BIRDCAGE RESONATOR DESIGN IN MAGNETIC RESONANCE IMAGING by

Circuit equations for the general Birdcage resonator are solved with a polynomial approach and an expression for the resonant frequencies is derived. The results are compared with numerical calculations and with experiments on a 12 mesh, low pass Birdcage. A design procedure for low pass Birdcages, which follows directly from the polynomial analysis, is presented. It is shown that the resonant frequencies can be divided into low and high impedance resonant modes and that the total number of resonant frequencies is equal to the number of meshes. The angular current distribution in the legs of the resonator is derived using the polynomial approach. Two methods of measuring the currents in the legs of the resonator are proposed and verified experimentally. A resonator tuned to its second mode can be viewed as a surface coil wrapped around the sample and thus yields an increased Signal to Noise ratio at the edge of the resonator. This increase is calculated theoretically for a spherical sample and the experimental value is in good agreement. A description of the transmission line is included since the concept is useful for the understanding of the Birdcage resonator. Thesis Supervisor for NED: Dr. Robert M. Weisskoff Thesis Supervisor for EE: Dr. Jerome L. Ackerman