Biomedical subjects

D Pusiol

Publications and source records attributed to D Pusiol.

4 recordsLinked to original sources

PubMed2001

Improving resolution in fast rotating-frame experiments.

The rapid rotating-frame technique allows significant reduction in data-acquisition time compared with the two-dimensional method by stroboscopic observation of the nuclear magnetization during its evolution in the rotating frame. A onefold reduction in the dimensionality of the original rotating-frame experiment is achieved by using a train of strong radiofrequency pulses separated by short acquisition windows. The penalty for shortening experimental time is a reduction in spectral resolution compared with the two-dimensional method due to relaxation of transverse magnetization components during the observation windows. A variant of the rapid-rotating frame technique for improving spectral resolution based on undersampling and self-phase encoding is presented. An M-fold resolution improvement requires M experiments, thus, making possible a tradeoff between spectral resolution and experimental time. The technique was applied for spatial localization of quadrupole nuclei in powder solids, and resolution improvement is demonstrated on one- and two-dimensional NQR images.

Journal Article↗

PubMed1999

Phase-modulated rotating-frame NQR techniques for spatial encoding

The rotating-frame method of localization for spatially resolved spectroscopy and imaging in the pure quadrupole regime relies on a gradient B(1) field in which spins experience a flip angle dependent on their position in the B(1) field strength. So far, the techniques have been implemented as amplitude-modulated methods, i.e., the spatial nuclear quadrupole distribution is encoded in the amplitude of the free-induction decay signals. In this work, we describe the implementation of phase-modulated variants of both two-dimensional and rapid rotating-frame imaging techniques. The experiments are discussed for both single crystalline and powder samples. The phase-modulated experiment offers some advantages over the amplitude-encoding technique: It enables one to distinguish the sign of the spatial coordinate and the signal-to-noise ratio is higher than for the simplest amplitude-encoding method. Copyright 1999 Academic Press.

Journal Article↗

PubMed1998

Mapping molecular orientation in solids by rotating-frame NQR techniques

A multi-dimensional NQR technique to image both the spatial distribution of quadrupolar nuclei and the local orientation of the electric field gradient tensor at the quadrupole sites in solids is reported. The encoding procedure is based on the irradiation of the sample by a pulse sequence composed of spatially homogeneous and inhomogeneous radiofrequency fields. A method that encodes the spatial and orientation information in the amplitudes of the free-induction decay signals and a proper three-dimensional reconstruction procedure that yields the space-orientation-dependent NQR spectra are described. A two-dimensional variant allows rapid measurement of the spatially dependent orientation distribution of molecules, disregarding the spectroscopic information. Copyright 1998 Academic Press.

Journal Article↗

PubMed1998

A new formalism for the evaluation of order-fluctuation modes in liquid crystals from field-cycling NMR-relaxometry data.

A numerical procedure is presented which permits one to derive a formal distribution of collective fluctuation modes from experimental field-cycling NMR-relaxometry data of an ordered system. The purpose is to distinguish true order-fluctuation modes from local reorientation mechanisms. The evaluation scheme is demonstrated using simulated as well as experimental data. Applications serving the elucidation and characterization of modified or limited director fluctuation modes as they occur with liquid crystals in pores or with lyotropic systems are discussed. Test experiments have been carried out with a potassium laurate system.

Crystallization↗