Optimal control RF pulses for excitation and suppression of NMR signals in a conductive medium

In this work, optimal control theory was used to design efficient excitation schemes in highly conductive materials, where both the radio frequency field strength and phase vary as a function of penetration depth. A pulse was designed to achieve phase alignment between signals at different depths within the conductor and thus to obtain higher signals from that region. In addition, an efficient suppression pulse was designed by insuring mutual suppression between the signals from various depths in the sample. The performance of the new approach was demonstrated experimentally for a bulk lithium sample for the excitation problem and for a biphasic metal/liquid sample for the selective suppression pulse.