A size-adaptive RF coil for MRI of the pediatric human brain at 7 T

The purpose of this work was to design and build a size-adaptive pediatric RF head coil for 7 T neuroimaging. The coil can be safely applied for imaging children 4-9 years old.

The pediatric head coil incorporates eight, transmit dipole elements for operation in parallel transmit (pTx) mode. The receive architecture is comprised of a 32-channel conformal, size-adaptive receive array. Receive elements were arranged into five sections of a mechanically adjustable 3D printed head former, allowing adjustment of the receive array according to child head size. The transmit coil was carefully simulated to calculate specific absorption rate (SAR) and B₁ ⁺ efficiency. Coil performance was then evaluated with a pediatric head phantom at both the largest and smallest dimensions of the receive former. In vivo imaging was carried out in 3 pediatric subjects (aged 5, 6, and 9 years old) to acquire B₁ ⁺ field maps and anatomical MP2RAGE images.

A comparison of simulated and experimental B₁ ⁺ performance in the pediatric head phantom was used to validate SAR models and to demonstrate that the coil was safe for pediatric imaging. The SNR performance in the pediatric phantom was improved by adjusting the position of the receive array to the smallest possible position. The in vivo B₁ ⁺ efficiency agreed with expectations, and the coil provided precise anatomical images of the brain.

The proposed size-adaptive coil enables safe, high-quality imaging of children at 7 T, with a range of ages and head sizes. Accurate SAR modeling enabled imaging using both combined circularly polarized and dynamic pTx modes.