Scalable and modular 8-channel transmit and 8-channel flexible receive coil array for 19F MRI of large animals
Ali Caglar Özen, Felix Spreter, Waldemar Schimpf, Johannes Fischer, Serhat Ilbey, Simon Reiss, Alexander Maier, Dominik von Elverfeldt, Timo Heidt, Constantin von zur Mühlen, Michael Bock
Purpose
To introduce an RF coil system consisting of an 8-channel transmit (Tx) and 8-channel receive (Rx) coil arrays for 19F MRI of large animals.
Methods
The Tx efficiency and homogeneity of the 8-element loop coil array (loop size: 6 × 15 cm2) were simulated for two different pig models rendered from MR images. An 8-channel Rx coil array consisting of a flexible 6-channel posterior and a 2-channel planar anterior array was designed to fit on the abdomen of an average-sized pig in supine position. Measurements were performed in a grid phantom and ex vivo on a pig model with perfluoroctylbromide (PFOB)–filled tubes inserted in the thorax.
Results
Measured and simulated Tx efficiency and homogeneity for the 8-channel and 5-channel arrays were in good agreement: 1.87 ± 0.22μT/√kW versus 1.96 ± 0.29μT/√kW, and 2.29 ± 0.39μT/√kW versus 2.41 ± 0.37μT/√kW. An isolation of 38 ± 8 dB is achieved between the 19F Tx and Rx elements, and over 30 dB between the 1H and 19F elements. The PFOB-filled vials could be clearly identified within the cadaver abdomen with an SNR of 275 ± 51 for a 3D gradient-echo sequence with 2-mm isotropic resolution and 12 averages, acquired in 9:52 min:s. Performance of the Tx array was robust against phase and amplitude mismatches at the input ports.
Conclusions
A modular and scalable Tx array offers improved Tx efficiency in 19F MRI of large animals with various sizes. Although conventional birdcage coils have superior Tx efficiency within the target region of interest, scalability of the Tx array to animal size is a major benefit. The described 19F coil provides homogeneous excitation and high sensitivity detection in large pig models.