Ultrashort echo time MR imaging with off-resonance saturation for characterization of pathologically altered Achilles tendons at 3 T.

Off-resonance radiofrequency saturation pulses applied prior to regular excitation in MR sequences can be used to modify signal contrast based on magnetization transfer and direct saturation effects. Clinical applicability and value of ultrashort echo time sequences combined with off-resonance saturation pulses was tested in 16 healthy and 14 tendinopathic as well as paratendinopathic Achilles tendons in vivo at 3 T. A 3D ultrashort echo time sequence in combination with a gaussian off-resonance saturation pulse (frequency offset: 1000-5000 Hz) was used to modify the detectable MR signal intensity from the Achilles tendon. Off-resonance saturation ratio was calculated as the relative reduction in signal intensity under selective off-resonance saturation in relation to a reference measurement without any saturation pulse. Off-resonance saturation ratio in tendons of healthy volunteers ranged from 0.52 ± 0.06 (1000 Hz) to 0.24 ± 0.02 (5000 Hz), whereas symptomatic tendinopathic tendons (0.35 ± 0.04 to 0.17 ± 0.02) and asymptomatic tendinopathic tendons (0.41 ± 0.06 to 0.21 ± 0.02) showed significantly lower mean off-resonance saturation ratio values. Off-resonance saturation ratio values might provide a sensitive and quantitative marker for assessment of pathological microstructure alterations of the Achilles tendon.