplantation factors affecting pathological changes determining homograft durability included morphological status of the graft itself and donor age; host-related factors included recipient age, endocarditis, native valve calcification, and host-donor matching (age difference between host and donor). A limited molecular mineralization may increase valvular durability, provided that no focal nodular calcifications exist that might adversely affect overall homograft integrity.

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↗