The Optimization of Adiabatic Pulses with Constant Amplitude Spin-lock for Magnetic Resonance $\mathrm{T}_{1\rho}$ Imaging

Quantitative magnetic resonance $\mathrm{T}_{1\rho}$ mapping is an important tool for a number of clinical applications, which can be used to obtain useful molecular information from diseased tissue non-invasively and without contrast agents. However, the stability of $\mathrm{T}_{1\rho}$ mapping is vulnerable to the influence of the magnetic field inhomogeneity, causing image artifacts and non-negligible quantization errors. Therefore, approaches using adiabatic pulses are proposed to alleviate the above deficiencies. This study proposes a method to optimize the HS and HSExp adiabatic pulses with constant amplitude spin-lock. The optimized pulse parameters were obtained through simulation which calculated the stability degree of the longitudinal magnetization Mz under a range of off-resonance values, and verified by phantom and in vivo experiments. The results of the experiment showed that the optimized adiabatic spin-lock pulses can achieve acceptable $\mathrm{T}_{1\rho}$-weighted imaging and $\mathrm{T}_{1\rho}$ mapping qualities.