Two end cap designs for bird cage coils for application in nuclear magnetic
resonance head imaging are presented. The objectives of the new design are
to improve the B-1 field homogeneity within the coil and to improve the SN
R, Design I extends the legs and one end ring of the bird cage coil onto th
e end cap. The radius of the end ring on the end cap is optimized to maximi
ze the axial field of view with a limited B-1 field homogeneity, Design II
uses a metal disk plate as a mirror placed at one end of the bird cage coil
; it is analyzed by using a moment method. The size of the metal plate is o
ptimized. An analysis of the two end cap designs is presented. The results
show that in design I the optimal radius of the end ring on the end cap is
about 2.5 times smaller than the coil radius; in design II, the inner radiu
s of the disk mirror should be as small as possible and the mirror should b
e as close as possible to the coil for B-1 field homogeneity; making the ou
ter radius of the disk larger than the coil radius does not much improve th
e B-1 field homogeneity.