Study of magnetization evolution by using composite spin-lock pulses for T1ρ imaging

B₀ and B₁ field inhomogeneities may generate banding-like artifacts in T_1ρ-weighted images and hence result in errors of T_1ρ quantification. Several types of composite spin-lock pulses have been proposed to alleviate such artifacts. In this study, magnetization evolution with T_1ρ and T_2ρ relaxation by using these composite spin-lock pulses are theoretically derived. The effectiveness and limitation of each spin-lock pulse are explicitly illustrated in mathematical forms and phantom T_1ρ-weighted images acquired by using each spin-lock pulse are presented. This study also provides a theoretical framework for T_1ρ quantification from T_1ρ-weighted images even with B₀ and B₁ inhomogeneity artifacts.