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Single-sided and mobile nuclear magnetic resonance (NMR) sensors have the advantages of portability, low cost, and low power consumption compared to conventional high-field NMR and magnetic resonance imaging (MRI) systems. We present fast, flexible, and easy-to-implement target field algorithms for mobile NMR and MRI magnet design. The optimization finds a global optimum in a cost function that minimizes the error in the target magnetic field in the sense of least squares. When the technique is tested on a ring array of permanent-magnet elements, the solution matches the classical dipole Halbach solution. For a single-sided handheld NMR sensor, the algorithm yields a 640 G field homogeneous to 16 100 ppm across a 1.9 cc volume located 1.5 cm above the top of the magnets and homogeneous to 32 200 ppm over a 7.6 cc volume. This regime is adequate for MRI applications. We demonstrate that the homogeneous region can be continuously moved away from the sensor by rotating magnet rod elements, opening the way for NMR sensors with adjustable "sensitive volumes."

Portable, single-sided NMR sensors can operate under conditions inaccessible to conventional NMR while featuring lower cost, portability, and the ability to analyze arbitrary-sized objects. Such sensors can nondestructively probe the interior of samples by collecting images and measuring relaxation and diffusion constants, and, given careful shimming schemes, even perform chemical analysis. The inherently strong magnetic-field gradients of single-sided sensors developed so far has prevented imaging of materials with high water content, such as biological tissues, over large volumes whereas designs with more homogeneous fields suffer from low field strength and typically cannot probe volumes larger than 10 cm3. We present a design with a continuously adjustable sensitive volume, enabling the effective volume to be enlarged several fold. This process allows for imaging in reasonable times of much bigger objects and opens the door to the possibility of clinical imaging with portable sensors. We demonstrate MRI in axial and saggital planes, at different depths of the sensitive volume and T1-weighted contrast in a tissue sample.

Single-sided and mobile nuclear magnetic resonance (NMR) sensors have the advantages of portability, low cost, and low power consumption compared to conventional high-field NMR and magnetic resonance imaging (MRI) systems. We present fast, flexible, and easy-to-implement target field algorithms for mobile NMR and MRI magnet design. The optimization finds a global optimum in a cost function that minimizes the error in the target magnetic field in the sense of least squares. When the technique is tested on a ring array of permanent-magnet elements, the solution matches the classical dipole Halbach solution. For a single-sided handheld NMR sensor, the algorithm yields a 640 G field homogeneous to 16 100 ppm across a 1.9 [cm.sup.3] volume located 1.5 cm above the top of the magnets and homogeneous to 32 200 ppm over a 7.6 [cm.sup.3] volume. This regime is adequate for MRI applications. We demonstrate that the homogeneous region can be continuously moved away from the sensor by rotating magnet rod elements, opening the way for NMR sensors with adjustable 'sensitive volumes.' Index Terms--Least-squares optimization, magnetic devices, magnetic resonance, magnetostatics, nuclear magnetic resonance.

A coaxial nuclear magnetic resonance (NMR) probe is built to measure diffusion and relaxation properties of liquid samples. In particular, we demonstrate the acquisition of two-dimensional (2D) distribution functions (T1-T2 and diffusion--T2), essential for fluids characterization. The compact design holds promise for miniaturization, thus enabling the measurement of molecular diffusion that is inaccessible to conventional micro-NMR setups. Potential applications range from crude oil characterization to biomolecular screening and detections. [ABSTRACT FROM AUTHOR]

Purpose: Diffusional kurtosis imaging (DKI) measures the deviation of the displacement probability from a normal distribution, complementing the data commonly acquired by diffusion MRI. It is important to elucidate the sources of kurtosis contrast, particularly in biological tissues where microscopic kurtosis (intrinsic kurtosis) and diffusional heterogeneity may co‐exist. Methods: We have developed a technique for microscopic kurtosis MRI, dubbed microscopic diffusional kurtosis imaging (µDKI), using a symmetrized double diffusion encoding (s‐DDE) EPI sequence. We compared this newly developed µDKI to conventional DKI methods in both a triple compartment phantom and in vivo. Results: Our results showed that whereas conventional DKI and µDKI provided similar measurements in a compartment of monosphere beads, kurtosis measured by µDKI was significantly less than that measured by conventional DKI in a compartment of mixed Gaussian pools. For in vivo brain imaging, µDKI showed small yet significantly lower kurtosis measurement in regions of the cortex, CSF, and internal capsule compared to the conventional DKI approach. Conclusions: Our study showed that µDKI is less susceptible than conventional DKI to sub‐voxel diffusional heterogeneity. Our study also provided important preliminary demonstration of our technique in vivo, warranting future studies to investigate its diagnostic use in examining neurological disorders. [ABSTRACT FROM AUTHOR]

The 2D nuclear magnetic resonance diffusion-relaxation experiment (NMR DT2) has proven to be a powerful method to characterize complex fluids. Molecular components with distinct diffusion coefficients are shown on DT2 maps as separate peaks. In porous media such as reservoir rocks, molecular diffusion is restricted such that the apparent diffusion coefficient is time dependent and the diffusion behavior is non-Gaussian. Such restricted diffusion effects can manifest on the DT2 maps and complicate the interpretation of the results, but so far, they have not been systematically investigated. We used controlled laboratory experiments to demonstrate the influence of non-Gaussian restricted diffusion on NMR DT2 maps under various conditions and to show how restricted diffusion effects on DT2 maps can be distinguished from multiphase fluids. NMR DT2 experiments were carried out on a series of water-saturated packs of glass beads and two rock cores. The results revealed the important role of two critical length scales controlling the restricted diffusion effects on NMR DT2 maps: the molecular diffusion length ℓD during the NMR diffusion encoding time and the characteristic pore size dpore. For ℓD « dpore, the effect of non-Gaussian diffusion was negligible and the NMR DT2 map showed only one peak. As ℓD approaches dpore, an additional peak with a smaller diffusion coefficient emerged (resembling the DT2 map of an unrestricted two molecular components fluid), and its relative intensity was maximized (to ~17%), when ℓD ≅ dpore. As ℓD further increased, the relative intensity of the additional peak started decreasing, in contrast to the scenario of DT2 maps of multiphase fluids. We determined the extent and influence of restricted diffusion on NMR DT2 maps, and we informed the interpretation of NMR DT2 measurements, which are commonly used to quantify gas, water, and oil signals in reservoir rocks. [ABSTRACT FROM AUTHOR]

State-of-the-art NMR spectrometers using superconducting magnets have enabled, with their ultrafine spectral resolution, the determination of the structure of large molecules such as proteins, which is one of the most profound applications of modern NMR spectroscopy. Many chemical and biotechnological applications, however, involve only small-to-medium size molecules, for which the ultrafine resolution of the bulky, expensive, and high-maintenance NMR spectrometers is not required. For these applications, there is a critical need for portable, affordable, and low-maintenance NMR spectrometers to enable in-field, on-demand, or online applications (e.g., quality control, chemical reaction monitoring) and co-use of NMR with other analytical methods (e.g., chromatography, electrophoresis). As a critical step toward NMR spectrometer miniaturization, small permanent magnets with high field homogeneity have been developed. In contrast, NMR spectrometer electronics capable of modern multidimensional spectroscopy have thus far remained bulky. Complementing the magnet miniaturization, here we integrate the NMR spectrometer electronics into 4-mm2 silicon chips. Furthermore, we perform various multidimensional NMR spectroscopies by operating these spectrometer electronics chips together with a compact permanent magnet. This combination of the spec-trometer-electronics-on-a-chip with a permanent magnet represents a useful step toward miniaturization of the overall NMR spectrometer into a portable platform. [ABSTRACT FROM AUTHOR]

Superparamagneticiron oxide (SPIO) nanoparticles have the potentialto be used in the characterization of porous rock formations in oilfields as a contrast agent for NMR logging because they are smallenough to traverse through nanopores and enhance contrast by shorteningNMR T2relaxation time. However, successfuldevelopment and application require detailed knowledge of particlestability and mobility in reservoir rocks. Because nanoparticle adsorptionto sand (SiO2) and rock (often CaCO3) affectstheir mobility, we investigated the thermodynamic equilibrium adsorptionbehavior of citric acid-coated SPIO nanoparticles (CA SPIO NPs) andpoly(ethylene glycol)-grafted SPIO nanoparticles (PEG SPIO NPs) onSiO2(silica) and CaCO3(calcium carbonate).Adsorption behavior was determined at various pH and salt conditionsvia chemical analysis and NMR, and the results were compared withmolecular theory predictions. Most of the NPs were recovered fromsilica, whereas far fewer NPs were recovered from calcium carbonatebecause of differences in the mineral surface properties. NP adsorptionincreased with increasing salt concentration: this trend was qualitativelyexplained by molecular theory, as was the role of the PEG graftingin preventing NPs adsorption. Quantitative disagreement between thetheoretical predictions and the data was due to NP aggregation, especiallyat high salt concentration and in the presence of calcium carbonate.Upon aggregation, NP concentrations as determined by NMR T2were initially overestimated and subsequently correctedusing the relaxation rate 1/T2, whichis a function of aggregate size and fractal dimension of the aggregate.Our experimental validation of the theoretical predictions of NP adsorptionto minerals in the absence of aggregation at various pH and salt conditionsdemonstrates that molecular theory can be used to determine interactionsbetween NPs and relevant reservoir surfaces. Importantly, this integratedexperimental and theoretical approach can be used to gain insightinto NP mobility in the reservoir. [ABSTRACT FROM AUTHOR]

Crude oils, which are complex mixtures of hydrocarbons, can be characterized by nuclear magnetic resonance diffusion and relaxation methods to yield physical properties and chemical compositions. In particular, the field dependence, or dispersion, of T1 relaxation can be used to investigate the presence and dynamics of asphaltenes, the large molecules primarily responsible for the high viscosity in heavy crudes. However, the T2 relaxation dispersion of crude oils, which provides additional insight when measured alongside T1, has yet to be investigated systematically. Here we present the field dependence of T1-T2 correlations of several crude oils with disparate densities. While asphaltene and resin-containing crude oils exhibit significant T1 dispersion, minimal T2 dispersion is seen in all oils. This contrasting behavior between T1 and T2 cannot result from random molecular motions, and thus, we attribute our dispersion results to highly correlated molecular dynamics in asphaltene-containing crude oils., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)