title: Pulsed arterial spin labelling at ultra-high field with a B 1 (+) -optimised adiabatic labelling pulse.
abstract: OBJECTIVE
  Arterial spin labelling (ASL) techniques benefit from the increased signal-to-noise ratio and the longer T 1 relaxation times available at ultra-high field. Previous pulsed ASL studies at 7 T concentrated on the superior regions of the brain because of the larger transmit radiofrequency inhomogeneity experienced at ultra-high field that hinders an adequate inversion of the blood bolus when labelling in the neck. Recently, researchers have proposed to overcome this problem with either the use of dielectric pads, through dedicated transmit labelling coils, or special adiabatic inversion pulses.
  
  
  METHODS
  We investigate the performance of an optimised time-resampled frequency-offset corrected inversion (TR-FOCI) pulse designed to cause inversion at much lower peak B 1 (+) . In combination with a PICORE labelling, the perfusion signal obtained with this pulse is compared against that obtained with a FOCI pulse, with and without dielectric pads.
  
  
  RESULTS
  Mean grey matter perfusion with the TR-FOCI was 52.5 ± 10.3 mL/100 g/min, being significantly higher than the 34.6 ± 2.6 mL/100 g/min obtained with the FOCI pulse. No significant effect of the dielectric pads was observed.
  
  
  CONCLUSIONS
  The usage of the B 1 (+) -optimised TR-FOCI pulse results in a significantly higher perfusion signal. PICORE-ASL is feasible at ultra-high field with no changes to operating conditions.
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Building 57, Research Road, St. Lucia, Brisbane, QLD, 4072, Australia.|Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Zimmer
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Building 57, Research Road, St. Lucia, Brisbane, QLD, 4072, Australia.|Siemens Healthcare Pty Ltd, Brisbane, Australia.
authors.forename: Kieran
authors.initials: K
authors.lastname: O'Brien
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Building 57, Research Road, St. Lucia, Brisbane, QLD, 4072, Australia.
authors.forename: Steffen
authors.initials: S
authors.lastname: Bollmann
authors.affiliation: Siemens Healthcare, Application Development, Erlangen, Germany.
authors.forename: Josef
authors.initials: J
authors.lastname: Pfeuffer
authors.affiliation: Siemens Healthcare, Boston, MA, USA.
authors.forename: Keith
authors.initials: K
authors.lastname: Heberlein
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Building 57, Research Road, St. Lucia, Brisbane, QLD, 4072, Australia. m.barth@uq.edu.au.
authors.forename: Markus
authors.initials: M
authors.lastname: Barth
mesh_terms: D000465:Algorithms; D001158:Arteries / Q000000981:diagnostic imaging*; D001931:Brain Mapping / Q000379:methods; D002560:Cerebrovascular Circulation; D066128:Gray Matter / Q000000981:diagnostic imaging; D064368:Healthy Volunteers; D006339:Heart Rate; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D015233:Models, Statistical; D010477:Perfusion; D019047:Phantoms, Imaging; D059629:Signal-To-Noise Ratio; D013113:Spin Labels
chemical_list: D013113:Spin Labels
keywords: Adiabatic inversion; Arterial spin labelling; Dielectric pads; Perfusion imaging; Ultra-high field