# Evaluation of 8-Channel Radiative Antenna Arrays for Human Head Imaging at 10.5 Tesla
## 2 Materials and Methods
### Experimental Setup  
A Siemens MAGNETOM console equipped with 16 independent transmit and 32 receive channels (Siemens, Erlangen, Germany) was used in conjunction with a Siemens SC72 body gradient coil inside the 88 cm diameter whole-body 10.5 T magnet (Agilent, Santa Clara, CA, USA). All data presented here were acquired using parallel transmit (pTx) with equal RF transmit power per channel. An in-house designed 8-channel transmit/receive interface (Virtumed, Minneapolis, MN, USA) with 25 dB receiver gain was used to connect the arrays to the MR scanner. The phantom with exactly the same physical dimensions and electrical properties of the simulation was used to compare the performance of arrays experimentally. The phantom was filled with sucrose, saline, and distilled water solution and measured with the DAKS-12 probe (SPEAG, Zurich, Switzerland) to confirm electrical properties [29]. The phantom was carefully positioned within each of the coil formers to achieve agreement between simulation and experiment and mimic the location for human brain imaging.  
For the basic experimental antenna element coupling evaluation of all antenna arrays, noise covariance matrices were obtained in a 10.5 T MR experiment, as illustrated in Supplementary Figure S1. Noise covariance matrices of the dipole antenna with further (Supplementary Figure S1a) and close (Supplementary Figure S1b) coaxial setup, the monopole antenna (Supplementary Figure S1c), and sleeve antenna (Supplementary Figure S1d) arrays were acquired to experimentally evaluate the crosstalk between the elements [30]. Transmit B\({}_{1}\)+-field efficiency maps of individual elements were obtained using an actual flip-angle imaging (AFI) sequence (TR\({}_{1}\)/TR\({}_{2}\) = 25/115 ms, TE = 3.39 ms, nominal flip angle = 60\({}^{\circ}\), GRAPPA (R = 2), and resolution = 2 mm \(\times\) 4 mm \(\times\) 6 mm) with the cylindrical phantom. The flip angle with short TR\({}_{1}\) and TR\({}_{2}\) was calculated by:  
\[\alpha=\arccos\frac{(\mathbf{r}\mathbf{n}-\mathbf{1})}{(\mathbf{n}-\mathbf{r})}, \tag{2}\]  
where \(\alpha\) = flip angle and n = TR\({}_{2}\)/TR\({}_{1}\), and r \(\approx\frac{\mathbf{i}\mathbf{+}\mathbf{n}\ \mathbf{cos}\ \alpha}{\mathbf{n}+\mathbf{ cos}\alpha}\)[31]. The flip angle was converted to B\({}_{1}\)+ with:  
\[\alpha=2\pi\gamma\ \text{B}_{1}\text{${}^{+}$}\tau, \tag{3}\]  
where \(\tau\) is the width in seconds of the RF pulse [32].  
To demonstrate overall imaging capabilities and brain coverage, we obtained high-resolution human cadaver images using B1-phase shimming with the 8-channel sleeve antenna array at 10.5 T. High-resolution human cadaver images were obtained for the evaluation of the 8-channel sleeve antenna array utilizing B1-phase shimming (defined as phase optimization using a pTx system). Turbo spin-echo (TSE) images (TR = 5000 ms, TE = 72 ms, TA = 15:18 min, BW = 488 Hz/pixel, NT = 4, FOV = 200 mm \(\times\) 159 mm, and resolution = 0.39 mm \(\times\) 0.39 mm \(\times\) 1.0 mm) and T1-weighted gradient-recalled echo (GRE) images (TR = 150 ms, TE = 3.4 ms, TA = 4:58 min, BW = 421 Hz/pixel, NT = 4, FOV = 200 mm \(\times\) 200 mm, and resolution = 0.3 mm \(\times\) 0.3 mm \(\times\) 1.8 mm) were acquired with the human cadaver.