Design of a RF-resonant set improving locally the B1+ efficiency. Applications for clinical MRI in andrology and urology.

Modern diagnostic imaging methods for andrology and urology fall behind other well-developed applications such as cardiology or neurology. Particularly, MRI despite its superior soft tissue contrast is hardly used for MR-imaging of the penis, primarily due to the lack of the corresponding receive or transmit coils. In order to fix this, a new radio frequency resonator, based on the birdcage operating principles has been designed, simulated, fabricated, tested and compared experimentally to existing RF coils. In order to provide high transmit efficiency and high sensitivity, while maintaining the coil safety, the resonator spatially separates alternating magnetic and electric fields. The transmitted magnetic field (B1+) is concentrated in the centre of the imaging volume, while the electric field remains on its edge and does not lead to tissue heating. The resonator design was optimised for human MRI in 1.5 T scanners. Both simulations and experiment showed the resonator to provide around 100-fold specific absorption rate reduction, around 10-fold improvement of the transmit efficiency and more than 10-fold enhancement of the signal to noise ratio (SNR) in a phantom compared to the body coil, around 2-fold SNR enhancement in a phantom compared to the commercial flexible 4-element coil, and up to 1.5-fold enhancement compared to the same coil in-vivo.