Toward whole‐cortex enhancement with an ultrahigh dielectric constant helmet at 3T

Purpose To present a 3T brain imaging study using a conformal prototype helmet constructed with an ultra‐high dielectric constant (uHDC; ε r ~ 1000) materials that can be inserted into standard receive head‐coils. Methods A helmet conformal to a standard human head constructed with uHDC materials was characterized through electromagnetic simulations and experimental work. The signal‐to‐noise ratio (SNR), transmit efficiency, and power deposition with the uHDC helmet inserted within a 20‐channel head coil were measured in vivo and compared with a 64‐channel head coil and the 20‐channel coil without the helmet. Seven healthy volunteers were analyzed. Results Simulation and in vivo experimental results showed that transmit efficiency was improved by nearly 3 times within localized regions for a quadrature excitation, with a measured global increase of 58.21 ± 6.54% over 7 volunteers. The use of a parallel transmit spokes pulse compensated for severe degradation of B 1 + homogeneity, at the expense of higher global and local specific absorption rate levels. A SNR histogram analysis with statistical testing demonstrated that the uHDC helmet enhanced a 20‐channel head coil to the level of the 64‐channel head coil, with the improvements mainly within the cortical brain regions. Conclusion A prototype uHDC helmet enhanced the SNR of a standard head coil to the level of a high density 64‐channel coil, although transmit homogeneity was compromised. Further improvements in SNR may be achievable with optimization of this technology, and could be a low‐cost approach for future radiofrequency engineering work in the brain at 3T.