Parallel Excitation: Making SENSE of High-Field Body MRI

MR imaging at high B0 field strength presents significant diagnostic opportunities derived from enhancements in SNR, spectral resolution and image contrast. However there are technical challenges that substantially hamper the practice of high-field MRI, including a major one that is related to the exploitation of the radio frequency EM field (B1 field and concomitant E field). As field strength increases, the degradation in B1 homogeneity due to increased wave behavior and source-subject interaction (1-5) may result in compromises in image uniformity or contrast fidelity, and the exacerbation in RF power deposition (SAR) at an increasing rate (2,6) may pose considerable constraints on the use of RF pulses or volume transmit coils. Both the B1 inhomogeneity and SAR problems become more prominent with an increase in object size. While in vivo head imaging has been robustly demonstrated at a B0 field strength of 7 Tesla or even higher (6,7), the lack of effective measures managing both the B1 inhomogeneity and SAR problems appears to be holding up the extension of the head imaging success to body imaging. This talk introduces promising solutions provided by parallel excitation, an emerging technology that is based on orchestrated RF transmit with a distributed array of coils, as opposed to the convention of single-channel transmit with a volume coil.