In-vivo Determination of Relaxation Times of Musculoskeletal Relevant Tissue at 1.5 T and 3 T

Purpose: The introduction of MR-systems with field strength of 3 T and higher is a logical step to achieve high-resolution images in-vivo. Musculoskeletal applications include imaging of small joints and morphologically complex and vulnerable structures such as articular cartilage. Optimization of image contrast requires knowledge of the relaxation times of the relevant tissues.

Methods: Relaxation times T1, T2, and T2* were determined in the right knee of 9 healthy volunteers at 1.5 T (Magnetom Sonata, Siemens) and 3.0 T (Magnetom Trio, Siemens). Identical sequence parameters were applied at both units. An inversion-recovery sequence (21 images, TI between 30 ms and 10000 ms) was applied for determination of T1. T2 and T2* were determined with a spin-echo sequence (32 images, TE=10–320 ms) and a gradient echo sequence (16 images, TE=5–79 ms), respectively. Parameter maps were calculated by a monoexponential fitting algorithm. Relaxation times were analyzed in musculature, cartilage, adipose tissue, synovial fluid, and femoral bone marrow.

Results: At 3T, T1 is increased in all evaluated tissues (range 14–23%) with articular cartilage showing the lowest and femoral bone marrow the highest changes. On the other hand, T2 as well as T2* decrease by 12–22%. Again, articular cartilage reveals the lowest changes and bone marrow the highest.

Conclusion: The evaluated relaxation times are prerequisites for improved visualization of fine structured details of certain critical joint components such as cartilage tissue. With this, musculoskeletal applications will markedly benefit from the higher field strength.