title: Optimization and comparison of two practical dual-tuned birdcage configurations for quantitative assessment of articular cartilage with sodium magnetic resonance imaging.
abstract: BACKGROUND
  In this study, two practical dual-tuned birdcage configurations for quantitative assessment of articular cartilage with sodium magnetic resonance imaging (MRI) were designed and compared.
  
  
  METHODS
  Two 1.5 T dual-tuned birdcages, a four-ring birdcage (FRB) and an alternating rungs birdcage (ARB), were built and then characterized by bench and MRI measurements. The relative uniformity (RU) and the efficiency of the coils were compared using (23)Na and (1)H B1 maps. In vivo images of a volunteer were acquired.
  
  
  RESULTS
  Bench measurements showed matching and decoupling coefficients of the quadrature channels lower than -20 dB. The RUs and 180° pulse amplitudes of the FRB/ARB were determined as: (1)H RU =94.4/74.4%, (23)Na RU =95.2/93.6%, (1)H 180° pulse amplitude =69.2/75.4 V and (23)Na 180° pulse amplitude =45.1/45.9 V. The in vivo (23)Na images acquired with the FRB show a signal-to-noise ratio (SNR) of 6 to 14 in the cartilage.
  
  
  CONCLUSIONS
  Due to its superior (1)H homogeneity and efficiency and its slightly better (23)Na homogeneity, the FRB is the overall preferred coil for the given requirements of this study. The achieved in vivo SNR is adequate for quantitative (23)Na and high resolution (1)H imaging.
authors.affiliation: 1 MRB Research Center for Magnetic Resonance Bavaria, Wuerzburg, Germany ; 2 Department of Experimental Physics 5 (Biophysics), University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Gunthard
authors.initials: G
authors.lastname: Lykowsky
authors.affiliation: 1 MRB Research Center for Magnetic Resonance Bavaria, Wuerzburg, Germany ; 2 Department of Experimental Physics 5 (Biophysics), University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Flavio
authors.initials: F
authors.lastname: Carinci
authors.affiliation: 1 MRB Research Center for Magnetic Resonance Bavaria, Wuerzburg, Germany ; 2 Department of Experimental Physics 5 (Biophysics), University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Düring
authors.affiliation: 1 MRB Research Center for Magnetic Resonance Bavaria, Wuerzburg, Germany ; 2 Department of Experimental Physics 5 (Biophysics), University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Weber
authors.affiliation: 1 MRB Research Center for Magnetic Resonance Bavaria, Wuerzburg, Germany ; 2 Department of Experimental Physics 5 (Biophysics), University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Jakob
authors.affiliation: 1 MRB Research Center for Magnetic Resonance Bavaria, Wuerzburg, Germany ; 2 Department of Experimental Physics 5 (Biophysics), University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Haddad
keywords: Sodium magnetic resonance imaging; birdcage; dual tuned