Three‐dimensional ultrashort echo time cones T1ρ (3D UTE‐cones‐T1ρ) imaging

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 .