Initial experience with synthetic MRI of the knee at 3T: comparison with conventional T 1 weighted imaging and T 2 mapping.

OBJECTIVE: To assess the feasibility and accuracy of synthetic MRI compared to conventional T1  weighted and multi-echo spin-echo (MESE) sequences for obtaining T2 values in the knee joint at 3 Tesla.

METHODS: This retrospective study included 19 patients with normal findings in the knee joint who underwent both synthetic MRI and MESE pulse sequences for T2 quantification. T2 values of the two sequences at the articular cartilage, bone marrow and muscle were measured. Relative signal intensity (SI) of each structure and relative contrast among structures of the knee were measured quantitatively by T1  weighted sequences.

RESULTS: The mean T2 values for cartilage and muscle were not significantly different between MESE pulse sequences and synthetic MRI. For the bone marrow, the mean T2 value obtained by MESE sequences (124.3 ± 3.6 ms) was significantly higher than that obtained by synthetic acquisition (73.1 ± 5.3 ms). There were no significant differences in the relative SI of each structure between the methods. The relative contrast of bone marrow to muscle was significantly higher with conventional T1  weighted images, while that for bone marrow to cartilage was similar for both sequences.

CONCLUSION: Synthetic MRI is able to simultaneously acquire conventional images and quantitative maps, and has the potential to reduce the overall examination time. It provides comparable image quality to conventional MRI for the knee joint, with the exception of the bone marrow. With further optimization, it will be possible to take advantage of the image quality of musculoskeletal tissue with synthetic imaging. Advances in knowledge: Synthetic MRI produces images of good contrast and is also a time-saving technique. Thus, it may be useful for assessing osteoarthritis in the knee joint in the early stages.