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.