Abstract
We report a novel three-dimensional (3D) ultrashort echo time (UTE) sequence employing Cones trajectory and T(1ρ) preparation (UTE-Cones-T(1ρ) ) for quantitative T(1ρ) assessment of short T(2) tissues in the musculoskeletal system. A basic 3D UTE-Cones sequence was combined with a spin-locking preparation pulse for T(1ρ) contrast. A relatively short TR was used to decrease the scan time, which required T(1) measurement and compensation using 3D UTE-Cones data acquisitions with variable TRs. Another strategy to reduce the total scan time was to acquire multiple Cones spokes (N(sp) ) after each T(1ρ) preparation and fat saturation. Four spin-locking times (TSL = 0-20 ms) were acquired over 12 min, plus another 7 min for T(1) measurement. The 3D UTE-Cones-T(1ρ) sequence was compared with a two-dimensional (2D) spiral-T(1ρ) sequence for the imaging of a spherical CuSO(4) phantom and ex vivo meniscus and tendon specimens, as well as the knee and ankle joints of healthy volunteers, using a clinical 3-T scanner. The CuSO(4) phantom showed a T(1ρ) value of 76.5 ± 1.6 ms with the 2D spiral-T(1ρ) sequence, as well as 85.7 ± 3.6 and 89.2 ± 1.4 ms for the 3D UTE-Cones-T(1ρ) sequences with N(sp) of 1 and 5, respectively. The 3D UTE-Cones-T(1ρ) sequence provided shorter T(1ρ) values for the bovine meniscus sample relative to the 2D spiral-T(1ρ) sequence (10-12 ms versus 16 ms, respectively). The cadaveric human Achilles tendon sample could only be imaged with the 3D UTE-Cones-T(1ρ) sequence (T(1ρ) = 4.0 ± 0.9 ms), with the 2D spiral-T(1ρ) sequence demonstrating near-zero signal intensity. Human studies yielded T(1ρ) values of 36.1 ± 2.9, 18.3 ± 3.9 and 3.1 ± 0.4 ms for articular cartilage, meniscus and the Achilles tendon, respectively. The 3D UTE-Cones-T(1ρ) sequence allows volumetric T(1ρ) measurement of short T(2) tissues in vivo.