Broadband slab selection with B mitigation at 7T via parallel spectral-spatial excitation
✍ Scribed by Kawin Setsompop; Vijayanand Alagappan; Borjan A. Gagoski; Andreas Potthast; Franz Hebrank; Ulrich Fontius; Franz Schmitt; L.L. Wald; E. Adalsteinsson
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 830 KB
- Volume
- 61
- Category
- Article
- ISSN
- 0740-3194
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✦ Synopsis
Abstract
Chemical 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 B 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 B mitigation methods, which are based on a type of echovolumnar trajectory referred to as “spokes” or “fast‐k~z~”. Although such pulses, in conjunction with parallel excitation methodology, can efficiently mitigate large B 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 B 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 B 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 B mitigation compared to the standard spoke‐based parallel RF design. Magn Reson Med 61:493–500, 2009. © 2009 Wiley‐Liss, Inc.