• Kawin Setsompop, Vijayanand Alagappan, Borjan A Gagoski, Andreas Potthast, Franz Hebrank, Ulrich Fontius, Franz Schmitt, L L Wald, and E Adalsteinsson.
• Department of Electrical Engineering and Computer Science, MIT, Cambridge, Massachustts 02139, USA. kawin@mit.edu
• Magn Reson Med. 2009 Feb 1; 61 (2): 493-500.

AbstractChemical shift imaging benefits from signal-to-noise ratio (SNR) and chemical shift dispersion increases at stronger main field such as 7 Tesla, but the associated shorter radiofrequency (RF) wavelengths encountered require B1+ mitigation over both the spatial field of view (FOV) and a specified spectral bandwidth. The bandwidth constraint presents a challenge for previously proposed spatially tailored B1+ mitigation methods, which are based on a type of echovolumnar trajectory referred to as "spokes" or "fast-kz". Although such pulses, in conjunction with parallel excitation methodology, can efficiently mitigate large B1+ inhomogeneities and achieve relatively short pulse durations with slice-selective excitations, they exhibit a narrow-band off-resonance response and may not be suitable for applications that require B1+ mitigation over a large spectral bandwidth. This work outlines a design method for a general parallel spectral-spatial excitation that achieves a target-error minimization simultaneously over a bandwidth of frequencies and a specified spatial-domain. The technique is demonstrated for slab-selective excitation with in-plane B1+ mitigation over a 600-Hz bandwidth. The pulse design method is validated in a water phantom at 7T using an eight-channel transmit array system. The results show significant increases in the pulse's spectral bandwidth, with no additional pulse duration penalty and only a minor tradeoff in spatial B1+ mitigation compared to the standard spoke-based parallel RF design.Copyright 2009 Wiley-Liss, Inc.

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