Magnetic resonance contrast-enhancing agents whose effects are altered by electric fields
Frank, Shachar
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Permalink
https://hdl.handle.net/2142/20210
Description
Title
Magnetic resonance contrast-enhancing agents whose effects are altered by electric fields
Author(s)
Frank, Shachar
Issue Date
1993
Doctoral Committee Chair(s)
Lauterbur, Paul C.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
The membrane potential is an important property of many cells and organelles. Changes in the potential of membranes control or accompany numerous biological processes including information transfer in neuronal networks. Magnetic resonance imaging (macroscopic and microscopic) is essentially a non-invasive 3-dimensional imaging modality and could record changes in membrane potential if they were accompanied by changes in water proton relaxation rates in the vicinity of the membrane, and thus become a powerful tool for studying neuronal activity and, ultimately, understanding how the brain functions. With that in mind, contrast-enhancing agents whose effects are changed by electric fields, similar in function to voltage sensitive dyes, were developed. It may also be possible to develop magnetic resonance contrast agents that respond to changes in temperature, pH, light, or concentrations of certain ions and molecules, as all these changes in the environment are known to induce volume phase transitions in some polyelectrolyte gels.
A polyelectrolyte gel, sodium polyacrylate, that undergoes a volume phase transition when an electric field is applied, was modified in such a way as to make it magnetic by the incorporation of small superparamagnetic iron oxide particles into the polymer's network. A suspension of magnetic gel microparticles that shrunk when an electric field was applied also showed an increase in the transverse relaxation rate of the water. A similar change occurred when the magnetic gel microparticles were put in a 10% red blood cell suspension and the cells were hyperpolarized by adding valinomycin. These experiments should be extended to excitable cells, both in vitro and in vivo, including MRI experiments.
Although the work concentrated on superparamagnetic-contrast agents, some preliminary work was carried out on Gd$\sp{3+}$-bound (paramagnetic) polyelectrolyte gel microparticles which showed a small decrease in the relaxation rate when an electric field was applied.
The mechanisms for the changes in relaxation rates that accompany the changes in size of the magnetic gel microparticles are not fully understood. Both long range effects of the magnetized gel microparticles on diffusing water molecules, and local changes within the shrinking or swelling gel microparticle can be important contributors.
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