title: Broadband slab selection with B1+ mitigation at 7T via parallel spectral-spatial excitation.
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 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.
authors.affiliation: Department of Electrical Engineering and Computer Science, MIT, Cambridge, Massachustts 02139, USA. kawin@mit.edu
authors.forename: Kawin
authors.initials: K
authors.lastname: Setsompop
authors.forename: Vijayanand
authors.initials: V
authors.lastname: Alagappan
authors.forename: Borjan A
authors.initials: BA
authors.lastname: Gagoski
authors.forename: Andreas
authors.initials: A
authors.lastname: Potthast
authors.forename: Franz
authors.initials: F
authors.lastname: Hebrank
authors.forename: Ulrich
authors.initials: U
authors.lastname: Fontius
authors.forename: Franz
authors.initials: F
authors.lastname: Schmitt
authors.forename: L L
authors.initials: LL
authors.lastname: Wald
authors.forename: E
authors.initials: E
authors.lastname: Adalsteinsson
mesh_terms: D000465:Algorithms; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D051598:Whole Body Imaging / Q000379:methods*