## 3 Results
\begin{table}
\begin{tabular}{c c c c c c} \hline  & **Case 1** & **Case 2** & **Case 3** & **Case 4** & **Case 5** \\ \hline \multicolumn{6}{c}{**Cylindrical Uniform Phantom**} \\ \hline B\({}_{1}^{+}\) Uniformity (\(\%\)) & 74.29 & 70.21 & 69.68 & 73.28 & 76.25 \\ \hline Total input power (watt) & 24.41 & 33.03 & 36.52 & 37.16 & 29.89 \\ normalized to 1 uT & & & & & \\ \hline Transmit efficiency & 0.202 & 0.174 & 0.166 & 0.164 & 0.187 \\ \(\left(\frac{\text{B}_{1}^{+}}{\sqrt{P}}\frac{\text{uT}}{\sqrt{\text{watt}}} \right)\) & & & & \\ \hline B\({}_{1}^{+}\) at 20 kW (uT) & 28.63 & 24.61 & 23.40 & 23.20 & 26.47 \\ \hline \multicolumn{6}{c}{**Human “Duke” Model**} \\ \hline Total input power (watt) & 21.57 & 31.46 & 25.96 & 30.37 & 24.21 \\ normalized to 1 uT & & & & \\ \hline Mean 10 g-avg SAR & 0.093 & 0.11 & 0.13 & 0.11 & 0.093 \\ (watt/kg) & 0.78 & 0.89 & 1.44 & 1.16 & 0.97 \\ \hline \multicolumn{6}{c}{Transmit efficiency } \\ \(\left(\frac{\text{B}_{1}^{+}}{\sqrt{P}}\frac{\text{uT}}{\sqrt{\text{watt}}} \right)\) & 0.22 & 0.18 & 0.20 & 0.18 & 0.20 \\ \hline \multicolumn{6}{c}{\(\text{B}_{1}^{+}\) at 20 kW (uT)} \\ \hline \end{tabular}
\end{table} 
Table 2: Summary of uniformity, input power, transmit efficiency, and maximum B\({}_{1}^{+}\) at 20 kW (most commercial MRI systems are equipped with 20 kW RF amplifier) in cylindrical uniform phantom; mean 10 g average SAR and peak 10 g average SAR in human “Duke” model for simulated RF coils in optimal driving mode, as shown in Figure 1. \begin{table}
\begin{tabular}{c c c c} \hline  & **Unloaded** & **Light Loader Phantom** & **Heavy Loader Phantom** \\ \hline Reflection Coef. (S11) & –7.73 dB & –18.09 dB & –24.62 dB \\ \hline Reflection Coef. (S22) & –5.05 dB & –16.03 dB & –20.35 dB \\ \hline Isolation Coef. (S12) & –17.96 dB & –22.69 dB & –22.17 dB \\ \hline Impedance (Z11) & 35.07–34.33 \(\Omega\) & 39.69–4.33 \(\Omega\) & 44.45–0.05 \(\Omega\) \\ \hline Impedance (Z22) & 20.54–31.6 \(\Omega\) & 38.61–8.23 \(\Omega\) & 47.17–8.93 \(\Omega\) \\ \hline Quality factor (Q) & 173.91 & 79.07 & 67.43 \\ \hline \end{tabular}
\end{table} 
Table 3: Experimental S-parameters and Q-factor measurement for constructed split-type elliptical birdcage in unloaded and loaded conditions. S-parameter was measured at each splitter/combiner port, and Q-factor was measured using two weakly coupled sniffer probes placed at opposite ends of the RF coil. Figure 4: **(a)** Illustration of experimental setup of cylindrical uniform phantom in axial, sagittal, and coronal orientations inside magnet bore; **(b)** SNR map acquired using T1w spin echo sequence; **(c)** FA map (nominal FA—180\({}^{\circ}\)) acquired using composite spin echo sequence in commercial circular birdcage (top row) and constructed split-type elliptical birdcage (bottom row). Note that values written below each map were calculated in 2D ROI of 30 cm in diameter. The SNR measurement shows that the mean SNR of the circular birdcage was higher than that of the split-type elliptical birdcage in the axial and the sagittal slices by 10% and 14.85%, respectively; however, the mean SNR of the split-type elliptical birdcage in the coronal slice was higher by 9.45%. The FA uniformity measurement shows that FA uniformity of the circular birdcage was higher than that of the split-type elliptical birdcage in the axial and the sagittal slices by 1.77% and 3.66%, respectively; however, the FA uniformity of the split-type elliptical birdcage in the coronal slice was higher by 0.86%. The mean SNR and the FA uniformity of both coils in a large FOV were similar, demonstrating the acceptable performance of the proposed split-type birdcage RF coil. Figure 5 shows the SNR and the FA maps of the in vivo human volunteers acquired in the axial and the coronal orientations. The SNR maps showed the reasonable performance of the proposed coil in comparison with that of the commercial birdcage coil.