Desmond Yau

A time-harmonic inverse methodology for the design of RF coils in MRI

An inverse methodology is described to assist in the design of radio-frequency (RF) coils for magnetic resonance imaging (MRI) applications. The time-harmonic electromagnetic Greens functions are used to calculate current on the coil and shield cylinders that will generate a specified internal magnetic field. Stream function techniques and the method of moments are then used to implement this theoretical current density into an RF coil. A novel asymmetric coil operating for a 4.5 T MRI machine was designed and constructed using this methodology and the results are presented.

An inverse design of an open, head/neck RF coil for MRI

Radio-frequency (RF) coils are a necessary component of magnetic resonance imaging (MRI) systems. When used in transmit operation, they act to generate a homogeneous RF magnetic field within a volume of interest and when in receive operation, they act to receive the nuclear magnetic resonance signal from the RF-excited specimen. This paper outlines a procedure for the design of open RF coils using the time-harmonic inverse method. This method entails the calculation of an ideal current density on a multipaned planar surface that would generate a specified magnetic field within the volume of interest. Because of the averaging effect of the regularization technique in the matrix solution, the specified magnetic field is shaped within an iterative procedure until the generated magnetic field matches the desired magnetic field. The stream-function technique is used to ascertain conductor positions and a method of moments package is then used to finalize the design. An open head/neck coil was designed to operate in a clinical 2T MRI system and the presented results prove the efficacy of this design methodology.

A Genetic Algorithm/Method of Moments Approach to the Optimization of an RF Coil for MRI Applications — Theoretical Considerations — Abstract

A Combined Genetic Algorithm and Method of Moments design methods is presented for the design of unusual near-field antennas for use in Magnetic Resonance Imaging systems. The method is successfully applied to the design of an asymmetric coil structure for use at 190MHz and demonstrates excellent radiofrequency field homogeneity.

A Genetic Algorithm/Method of Moments Approach to the Optimization of an RF Coil for MRI Applications --- Theoretical Considerations

A Combined Genetic Algorithm and Method of Moments design methods is presented for the design of unusual near-field antennas for use in Magnetic Resonance Imaging systems. The method is successfully applied to the design of an asymmetric coil structure for use at 190MHz and demonstrates excellent radiofrequency field homogeneity.

Numerical analysis of coupling between dielectric image guide and microstrip

An integral equation method of moments formulation of the coupling between dielectric image guide and microstrip is studied. The formulation implements a surface equivalence using rooftop and traveling wave basis functions. The specific structure under consideration is the aperture coupled microstrip image guide transition. Analysis of the structure and typical results are compared to measurements on a simple prototype transition.

A moment method analysis of an aperture coupled rectangular dielectric resonator antenna

An efficient but rigorous model based on the surface integral equation (SIE) approach is proposed for the analysis of the antenna. The dielectric resonator (DR) is modeled in terms of equivalent surface electric and magnetic currents using combined field integral equations (CFIE) formulation. The CFIE, the microstrip feedline and the associated coupling mechanism are formulated as a set of coupled equations in the spatial domain in the form of the mixed potential integral equations (MPIE). The coupled integral equations are solved by use of the method of moments (MoM) using Galerkins procedure. In the microstrip region, closed-form Greens functions are employed in the calculation to enhance the numerical efficiency. It is demonstrated that the proposed model is very economical in usage of computer resources for generating accurate results for the input impedance.

Asymmetric MRI systems: shim and RF coil designs

We have recently introduced the concept of asymmetric clinical MRI systems. The potential advantages of these systems include a reduced perception of claustrophobia by patients and better physician access to the patient. For asymmetric magnet systems to be useful as a clinical system, asymmetric shims and RF coils must be implemented, and in this work we describe new design methodologies for both.

Asymmetric MRI systems

We have recently introduced the concept of asymmetric clinical MRI systems. The potential advantages of these systems include a reduced perception of claustrophobia by patients and better physician access to the patient. For asymmetric magnet systems to be useful as a clinical system, asymmetric shims and RF coils must be implemented, and in this work we describe new design methodologies for both.