Ultrashort TE imaging with off‐resonance saturation contrast (UTE‐OSC)

Abstract

Short T(2) species such as the Achilles tendon and cortical bone cannot be imaged with conventional MR sequences. They have a much broader absorption lineshape than long T(2) species, therefore they are more sensitive to an appropriately placed off-resonance irradiation. In this work, a technique termed ultrashort TE (UTE) with off-resonance saturation contrast (UTE-OSC) is proposed to image short T(2) species. A high power saturation pulse was placed +1 to +2 kHz off the water peak to preferentially saturate signals from short T(2) species, leaving long T(2) water and fat signals largely unaffected. The subtraction of UTE images with and without an off-resonance saturation pulse effectively suppresses long T(2) water and fat signals, creating high contrast for short T(2) species. The UTE-OSC technique was validated on a phantom, and applied to bone samples and healthy volunteers on a clinical 3T scanner. High-contrast images of the Achilles tendon and cortical bone were generated with a high contrast-to-noise ratio (CNR) of the order of 12 to 20 between short T(2) and long T(2) species within a total scan time of 4 to 10 min.