Development of Compact and Flexible Quadrature Hybrid Coupler Using Coaxial Cable With Capacitive Loading for 1.5T Indigenous Mri System

Abstract

Quadrature feeding is essential in magnetic resonance imaging radio frequency (MRI-RF) coils, to improve the homogeneity of the magnetic field of surface coil, the signal to noise ratio (SNR) of the image by a factor of √ 2, and to create a circularly polarized magnetic field inside the volume coil. The quadrature feeding is incorporated, using hybrid coupler. However, at 63.87 MHz the Larmor frequency of hydrogen proton, corresponding to 1.5 Tesla, the size of the hybrid coupler and other microwave circuits become large. So, to minimize its physical size, a coaxial cable transmission line with lumped capacitive loading has been proposed. The size of the proposed hybrid coupler is reduced by 68%, as compared to the conventional hybrid coupler. The proposed device is then fabricated as a both rigid and flexible structure, which provides isolation (S 41) of around 19 dB and a 90 • phase difference between coupled and the through ports. Both structures provide return loss S 11 > −15 dB and coupling at output ports S 21 , S 31 around 3 dB.

A Comparative Study of Birdcage RF Coil Configurations for Ultra-High Field Magnetic Resonance Imaging

“…The required RF power to excite a spin system increases with the B 0 -field strength. B 1 -field sensitivity is of particular concern in UHF MRI because, as the magnetic field increases, a greater RF frequency is needed to excite the proton ( 1 H) nuclei in the human body using an RF pulse, which is critical for high signal sensitivity of the RF coil [16][17][18][19]. Additionally, an insufficient input RF power level causes RF power deposition [20][21][22][23][24], which leads to problems in the SAR.…”