A robust adiabatic constant amplitude spin-lock preparation module for myocardial T1ρ quantification at 3 T

Abstract

T_1ρ quantification has the potential to assess myocardial fibrosis without contrast agent. However, its preparation spin-lock pulse is sensitive to B₁ and B₀ inhomogeneities, resulting in severe banding artifacts in the heart region, especially at high magnetic field such as 3 T. We aimed to design a robust spin-lock (SL) preparation module that can be used in myocardial T_1ρ quantification at 3 T. We used the tan/tanh pulse to tip up and tip down the magnetization in the spin-lock preparation module (tan/tanh-SL). Bloch simulation was used to optimize pulse shape parameters of the tan/tanh with a pulse duration (T_p ) of 8, 4, and 2 ms, respectively. The designed tan/tanh-SL modules were implemented on a 3-T MR scanner. They were evaluated in phantom studies under three different cases of B₀ and B₁ inhomogeneities, and tested in cardiac T_1ρ quantification of healthy volunteers. The performance of the tan/tanh-SL was compared with the composite SL preparation pulses and the commonly used hyperbolic secant pulse for spin-lock (HS-SL). Feasible pulse shape parameters were obtained using Bloch simulation. Compared with HS-SL, the quantification error of tan/tanh-SL was reduced by 27.7% for T_p = 8 ms (mean ∆Q = 126.15 vs. 174.42) and 75.6% for T_p = 4 ms (mean ∆Q = 136.65 vs. 559.53). In the phantom study, tan/tanh-SL was less sensitive to B₁ and B₀ inhomogeneity compared with composite SL pulses and HS-SL. In cardiac T_1ρ quantification, the T_1ρ maps using tan/tanh-SL showed fewer banding artifacts than using composite SL pulses and HS-SL. The proposed tan/tanh-SL preparation module greatly improves the robustness to B₀ and B₁ field inhomogeneities and can be used in cardiac T_1ρ quantification at 3 T.

Keywords: adiabatic constant amplitude spin-lock preparation; myocardial T1ρ mapping.