Iterative RF pulse design for multidimensional, small-tip-angle selective excitation

• Published in: Magnetic resonance in medicine 2005-10, Vol.54 (4), p.908-917
• Main Authors: Yip, Chun-yu, Fessler, Jeffrey A., Noll, Douglas C.
• Format: Article
• Language: English
• Subjects: Algorithms; constrained minimization; excitation k-space; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Imaging, Three-Dimensional - methods; iterative pulse design; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; Phantoms, Imaging; Radio Waves; Reproducibility of Results; selective excitation; Sensitivity and Specificity; Signal Processing, Computer-Assisted; small tip angle
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.20631

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.