3D‐T1ρ prepared zero echo time‐based PETRA sequence for in vivo biexponential relaxation mapping of semisolid short‐T2 tissues at 3 T

Background

In addition to the articular cartilage, osteoarthritis (OA) affects several other tissues such as tendons, ligaments, and subchondral bone. T1_ρ relaxation study of these short T₂ tissues may provide a more comprehensive evaluation of OA.

Purpose

To develop a 3D spin‐lattice relaxation in the rotating frame (T_1ρ) prepared zero echo time (ZTE)‐based pointwise encoding time reduction with radial acquisition (3D‐T_1ρ‐PETRA) sequence for relaxation mapping of semisolid short‐T₂ tissues on a clinical 3 T scanner.

Study Type

Prospective.

Population

Phantom, two bovine whole knee joint and Achilles tendon specimens, 10 healthy volunteers with no known inflammation, trauma or pain in the knee or ankle.

Field Strength/Sequence

A customized PETRA sequence to acquire fat‐suppressed 3D T_1ρ‐weighted images tissues with semisolid short T₂/ relaxation times in the knee and ankle joints at 3 T.

Assessment

Mono‐ and biexponential T_1ρ relaxation components were assessed in the patellar tendon (PT), anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), and Achilles tendon (AT).

Statistical Tests

Kruskal–Wallis with post‐hoc Dunn's test for multiple pairwise comparisons.

Results

Phantom and ex vivo studies showed the feasibility of T_1ρ relaxation mapping using the proposed 3D‐T_1ρ‐PETRA sequence. The in vivo study demonstrated an averaged mono‐T_1ρ relaxation of (median [IQR]) 15.9 [14.5] msec, 23.6 [9.4] msec, 17.4 [7.4] msec, and 5.8 [10.2] msec in the PT, ACL, PCL, and AT, respectively. The bicomponent analysis showed the short and long components (with their relative fractions) of 0.65 [1.0] msec (46.9 [15.3]%) and 37.3 [18.4] msec (53.1 [15.3]%) for PT, 1.7 [2.1] msec (42.5 [12.5]%) and 43.7 [17.8] msec (57.5 [12.5]%) for ACL, and 1.2 [1.9] msec (42.6 [14.0]%) and 27.7 [14.7] msec (57.3 [14.0]%) for PCL and 0.4 [0.02] msec (58.8 [13.3]%/) and 31.3 [10.8] msec (41.2 [13.3]%) for AT. Statistically significant (P ≤ 0.05) differences were observed in the mono‐ and biexponential relaxation between several regions.

Data Conclusion

The 3D‐T_1ρ‐PETRA sequence allows volumetric, isotropic (0.78 × 0.78 × 0.78 mm), biexponential T_1ρ assessment with corresponding fractions of the tissues with semisolid short T₂/.

Level of Evidence: 2

Technical Efficacy Stage: 1

J. Magn. Reson. Imaging 2019.

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