Development of a Multi-Channel Transmit Extension for a Broadband RF-Electronics and its Evaluation on a 9.4 T Animal Scanner with 8 Transmit Channels

Abstract

In the last years the concept of parallel RF transmission has gained considerable interest, especially in the domain of high field MRI. In essence two principal application domains have emerged from this concept: the field of static B1-inhomogeneity compensation, also known as B1-shimming [1,2,3], and the technique of accelerated spatially-selective excitation (SSE), also known as Parallel Excitation (PEX) or Transmit SENSE [4,5], for improving the performance of many useful applications of SSE such as inner-volume imaging or targeted spectroscopy. In the field of B1-shimming the demands on the RF system are moderate. The RF system must only be capable of generating the same RF pulse on different channels with individual, but time-constant amplitude scaling and phase offsets. This can be realized by RF splitters, amplitude modulators and phase shifters. In contrast, to perform PEX-experiments the RF system must be capable of generating different complex RF waveforms on multiple transmit channels with high accuracy. Recently, several experimental studies of PEX with 4 and 8 transmit channels have been performed [6,7,8] and it has been shown that for doing PEX with high spatial resolution and high acceleration factors, the RF system must be equipped with a sufficient number of transmit channels. Therefore, the aim of this work was to develop a multichannel transmit extension for a broadband RF electronics with the potential of driving large numbers of transmit channels and to implement this electronics concept on a 9.4 T animal scanner with 8 transmit and receive channels