Whole body 3T MRI system with eight parallel RF transmit/receive channels and dual operation modes

Whole body imaging at 3T and above may be disturbed by B1 field inhomogeneity caused by wave propagation effects. Simulations [1] have shown that RF shimming techniques can compensate such inhomogeneities. Furthermore, the acceleration of 2/3D spatially selective excitations enables new and/or improved technical features like zoom imaging, navigators or arterial spin labeling and other advanced parallel transmission techniques [2–4].

This paper describes the first fully integrated MRI prototype system based on a standard commercial 3T Philips MRI scanner, which features a fully integrated multi-element body coil (MBC) as well as an integrated control and data acquisition system (CDAS).

A single- and multi-channel RF transmit mode was implemented. In the multi-transmit mode, the individual RF signals of the eight independent transmitters (Tx1-Tx8, Fig.1, blue) are amplified by individual solid-state RF amplifiers. For patient safety reasons, a shutdown unit (SDU) prevents RF transmission if any of the eight transmit channels fails. The RF signals are routed via individual circulators and transmit/receive switches to the Tx/Rx TEM resonators of a MBC. In the single-channel mode, a circularly polarized B1-field is generated by using transmitter board Tx, a single RF-amplifier, a RF power splitter, and phase shifters (Fig.1, orange).

Parallel phantom and in-vivo experiments were carried out using parallel transmission (TxSENSE with reduction factors R=1...8) as well as reception (RxSENSE factors up to 4).

References:

1. Ibrahim TS et al. [2000] MRI 18:733–742.

2. Katscher U et al. [2003] MRM 49:144–150.

3. Zhu Y [2004] MRM 51:775–784.

4. Grissom W et al. [2005] ISMRM 13:19

Fig.1: Block diagram of an eight-channel Tx/Rx MR system architecture with two operation modes.