Generalized RF Pulse Train with Insensitivity to B ₁ Inhomogeneity

Abstract

Adiabatic inversion recovery radiofrequency (RF) pulse techniques are used to address B ₁ inhomogeneity; however, the specific absorption rates of these techniques are significantly higher than that of non-adiabatic RF pulse techniques. In addition, time efficiency is poorer because of the required longer inversion recovery time. Therefore, an RF pulse train with three subpulses was previously developed and reported. The purpose of this article was to generalize the RF pulse train for tissues with different T ₁ relaxation times and in a different application. The RF pulse train B ₁ insensitivities and frequency responses were calculated with different T ₁ relaxation times and different subpulse durations using the Bloch equation. The previously reported optimal flip angle (FA) combination was used. When using the optimal FA combination, the RF pulse train B ₁ insensitivity did not change even if the T ₁ relaxation times and the subpulse durations did change. In other words, the optimal FA combination does not require adjustments according to the T ₁ and subpulse duration. The RF pulse train frequency responses with these subpulses can be dramatically improved even if the inherent subpulse frequency response is poor. This finding will facilitate RF pulse train technique implementation on magnetic resonance imaging scanners.