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

Magn Reson Med. 2025 Mar;93(3):1205-1219. doi: 10.1002/mrm.30350. Epub 2024 Oct 24.

Abstract

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 ( B 1 - $$ {\mathrm{B}}_1^{-} $$ ) 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 ( B 1 + $$ {\mathrm{B}}_1^{+} $$ ), B 1 - $$ {\mathrm{B}}_1^{-} $$ , and MRI SNR maps from the entire human brain were measured and compared.

Results: Simulations showed that averaged B 1 - $$ {\mathrm{B}}_1^{-} $$ 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 B 1 + $$ {\mathrm{B}}_1^{+} $$ improvement over the human brain was 14.5% with the two-piece HPM slurry (εr ≈ 170) helmet, and the average B 1 - $$ {\mathrm{B}}_1^{-} $$ 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.

Keywords: High‐permittivity slurry helmet; RF coil sensitivity; RF head array coil; human‐brain MRI; signal‐to‐noise; ultrahigh‐field MRI.

MeSH terms

  • Brain* / diagnostic imaging
  • Computer Simulation
  • Equipment Design*
  • Head / diagnostic imaging
  • Head Protective Devices
  • Humans
  • Magnetic Fields
  • Magnetic Resonance Imaging* / instrumentation
  • Phantoms, Imaging*
  • Radio Waves
  • Signal-To-Noise Ratio*