# Evaluation of 8-Channel Radiative Antenna Arrays for Human Head Imaging at 10.5 Tesla
## 5 Conclusions  
We evaluated three types of 8-channel radiative antenna arrays for UHF MRI. Among them, the sleeve antenna array showed clear advantages in terms of lower peak 10 g SAR and higher SAR efficiency compared to the dipole and monopole antenna arrays. Finally, the incorporation of a sleeve into the feed structure has significant positive practical implications, and the variation in sleeve length adds an important degree of design freedom.  
The sleeve antenna concepts can also support tighter element spacing, and thus, potentially, could allow for increased density of antenna elements in array configurations. The deliberate lower element counts of arrays presented in this work support better comparison of head-sized dipole and monopole antenna arrays, and they represent an important validation step. For future in vivo human brain imaging research with antenna arrays, the sleeve antenna concept can be further expanded towards a higher number of elements through, for example, dual row layouts and variations in the length of individual antennas. Eventually, we plan to explore combinations of sleeve transmitters with dedicated receiver inserts as an important step towards higher channel array configuration in excess of 32 receive elements. Furthermore, incorporation of high-permittivity materials in support of shorter elements will be considered in addition to further improved geometry arrangements for SAR optimization.  
The future experiments will also utilize enhanced B1 field control techniques using pTx with individual control of the phase, amplitude, and RF pulse shape of each coil element and the possibility for significantly improved transmit homogeneity.  
The following are available online at [[https://www.mdpi.com/article/10.3390/s21186000/s1](https://www.mdpi.com/article/10.3390/s21186000/s1)]([https://www.mdpi.com/article/10.3390/s21186000/s1](https://www.mdpi.com/article/10.3390/s21186000/s1)), Figure S1: Noise correlation values of the 8-channel dipole (further (a) and tight (b) coaxial cables setup), monopole (c), and sleeve antenna (d) arrays., Table S1: S-parameters of the 8-channel inductor-shortened dipole, monopole and sleeve antenna arrays. S21 of each array was measured between the nearest, the second nearest, and the third nearest elements.  
[PERSON] built the coils and designed the simulation and experiments. [PERSON] and [PERSON] collected the data. [PERSON] and [PERSON] designed the model of the coil former. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], S.-H.O., [PERSON] and [PERSON] analyzed the results. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] wrote the manuscript. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the U.S. Department of National Institutes of Health under Grants U01-EB025144, S10-RR029672, P41-EB015894, P41-EB027061, P30-NS076408, BK21 FOUR program of the Education and Research Program for Future ICT Pioneers, Seoul National University in A0426-20210100, National Research Foundation of Korea (NRF-2020R1A2C4001623), and the Hankuk University of Foreign Studies Research Fund.  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the restriction of local law and government policy.  
The authors would like to thank [PERSON], [PERSON], and [PERSON] (all with the Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA) for their help with 3D printing, discussion, and feedback.  
The authors declare no conflict of interest.