Use of transmission line analysis for multi-tuning of birdcage resonators

A general analysis for double- and higher order tuning of birdcage resonators is presented based on a lumped element transmission line model. Expressions were developed for the determination of the resonant frequencies of bandstop and bandpass birdcage coils and, with specific restrictions, for capacitor values required to obtain any two desired mode one resonant frequencies. Experimental measurements on three variants each of an eight-column bandstop and an eight-column bandpass were in excellent agreement with theory; the average absolute frequency difference and percent deviation were 1.51 +/- 1.57 MHz and 2.61 +/- 2.36%, respectively. In addition, 31P and 1H phantom images were obtained at 2.0 T using a representative bandstop coil.