Sajad Hosseinnezhadian

Purpose: The design of radiofrequency (RF) coils tailored for the target anatomy is necessary to overcome the transmit field homogeneity and penetration issues at Ultra‐High‐Field (UHF). For the spinal cord, the optimal design has not yet been determined. This work intends to demonstrate the added value of a pair of passive dipoles placed under a conventional thoracic spine 4 × 2‐loop array. Methods: The conventional loop array produces a broad transmit field with unnecessary lateral spread. To address this, two passive dipoles were incorporated and tuned out‐of‐phase to actively suppress these lateral side‐lobes and increase field penetration the spinal cord region. The design was numerically optimised using a homogeneous phantom, followed by human voxel model simulations to evaluate performance and specific absorption rate (SAR). Finally, a prototype was tested in a 7T scanner using a homogeneous phantom to acquire experimental maps. Results: Human voxel model simulations demonstrated that the passive dipoles improve the transmit field distribution and predicted a 35% gain in SAR efficiency in the spinal cord region. Correspondingly, phantom experiments showed a 25% gain in transmit efficiency and 15% gain in homogeneity in a selected region of interest compared to the loop‐array‐only reference. Conclusion: Incorporating passive dipoles effectively suppresses unwanted lateral field spread, increasing penetration depth and efficiency in the thoracic spinal cord region. While homogeneous phantom results offer proof of concept, numerical simulations suggest reliable performance in realistic spine anatomy as well as substantial SAR reduction.

Purpose: The newly operational 11.7T Iseult scanner provides an improved global SNR in the human brain. This gain in SNR can be pushed even further locally by designing region‐focused dense receive arrays. The temporal lobes are particularly interesting to neuroscientists as they are associated with language and concept recognition. Our main goal was to maximize the SNR in the temporal lobes and provide high‐acceleration capabilities for fMRI studies.Methods: We designed and developed a 32‐channel receive array made of non‐overlapped hexagonal loops. The loops were arranged in a honeycomb pattern and targeted the temporal lobes. They were placed on a flexible neoprene cap closely fitting the head. A new stripline design with a high impedance was proposed and applied for the first time at 11.7T. Specific homebuilt miniaturized low‐impedance preamplifiers were directly mounted on the loops, providing preamplifier decoupling in a compact and modular design. Using an anatomical phantom, we experimentally compared the SNR and parallel imaging performance of the region‐focused cap to a 32‐channel whole‐brain receive array at 11.7T.Results: The experimental results showed a 1.7‐time higher SNR on average in the temporal lobes compared to the whole brain receive array. The g‐factor is also improved when undersampling in the antero‐posterior and head‐foot directions.Conclusion: A significant SNR boost in the temporal lobes was demonstrated at 11.7T compared to the whole‐brain receive array. The parallel imaging capabilities were also improved in the temporal lobes in some acceleration directions.