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Iterative RF pulse design for multidimensional, small‐tip‐angle selective excitation
Author(s) -
Yip Chunyu,
Fessler Jeffrey A.,
Noll Douglas C.
Publication year - 2005
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.20631
Subject(s) - excitation , k space , conjugate gradient method , pulse (music) , regularization (linguistics) , computer science , range (aeronautics) , algorithm , nuclear magnetic resonance , control theory (sociology) , optics , physics , mathematical optimization , mathematics , materials science , mathematical analysis , artificial intelligence , control (management) , quantum mechanics , fourier transform , detector , composite material
The excitation k ‐space perspective on small‐tip‐angle selective excitation has facilitated RF pulse designs in a range of MR applications. In this paper, k ‐space‐based design of multidimensional RF pulses is formulated as a quadratic optimization problem, and solved efficiently by the iterative conjugate‐gradient (CG) algorithm. Compared to conventional design approaches, such as the conjugate‐phase (CP) method, the new design approach is beneficial in several regards. It generally produces more accurate excitation patterns. The improvement is particularly significant when k ‐space is undersampled, and it can potentially shorten pulse lengths. A prominent improvement in accuracy is also observed when large off‐resonance gradients are present. A further boost in excitation accuracy can be accomplished in regions of interest (ROIs) if they are specified together with “don't‐care” regions. The density compensation function (DCF) is no longer required. In addition, regularization techniques allow control over integrated and peak pulse power. Magn Reson Med, 2005. © 2005 Wiley‐Liss, Inc.