Multi‐band Adiabatic Inversion Pulses for Use with the 8th‐order Hadamard Spectroscopic Imaging Technique

Abstract

AbstractRf pulses with frequency responses which correspond to the rows of the 8th‐order Hadamard matrix are developed. These pulses can be used in the B1 insensitive Hadamard Spectroscopic Imaging multi‐volume localization technique. It is shown how any adiabatic rf pulse, which inverts spin population at a well defined frequency band, can be modified to invert populations at several frequency bands simultaneously. Conditions on the frequency and amplitude functions which allow such modifications are defined. For increasing amplitude the interaction between the bands produces nonlinear irradiation at several frequencies. By using an integrated form of the Floquet formalism and perturbation theory, the interaction between the bands is described analytically by an effective Hamiltonian. From this description the conditions which guarantee minimization of the unwanted irradiation are defined. The experimental results agree very well with the theoretical predications.