Biomedical subjects

C C Lester

Publications and source records attributed to C C Lester.

4 recordsLinked to original sources

PubMed1992

Magnetically coupled paramagnetic relaxation agents.

Measurements of the spin-lattice relaxation rates of water protons made over a wide frequency range have demonstrated that the effects of paramagnetic relaxation agents may be considerably enhanced when the paramagnetic center is incorporated into a compact structure macromolecule such as a protein that is rotationally constrained. The immobilization of the macromolecule profoundly changes the nature of the magnetic field dependence of the relaxation rate for both the diamagnetic and the paramagnetic samples. The immobilization also amplifies the effect of the paramagnetic center as a water-proton relaxation agent. The direct exchange of labile water molecules or protons is not a requirement for the high efficiency of this class of magnetic relaxation agents.

Animals↗

PubMed1991

The magnetic field dependence of proton spin relaxation in tissues.

The magnetic field dependence of water-proton relaxation is reported for a simple protein solution, a cross-linked protein solution, and a series of rat tissues, fresh, dried and rehydrated. The shape of the magnetic field dependence associated with water proton relaxation in tissues is accounted for by magnetic dipole-dipole interactions between the mobile water spins and the immobile spin populations of the nonrotating components of the tissue coupling the behavior of the immobilized spin system to that of the mobile water spin system. The effect of this coupling is to impart the field dependence of the relaxation associated with the immobilized spin population to that of the mobile water spins that are observed in most relaxation and imaging experiments.

Animals↗

PubMed1991

Water-proton nuclear magnetic relaxation in heterogeneous systems: hydrated lysozyme results.

Spin-lattice relaxation rates of water protons in hydrated immobilized lysozyme are measured as a function of magnetic field strength. The dependence of water relaxation versus hydration is presented from 35 to 55% by weight water content. The water-proton relaxation is directly coupled to that of the protein and the coupling exists in the absence of chemical exchange. A model is applied where relaxation within the two proton phases is coupled through a dipolar cross-relaxation mechanism as well as chemical exchange. The observed amplitudes of the water-proton relaxation profiles scale with the ratio of protein to water protons as well as the protein-proton relaxation rate. The field dependence of the protein-proton spin-lattice relaxation is presented in the presence of D2O where a cross-relaxation coupling is absent. The coupled relaxation model accounts well for the NMR relaxation data as a function of magnetic field strength which is similar to measurements on other heterogeneous systems such as tissues.

Magnetic Resonance Spectroscopy↗

PubMed1991

Comparison of agarose and cross-linked protein gels as magnetic resonance imaging phantoms.

Measurements of the magnetic field dependence of spin-lattice relaxation rates and the response of the water-proton signal intensity to off-resonance radio frequency fields show that the commonly used agarose phantom provides a less faithful representation for the magnetic response of tissue than does a cross-linked protein system. The origin of these differences lies in the structure and intramolecular dynamics of the macromolecular system used to make the gel. These distinctions will also cause differences in the magnetic response of the water spin system when paramagnetic relaxation agents or contrast agents are incorporated. Use of a thermally cross-linked bovine serum albumin phantom is suggested.

Animals↗