In vivo T1ρ mapping in cartilage using 3D magnetization-prepared angle-modulated partitioned k-space spoiled gradient echo snapshots (3D MAPSS)

For T-1 rho quantification, a three-dimensional (3D) acquisition is desired to obtain high-resolution images. Current 3D methods that use steady-state spoiled gradient-echo (SPGR) imaging suffer from high SAR, low signal-to-noise ratio (SNR), and the need for retrospective correction of contaminating T, effects. In this study, a novel 3D acquisition scheme-magnetization-prepared angle-modulated partitioned-k-space SPGR snapshots (3D MAPSS)-was developed and used to obtain in vivo T-1 rho maps. Transient signal evolving towards the steady-state were acquired in an interleaved segmented elliptical centric phase encoding order immediately after a Tip magnetization preparation sequence. RF cycling was applied to eliminate the adverse impact of longitudinal relaxation on quantitative accuracy. A variable flip angle train was designed to provide a flat signal response to eliminate the filtering effect in k-space caused by transient signal evolution. Experiments in phantoms agreed well with results from simulation. The T-1 rho values were 42.4 +/- 5.2 ms in overall cartilage of healthy volunteers. The average coefficient-of-variation (CV) of mean T-1 rho values (N = 4) for overall cartilage was 1.6%, with regional CV ranging from 1.7% to 8.7%. The fitting errors using MAPSS were significantly lower (P < 0.05) than those using sequences without RF cycling and variable flip angles.