A method for calculating B1 field strength and homogeneity as functions of radiofrequency shield geometry is presented. The method requires use of three-dimensional finite-element analysis, birdcage-coil theory, and antenna-array theory. Calculations were performed for a 12-element birdcage coil (19 cm diameter, 21 cm length) at 125 MHz. Calculated B1 field strengths and homogeneities for the coil in 25 different shields and in no shield are given. For configurations where the shield is longer than the coil, both B1 field strength and homogeneity decrease as shield diameter decreases or as shield length increases. In configurations where the shield is shorter than the coil and has a diameter of 25.6 cm, B1 homogeneity is greater than in an unshielded coil. B1 field strength was measured experimentally at 125 MHz in a birdcage coil of the same geometry as the model within shields of four different diameters. Calculated results very closely matched experimental measurement.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Condensed Matter Physics