Cardiorenal sodium MRI in small rodents using a quadrature birdcage volume resonator at 9.4 T

OBECTIVE: Design, implementation, evaluation and application of a quadrature birdcage radiofrequency (RF) resonator tailored for renal and cardiac sodium ((23)Na) magnetic resonance imaging (MRI) in rats at 9.4 T. MATERIALS AND METHODS: A low pass birdcage resonator (16 rungs, d(in) = 62 mm) was developed. The transmission field (B(1)(+)) was examined with EMF simulations. The scattering parameter (S-parameter) and the quality factor (Q-factor) were measured. For experimental validation B(1)(+)-field maps were acquired with the double-angle method. In vivo sodium imaging of the heart (spatial resolution: (1 × 1 × 5) mm(3)) and kidney (spatial resolution: (1 × 1 × 10) mm(3)) was performed with a FLASH technique. RESULTS: The RF resonator exhibits RF characteristics, transmission field homogeneity and penetration that afford (23)Na MR in vivo imaging of the kidney and heart at 9.4 T. For the renal cortex and medulla a SNRs of 8 and 13 were obtained and a SNRs of 14 and 15 were observed for the left and right ventricle. DISCUSSION: These initial results obtained in vivo in rats using the quadrature birdcage volume RF resonator for (23)Na MRI permit dedicated studies on experimental models of cardiac and renal diseases, which would contribute to translational research of the cardiorenal syndrome.