## 4 Discussion and Conclusions
During construction, one of the main problems encountered was the effect of the unshielded coaxial cable traps on the frequency response due to its coupling with the coaxial cable and the RF shield as well as the different loading conditions, which were solved by shielding of cable traps (further details are provided in Supplementary Materials Section C). The MRI experiments were performed with quadrature driving because of incomplete resources for elliptical driving, such as additional RF amplifiers, TX waveform generators, high-power isolators, and high-power RF dummy loads, to allow precise handling of the reflected power for guaranteeing the safety of both the MRI hardware and the attendants. The experimental analysis showed that the SNR of the acquired MR image through the birdcage coil can be further improved using a dual-preamplifier at reception [43]. Compared with the commercial two-port circular birdcage, the proposed elliptical birdcage requires approximately 20% higher RF input power, which is reasonable. In context with the birdcage builder toolbox [38], the birdcage builder only performs the numerical calculations with symmetric circular and elliptical configurations. It was found that the birdcage builder had higher uncertainty than the proposed method, especially for the larger-body size birdcage RF coil. The absolute errors in calculated capacitance for the circular birdcage coil using the birdcage builder and the proposed method were 32.3% and 11.86%, respectively, in comparison to the practical capacitance value used in our commercial system. The birdcage builder cannot be used for the split-leg elliptical birdcage RF coil due to unavailability of asymmetric configuration, however, the absolute error between the proposed method and the practical values was 12.05%. The difference between the calculated and the practical values was due to the effect of unspecified configuration of the RF shield and other components such as patient bed, gradient coil, and magnet of the MRI scanner. During the construction of an elliptical birdcage RF coil, it was realized that there could be an effect from the number of legs on the magnitude of isolation between the ports, which was not investigated in this work. Additionally, if the proposed RF coil is implemented in wide-bore MRI systems with an optimal RF shield geometry, then the B1+field uniformity and the transmission efficiency as well as the isolation between ports can be further improved, because the B1+ magnitude increases when the shield-to-coil-diameter ratio decreases [44; 45]. In conclusion, we report an RF coil circuit co-simulation approach for the optimization of a four-port split-type asymmetric elliptical whole-body birdcage coil and its construction design. We evaluated the coil performance through phantom and in vivo human experiments using a 1.5 T MRI system. The elliptical configuration permitted a larger imaging space horizontally without degrading the B1+-field uniformity and the transmission efficiency considerably compared with the commercial smaller circular birdcage RF coil. The RF coil circuit co-simulation approach showed efficient strategy for tuning, matching, and optimization of the RF coil; hence, it can be applied to any desired resonant frequencies and any arbitrary geometries of the birdcage coil. The proposed split-type elliptical birdcage coil MRI experiments demonstrated acceptable SNRs and B1+-field uniformities in an adequate FOV for whole-body applications in MRI. The following are available online at [[https://www.mdpi.com/article/10.3390/app11167448/s1](https://www.mdpi.com/article/10.3390/app11167448/s1)]([https://www.mdpi.com/article/10.3390/app11167448/s1](https://www.mdpi.com/article/10.3390/app11167448/s1)), (A) description of optimal capacitor value calculation in MATLAB; (B) description of flip angle (FA) maps using composite spin-echo pulse sequence; (C) description of shielded cable traps design. [PERSON] and [PERSON] conceptualized the proposed idea. S.K.