Improving central transmit efficiency and homogeneity using interleaved shielded dielectric discs and coil elements in a 4- element transmit/receive array at 7 T
Manushka V. Vaidya, Christopher M. Collins, Ryan Brown, Daniel K. Sodickson, Riccardo Lattanzi
1st January 0001
Magnetic resonance (MR) imaging of deep anatomical structures at 7T is challenging, because of B1 field inhomogeneities and safety limitations on RF power. Placing an RF shield above the coil elements of an array can increase transmit (Tx) and receive (Rx) efficiency near the surface of the object, but reduces field efficiency in deeper regions1. Parallel Tx techniques improve efficiency for deep structures2, but cost and complexity currently prevent their widespread use. High permittivity materials, placed between an RF coil and the sample, can improve Tx efficiency, signal-to-noise ratio (SNR), and RF homogeneity in various MR applications3,4. However, the benefits reported in previous studies are limited to regions near the dielectric materials. A recent simulation study showed that
placing dielectric discs covered with passive conductive shields at various positions on the surface of the sample could shape the B1 field of a Tx coil5 in a favorable manner. Here we show, in both simulation and experiment, the advantage of interleaving shielded dielectrics with RF coils in a four-element Tx/Rx array.
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