Computed tomography and magnetic resonance fusion imaging in cholesteatoma preoperative assessment.

The purpose of this study is to describe a method for developing fusion imaging for the preoperative evaluation of cholesteatoma. In 33 patients diagnosed with cholesteatoma, a high-resolution temporal bone computed tomography (CT) scan without intravenous contrast and propeller diffusion-weighted magnetic resonance imaging (MRI) were performed. Both studies were then sent to the BrainLAB work station, where the images were fused to obtain a morphological and color map. Intraoperative findings coincided with fusion CT-MRI imaging in all but two patients. In addition, one false positive and one false negative case were observed. CT and diffusion-weighted MRI are complementary techniques that should be employed to assess a cholesteatoma prior to surgery in many cases. Hence, to combine the advantages of each technique, we developed a fusion image technique similar to those that are routinely employed for radiotherapy planning and positron emission tomography-CT imaging. Fusion images can prove useful in selected cases.

Assisted Protection Headphone Proposal to Prevent Chronic Exposure to Percussion Instruments on Musicians.

The effects of chronic exposure to high sound pressure levels (SPLs) are widely studied in the industry environment. However, the way that SPLs affect music students has not been thoroughly examined. In this paper, we study the SPL exposure of batucada students and we propose an assisted protection headphone as a part of e-health system. We measured the SPL reached during a regular percussion class. Pure-tone audiometries were performed to a set of percussion students. The gathered data were statistically analyzed. The assisted protection headphones and their operation are detailed and tested during a regular class. Our results show that 35% of the musicians present with a noise-induced hearing loss, considered as two frequencies with hearing loss of 25 dB or more or one frequency with a hearing loss of 30 dB or more. Our data also shows that those students that do not use any protection have a greater hearing loss. However, the students that use protection headphones are also suffering hearing loss. There might be a problem in the way that musicians are using the protection headphones. Our assisted protection headphones as a part of e-health measures can diminish the negative effects of percussion instruments for musicians.

Size-exclusion chromatographic determination of polymer molar mass averages using a fractal calibration.

The characterization of polymers by size-exclusion chromatography basically consists of the determination of the weight-average molar mass (Mw), number-average molar mass (Mn), and polydispersity index (I). An accurate estimation of these magnitudes requires the use of a reliable and trusted calibration curve. Three procedures for building up a calibration curve are analyzed in this work. The first is the classical universal calibration (UC), based on the elution of tetrahydrofuran-polystyrene in a system as reference. The second is based on the proper calibration curve made with standards of the sample under study. However, two main drawbacks arise when using these methodologies: the nonfulfilment of the UC when secondary mechanisms, other than pure size-exclusion, are present in the separation process; and the lack of a broad set of narrow standards of the sample under analysis in the second procedure. In order to circumvent these difficulties, a third, recently-proposed approach based on fractal considerations is applied. The accuracy and reliability of this method is proven through the calculation of the deviations observed in the estimation of the Mw values for polymer samples in different solvent-gel chromatographic systems. Whereas the classical UC shows a mean deviation of approximately 80% relative to the values given by the manufacturer, the fractal calibration yields a mean deviation of approximately 16%, similar to that obtained from the proper calibration. Moreover, the fractal procedure only needs one polymeric sample to generate the calibration curve.

Preferential solvation of poly(methyl methacrylate) and a bisphenol A diglycidyl ether by size-exclusion chromatography.

The preferential adsorption coefficient, lambda, of poly(methyl methacrylate), PMMA, in solutions formed by an epoxy resin in tetrahydrofuran (THF), was studied by size-exclusion chromatography (SEC). Only PMMA of lowest molar mass was preferentially solvated by epoxy but at low concentrations of epoxy in the mixture. At higher epoxy content PMMA was preferentially solvated by THF. A simultaneous and competitive solvation between the specific interactions PMMA-epoxy and the self association of epoxy at high concentrations would be the responsible of this inversion point. The more compacted coil of PMMA of higher molecular weights in solution could explain the lack of interaction of these polymers with epoxy. The results also indicated that lambda decreased with the molar mass. This variation has been attributed to the influence of the coil segment density on preferential adsorption.

Fractal calibration in size-exclusion chromatography I. An introduction.

The elution behaviour of different polymer-solvent systems in three types of organic columns for SEC has been compared and interpreted. The experimental data show that the classical universal calibration is not accomplished. Deviations from a unique curve are observed due to the binary and ternary interactions between the components of the system (solvent, polymer and gel) which results on secondary mechanisms accompanying the main pure or "ideal" SEC separation mechanism. Both, enthalpic and entropic effects are interpreted in terms of the swelling and crosslinking degrees of the gel packings, and are also related with the fractal characteristics of their surfaces, such as the fractal dimension and the available pore size. Moreover, a relationship between the fractal dimension of the pore surface and the chromatographic distribution coefficient is proposed.

Preferential solvation of a dicyanate ester monomer and poly(sulfone) in different organic solvents by size-exclusion chromatography.

Preferential solvation parameters A in the ternary systems solvent (1) -monomer (2) -polymer (3) were determined as a tool to measure the compatibility between the cyanate ester monomer Arocy B10 and poly(sulfone), PSF, in the presence of three organic solvents: tetrahydrofuran, dimethylformamide and dicloromethane. The A parameter was measured by size-exclusion chromatography at different monomer-to-polymer ratios. The quantitative evaluation was rigorously made at polymer-diluted conditions. PSF was found to be preferentially solvated by the monomer. Concerning the solvent used, systems containing tetrahydrofuran showed the strongest solvation, the lowest A values being those obtained in dicloromethane. These results were in accordance with the intrinsic viscosity values of the PSF-solvent systems. The variation of A values with the Arocy B10 concentration is strongly dependent upon the nature of the solvent.

Interaction of quinine with model lipid membranes of different compositions.

The binding of a drug such as Quinine with neutral and negatively charged small unilamellar lipid vesicles at pH 7 and 37 degrees C was investigated. Changes in the fluorescence properties of the drug after association with the liposomes were used to obtain binding isotherms over a range of phospholipid compositions at different ionic strengths. Under such conditions, the association was strongly enhanced by the negative net charge of the bilayer but diminished by the increasing presence of electrolytes in the aqueous media. Binding data were analyzed in terms of a surface partition equilibrium without and after correcting for electrostatic effects by means of the Gouy-Chapman theory. The intrinsic (hydrophobic) constant, obtained after charge correction, was smaller than the apparent binding constant determined without taking into account such an effect. A new analysis considering the two components not fully dissociated and affected by an identical screening factor has been introduced. It yielded rather similar hydrophobic partition coefficients for all conditions, independent of both the surface charge density of the lipid vesicles and the ionic strength, with an average value estimated to be (3 +/- 1) x 10(3) M(-1). All the findings suggested that the association of Quinine to liposomes is controlled primarily through electrostatic attractions, and, in a lesser extent, by hydrophobic forces. Because electrostatic and hydrophobic interactions play a crucial role in both the drug-membrane affinity and the location of the drug, their quantitative evaluation can shed light on the mechanism for a next therapeutic "action."

Comparative evaluation of the swelling and degrees of cross-linking in three organic gel packings for SEC through some geometric parameters.

The size exclusion chromatographic (SEC) behavior of five solvent/polymer systems in three organic column packings based on polystyrene/divinylbenzene (PS/DVB) copolymer, TSK-Gel H(HR), mu-styragel and TSK-Gel H(XL), has been compared. All the packings offer similar characteristics (pore size, particle size and efficiency) but some differences have been found when eluting the same systems. The different elution behavior observed in both polymeric gels has been analyzed in terms of their swelling and cross-linking degrees and of the fractal parameters. From the Universal Calibration plots, values of the chromatographic partition coefficient, K(p), have been obtained and using some equations previously reported, values of the volume fraction of the network in the swollen state have been determined for the three sets of columns. Overall, for a given hydrodynamic volume and solvent-polymeric solute system the fraction of cross-linked polymer in the stationary phase was ordered according to: TSK-Gel H(XL)>mu-styragel>TSK-Gel H(HR). This means an enhanced swelling degree for TSK-Gel H(HR). In general, fractal calculations support the thermodynamic predictions since both the fractal dimension and the pore size can be ordered as TSK-Gel H(HR)>mu-styragel>TSK-Gel H(XL) (in 10 of the 15 situations studied). The exceptions can be explained in terms of strong preferential solvation.

Thermodynamic study of small hydrophobic ions at the water-lipid interface.

The thermodynamics of binding of two small hydrophobic ions such as norharman and tryptophan to neutral and negatively charged small unilamellar vesicles was investigated at pH 7.4 using fluorescence spectroscopy. Vesicles were formed at room temperature from dimyristoyl phosphatidylcholine (DMPC) or DMPC/dimyristoylphosphatidic acid and DMPC/dimyristoylphosphatidylglycerol. The changes in fluorescence properties were used to obtain association isotherms at variable membrane surface negative charge and at different ionic strengths. The binding of both ions was found to be quantitatively enhanced as the percentage of negative phospholipid increases in the membrane. Also, a decrease in ion binding was found to occur as the concentration of monovalent salt was increased (0.045-0.345 M). If electrostatic effects were ignored, the experimental data showed biphasic behavior in Scatchard plots. When electrostatic effects were taken into account by means of the Gouy-Chapman theory, the same data yielded linear Scatchard plots that were described by a simple partition equilibrium of the hydrophobic ion into the lipid-water interface. We demonstrate that the effective interfacial charge, nu, of the ion is a determinant factor to obtain a unique value of the intrinsic (hydrophobic) binding constant independently of the surface charge density of the lipid membrane.

Study on resolution capacity and secondary mechanisms of three different TSK gels for organic SEC.

A comparative study on the elution behavior in size-exclusion chromatography (SEC) of three polymeric TSK gel packings, named H, H(HR), and H(XL) types, is performed. The deviations of the universal calibration (u.c.) curves of seven solvent-polymer systems show evidence that the existence of secondary effects accompanying the main SEC mechanism. These secondary mechanisms are a consequence of the binary enthalpic interactions between the different components of the chromatographic system, such as polymer-solvent, polymer-gel and solvent-gel. However, in the present case, the observed deviations from a unique u.c. curve can mainly be attributed to adsorption of polymeric solutes (analytes) onto the residual moieties of the gel surfaces, (i.e., to polymer-gel interactions). These enthalpic interactions can be quantitated by the values of the distribution coefficient, Kp, which follows the order: Kp (gel H(XL)) > Kp (gel H(HR)) > Kp (gel H). Moreover, the specific resolution of the three types of packings is also estimated, and its comparison yields that Rsp (gel H(HR)) > Rsp (gel H(XL)) > Rsp (gel H), in good agreement with their increasing particle size and decreasing crosslinking degrees. Finally, the errors and inaccuracies committed on the estimation of the sample average molar masses from their respective calibration curves serves the assessment that the packing with lesser secondary mechanisms is the H-type.

The fractal calibration method applied to the characterization of polymers in solvent mixtures and in mixed gel packings by SEC.

The size-exclusion chromatographic (SEC) behaviour of different solvent/polymer systems in three packing sets has been analysed from fractal considerations. The three-column sets studied are specifically formed by: (i) 'pure' micro-styragel, (ii) 'mixed' TSK Gel H(HR + XL + HR) and (iii) mixed TSK Gel H(XL + HR + XL). The experimental data reveals that in most of the systems assayed the classical universal calibration (UC) is not fulfilled, denoting the existence of secondary effects accompanying the main SEC mechanism. In order to obtain an accurate characterization of different polymers eluted in solvent mixtures and/or mixed packings, the use of a reliable and trusted calibration curve is required. In this sense, two alternative procedures have been analysed: the specific (SC) and the fractal (FC) calibrations. The results have evidenced that the use of the FC instead of the classical universal method diminishes up to nine times (in the case of the micro-styragel set) the mean deviation on the calculated molar mass with respect to the value given by the supplier. In the case of TSK Gel-based sets, the mean deviation is reduced to the half. The SC curve made with standards of the sample under study also reduces the mean deviation values but needs a broad set of narrow standards, whereas the fractal approach only needs one polymeric sample to build up the calibration curve.

Quistes dentígeros múltiples en los maxilares, presentación de un caso / Multiple dentigerous cysts in jaws. Case study

Presentamos un caso de un paciente de ocho años de edad con quistes dentigeros múltiples en los maxilares. Se discuten los posibles diagnósticos diferenciales y el tratamiento.