A comparison of emulsifiers for the formation of oil-in-water emulsions: stability of the emulsions within 9 h after production and MR signal properties

Objective

To provide a basis for the selection of suitable emulsifiers in oil-in-water emulsions used as tissue analogs for MRI experiments. Three different emulsifiers were investigated with regard to their ability to stabilize tissue-like oil-in-water emulsions. Furthermore, MR signal properties of the emulsifiers themselves and influences on relaxation times and ADC values of the aqueous phase were investigated.

Materials and methods

Polysorbate 60, sodium dodecyl sulfate (SDS) and soy lecithin were used as emulsifiers. MR characteristics of emulsifiers were assessed in aqueous solutions and their function as a stabilizer was examined in oil-in-water emulsions of varying fat content (10, 20, 30, 40, 50%). Stability and homogeneity of the oil-in-water emulsions were evaluated with a delay of 3 h and 9 h after preparation using T₁ mapping and visual control. Signal properties of the emulsifiers were investigated by ¹H-MRS in aqueous emulsifier solutions. Relaxometry and diffusion weighted MRI (DWI) were performed to investigate the effect of various emulsifier concentrations on relaxation times (T₁ and T₂) and ADC values of aqueous solutions.

Results

Emulsions stabilized by polysorbate 60 or soy lecithin were stable and homogeneous across all tested fat fractions. In contrast, emulsions with SDS showed a significantly lower stability and homogeneity. Recorded T₁ maps revealed marked creaming of oil droplets in almost all of the emulsions with SDS. The spectral analysis showed several additional signals for polysorbate and SDS. However, lecithin remained invisible in ¹H-MRS. Relaxometry and DWI revealed different influences of the emulsifiers on water: Polysorbate and SDS showed only minor effects on relaxation times and ADC values of aqueous solutions, whereas lecithin showed a strong decrease in both relaxation times (r_1,lecithin = 0.11 wt.%⁻¹ s⁻¹, r_2,lecithin = 0.57 wt.%⁻¹ s⁻¹) and ADC value (Δ(ADC)_lecithin =  − 0.18 × 10^–3 mm²/s⋅wt.%) with increasing concentration.

Conclusion

Lecithin is suggested as the preferred emulsifier of oil-in-water emulsions in MRI as it shows a high stabilizing ability and remains invisible in MRI experiments. In addition, lecithin is suitable as an alternative means of adjusting relaxation times and ADC values of water.

     

A Unified Analysis of Structured Sonar-Terrain Data Using Bayesian Functional Mixed Models

Sonar emits pulses of sound and uses the reflected echoes to gain information about target objects. It offers a low cost, complementary sensing modality for small robotic platforms. Although existing analytical approaches often assume independence across echoes, real sonar data can have more complicated structures due to device setup or experimental design. In this article, we consider sonar echo data collected from multiple terrain substrates with a dual-channel sonar head. Our goals are to identify the differential sonar responses to terrains and study the effectiveness of this dual-channel design in discriminating targets. We describe a unified analytical framework that achieves these goals rigorously, simultaneously, and automatically. The analysis was done by treating the echo envelope signals as functional responses and the terrain/channel information as covariates in a functional regression setting. We adopt functional mixed models that facilitate the estimation of terrain and channel effects while capturing the complex hierarchical structure in data. This unified analytical framework incorporates both Gaussian models and robust models. We fit the models using a full Bayesian approach, which enables us to perform multiple inferential tasks under the same modeling framework, including selecting models, estimating the effects of interest, identifying significant local regions, discriminating terrain types, and describing the discriminatory power of local regions. Our analysis of the sonar-terrain data identifies time regions that reflect differential sonar responses to terrains. The discriminant analysis suggests that a multi- or dual-channel design achieves target identification performance comparable with or better than a single-channel design. Supplementary materials for this article are available online.     

Repurposing the Pummerer Rearrangement: Determination of Methionine Sulfoxides in Peptides

The reversible oxidation of methionine residues in proteins has emerged as a biologically important post-translational modification. However, detection and quantitation of methionine sulfoxide in proteins is difficult. Our aim is to develop a method for specifically derivatizing methionine sulfoxide residues. We report a Pummerer rearrangement of methionine sulfoxide treated sequentially with trimethylsilyl chloride and then 2-mercaptoimidazole or pyridine-2-thiol to produce a dithioacetal product. This derivative is stable to standard mass spectrometry conditions, and its formation identified oxidized methionine residues. The scope and requirements of dithioacetal formation are reported for methionine sulfoxide and model substrates. The reaction intermediates have been investigated by computational techniques and by ¹³C NMR spectroscopy. These provide evidence for an α-chlorinated intermediate. The derivatization allows for detection and quantitation of methionine sulfoxide in proteins by mass spectrometry and potentially by immunochemical methods.     

User Interface Functions for an Analysis Idealization System

Abstract: The user interface for an analysis idealization system is described, which is intended for use by design experts. The interface is part of a system to automatically execute analysis for PDEs (Partial Differential Equations), especially by means of the finite element method, and to control the idealizations used in the analysis. The system is designed to be used with commercial modelers and analysis packages, makes use of geometric, attribute and functional models, and addresses the need for multi-disciplinary analysis support throughout an evolving design. The basics of X/Xt/Motif programming are explained in order to understand the construction of the user interface, and the interface operations are illustrated with examples.     

Runoff of particle bound pollutants from urban impervious surfaces studied by analysis of sediments from stormwater traps

Runoff sediments from 68 small stormwater traps around the harbor of urban Bergen, Norway, were sampled and the concentrations of polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), heavy metals, and total organic carbon (TOC) were determined in addition to grain size. Our study provides empirical data from a large area in the interface between the urban and marine environment, studying the active transport of pollutants from land-based sources. The results of the analyses clearly demonstrate the importance of the urban environment representing a variety of contamination sources, and that stormwater runoff is an important dispersion mechanism of toxic pollutants. The concentrations of different pollutants in urban runoff sediments show that there are several active pollution sources supplying the sewage systems with PCBs, PAHs and heavy metals such as lead (Pb), zinc (Zn) and cadmium (Cd). The concentration of PCB7 in the urban runoff sediments ranged between < 0.0004 and 0.704 mg/kg. For PAH16, the concentration range was < 0.2-80 mg/kg, whereas the concentration ranges of Pb, Zn and Cd were 9-675, 51.3-4670 and 0.02-11.1 mg/kg respectively. Grain size distribution in 21 selected samples varied from a median particle diameter of 13 to 646 microm. However, several samples had very fine-grained particles even up to the 90 percentile of the samples, making them available for stormwater dispersion in suspended form. The sampling approach proposed in this paper will provide environmental authorities with a useful tool to examine ongoing urban contamination of harbors and similar recipients.