Biomedical subjects

Wilson Barros

Publications and source records attributed to Wilson Barros.

6 recordsLinked to original sources

PubMed2006

Enhanced Overhauser contrast in proton-electron double-resonance imaging of the formation of an alginate hydrogel.

Proton-electron double-resonance imaging (PEDRI) was recently employed to monitor the process of formation of a calcium alginate hydrogel at a field of 16mT. Here, under the same experimental conditions, images obtained through this technique are compared to images obtained by conventional T(2)-weighted method. The results confirm that the image contrast obtained using PEDRI, thanks to the Overhauser effect, exhibits an improved sensitivity with respect to changes in water mobility as previously suggested in the literature. Furthermore, by increasing the echo time interval for the T(2)-weighted images, important features of the gelling dynamics obtained via PEDRI could not be reproduced.

Alginates↗

PubMed2005

Simultaneous measurement of D and T2 using the distant dipolar field.

The presence of long-range dipolar fields in liquids is known to introduce a non-linear term in the Bloch-Torrey equations which is responsible for many interesting effects in nuclear magnetic resonance as well as in magnetic resonance imaging. We show here, for the first time, that the diffusion coefficient D and the spin-spin relaxation time T2 can be obtained simultaneously from the time evolution profile of the long-range dipolar field refocused signal. In a COSY Revamped by Z-asymmetric Echo Detection sequence, the analytical first-order approximation solution of the Bloch-Torrey equations modified to include the effect of the distant dipolar field is used to demonstrate the technique in an experiment using doped water.

Diffusion↗

PubMed2005

Distant-dipole field in liquids and diffusion: a perturbative approach.

A perturbative approach is employed to solve the Bloch-Torrey equations in the presence of distant-dipole fields in nuclear magnetic resonance. The procedure, although only carried out to first order in the perturbation parameter a=1/k2Dtaud, could, in principle, be generalized to higher orders. Here D is the diffusivity, taud the dipolar demagnetization time, and k is the wave vector of the spatial modulation of magnetization produced by the magnetic field gradient. The results are especially interesting for dilute binary mixtures consisting of molecular species with different diffusivities. In this case the calculated two-dimensional correlation spectroscopy revamped by asymmetric Z-gradient echo detection spectra are shown to be free from some inadequacies resulting from a simplistic application of standard approximations.

Journal Article↗

PubMed2004

Intermolecular double-quantum coherences in two-dimensional spectra of binary mixtures in solution. The role of diffusion.

Proton NMR two-dimensional 2-D spectra of binary mixtures, obtained with the correlation spectroscopy revamped by asymmetric Z gradient echo detection pulse sequence, were employed to test various assumptions usually adopted to describe the role of diffusion in intermolecular double quantum coherences. When two molecular species, with significantly different diffusivities, are considered, the relative amplitudes of the peaks, and their widths, furnish a stringent test that unveils some inadequacies in standard approximations.

Journal Article↗

PubMed2003

Enhanced migration and ionic transport through membranes.

The effect of Coulomb forces upon transport enhancement of mobile ions, in the presence of slowly migrating charged polymeric chains, is investigated in a nonequilibrium regime brought about by a semipermeable membrane and a chemical reaction. By means of a numerical solution of the Nernst-Planck-Poisson equations, we predict the size of the effect, the conditions for positive or negative enhancement, and the dependence upon all relevant parameters. The limitations of the description of migration enhancement by an effective diffusion coefficient are also established.

Journal Article↗

PubMed2003

Low field intermolecular double-quantum coherence imaging via the Overhauser effect.

Intermolecular double-quantum coherence (i-DQC) signals in liquids are usually associated with high magnetic fields. We demonstrate that, in a magnetic field of only 16mT, i-DQC imaging of water protons is feasible thanks to the nuclear magnetization enhancement produced by the Overhauser effect. i-DQC images of a phantom containing an aqueous solution of a trityl free radical, with phase encoding in the DQC evolution period or in the acquisition period, are presented. Possible applications of low field i-MQC images are proposed.

Feasibility Studies↗