In vivo T1 and T2 mapping of human knee at 0.05 Tesla

Motivation: To study knee tissue properties at Ultra-low-field (ULF) for sequence design/optimization, enabling ULF MRI for wide-ranging applications. Goal(s): To measure the T2 and T1 values of various tissues in vivo human knee at 0.05T. Approach: Multiple TE and TR measurements were conducted on a home-built and RF shielding-free 0.05T MRI scanner for T2 and T1 mapping through pixel-wise numerical fitting. Results: Phantom results exhibited a linear relationship between the Gadolinium concentration and relaxation rate, demonstrating the feasibility of mapping procedure. Additionally, the T2 and T1 values of cartilage, tendon, fat, and skeletal muscle in human knee were estimated and reported. Impact: The estimated Gadolinium T2 and T1 relaxivities at 0.05 Tesla are significantly higher than those at 1.5T and 3.0T, guiding the usage of contrast agent dose. Moreover, T2 and T1 mapping of musculoskeletal tissues can facilitate sequence design/optimization.