Heteronuclear decoupling by optimal tracking |
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Authors: | Jorge L. Neves, Bj rn Heitmann, Navin Khaneja,Steffen J. Glaser |
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Affiliation: | aDepartment of Chemistry, Technische Universität München, 85747 Garching, Germany;bDivision of Applied Sciences, Harvard University, Cambridge, MA 02138, USA |
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Abstract: | The problem to design efficient heteronuclear decoupling sequences is studied using optimal control methods. A generalized version of the gradient ascent engineering (GRAPE) algorithm is presented that makes it possible to design complex non-periodic decoupling sequences which are characterized by tens of thousands of pulse sequence parameters. In contrast to conventional approaches based on average Hamiltonian theory, the concept of optimal tracking is used: a pulse sequence is designed that steers the evolution of an ensemble of spin systems such that at a series of time points, a specified trajectory of the density operator is tracked as closely as possible. The approach is demonstrated for the case of low-power heteronuclear decoupling in the liquid state for in vivo applications. Compared to conventional sequences, significant gains in decoupling efficiency and robustness with respect to offset and inhomogeneity of the radio-frequency field were found in simulations and experiments. |
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Keywords: | Heteronuclear decoupling Optimal control theory GRAPE algorithm Tracking Average Hamiltonian theory |
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