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

Abstract

For T_1ρ 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 T₁ 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_1ρ maps. Transient signal evolving towards the steady‐state were acquired in an interleaved segmented elliptical centric phase encoding order immediately after a T_1ρ 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_1ρ values were 42.4 ± 5.2 ms in overall cartilage of healthy volunteers. The average coefficient‐of‐variation (CV) of mean T_1ρ 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. Magn Reson Med 59:298–307, 2008.