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

B(0) and B(1) 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 B(0) and B(1) inhomogeneity artifacts.