Quantitative magnetization transfer ultrashort echo time imaging of the Achilles tendon

Ultrashort echo time imaging allows the short T(2) Achilles tendon to be directly visualized with MRI. Radiofrequency saturation 1 kHz or less off-resonance has been used previously to improve image contrast. In this study, magnetization transfer was investigated in the Achilles tendon of eight normal volunteers and one patient with psoriatic arthritis. 2D Ultrashort echo time images were acquired using saturation pulses 2-100 kHz off-resonance at 4 pulse powers. On-resonance saturation recovery images were also obtained to estimate T(1). The results were fitted to a two compartment quantitative magnetization transfer model. The estimated bound proton fraction for the eight healthy volunteers was 21.0 ± 1.2% (mean ± standard deviation) compared to 16.4% in the patient with psoriatic arthritis (P < 0.05). The T(2) of the bound protons was measured as 6.1 ± 0.3 microsec in the healthy volunteers and 6.0 microsec in the patient. This technique appears clinically feasible and may be useful for assessing the collagen and water changes which occur in Achilles tendinopathy.