Effects of end‐ring/shield configuration on homogeneity and signal‐to‐noise ratio in a birdcage‐type coil loaded with a human head

We modeled four different end‐ring/shield configurations of a birdcage coil to examine their effects on field homogeneity and signal‐to‐noise ratio (SNR) at 64 MHz and 125 MHz. The configurations are defined as: 1) conventional: a conventional cylindrical shield; 2) surrounding shield: a shield with annular extensions to closely shield the end rings; 3) solid connection: a shield with annular extensions connected to the rungs; and 4) thin wire connection: a shield with thin wires connected to the rungs. At both frequencies, the coil with conventional end‐ring/shield configuration produces the most homogeneous RF magnetic ( B 1 ) field when the coil is empty, but produces the least homogeneous B 1 field when the coil is loaded with a human head. The surrounding shield configuration results in the most homogeneous B 1 and highest SNR in the coil loaded with the human head at both frequencies, followed closely by the solid connection configuration. Magn Reson Med 51:217–221, 2004. © 2003 Wiley‐Liss, Inc.