Whole knee joint mapping using a phase modulated UTE adiabatic T<sub>1ρ</sub> (<scp>PM‐UTE‐AdiabT<sub>1ρ</sub></scp>) sequence
Yajun Ma, Michael Carl, Qingbo Tang, Dina Moazamian, Jiyo Athertya, Hyungseok Jang, Susan V. Bukata, Christine B. Chung, Eric Y. Chang, Jiang Du
Abstract
Abstract Purpose To develop a 3D phase modulated UTE adiabatic T 1ρ (PM‐UTE‐AdiabT 1ρ ) sequence for whole knee joint mapping on a clinical 3 T scanner. Methods This new sequence includes six major features: (1) a magnetization reset module, (2) a train of adiabatic full passage pulses for spin locking, (3) a phase modulation scheme (i.e., RF cycling pair), (4) a fat saturation module, (5) a variable flip angle scheme, and (6) a 3D UTE Cones sequence for data acquisition. A simple exponential fitting was used for T 1ρ quantification. Phantom studies were performed to investigate PM‐UTE‐AdiabT 1ρ 's sensitivity to compositional changes and reproducibility as well as its correlation with continuous wave–T 1ρ measurement. The PM‐UTE‐AdiabT 1ρ technique was then applied to five ex vivo and five in vivo normal knees to measure T 1ρ values of femoral cartilage, meniscus, posterior cruciate ligament, anterior cruciate ligament, patellar tendon, and muscle. Results The phantom study demonstrated PM‐UTE‐AdiabT 1ρ 's high sensitivity to compositional changes, its high reproducibility, and its strong linear correlation with continuous wave–T 1ρ measurement. The ex vivo and in vivo knee studies demonstrated average T 1ρ values of 105.6 ± 8.4 and 77.9 ± 3.9 ms for the femoral cartilage, 39.2 ± 5.1 and 30.1 ± 2.2 ms for the meniscus, 51.6 ± 5.3 and 29.2 ± 2.4 ms for the posterior cruciate ligament, 79.0 ± 9.3 and 52.0 ± 3.1 ms for the anterior cruciate ligament, 19.8 ± 4.5 and 17.0 ± 1.8 ms for the patellar tendon, and 91.1 ± 8.8 and 57.6 ± 2.8 ms for the muscle, respectively. Conclusion The 3D PM‐UTE‐AdiabT 1ρ sequence allows volumetric T 1ρ assessment for both short and long T 2 tissues in the knee joint on a clinical 3 T scanner.