Design Of Optimal Pulse In Nuclear Magnetic Resonance

Pulse sequence is a core module in magnetic resonance devices and it is anessential technique to optimize pulse for Nuclear Magnetic Resonance (NMR)spectroscopy and Magnetic Resonance Imaging (MRI). This article focuses on theapplication of optimal control method in the magnetic resonance pulse design.A brief introduction of the research’s background and prospect wasdemonstrated firstly. A summary about the developing history of pulses’ design andoptimization was given as follows. To illustrate the optimization algorithms ofmagnetic resonance pulse design, the theoretical model of optimal control methodfor the spin system in NMR pulse design was derived in this article. Four mainlyutilized optimization algorithms including the gradient ascent pulse engineeringalgorithm (GRAPE), the Krotov algorithm, the pseudospectrum method and thegeometric control method were compared. Choosing GRAPE algorithm as apowerful tool for further optimization and utilizing the line search method andquasi-Newton method to improve the stepsize and gradient in GRAPE algorithm,some imperfect factors like resonance offsets, radio frequency inhomogeneity andrelaxation were compensated by the optimal control method. Several simulation andexperimental results from magnetic resonance scanner of Pure Device company weregiven and compared. These results promoted each other and a broadband pulsecompensating resonance offsets and rf inhomogeneity was derived finally. It proved that the optimal control method could improve the sensitivity of the magneticresonance experiments.