Journal
MAGNETIC RESONANCE IN MEDICINE
Volume 54, Issue 4, Pages 908-917Publisher
WILEY
DOI: 10.1002/mrm.20631
Keywords
iterative pulse design; small tip angle; selective excitation; excitation k-space; constrained minimization
Funding
- NIDA NIH HHS [DA15410] Funding Source: Medline
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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.
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