Generalized electrical analysis of low-pass and high-pass birdcage resonators |
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Authors: | R J Pascone B J Garcia T M Fitzgerald T Vullo R Zipagan P T Cahill |
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Affiliation: | Department of Electrical Engineering, Manhattan College, Riverdale, New York 10471. |
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Abstract: | The radio-frequency 'birdcage resonator' has found wide use in MRI/MRS for its field homogeneity and signal-noise characteristics. This paper presents a general analysis, derived from lumped element transmission line theory, of the electrical behavior of unloaded, N-column birdcage resonators applicable to several versions of the basic design including low-pass and high-pass coils. Analytic expressions and computer results are presented for both types of coil describing resonant frequencies, input and characteristic impedances, dispersion relations, pass-bands, resonant peak bandwidth and Q. Theoretical expressions for normalized resonant frequency difference ratios independent of element values and resonator geometry have been developed for generic low- and high-pass coils. Experimental measurements of resonant frequencies were made for six coils, and the average agreement with theoretical predictions was approximately 4%. |
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