title: Design of phase-modulated broadband refocusing pulses.
abstract: Broadband linear-phase refocusing pulses were designed with the Shinnar-Le Roux (SLR) transformation and verified experimentally. The design works in several steps: initially, a linear-phase B polynomial is created with the Parks-McClellan/Remez exchange algorithm. The complementary A polynomial required for the SLR transformation is generated with the Hilbert transformation, yielding the minimum-phase response. The phase response of the A polynomial is altered by zero-flipping, which changes the overall pulse shape while retaining its refocusing profile. Optimal pulses in terms of minimal B(1max) and hence broadest bandwidth were found with non-linear optimisation of the zero-flipping pattern. These pulses are generally phase modulated with a time-symmetric amplitude and anti-symmetric phase modulation. In this work, a whole range of pulses were designed to demonstrate the underlying relationships. Five exemplary pulses were implemented into a PRESS sequence and validated by acquiring images of a water-oil phantom and lactate spectra at TE = 144 ms.
authors.affiliation: GE Global Research, Munich, Germany. rolf.schulte@research.ge.com
authors.forename: Rolf F
authors.initials: RF
authors.lastname: Schulte
authors.forename: Patrick
authors.initials: P
authors.lastname: Le Roux
authors.forename: Mika W
authors.initials: MW
authors.lastname: Vogel
authors.forename: Hartmut
authors.initials: H
authors.lastname: Koenig
mesh_terms: D000465:Algorithms; D009682:Magnetic Resonance Spectroscopy; D019047:Phantoms, Imaging; D011846:Radio Waves; D013997:Time Factors