title: Tailored spiral in-out spectral-spatial water suppression pulses for magnetic resonance spectroscopic imaging.
abstract: OBJECTIVE
  To develop short water suppression sequences for 7 T magnetic resonance spectroscopic imaging, with mitigation of subject-specific transmit RF field ( B1+) inhomogeneity.
  
  
  METHODS
  Patient-tailored spiral in-out spectral-spatial saturation pulses were designed for a three-pulse WET water suppression sequence. The pulses' identical spatial subpulses were designed using patient-specific B1+ maps and a spiral in-out excitation k-space trajectory. The subpulse train was weighted by a spectral envelope that was root-flipped to minimize peak RF demand. The pulses were validated in in vivo experiments that acquired high resolution magnetic resonance spectroscopic imaging data, using a crusher coil for fast lipid suppression. Residual water signals and MR spectra were compared between the proposed tailored sequence and a conventional WET sequence.
  
  
  RESULTS
  Replacing conventional spectrally-selective pulses with tailored spiral in-out spectral-spatial pulses reduced mean water residual from 5.88 to 2.52% (57% improvement). Pulse design time was less then 0.4 s. The pulses' specific absorption rate were compatible with magnetic resonance spectroscopic imaging TRs under 300 ms, which enabled spectra of fine in plane spatial resolution (5 mm) with good quality to be measured in 7.5 min.
  
  
  CONCLUSIONS
  Tailored spiral in-out spectral-spatial water suppression enables efficient high resolution magnetic resonance spectroscopic imaging in the brain. Magn Reson Med 79:31-40, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.|Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Ma
authors.affiliation: Department of Radiology, University Medical Centre Utrecht, Utrecht, the Netherlands.
authors.forename: Carrie
authors.initials: C
authors.lastname: Wismans
authors.affiliation: Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.|Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: Zhipeng
authors.initials: Z
authors.lastname: Cao
authors.affiliation: Department of Radiology, University Medical Centre Utrecht, Utrecht, the Netherlands.
authors.forename: Dennis W J
authors.initials: DWJ
authors.lastname: Klomp
authors.affiliation: Department of Radiology, University Medical Centre Utrecht, Utrecht, the Netherlands.
authors.forename: Jannie P
authors.initials: JP
authors.lastname: Wijnen
authors.affiliation: Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.|Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: Grissom
mesh_terms: D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging*; D001931:Brain Mapping / Q000379:methods; D003198:Computer Simulation; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D007091:Image Processing, Computer-Assisted; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D019047:Phantoms, Imaging; D011846:Radio Waves; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D059629:Signal-To-Noise Ratio; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water
keywords: RF pulse design; RF pulses; optimization; selective excitation; spectroscopy; ultra-high field MRI