Biomedical subjects

M D Harpen

Publications and source records attributed to M D Harpen.

59 records · Page 4Linked to original sources

PubMedDate not supplied

Magnetically induced surface charges on samples in magnetic resonance imaging radio-frequency coils: effect on electric fields, sample losses, and coil resonance.

We present a solution to Maxwell's equations which describe the inductive interaction between an irregularly shaped sample in a magnetic resonance imaging rf coil. It is demonstrated that the inductive interaction between the coil and sample can induce charge densities on the sample surface and that these charge densities lead to observable changes in coil Q, resonant frequency offset and sample power dissipation.

Humans↗

PubMedDate not supplied

Theoretical description of the interaction between birdcage coils and lossy samples.

An analysis is presented of the interaction between a long cylindrical imaging coil, commonly called a low-pass birdcage coil, and a cylindrical sample. Predicted and measured values of coil Q are shown to compare well throughout the resonance spectrum of an experimental coil-sample system. The analysis may be used to calculate feed-point impedances and is easily extended to high-pass coils.

Humans↗

PubMedDate not supplied

Analysis of sample power loss in MRI gradient fields.

A derivation of the power dissipation in a conducting spherical sample in a time-dependent gradient magnetic field is presented and the predicted values are compared with those observed in an experimental apparatus consisting of a four-element saddle coil and a Maxwell coil pair. The derived expressions for power dissipation are shown to agree with values obtained experimentally via Q measurements of the loaded coils. It is also shown the large rapidly fluctuating gradient fields encountered in echo planar imaging produce relatively small levels of absorbed power.

Magnetic Resonance Imaging↗

PubMedDate not supplied

Distributed self-capacitance of magnetic resonance imaging birdcage coils.

Presented is a theoretical description of the self-capacitance of a low-pass birdcage coil. The problem considered is that the modification of the distributed self-capacitance produced by the electric interaction between the coil and a cylindrical Faraday screen and illustrates the phenomenon of coil self-capacitance as well as the influence of Faraday screens. Changes in coil self-capacitance produced by the presence of the screens are shown to be consistent with measured shifts in coil resonant frequencies.

Magnetic Resonance Imaging↗

PubMedDate not supplied

Uniform oscillating gradient produced by spherical birdcage resonator.

The theory and operation of a resonator which produces a uniform oscillating magnetic field gradient is described. When the resonator is operated at audio frequency, it will produce the oscillating magnetic field gradient required for use in spatial encoding in rapid acquisition magnetic resonance imaging.

Biophysical Phenomena↗