[Variation in X-ray dose quantity using an amorphous selenium based flat-panel detector -- a study on the dose reduction rate up to the limit of diagnostical utilization]. / Dosisvariation mit einem direkten Selen-Flachbilddetektor -- Eine Studie zur Dosisreduktion bis an die Grenzen der diagnostischen Verwertbarkeit.

PURPOSE: To evaluate the diagnostic quality and minimum required dose to obtain acceptable images for diagnostic purposes in the field of musculoskeletal radiology. MATERIALS AND METHODS: A critical comparison of the image quality produced by a novel flat panel detector and the conventional screen/film system using a contrast-detail phantom was performed in phase I. Images from both systems were obtained with the same dose and displayed with similar contrast and density. In phase II images of significant anatomical structures in cadaver extremities obtained using the digital detector system and the standard film/screen system were critically evaluated. After a successive reduction in the X-ray dose for 84 patients in phase III, eight independent radiologists compared the image quality of the screen/film system to that of the novel flat panel detector. RESULTS: Phases I and II revealed a difference in the image quality achieved by the standard screen/film system and the digital detector system to the advantage of the digital detector system. In 77 of 84 patients (91.7 %), phase III showed equal image quality after a 50 % reduction in the X-ray dose. In 3 cases (3.6 %) the image quality and the level of contrast were better. No unified statement could be made for 4 patients (4.7 %). CONCLUSION: Digital imaging of skeletal disorders using the novel flat panel detector makes it possible to reduce the X-ray dose by 50 % with equal or even better image quality.

[Comments on the standards for acceptance and consistency testing of systems for digital radiography]. / Kommentierungen zu den Normen zu Abnahme- und Konstanzprüfungen bei digitalen Radiographiesystemen (Projektionsradiographie).

Due to German regulations, acceptance and consistency tests have to be obtained by 12.31.2005 for all equipment used for computed radiography according to special standards published in DIN 6868. This article familiarizes all users with the most important aspects of these standards. In addition, explanatory and background information for establishing these regulations are provided.

Osmotic properties of sulfobutylether and hydroxypropyl cyclodextrins.

PURPOSE: The purpose of this study was to determine the osmolality of sulfobutylether (SBE) and hydroxypropyl (HP) derivatives of cyclodextrins (CDs) via vapor pressure osmometry (VPO) and freezing point depression (FPD). (SBE) and HP-CDs are efficient excipients capable of solubilizing and stabilizing poorly water-soluble drugs in parenteral formulations. (SBE)-CDs have also been used as solubility enhancers and osmotic agents for the sustained release of poorly water-soluble drugs from osmotic pump tablets. The knowledge of the CD's osmolality in solution or inside such tablets would allow one to further characterize the release mechanisms. METHODS: Experiments were conducted at 37 degrees C with eight types of HP and (SBE)-CDs. The aqueous solutions ranged from 0.005-0.350 mol(-1). Methods were developed to allow the measurement of high osmolalities using a vapor pressure osmometer or a differential scanning calorimeter. RESULTS: The osmolality calculations from the VPO and FPD measurements correlated well. The osmolality of (SBE)-CDs was significantly higher than the osmolality of HP-CDs and increased with the total degree of substitution (TDS). All CDs showed deviations from ideality at high concentrations. CONCLUSIONS: Empirical correlations of osmolality with concentration and TDS allowed the prediction of osmolality over a wide concentration range. This study also gave some useful insights into the behavior of CD derivatives in solution.

Dextrose adduct formation in aqueous teicoplanin solutions.

The interaction of Teicoplanin, a glycopeptide antibiotic, with dextrose in aqueous solution has been investigated. The equilibrium concentrations of the adduct formed by the interaction of the dextrose aldehyde and the Teicoplanin amino group is shown to be directly related to the concentration of the dextrose and is thought to be inversely proportional to the hydrogen ion concentration. It was also found that phosphate ion catalyzed the reverse reaction. Approximately 30 days were required to reach equilibrium a 4 degrees C, while equilibrium was established in about 7 days at room temperature. The reaction is reversed with dilution and the rate of the reverse reaction is two to three times faster than expected when phosphate ion is present at 0.05 M. From the temperature dependence of the rate constants, the activation energies for the various reactions were determined to be in the range 67-80 kjoules (16-19 kcal)/mol.

General treatment of pH-solubility profiles of weak acids and bases and the effects of different acids on the solubility of a weak base.

The pH-solubility profile of a weak acid or base is shown to be a function of its pKsp, pKa, and uncharged species solubility. Equations are presented that can be used to calculate the solubility as a function of pH. These equations can also be used when there is added salt present. Experimental data was obtained in three cosolvent systems consisting of methanol-water and ethanol-water. Also, the effect of different acids on the solubility of a weak base is reported. A pronounced effect on the solubility by the addition of salt is explained in terms of the Ksp.

Determination of the ionization constants of compounds which precipitate during potentiometric titration using extrapolation techniques.

It is shown that the ionization constants of diacidic compounds can be determined by utilizing potentiometric titration data, even when a precipitate forms during the titration. The two methods presented are particularly useful for compounds for which the pK alpha values are close together. A third method is presented which can be used with monoacidic compounds or compounds for which the pK alpha values are far apart and form a precipitate during the titration. Four symmetrical diacidic compounds were studied which had similar pK alpha values, and one compound was studied which had pK alpha values that were far apart. Comparison of the second pK alpha of the latter compound with that previously reported determined by a spectrophotometric procedure showed excellent correlation.

Cimetidine-theophylline complex formation.

Cimetidine forms a complex with theophylline in vitro in both pH 7.4 buffer and human plasma. The increase in the amount of theophylline in solution is about 20% in the buffer system and about 36% in plasma. It is hypothesized that this complex formation may contribute to and be part of the mechanism of the clinically observed decreased theophylline clearance in man in presence of cimetidine.

Osmolality of parenteral solutions.

Osmolality-concentration profiles for individual and mixed solute systems are presented. Linear relationships between osmolality and concentration held true in all systems examined at concentrations below 0.2 molal levels. At higher concentrations, linearity existed only in select systems. Deviations from linearity can be greater or less than extrapolated values. In view of the need to determine an osmolarity conversion factor for each parenteral formulation and the many errors possible in the use of these values, adoption of osmolality values for labeling parenteral products rather than osmolarity, as stipulated in USP XIX-NF XIV third supplement, strongly recommended.

Microionization constants of commercial cephalosporins.

The equilibrium constants of five commercial cephalosporins were determined. Two are monoacidic and possess one Ka while three are amphoteric and have four microconstants. Although several assumptions were made in the calculations, good agreement was found between the compounds and with previously reported macroionization constants. By utilizing the microionization constants, the ratios of zwitterion to unchanged species were calculated to be in the 900-50,000 range and to have a maximum concentration between pH 3.5 and 5.

Relationship between osmolality and osmolarity.

Since the compendia require the osmolarity of certain parenterals to be labeled and since experimentally only the osmolality can be measured, it is necessary to obtain the relationship between these two quantities. This relationship was determined by considering fundamental physical-chemical definitions. The osmolality of a solution was found to be simply related to the osmotic coefficient. The conversion to osmolarity requires the use of the partial molal volume(s) of the solute(s). A single conversion factor is required for a particular solute system; i.e., the conversion factor is independent of the solution concentration.

[O-Methylation of epinephrine, 3,4-dihydroxybenzoic acid and 6,7-dihydroxycoumarin in yeasts (author's transl)]. / O-Methylierung von Adrenalin, 3.4-Dihydroxybenzoesäure und 6.7-Dihydroxycumarin in Sprosspilzen

In the yeasts C. albicans, C. tropicalis, and C. stellatoidea but not in C. krusei, R.rubra, and S. cerevisiae enzyme activity was found by which--as by the catechol-O-methyltransferase (EC 2.1.1.6) found in the liver--the O-methylation of epinephrine to metanephrine and paranephrine, of 3,4-dihydroxybenzoic acid to 4-hydroxy-3-methoxybenzoic acid and 3-hydroxy-4-methoxybenzoic acid, and of 6,7-dihydroxycoumarin to 7-hydroxy-6-methoxycoumarin and 6-hydroxy-7-methoxycoumarin is catalysed. When the substrates 3,4-dihydroxybenzoic acid, or 6,7-dihydroxycoumarin or epinephrine were incubated in the presence of S-adenosyl-L-[methyl-14C]methionine and S-adenosylmethionine hydrogensulfate with a 100 000 X g supernatant of C. albicans, C. tropicalis or C. stellatoidea the corresponding O-methylethers were detected in the extracts of the incubation medium by thin-layer chromatography. Final identification of the isomeric radioactive O-methylethers obtained from 3,4-dihydroxybenzoic acid and 6,7-dihydroxycoumarin was performed after thin-layer chromatographic separation by the reversed isotope dilution technique. The radioactive m- and p-O-methyl derivatives from epinephrine were separated by thin-layer chromatography and then cleaved with periodate to the corresponding aldehydes which were also identified mainly by the reversed isotope dilution technique.

Ionization constants of cephalosporin zwitterionic compounds.

The microionization constants for two zwitterionic compounds were determined by incorporating two experimental techniques. These compounds have chromophoric changes dependent upon the solution pH. By combining the spectrophotometric measurements with potentiometric mmeasurements, all four microionization constants were calculated. The method used is completely general and is applicable to all diprotic compounds that exhibit this spectrophotometric behavior. The observed pKa's had differences of at most 1.2 units for either compound and were in the 1-4 range. A comparison of the results with each compound and similar compounds indicates that the values are resonable.

Diffusion model for fluidized-bed drying.

A sucrose-lactose-starch granulation was used to study particulate motion and attrition in a fluid bed dryer. There is some classification of material in the dryer as drying proceeds; fine particles are dried faster and become less dense, and the less dry but denser large particles show some (although not great) accumulation tendencies in the lower central area. Unlike countercurrent rotary drying, fluid bed drying cannot be accounted for by water diffusion inside the granule as the rate-limiting step. In its place, a model of external water vapor diffusion is proposed and is supported by vapor-concentration curves and by the linear dependence of the rate constants on the linear air velocities. The dried granulation exhibits the same trend as does countercurrent dried material in that larger particles have higher moisture contents than do smaller particles. Quantitative relationships between content of moisture and size were developed and are supported by experimental data. The granulation, upon storage, does not equilibrate, indicating that this type of water distribution is a problem in batch process granulations as well as in the earlier reported case of granulations for continuous production.

Nonisothermal kinetic studies III: rapid nonisothermal-isothermal method for stability prediction.

A continuous nonisothermal-isothermal method for stability prediction was developed. The approach yields all necessary parameters for prediction, including reaction order. The experimental procedure involves changing the temperature of the samples being studied until degradation is rapid enough to proceed at a convenient isothermal rate for a sufficient number of half-lives with adequate analytical sensitivity so that the reaction order can be unambiguously determined. The analytical information obtained during the nonisothermal and isothermal portions of the experiment is utilized without curve matching in calculating the activation energy and determining the reaction order, reaction rate, and stability prediction at any desired temperature. Model experiments include the acid-catalyzed hydrolysis of acetylcholine bromide and the inversion of sucrose.