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PubMed2004

[Theophylline release and diffusion from a compressed ethylcellulose matrix through an artificial membrane].

The aim of this work was to study theophylline dissolution and diffusion from a compressed ethylcellulose matrix through an artificial membrane. The sustained release tablets were manufactured manufactured by direct compression. Dissolution and diffusion studies were performed using an absorption simulator. In the donor compartment, different pH media were used: i) 1.2, 5, 6, ii) the same media supplemented with 10% glucose and iii) an amino acid medium. The receiver medium was held at pH 7.4. The Higuchi equation was used to elucidate the dissolution mechanism. Results showed that dissolution was mainly influenced by theophylline solubility with a mechanism based on diffusion. Diffusion rate was assessed by calculating the diffusion coefficients. Diffusion was essentially dependent on rate of theophylline release.

Algorithms↗
PubMed2001

Volumetric characterization of the hydration properties of heterocyclic bases and nucleosides.

We have determined the partial molar volumes, expansibilities, and adiabatic compressibilities of six heterocyclic nucleic acid bases, five ribonucleosides, and six 2'-deoxyribonucleosides within the temperature range 18-55 degrees C. We interpret the resulting data in terms of the hydration of the component hydrophobic and polar atomic groups. From our temperature-dependent volumetric studies, we found that the total contraction of water caused by polar groups of each individual heterocyclic base and nucleoside depends on the proximity and chemical nature of other functional groups of the solute. In addition, the compressibility contributions of polar groups vary greatly in sign and magnitude depending on the surrounding functional groups. In agreement with previous studies, our results are suggestive of little or no interaction between the sugar and base moieties of a nucleoside. In general, our data shed light into the hydration properties of individual heterocyclic bases and nucleosides, which may have significant implications for the sequence-dependent hydration of nucleic acids. We discuss the potential importance of our results for developing an understanding of the role that solvent plays in the stabilization/destabilization of nucleic acid structures.

Algorithms↗
PubMed2005

Representing images using points on image surfaces.

This paper presents a new approach to represent an image by "verge points," which are defined as high-curvature points on the image surface. This representation offers a compact and reversible way to preserve the essence of the original image. Various applications, such as compression, edge detection, image enhancement, and image editing, can be achieved based on this representation. In this paper, the whole procedure for verge point representation is presented. Based on these verge points, image reconstruction can be easily achieved via iterative linear interpolation. These extracted verge points with compatible properties are further linked into verge curves to offer more compact representation. Progressive representation is also developed based on a multiscale extraction scheme. Some potential applications are then presented to demonstrate the versatility of this representation.

Algorithms↗
PubMed2006

Response times seen as decompression times in Boolean concept use.

This paper reports a study of a multi-agent model of working memory (WM) in the context of Boolean concept learning. The model aims to assess the compressibility of information processed in WM. Concept complexity is described as a function of communication resources (i.e., the number of agents and the structure of communication between agents) required in WM to learn a target concept. This model has been successfully applied in measuring learning times for three-dimensional (3D) concepts (Mathy and Bradmetz in Curr Psychol Cognit 22(1):41-82, 2004). In this previous study, learning time was found to be a function of compression time. To assess the effect of decompression time, this paper presents an extended intra-conceptual study of response times for two- and 3D concepts. Response times are measured in recognition phases. The model explains why the time required to compress a sample of examples into a rule is directly linked to the time to decompress this rule when categorizing examples. Three experiments were conducted with 65, 49, and 84 undergraduate students who were given Boolean concept learning tasks in two and three dimensions (also called rule-based classification tasks). The results corroborate the metric of decompression given by the multi-agent model, especially when the model is parameterized following static serial processing of information. Also, this static serial model better fits the patterns of response times than an exemplar-based model.

Adolescent↗
PubMed1998

Disparity mapping applied to sonography of the breast: technical note.

A two-dimensional sonoelastographic technique called "disparity mapping" was applied to breast sonographic examinations in eight patients to test discrimination between benign and malignant lesions. With probe compression, pairs of gray-scale sonographic scans were obtained about 1 second apart. The disparity mapping procedure calculated the apparent displacement of the speckle pattern about each point in the image and presented that information in the form of a disparity map. Findings were consistent with a firm lesion in two of the three cancers, were indistinguishable from normal tissue in all three fibroadenomas, were indistinguishable from normal findings in one cyst, and showed no disparity in one cyst because it had few internal echoes.

Adult↗
PubMed2000

Diagnosis of acute pulmonary embolism: an update.

Considerable progress has been made in pulmonary embolism diagnosis during the last ten years. New diagnostic instruments such as plasma D-dimer measurement and lower venous compression ultrasonography have been developed. Clinical evaluation of the likelihood of pulmonary embolism has been rehabilitated and proven accurate and valid. The interpretation of lung scan results has become more simple and clear to clinicians. Finally, two diagnostic strategies have been validated in large scale outcome studies. Both rely on a sequential combination of the above mentioned instruments and have been able to safely manage more than 90% of patients without a pulmonary angiogram. The 3-month venous thromboembolic risk in patients without pulmonary embolism and, hence, not anticoagulated was less than 1% in both studies. In the absence of a formal comparison of their respective cost-effectiveness, choosing between these strategies may rest on local preferences or logistics. Finally, spiral CT scan is highly promising and may considerably modify the diagnostic workup of pulmonary embolism in the near future. However, it is insufficiently validated and its position in a rational algorithm for diagnosing pulmonary embolism is not yet defined.

Acute Disease↗
PubMed2006

Predicting the tensile strength of compacted multi-component mixtures of pharmaceutical powders.

PURPOSE: Pharmaceutical tablets are generally produced by compacting a mixture of several ingredients, including active drugs and excipients. It is of practical importance if the properties of such tablets can be predicted on the basis of the ones for constituent components. The purpose of this work is to develop a theoretical model which can predict the tensile strength of compacted multi-component pharmaceutical mixtures. METHODS: The model was derived on the basis of the Ryshkewitch-Duckworth equation that was originally proposed for porous materials. The required input parameters for the model are the relative density or solid fraction (ratio of the volume of solid materials to the total volume of the tablets) of the multi-component tablets and parameters associated with the constituent single-component powders, which are readily accessible. The tensile strength of tablets made of various powder blends at different relative density was also measured using diametrical compression. RESULTS: It has been shown that the tensile strength of the multi-component powder compacts is primarily a function of the solid fraction. Excellent agreement between prediction and experimental data for tablets of binary, ternary and four-component blends of some widely used pharmaceutical excipients was obtained. CONCLUSION: It has been demonstrated that the proposed model can well predict the tensile strength of multi-component pharmaceutical tablets. Thus, the model will be a useful design tool for formulation engineers in the pharmaceutical industry.

Algorithms↗
PubMed2002

Influence of physical parameters and lubricants on the compaction properties of granulated and non-granulated cross-linked high amylose starch.

Cross-linked high amylose starch (CLA) is a pharmaceutical excipient used in direct compression for the preparation of controlled release tablets and implants. In this work the compression properties of CLA in bulk and granulated forms (without binder) were evaluated for the first time. Tablets were prepared on an instrumented single punch machine. The flow properties and the compression characteristics (compressibility, densification behavior, work of compression) of the materials as well as the mechanical strength of the finished compacts (compactibility) were systematically examined. Wet granulation was found to improve the flowability and the compressibility of CLA but concomitantly reduced its compactibility. It was demonstrated that CLA was a plastically deforming material with a plasticity index and a yield pressure value comparable to those of pregelatinized starch. The compactibility of granulated CLA was independent of particle size in the range of 75 to 500 microm, but slightly decreased when the percentage of the fine particles (<75 microm) in the bulk powder was increased. Water and colloidal silicone dioxide facilitated the consolidation of CLA, while magnesium stearate had an opposite effect on the tablet crushing force.

Adsorption↗
PubMed2005

CT volumetry of intravertebral cement after kyphoplasty. Comparison of polymethylmethacrylate and calcium phosphate in a 12-month follow-up.

This study was intended to measure the volume of intravertebral cement after balloon kyphoplasty with high resolution computed tomography (CT) and dedicated software. Volume changes of biocompatible calcium phosphate cement (CPC) were detected during a follow-up of 12 months. Measurements were compared with a control group of patients treated with polymethylmethacrylate (PMMA). Twenty-three vertebrae (14 CPC, 9 PMMA) of 12 patients were examined with CT using an identical imaging protocol. Dedicated software was used to quantify intravertebral cement volume in subvoxel resolution by analyzing each cement implant with a density-weighted algorithm. The mean volume reduction of CPC was 0.08 ml after 12 months, which corresponds to an absorption rate of 2 vol%. However, the difference did not reach significance level (P>0.05). The mean error estimate was 0.005 ml, indicating excellent precision of the method. CT volumetry appears a precise tool for measurement of intravertebral cement volume. CT volumetry offers the possibility of in vivo measurement of CPC resorption.

Bone Cements↗
PubMed2005

Stress, strain, and NMR.

Experimental and ab initio results that demonstrate the effect of stress on the nuclear magnetic resonance spectra of materials are shown. The design of a cell that generates uniaxial compressive stress is presented, and results on gallium phosphide and lead nitrate single crystals that illustrate the observable results of the stress are shown. Tensors that relate stress and strain to changes in the chemical shielding tensors and the electric field gradient tensors are defined formally. The elements of these tensors are then computed by a density functional theory approach that makes use of planewaves and pseudopotentials. The experimental results are interpreted with the aid of the calculations. Extensions to spinning samples and to the interpretation of optical phenomena in materials are discussed.

Algorithms↗
PubMedDate not supplied

In vitro release kinetics of Tolmetin from tabletted Eudragit microparticles.

In a previous paper the preparation has been described, by three different techniques, of microparticles made of Eudragit RS 100 and RL 100 containing a NSAI agent, Tolmetin. Freely flowing microparticles failed to affect significantly the in vitro drug release, which displayed a similar dissolution profile after micro-encapsulation to the free drug powder. Microparticles were then converted into tablets and the effect of compression on drug delivery, as well as that of the presence of co-additives, was studied in the present work. Furthermore, microparticles were also prepared by adding MgO to the polymer matrix, to reduce the sensitivity of the drug to pH changes during its dissolution. Similarly, magnesium stearate was also used for microparticle formation as a droplet stabilizer, in order to reduce particle size and hinder rapid drug release. A mathematical evaluation, by using two semi-empirical equations, was applied to evaluate the influence of dissolution and diffusion phenomena upon drug release from microparticle tablets.

Acrylic Resins↗
PubMed2005

The treatment of acetabular bone defects with an associated pelvic discontinuity.

UNLABELLED: Pelvic discontinuity is encountered frequently during acetabular revision in patients with severe acetabular bone loss. Prompt recognition of the discontinuity and appropriate intraoperative treatment are essential for a successful clinical outcome. The treatment of the discontinuity is dependent on the remaining host bone, the potential for healing of the discontinuity, and the potential for biologic ingrowth of acetabular components. If healing potential of the discontinuity exists, the discontinuity should be treated in compression with a posterior column plate and structural allograft or with the use of trabecular metal acting as an internal plate. If healing potential for the discontinuity does not exist, the discontinuity should be bridged and treated in distraction with an acetabular transplant supported with a cage, a trabecular metal component with trabecular metal augmentation, or with the use of a custom triflange implant. LEVEL OF EVIDENCE: Therapeutic study, Level III-1 (case-control study). See the Guidelines for Authors for a complete description of levels of evidence.

Acetabulum↗
PubMed2003

Dual-energy digital mammography: calibration and inverse-mapping techniques to estimate calcification thickness and glandular-tissue ratio.

Breast cancer may manifest as microcalcifications in x-ray mammography. Small microcalcifications, essential to the early detection of breast cancer, are often obscured by overlapping tissue structures. Dual-energy imaging, where separate low- and high-energy images are acquired and synthesized to cancel the tissue structures, may improve the ability to detect and visualize microcalcifications. Transmission measurements at two different kVp values were made on breast-tissue-equivalent materials under narrow-beam geometry using an indirect flat-panel mammographic imager. The imaging scenario consisted of variable aluminum thickness (to simulate calcifications) and variable glandular ratio (defined as the ratio of the glandular-tissue thickness to the total tissue thickness) for a fixed total tissue thickness--the clinical situation of microcalcification imaging with varying tissue composition under breast compression. The coefficients of the inverse-mapping functions used to determine material composition from dual-energy measurements were calculated by a least-squares analysis. The linear function poorly modeled both the aluminum thickness and the glandular ratio. The inverse-mapping functions were found to vary as analytic functions of second (conic) or third (cubic) order. By comparing the model predictions with the calibration values, the root-mean-square residuals for both the cubic and the conic functions were approximately 50 microm for the aluminum thickness and approximately 0.05 for the glandular ratio.

Absorptiometry, Photon↗
PubMed2006

Alcohols reduce lateral membrane pressures: predictions from molecular theory.

We explore the effects of alcohols on fluid lipid bilayers using a molecular theory with a coarse-grained model. We show that the trends predicted from the theory in the changes in area per lipid, alcohol concentration in the bilayer, and area compressibility modulus, as a function of alcohol chain length and of the alcohol concentration in the solvent far from the bilayer, follow those found experimentally. We then use the theory to study the effect of added alcohol on the lateral pressure profile across the membrane, and find that added alcohol reduces the surface tensions at both the headgroup/solvent and headgroup/tailgroup interfaces, as well as the lateral pressures in the headgroup and tailgroup regions. These changes in lateral pressures could affect the conformations of membrane proteins, providing a nonspecific mechanism for the biological effects of alcohols on cells.

Alcohols↗
PubMed2006

Using predicted disease outcome to provide differentiated treatment of early rheumatoid arthritis.

OBJECTIVE: To determine the usefulness of a prediction model for making treatment decisions in early rheumatoid arthritis (RA). METHODS: In 152 patients with early RA, progression of radiological damage during the first year [Sharp-van der Heijde (SH) score > 0] was assessed and used to define actual disease outcome. Available variables at baseline were entered in a multivariate regression analysis with progression score as dependent variable. This model was used to predict disease outcome in every patient. Using the standard deviations of the predicted disease outcome, patients were divided into 3 groups: (1) severe disease: high probability (> or = 0.8) for progression > 0, (2) mild disease: high probability (> or =0.8) for progression < or = 0, and (3) not classified: no high probability for either option. It was determined how many patients could be classified by using this model. RESULTS: One hundred nine patients (71.7%) showed joint damage progression during the first year. Baseline variables available were: age, sex, duration of symptoms, duration of morning stiffness, patient's global assessment of disease activity, Health Assessment Questionnaire score, swollen and painful joint count, bilateral compression pain in metatarsophalangeals, rheumatoid factor positivity, erythrocyte sedimentation rate, shared epitope positivity, SH-score, and the presence of erosions. The R2 value (approximately variation explained) of the prediction model was 0.36. By using this model 46.3% of patients could be classified as having severe disease, 0% as having mild disease, and 53.7% could not be classified. CONCLUSION: To be able to make treatment decisions in early RA based on predicted disease outcome, a better prediction of disease outcome is needed, making the search for better prognostic variables urgent.

Aged↗
PubMed1993

ECG data compression with time-warped polynomials.

This paper presents a new adaptive compression method for ECG's. The method represents each R-R interval by an optimally time-warped polynomial. It achieves a high-quality approximation at less than 250 bits/s. The article shows that the corresponding rates for other transform based schemes (the DCT and the DLT) are always higher. Also, the new method is less sensitive to errors in QRS detection and it removes more (white) noise from the signal. The reconstruction errors are distributed more uniformly in the new scheme and the peak error is usually lower. The reconstruction method is also useful for adaptive filtering of noisy ECG signals.

Algorithms↗
PubMedDate not supplied

Noise-resistant fitting for spherical harmonics.

Spherical harmonic (SH) basis functions have been widely used for representing spherical functions in modeling various illumination properties. They can compactly represent low-frequency spherical functions. However, when the unconstrained least square method is used for estimating the SH coefficients of a hemispherical function, the magnitude of these SH coefficients could be very large. Hence, the rendering result is very sensitive to quantization noise (introduced by modern texture compression like S3TC, IEEE half float data type on GPU, or other lossy compression methods) in these SH coefficients. Our experiments show that, as the precision of SH coefficients is reduced, the rendered images may exhibit annoying visual artifacts. To reduce the noise sensitivity of the SH coefficients, this paper first discusses how the magnitude of SH coefficients affects the rendering result when there is quantization noise. Then, two fast fitting methods for estimating the noise-resistant SH coefficients are proposed. They can effectively control the magnitude of the estimated SH coefficients and, hence, suppress the rendering artifacts. Both statistical and visual results confirm our theory.

Algorithms↗
PubMed2002

MR validation of soft tissue mimicing phantom deformation as modeled by nonlinear finite element analysis.

A study of the applicability of nonlinear finite element analysis (FEA) to predict soft tissue deformation was validated with phase contrast magnetic resonance velocity imaging. A phantom of varying stiffness was placed in a special purpose, computer controlled MR compatible compression apparatus which provided precise, time varying compression with surface deformations on the order of 11%. The resulting motion was measured with MR velocity images acquired throughout the cycle of compression. The phantom geometry was modeled with a finite element mesh and the mechanical properties of the phantom material were measured and incorporated in the FEA model. The motion as calculated by the FEA model was compared to the motion measured with MRI and the results were found to vary with the material's Poisson's ratio and the coefficient of friction. A minimum difference was reached when the Poisson's ratio and coefficient of friction were set to 0.485 and 0.3, respectively. Under these conditions, the root mean square difference was found to be 14.4%.

Agar↗