Original Article
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 23Na and 1H 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: 1H RU =94.4/74.4%, 23Na RU =95.2/93.6%, 1H 180° pulse amplitude =69.2/75.4 V and 23Na 180° pulse amplitude =45.1/45.9 V. The in vivo 23Na images acquired with the FRB show a signal-to-noise ratio (SNR) of 6 to 14 in the cartilage.
Conclusions: Due to its superior 1H homogeneity and efficiency and its slightly better 23Na homogeneity, the FRB is the overall preferred coil for the given requirements of this study. The achieved in vivo SNR is adequate for quantitative 23Na and high resolution 1H imaging.
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 23Na and 1H 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: 1H RU =94.4/74.4%, 23Na RU =95.2/93.6%, 1H 180° pulse amplitude =69.2/75.4 V and 23Na 180° pulse amplitude =45.1/45.9 V. The in vivo 23Na images acquired with the FRB show a signal-to-noise ratio (SNR) of 6 to 14 in the cartilage.
Conclusions: Due to its superior 1H homogeneity and efficiency and its slightly better 23Na homogeneity, the FRB is the overall preferred coil for the given requirements of this study. The achieved in vivo SNR is adequate for quantitative 23Na and high resolution 1H imaging.
