Transmitting and receiving radio frequency signals for NMR signal excitation and response has been developed since the first crossed-pair coils used by Bloch for his co-discovery (together with Purcell) of NMR in 1945. In a more modern sense using multiple transmit and receive channels in parallel to acquire more signal from more volume, and/or to target specific regions of interest more optimally, multi-channel MRI has been under development and in practice since my presentation of “Parallel Imaging for MRI” in poster at the 1986 New York Academy of Science meeting. Of course multi-channel receive arrays, and parallel imaging with them, took off with Pete Roemer’s patent in 1989 followed by the advent of parallel imaging from Sodickson’s SMASH in 1996 followed by Pruessmann’s SENSE techniques, and still represent the State-of-the-Art in clinics today. All the while, multi-channel transmit approaches to solve problems and enhance performance especially for ultra-high field MRI have been pursued by myself and others since the first 2T system in 1984. In 1992 and since I have demonstrated both the need for and the application of what is known today as B1 shimming. I have used this term to more broadly apply to the ability and utility of manipulating the RF EM field generated by a coil, over five degrees of freedom (phase, magnitude, frequency, space, time), by adjusting the currents on multiple, independent coil elements or channels accordingly. Multi-channel transmit demonstrated use and potential for optimizing RF field uniformity, SAR, SNR, transmit efficiency, speed, and other benefits, especially important in modern, ultra-high field MRI where the shorter Larmor wavelengths are leading to increasing interference patterns and loss adversely effecting the success and safety of human studies. Additional avenues of multi-channel MRI development in our lab include on-coil, channel dedicated RF/analog front-ends and channel dedicated, FPGA facilitated, automated tune, match, and isolation functions for the ultimate versatility and optimization of RF technology and techniques for MRI. Finally, new research in simulation and validation of multi-channel RF safety principles and practices will be presented.
