Large improvement in RF magnetic fields and imaging SNR with whole‐head high‐permittivity slurry helmet for human‐brain MRI applications at 7 T

Purpose To optimize the design and demonstrate the integration of a helmet‐shaped container filled with a high‐permittivity material (HPM) slurry with RF head coil arrays to improve RF coil sensitivity and SNR for human‐brain proton MRI. Methods RF reception magnetic fields (B1−$$ {\mathrm{B}}_1^{-} $$) of a 32‐channel receive‐only coil array with various geometries and permittivity values of HPM slurry helmet are calculated with electromagnetic simulation at 7 T. A 16‐channel transmit‐only coil array, a 32‐channel receive‐only coil array, and a 2‐piece HPM slurry helmet were constructed and assembled. RF transmission magnetic field (B1+$$ {\mathrm{B}}_1^{+} $$), B1−$$ {\mathrm{B}}_1^{-} $$, and MRI SNR maps from the entire human brain were measured and compared. Results Simulations showed that averaged B1−$$ {\mathrm{B}}_1^{-} $$ improvement with the HPM slurry helmet increased from 57% to 87% as the relative permittivity (εr) of HPM slurry increased from 110 to 210. In vivo experiments showed that the average B1+$$ {\mathrm{B}}_1^{+} $$ improvement over the human brain was 14.5% with the two‐piece HPM slurry (εr ≈ 170) helmet, and the average B1−$$ {\mathrm{B}}_1^{-} $$ and SNR were improved 63% and 34%, respectively, because the MRI noise level was increased by the lossy HPM. Conclusion The RF coil sensitivity and MRI SNR were largely improved with the two‐piece HPM slurry helmet demonstrated by both electromagnetic simulations and in vivo human head experiments at 7 T. The findings demonstrate that incorporating an easily producible HPM slurry helmet into the RF coil array significantly enhances human‐brain MRI SNR homogeneity and quality at ultrahigh field. Greater SNR improvement is anticipated using the less lossy HPM and optimal design.