Purpose To design, construct and validate radiofrequency (RF) transmit and receive phased array coils for high-resolution visual cortex imaging at 7 Tesla. Methods A 4 channel transmit and 16 channel receive array was constructed on a conformal polycarbonate former. Transmit field efficiency and homogeneity were simulated and validated, along with the Specific Absorption Rate, using B1+ mapping techniques and electromagnetic simulations. Receiver signal-to-noise ratio (SNR), temporal SNR (tSNR) across EPI time series, g-factors for accelerated imaging and noise correlations were evaluated and compared with a commercial 32 channel whole head coil. The performance of the coil was further evaluated with human subjects through functional MRI (fMRI) studies at standard and submillimeter resolutions of upto 0.8mm isotropic. Results The transmit and receive sections were characterized using bench tests and showed good interelement decoupling, preamplifier decoupling and sample loading. SNR for the 16 channel coil was∼1.5 times that of the commercial coil in the human occipital lobe, and showed better g-factor values for accelerated imaging. fMRI tests conducted showed better response to Blood Oxygen Level Dependent (BOLD) activation, at resolutions of 1.2mm and 0.8mm isotropic. Conclusion The 4 channel phased array transmit coil provides homogeneous excitation across the visual cortex, which, in combination with the dual row 16 channel receive array, makes for a valuable research tool for high resolution anatomical and functional imaging of the visual cortex at 7T.
Bibliographical noteFunding Information:
This work was supported by the NWO Middelgroot Grant (#36020201N) to RG [http://www.nwo.nl/en]. AR was supported by an ERC Starting Grant (MULTICONNECT, #639938) [https://erc.europa.eu/projects-and-results/erc-funded-projects/multiconnect]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. We would like to thank Christopher J. Wiggins for his help with the project. This work was supported by the NWO Middelgroot Grant (#36020201N). Alard Roebroeck was supported by an ERC Starting Grant (MULTICONNECT, #639938).
© 2016 Sengupta et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.