Biomedical subjects

Yi-Qiao Song

Publications and source records attributed to Yi-Qiao Song.

10 recordsLinked to original sources

PubMed2005

Quantitative characterization of food products by two-dimensional D-T2 and T1-T2 distribution functions in a static gradient.

We present new NMR techniques to characterize food products that are based on the measurement of two-dimensional diffusion-T2 relaxation and T1-T2 relaxation distribution functions. These measurements can be performed in magnets of modest strength and low homogeneity and do not require pulsed gradients. As an illustration, we present measurements on a range of dairy products that include milks, yogurt, cream, and cheeses. The two-dimensional distribution functions generally exhibit two distinct components that correspond to the aqueous phase and the liquid fat content. The aqueous phase exhibits a relatively sharp peak, characterized by a large T1/T2 ratio of around 4. The diffusion coefficient and relaxation times are reduced from the values for bulk water by an amount that is sample specific. The fat signal has a similar signature in all samples. It is characterized by a wide T2 distribution and a diffusion coefficient of 10(-11) m2/s for a diffusion time of 40 ms, determined by bounded diffusion in the fat globules of 3 microm diameter.

Dairy Products↗

PubMed2005

Rapid T1 measurement via decay-recovery decomposition: applications in fringe field and distributed relaxation experiments.

Spin-lattice relaxation time (T(1)) measurements are often time-consuming due to the need to measure the full equilibrium magnetization with a long wait time. However, any magnetization recovery can be decomposed into pure recovery and pure decay components, the latter of which lends itself to a much simpler and faster extraction of T(1). We demonstrate several pulse sequences that accomplish this decomposition experimentally and illustrate its applications in a steady magnetic field gradient, and in materials possessing a broad distribution of T(1).

Algorithms↗

PubMed2005

Determining the resolution of Laplace inversion spectrum.

In experiments involving decaying signals, it is often desirable to analyze the data as a sum of exponential decays using the Laplace inversion method. However, Laplace inversion is an ill-conditioned problem, and it is difficult to ascertain the stability of the reconstruction method and resolution of the resulting spectrum. This paper provides an easily computed approximate bound of the resolution and offers guidelines on how to design experiments to improve the spectral resolution.

Journal Article↗

PubMed2005

Scaling laws for diffusion coefficients in mixtures of alkanes.

Natural fluids, such as crude oils, are often mixtures of a broad range of different molecules, and in situ measurement of their composition is highly desirable. Furthermore, the relationship between their composition and their physical properties has always been a challenge for such mixtures. We have analyzed diffusion in alkane mixtures to find a power law for the self-diffusion coefficient in terms of molecular sizes. We demonstrate that this power law can be used to obtain the molecular size distribution of crude oils using noninvasive measurements of diffusion distributions.

Journal Article↗

PubMed2005

An NMR technique for rapid measurement of flow.

We present a one-scan method for determining fluid flow velocity within a few milliseconds in the presence of a static field gradient, and without the need of multiple scans. A few RF-pulses populate a series of coherence pathways, each of which exhibits a phase shift that is proportional to fluid velocity. These coherence pathways produce spin echoes separated in the time domain, thus eliminating the need for phase cycling.

Magnetic Resonance Spectroscopy↗

PubMed2005

Multiple modulation multiple echoes: a one-shot method.

This paper reviews a recently reported NMR method capable of determining the diffusion constant within milliseconds and without the need of multiple scans. The method can be used with static or pulsed magnetic field gradients.

Diffusion↗

PubMed2004

Simultaneous measurement of diffusion along multiple directions.

This paper introduces the first NMR approach for simultaneously measuring the full diffusion tensor. Using magnetic field gradients of different directions to generate multiple modulations of nuclear spin magnetization, multiple echoes of different modulations are acquired in a single scan to simultaneously measure diffusion along different directions. The experimental demonstrations were conducted in both isotropic and anisotropic systems. Since the diffusion anisotropy holds structural and dynamical information, this approach may be useful for monitoring liquid crystals and electrolytes in metastable states and for studying fluidity in situ in porous networks and in vivo in biological systems.

Anisotropy↗

PubMed2004

A one-shot method for measurement of diffusion.

This paper describes an NMR method capable of determining the diffusion constant of a material within a few milliseconds and without the need of multiple scans. The method can be used with static or pulsed magnetic field gradients. It may be used to detect time-dependent processes, such as in chemical reactions, production monitoring, and medical MRI.

Diffusion↗

PubMed2002

Nonresonant multiple spin echoes.

Nonresonant manipulation of nuclear spins can probe large volumes of sample situated in inhomogeneous fields outside a magnet, a geometry suitable for mobile sensors for the inspection of roads, buildings, and geological formations. However, the interference by Earth's magnetic field causes rapid decay of the signal within a few milliseconds for protons and is detrimental to this method. Here we describe a technique to suppress the effects of Earth's field by using adiabatic rotations and sudden switching of the applied fields. We observed hundreds of spin echo signals lasting for more than 600 milliseconds and accurately measured the relaxation times of a liquid sample.

Journal Article↗

PubMedDate not supplied

Novel NMR techniques for porous media research.

Diffusion in porous media has been used as a probe of pore geometry in various NMR techniques. We will examine the effect of time-dependent diffusion in CPMG by showing that the diffusion time in CPMG is approximately the echo time, even in grossly inhomogeneous magnetic fields. Extension of the diffusion time in modified CPMG sequences is discussed. Diffusion in the susceptibility-contrast induced internal field is discussed as a means to probe pore size and pore shape. Finally, we present the general concept of two-dimensional relaxation-type experiments for study of molecules, fluids, materials and their dynamics that are characterized by spin relaxation and diffusion.

Diffusion↗