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Broadband slab selection with B 1 + mitigation at 7T via parallel spectral‐spatial excitation
Author(s) -
Setsompop Kawin,
Alagappan Vijayanand,
Gagoski Borjan A.,
Potthast Andreas,
Hebrank Franz,
Fontius Ulrich,
Schmitt Franz,
Wald L.L.,
Adalsteinsson E.
Publication year - 2009
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21834
Subject(s) - bandwidth (computing) , excitation , computer science , broadband , imaging phantom , optics , pulse duration , physics , acoustics , telecommunications , laser , quantum mechanics
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 1 +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 1 +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 1 +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 1 +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 1 +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 1 +mitigation compared to the standard spoke‐based parallel RF design. Magn Reson Med 61:493–500, 2009. © 2009 Wiley‐Liss, Inc.