Three‐dimensional ultrashort echo time cones T_1ρ (3D UTE‐cones‐T_1ρ) imaging

Abstract

We report a novel three-dimensional (3D) ultrashort echo time (UTE) sequence employing Cones trajectory and T1ρ preparation (UTE-Cones-T1ρ) for quantitative T1ρ assessment of short T2 tissues in the musculoskeletal system. A basic 3D UTE-Cones sequence was combined with a spin-locking preparation pulse for T1ρ contrast. A relatively short TR was used to decrease scan time, which required T1 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 (Nsp) after each T1ρ preparation and fat saturation. A total of four spin-locking times (TSLs = 0 – 20 ms) were acquired under 12 minutes plus another 7 minutes for T1 measurement. The 3D UTE-Cones-T1ρ sequence was compared with a 2D spiral-T1ρ sequence for imaging of a spherical CuSO4 phantom and ex vivo meniscus and tendon specimens, as well as the knee and ankle joints of healthy volunteers using a clinical 3T scanner. The CuSO4 phantom showed a T1ρ value of 76.5 ± 1.6 ms with the 2D spiral-T1ρ sequence, as well as 85.7 ± 3.6 ms and 89.2 ± 1.4 ms for the 3D UTE-Cones-T1ρ sequences with Nsp of 1 and 5, respectively. The 3D UTE-Cones-T1ρ sequence provided shorter T1ρ values for the bovine meniscus sample compared to the 2D spiral-T1ρ sequence (10 – 12 ms vs 16 ms, respectively). The cadaveric human Achilles tendon sample could only be imaged with the 3D UTE-Cones-T1ρ sequence (T1ρ = 4.0 ± 0.9 ms), with the 2D spiral-T1ρ sequence demonstrating near zero signal intensity. Human studies yielded T1ρ values of 36.1 ± 2.9 ms, 18.3 ± 3.9 ms and 3.1 ± 0.4 ms for articular cartilage, meniscus and the Achilles tendon, respectively. The 3D UTE-Cones-T1ρ sequence allows volumetric T1ρ measurement of short T2 tissues in vivo.

3D adiabatic T1ρ prepared ultrashort echo time cones sequence for whole knee imaging

“…In our previous conventional CW‐T 1ρ study with 5 spokes per T 1ρ preparation, acceptable T 1ρ values were obtained by fitting the single spoke acquisition equation (Eq. ) . However, Eq.…”

“…However, both CW‐T 1ρ and AdiabT 1ρ measurements based on conventional MRI pulse sequences (such as GRE and FSE) are of limited value for detecting early PG depletion in short T 2 tissues or tissue components such as the deep radial and calcified cartilage, menisci, ligaments, and tendons. These tissues or tissue components typically have T 2 s ranging from sub‐milliseconds to several milliseconds and therefore provide little or no detectable signal using conventional sequences …”

Evaluation of normal cadaveric Achilles tendon and enthesis with ultrashort echo time (UTE) magnetic resonance imaging and indentation testing

“…We have developed three‐dimensional ultrashort echo time (3D UTE) pulse sequences with nominal T E values much shorter than those of clinical sequences . These UTE sequences allow us to directly image the clinically “MR invisible” Achilles tendon and its enthesis.…”

Whole knee joint T1 values measured in vivo at 3T by combined 3D ultrashort echo time cones actual flip angle and variable flip angle methods

“…Accurate T 1 measurements of the major knee joint tissues can be used for optimization of signal intensity and image contrast . Additionally, T 1 relaxation is a fundamental property of a tissue and may be directly useful as a biomarker of disease or degeneration or used to measure other quantitative MRI biomarkers, such as the macromolecular proton fraction from magnetization transfer modeling or low frequency exchange information from T 1ρ imaging …”