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Nuclear magnetic resonance (NMR) spectroscopy and NMR imaging require a sample to be positioned in a homogeneous magnetic field inside a strong magnet. The instrumentation is large, and the sample […]

Test samples of LDPE (low-density polyethylene) were electrically aged until PD (partial discharge) and electrical treeing occurred. Investigations on the spatial distribution of microscopic domain sizes in the lameliar morphology of the samples were carried out applying a novel method of proton NMR imaging which probes magnetization transfer by spin diffusion. Spatial changes of LDPE morphology are detected due to the appearance of PD.

Measures the residual dipolar couplings by hydrogen dipolar-encoded longitudinal magnetization, double and triple-quantum nuclear magnetic resonance (NMR) in cross-linked elastomers. Correlation with cross-link density; Reconversion of multiple quantum coherences.

The NMR spin-diffusion process-taking place in morphology represented by three different domains with arbitrary sizes and diffusivities is investigated. The effects of large changes in the size of the interface domain and the spin-diffusion coefficients of this domain on the spin-diffusion decay and build-up curves were analyzed by numerical simulations.

A novel scheme is presented for the measurement of two-dimensional stochastic magnetic resonance spectra. The excitation consists of a time-shifted sum of noise signals at the Larmor frequency. Longitudinal magnetization is detected in the audiofrequency regime so that excitation and response are well decoupled for accessing large bandwidths. Because noise excitation saves RF power, the method shows promise for applications in the spectroscopic detection of magnetic resonance signals from large objects. [ABSTRACT FROM AUTHOR]

In this article, we present a portable NMR relaxometry system optimized for the point-of-care analysis of body liquids such as blood. The presented system is centered on an NMR-on-a-chip transceiver ASIC, a reference frequency generator with arbitrary phase control, and a custom-designed miniaturized NMR magnet with a field strength of 0.29 T and a total weight of 330 g. The NMR-ASIC co-integrates a low-IF receiver, a power amplifier, and a PLL-based frequency synthesizer on a total chip area of 1100 × 900 μm 2 . The arbitrary reference frequency generator enables the use of conventional CPMG and inversion sequences, as well as modified water-suppression sequences. Moreover, it is used to implement an automatic frequency lock to correct temperature-induced magnetic field drifts. Proof-of-concept measurements on NMR phantoms and human blood samples show an excellent concentration sensitivity of v[Formula: see text] = 2.2 mM/[Formula: see text]. This very good performance renders the presented system an ideal candidate for the future NMR-based point-of-care detection of biomarkers such as the blood glucose concentration.

Objective: In biomanufacturing there is a need for quantitative methods to map cell viability and density inside 3D bioreactors to assess health and proliferation over time. Recently, noninvasive MRI readouts of cell density have been achieved. However, the ratio of live to dead cells was not varied. Herein we present an approach for measuring the viability of cells embedded in a hydrogel independently from cell density to map cell number and health., Methods: Independent quantification of cell viability and density was achieved by calibrating the 1 H magnetization transfer- (MT) and diffusion-weighted NMR signals to samples of known cell density and viability using a multivariate approach. Maps of cell viability and density were generated by weighting NMR images by these parameters post-calibration., Results: Using this method, the limits of detection (LODs) of total cell density and viable cell density were found to be 3.88 ×10 8 cells · mL -1 · Hz -1/2 and 2.36 ×10 9 viable cells · mL -1 · Hz -1/2 respectively., Conclusion: This mapping technique provides a noninvasive means of visualizing cell viability and number density within optically opaque bioreactors., Significance: We anticipate that such nondestructive readouts will provide valuable feedback for monitoring and controlling cell populations in bioreactors.

Objective: For tissue engineering, there is a need for quantitative methods to map cell density inside three-dimensional (3-D) bioreactors to assess tissue growth over time. The current cell mapping methods in 2-D cultures are based on optical microscopy. However, optical methods fail in 3-D due to increased opacity of the tissue. We present an approach for measuring the density of cells embedded in a hydrogel to generate quantitative maps of cell density in a living, 3-D tissue culture sample., Methods: Quantification of cell density was obtained by calibrating the 1 H T 2 , magnetization transfer (MT) and diffusion-weighted nuclear magnetic resonance (NMR) signals to samples of known cell density. Maps of cell density were generated by weighting NMR images by these parameters post-calibration., Results: The highest sensitivity weighting arose from MT experiments, which yielded a limit of detection (LOD) of [Formula: see text] cells/mL/ √{Hz} in a 400 MHz (9.4 T) magnet., Conclusion: This mapping technique provides a noninvasive means of visualizing cell growth within optically opaque bioreactors., Significance: We anticipate that such readouts of tissue culture growth will provide valuable feedback for controlled cell growth in bioreactors.

A generalized approach to obtain two-dimensional maps of spatial particle coordinates and their derivatives with respect to time by PFG-NMR employing multiple gradient pulses is presented. A sequence of n magnetic field gradient pulses makes it possible, after independent stepping of each pulse and subsequent Fourier transformation, to plot the spin density distribution in coordinate space at n times and along the respective directions of the gradient pulses. In particular, two gradient pulses of effective area k(1) and k(2) separated by a time interval Delta lead to a plot of the combined two-time probability density, W(2)(r(1), 0; r(2), Delta), to find a particle at a coordinate r(1) at t = 0 and at r(2) at t = Delta. A conventional experiment for measuring transport properties by simultaneous stepping of the gradients under the condition k(1) = -k(2) is equivalent to a projection onto the secondary diagonal in the [r(1), r(2)] plot. The main diagonal represents an average position between the two timepoints t = 0 and t = Delta, so that a rotation of the coordinate plot by an angle of 45 degrees allows one to correlate the displacement R = r(2) - r(1) with the averaged position r parallel to the gradient direction. While an average velocity during the time interval Delta can be defined as &vmacr; = R/Delta, an extension toward acceleration and higher order derivatives is straightforward by modification of the pulse sequence. We discuss this concept by application to flow through a circular and a narrowing pipe (confusor), respectively, the experimental results of which are compared to numerical simulations. Copyright 2000 Academic Press.

The response of the spin system has been investigated by numerical simulations in the case of a nuclear magnetic resonance (NMR) experiment performed in inhomogeneous static and radiofrequency fields. The particular case of the NMR-MOUSE was considered. The static field and the component of the radiofrequency field perpendicular to the static field were evaluated as well as the spatial distribution of the maximum NMR signal detected by the surface coil. The NMR response to various pulse sequences was evaluated numerically for the case of an ensemble of isolated spins (1/2). The behavior of the echo train in Carr-Purcell-like pulse sequences used for measurements of transverse relaxation and self-diffusion was simulated and compared with the experiment. The echo train is shown to behave qualitatively differently depending on the particular phase schemes used in these pulse sequences. Different echo trains are obtained, because of the different superposition of Hahn and stimulated echoes forming mixed echoes as a result of the spatial distribution of pulse flip angles. The superposition of Hahn and stimulated echoes originating from different spatial regions leads to distortions of the mixed echoes in intensity, shape, and phase. The volume selection produced by Carr-Purcell-like pulse sequences is also investigated for the NMR-MOUSE. The developed numerical simulation procedure is useful for understanding a variety of experiments performed with the NMR-MOUSE and for improving its performance. Copyright 2000 Academic Press.

NMR imaging and one- and two-dimensional self-diffusion propagator measurements of the liquid phase in salt water ice are presented. The properties of the network of brine-filled pores are found to depend on the growth conditions of the ice. Two types of samples are compared: (a) shock-frozen ice produced in the probe in situ and (b) ice grown over several hours under controlled conditions. By shock-freezing, an ice structure could be produced which featured streak-like porous channels of diameters of up to 300 &mgr;m allowing almost unrestricted self-diffusion along one preferential axis but reduced diffusivities in the remaining directions. In ice grown under controlled conditions, the pore sizes are near the resolution limit of the imaging experiment of typically 50 &mgr;m. For this type of samples, strongly non-Gaussian self-diffusion propagators are obtained, indicating restricted self-diffusion on rms scales of 30 &mgr;m. Common to all samples was the observation of highly anisotropic self-diffusion. One- and two-dimensional propagators are compared in order to estimate the degree of anisotropy and the size of the restrictions. Copyright 2000 Academic Press.