Mobile Universal Surface Explorer Research Articles

A scannable unilateral permanent magnet system for the EPR MOUSE

A prototype scannable unilateral permanent (SUPER) magnet for use with the electron paramagnetic resonance (EPR) mobile universal surface explorer (MOUSE) is described. The unilateral magnetic field is scannable from -94 to 94 mT by changing the relative angles of two fixed position ring magnets. The angular dependence of the modeled and measured magnetic fields are in agreement. The SUPER magnet is demonstrated on both the narrow spectral line sample DPPH as well as the broad spectral line sample rhodochrosite using the EPR MOUSE.

The Ability of the EPR MOUSE to Study Underpaintings

The possibility of using the electron paramagnetic resonance (EPR) mobile universal surface explorer (MOUSE) to study underpaintings is validated. The depth sensitivity of the EPR MOUSE is measured using an EPR standard, and is verified using three paramagnetic pigments in an acrylic binder under opaque acrylic layers of titanium white and lead white. The ability to distinguish and identify two layers of EPR signal-bearing pigments is shown using pairwise sets of ultramarine, Egyptian, and Han blue pigments in an acrylic binder. And finally, the spatial imaging capability is demonstrated using a printed design of magnetite black covered with a solid second layer of the pigment. These studies demonstrate that EPR spectroscopy with the EPR MOUSE is a viable method for studying paramagnetic and ferrimagnetic underlayers of pigments.

NMR Profiling of Reaction and Transport in Thin Layers: A Review.

Reaction and transport processes in thin layers of between 10 and 1000 µm are important factors in determining their performance, stability and degradation. In this review, we discuss the potential of high-gradient Nuclear Magnetic Resonance (NMR) as a tool to study both reactions and transport in these layers spatially and temporally resolved. As the NMR resolution depends on gradient strength, the high spatial resolution required in submillimeter layers can only be achieved with specially designed high-gradient setups. Three different high-gradient setups exist: STRAFI (STRay FIeld), GARField (Gradient-At-Right-angles-to-Field) and MOUSE (MObile Universal Surface Explorer). The aim of this review is to provide a detailed overview of the three techniques and their ability to visualize reactions and transport processes using physical observable properties such as hydrogen density, diffusion, - and -relaxation. Finally, different examples from literature will be presented to illustrate the wide variety of applications that can be studied and the corresponding value of the techniques.

Portable single-sided NMR measurements at variable temperatures: Implementation of a thermo-controlled device and application to the heating of bread dough.

A temperature control unit was implemented to vary the temperature of samples studied on a commercial Mobile Universal Surface Explorer nuclear magnetic resonance (MOUSE-NMR) apparatus. The device was miniaturized to fit the maximum MOUSE sampling depth (25 mm). It was constituted by a sample holder sandwiched between two heat exchangers placed below and above the sample. Air was chosen as the fluid to control the temperature at the bottom of the sample, at the interface between the NMR probe and the sample holder, in order to gain space. The upper surface of the sample was regulated by the circulation of water inside a second heat exchanger placed above the sample holder. The feasibility of using such a device was demonstrated first on pure water and then on several samples of bread dough with different water contents. For this, T1 relaxation times were measured at various temperatures and depths and were then compared with those acquired with a conventional compact closed-magnet spectrometer. Discussion of results was based on biochemical transformations in bread dough (starch gelatinization and gluten heat denaturation). It was demonstrated that, within a certain water level range, and because of the low magnetic field strength of the MOUSE, a linear relationship could be established between T1 relaxation times and the local temperature in the dough sample.

Mapping Pigments in a Painting with Low Frequency Electron Paramagnetic Resonance Spectroscopy

An electron paramagnetic resonance (EPR) mobile universal surface explorer (MOUSE) was recently introduced for noninvasively studying paramagnetic pigments in paintings. This study determined that the EPR MOUSE could map the spatial locations of four pigments in a simple impasto painting. Results from three spectral identification algorithms were examined to assess their ability to identify the pigments using an unsupervised approach. Resulting pigment maps are displayed as colorized images of the spatial distribution of the pigments. All three algorithms produced reasonable representations of the painting. The algorithms achieved excellent true positive, true negative, false positive, and false negative rates of ≥0.95, ≥0.98, ≤0.02, and ≤0.05, respectively, for the identification of the pigments. We conclude that the EPR MOUSE is suitable for accurately mapping the location of paramagnetic pigments in a painting.

When the MOUSE leaves the house.

Change is inherent to time being transient. With the NMR-MOUSE (MObile Universal Surface Explorer) having matured into an established NMR tool for nondestructive testing of materials, this forward-looking retrospective assesses the challenges the NMR-MOUSE faced when deployed outside a protected laboratory and how its performance quality can be maintained and improved when operated under adverse conditions in foreign environments. This work is dedicated to my dear colleague and friend Geoffrey Bodenhausen on the occasion of his crossing an honorable timeline in appreciation of his ever-continuing success of fueling the dynamics of magnetic resonance.

Attempts at the Characterization of In-Cell Biophysical Processes Non-Invasively-Quantitative NMR Diffusometry of a Model Cellular System.

In the literature, diffusion studies of cell systems are usually limited to two water pools that are associated with the extracellular space and the entire interior of the cell. Therefore, the time-dependent diffusion coefficient contains information about the geometry of these two water regions and the water exchange through their boundary. This approach is due to the fact that most of these studies use pulse techniques and relatively low gradients, which prevents the achievement of high b-values. As a consequence, it is not possible to register the signal coming from proton populations with a very low bulk or apparent self-diffusion coefficient, such as cell organelles. The purpose of this work was to obtain information on the geometry and dynamics of water at a level lower than the cell size, i.e., in cellular structures, using the time-dependent diffusion coefficient method. The model of the cell system was made of baker’s yeast (Saccharomyces cerevisiae) since that is commonly available and well-characterized. We measured characteristic fresh yeast properties with the application of a compact Nuclear Magnetic Resonance (NMR)-Magritek Mobile Universal Surface Explorer (MoUSE) device with a very high, constant gradient (~24 T/m), which enabled us to obtain a sufficient stimulated echo attenuation even for very short diffusion times (0.2–40 ms) and to apply very short diffusion encoding times. In this work, due to a very large diffusion weighting (b-values), splitting the signal into three components was possible, among which one was associated only with cellular structures. Time-dependent diffusion coefficient analysis allowed us to determine the self-diffusion coefficients of extracellular fluid, cytoplasm and cellular organelles, as well as compartment sizes. Cellular organelles contributing to each compartment were identified based on the random walk simulations and approximate volumes of water pools calculated using theoretical sizes or molar fractions. Information about different cell structures is contained in different compartments depending on the diffusion regime, which is inherent in studies applying extremely high gradients.

The Noninvasive Analysis of Paint Mixtures on Canvas Using an EPR MOUSE

Many artists create the variety of colors in their paintings by mixing a small number of primary pigments. Therefore, analytical techniques for studying paintings must be capable of determining the components of mixtures. Electron paramagnetic resonance (EPR) spectroscopy is one of many techniques that can achieve this, however it is invasive. With the recent introduction of the EPR mobile universal surface explorer (MOUSE), EPR is no longer invasive. The EPR MOUSE and a least squares regression algorithm were used to noninvasively identify pairwise mixtures of seven different paramagnetic pigments in paint on canvas. This capability will help art conservators, historians, and restorers to study paintings with EPR spectroscopy.

An electron paramagnetic resonance mobile universal surface explorer

Many samples cannot be studied by electron paramagnetic resonance (EPR) spectroscopy because they are too large to fit into the spectrometer and too precious to be destructively sampled for study. An EPR mobile universal surface explorer (MOUSE), also known as a unilateral EPR spectrometer, was constructed for studying this class of sample. The EPR MOUSE can nondestructively record a low frequency EPR (LFEPR) spectrum of a small region of any size object by placing the MOUSE against the object. The capabilities of the EPR MOUSE are demonstrated on paramagnetic paint pigments on canvas, magnetic ink on paper, and a ceramic candlestick. The mobile nature of the MOUSE will allow the spectrometer to be brought to the sample, thus opening new applications of EPR spectroscopy.

Investigation of Drying of Building Materials by Single-sided NMR

Single-sided NMR devices, like NMR MOUSE (MObile Universal Surface Explorer), are designed to allow NMR surface measurements to be conducted on arbitrarily large samples, and are therefore valuable tools to evaluate non-invasively moisture content “inside” a planar object. In this work, we aim to perform “in situ” studies of moisture transport in building materials during drying experiments with NMR MOUSE. The local moisture content was monitored over time and mapped over sample thickness with a depth resolution of 0.5mm and a maximum penetration depth of 15mm. In addition, NMR MOUSE allows measuring transverse relaxation time T2. Experimental results show that moisture content is homogeneously distributed over the thickness, which indicates that moisture is transferred through capillary processes. Furthermore, transverse relaxation time distribution measurements revealed that the drainage of pore water occurs sequentially from larger pores to smaller pores.

Investigation of the extraction process in gel‐spinning technology for ultrahigh‐molecular‐weight polyethylene fibers by low‐field nuclear magnetic resonance

ABSTRACTA portable, low‐field nuclear magnetic resonance scanner, the nuclear magnetic resonance mobile universal surface explorer, is introduced as a tool for investigating the extraction process of mineral oil in the gel‐spinning technology of ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers. Factors affecting the extraction process were studied systematically; these included the UHMWPE type, extraction agent type, and concentration and ultrasound. We found that the extraction process could be described by a replacement–dilution dual‐effect model. The extraction agent not only replaced and extracted the mineral oil but also considerably decreased the viscosity of mineral oil and thus enhanced the molecular motion and diffusion of mineral oil. Although chloroform had a smaller molecular size and lower boiling point, benzene and cyclohexane were found to exhibit more efficient extraction and dilution effects on mineral oil. The extraction efficiency could be characterized by the diffusion of mineral oil in the mineral oil/UHMWPE gel/deuterated extraction agent multicomponent systems during the extraction. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42018.

Evaluation of a mobile NMR sensor for determining skin layers and locally estimating the T2eff relaxation time in the lower arm

The nuclear magnetic resonance (NMR) mobile-universal-surface-explorer (MOUSE) was evaluated in a pilot study to determine its ability to detect physiological changes in human skin caused by physical or pharmacological interventions. The left lower arm skin thicknesses of ten male subjects were measured five times using a Profile NMR-MOUSE(®) ((1)H, 19 MHz) before and after a venous occlusion manoeuvre. In five of the subjects, the T(2eff) relaxation times were derived from a bi-exponential fitting and were determined in the dermis and subcutis before and after applying a salve containing capsaicin. The dermis (including the epidermis) showed rather homogeneous signal amplitudes. The subcutis was characterised by higher and more variable amplitudes. The full-skin thickness values were affirmed by ultrasound imaging. The NMR profiles did not show significant skin swelling due to venous occlusion. In the dermis, capsaicin caused significant (p < 0.05) decreases in both components of T(2eff) (100 ± 19 ms-19 ± 10 ms; 9.5 ± 0.5 ms-7.2 ± 1.6 ms). In the subcutis, the T(2eff) was not affected. In principle, NMR-MOUSE profiles are capable of detecting skin structure. However, precise measurements are jeopardised by poor reproducibility, long acquisition times, and incompatibility between the geometries of the sensitive area of the instrument and the non-planar structure of the skin. In the dermis, T(2eff) contrast could be used to detect the changes in tissue composition caused by inflammatory reactions.

The Incredible Shrinking Scanner

A personal narrative is presented which explores the author's experience of helping to develop a nuclear magnetic resonance mobile universal surface explorer (NMR-MOUSE) portable imaging device.

Non-invasive ‘through-package’ assessment of the microstructural quality of a model food emulsion by the NMR MOUSE

Recently, NMR has been demonstrated in a truly non-invasive through-package ‘sensor’ mode, also denoted as the MObile Universal Surface Explorer (MOUSE). In this feasibility study, we present a first example where we use the MOUSE sensor for assessment of the microstructural quality of a food material. We have taken model systems consisting of protein-stabilized oil-in-water emulsions, where an important microstructural quality parameter is water exudation (WE). In order to establish a sound relation between MOUSE signals and WE, it was necessary to deploy multivariate calibration techniques. It was found that the performance of the MOUSE is comparable to that of conventional benchtop NMR. Thus it was demonstrated that the NMR MOUSE presents a good option for non-invasive assessment of microstructural quality parameters, e.g. in manufacturing and in the supply chain.

Characterization of local deformation in filled-silicone elastomers subject to high strain – NMR MOUSE and Magnetic Resonance Imaging as a diagnostic tool for detection of inhomogeneities

Magnetic Resonance Imaging (MRI) and unilateral Nuclear Magnetic Resonance (NMR) relaxometry with the NMR MOUSE (MObile Universal Surface Explorer) have been used to characterize local permanent deformation in silicone parts subject to high compressive strain. Samples returned from field service have been characterized by areas of high compression set. Materials excised from these damaged sections have been shown to be clearly distinguishable from undeformed material from the same part and from pristine material by NMR spin-echo, NMR MOUSE and MRI protocols. The results of these studies have been interpreted in the context of studies of model materials of varying crosslink density. The areas of local deformation have been characterized by a reduction in the residual dipolar coupling, which is proportional to the crosslink density and in the non-network sol fraction. These differences were likely to be present in these polymers at the time of production due to inefficient mixing. Additionally, both T 2 weighted Single Point Imaging (SPI) and T 2 weighted MRI experiments have been used to map out the location of different crosslink densities, ultimately determining the quality or homogeneity in silicone components.

Magnetic resonance studies of cement based materials in inhomogeneous magnetic fields

Single-sided magnets give hope that Nuclear Magnetic Resonance (NMR) might in future be used for in situ characterisation of hydration and water transport in the surface layers of concrete slabs. Towards that end, a portable NMR-MOUSE (MObile Universal Surface Explorer) has been used to follow the hydration of gypsum based plaster, a Portland cement paste and concrete mortar. The results compare favourably to those obtained using a standard laboratory bench-top spectrometer. Further, stray field imaging (STRAFI) based methods have been used with embedded NMR detector coils to study water transport across a mortar/topping interface. The measured signal amplitudes are found to correlate with varying sample conditions.

Mobile NMR for Analysis of Polyethylene Pipes

R(nuclear magnetic resonance mobile universal surface explorer) was explored in this work to supply morphological data of poly(ethylene) pipes nondestructively. PE-100 pipes were investigated in the new state, after squeezing them ∞at, and after annealing well below the glass temperature. Furthermore, the change in morphology induced by a pressure load from the inside and a point load from the outside was investigated as a function of depth, and the morphology change across a welding line was imaged. A shear-band was detected by destructive high-fleld NMR imaging in an area of severe deformation of a pipe, where an anomalous depths proflle was observed by the NMR-MOUSE. These results demonstrate that the NMR-MOUSE is a suitable tool for non-destructive state assessment of polymer pipes on the basis of laboratory reference data.

New technologies to determine solid fat content on‐line

AbstractThe determination of solid fat content (SFC) is an important analytical procedure in the food industry. The most common way to determine SFC is by low‐resolution pulsed NMR (p‐NMR). Although this technique is very sensitive and easy to use, it has the disadvantage that it cannot be used for on‐line measurements. The present work compares new technologies to determine SFC on‐line. On‐line ultrasonic spectroscopy and NMR‐MOUSE (NMR mobile universal surface explorer) techniques were compared with off‐line p‐NMR measurements and there was a good correlation between the values obtained. Ultrasonic measurements accurately described the SFC variation, whereas NMR‐MOUSE determinations need to be improved to some extent owing to a strong temperature and motion dependence. These two techniques can be used as on‐line methodologies to determine SFC during the crystallization of fats.

Advances of unilateral mobile NMR in nondestructive materials testing

Unilateral mobile NMR employs portable instrumentation with sensors, which are applied to the object from one side. Based on the principles of well-logging NMR, a hand-held sensor, the NMR-MOUSE (MObile Universal Surface Explorer) has been developed for nondestructive materials testing. In the following, a number of new applications of unilateral NMR in materials science are reviewed. They are the state assessment of polyethylene pipes, the characterization of wood, the in situ evaluation of stone conservation treatment, high-resolution profiling of rubber tubes and 2-D imaging for defect analysis in rubber products.

Thermo-oxidative aging of elastomers: a temperature control unit for operation with the NMR-MOUSE

Temperature-controlled measurements of the transverse relaxation time were conducted with the NMR-MOUSE (nuclear magnetic resonance mobile universal surface explorer) at 50°C to investigate the heterogeneity of rubber sheets induced by thermo-oxidative aging. With temperature stabilization the relative error ofT2 decreased by a factor of 4 on the short time scale. Without temperature stabilization it may reach 30% in the long-time range because of temperature changes in the laboratory. Two different types of mobile temperature control units operating with the NMR-MOUSE are described. These temperature control units are small and portable like the NMR-MOUSE.