Whole knee joint mapping using a phase modulated UTE adiabatic T₁ (PM-UTE-AdiabT₁) sequence

Purpose: To develop a 3D phase modulated UTE adiabatic T-1 rho (PM-UTE-AdiabT(1 rho)) 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-1 rho quantification. Phantom studies were performed to investigate PM-UTE-AdiabT(1 rho)'s sensitivity to compositional changes and reproducibility as well as its correlation with continuous wave-T-1 rho measurement. The PM-UTE-AdiabT(1 rho) technique was then applied to five ex vivo and five in vivo normal knees to measure T-1 rho values of femoral cartilage, meniscus, posterior cruciate ligament, anterior cruciate ligament, patellar tendon, and muscle. Results: The phantom study demonstrated PM-UTE-AdiabT(1 rho)'s high sensitivity to compositional changes, its high reproducibility, and its strong linear correlation with continuous wave-T-1 rho measurement. The ex vivo and in vivo knee studies demonstrated average T-1 rho values of 105.6 +/- 8.4 and 77.9 +/- 3.9ms for the femoral cartilage, 39.2 +/- 5.1 and 30.1 +/- 2.2ms for the meniscus, 51.6 +/- 5.3 and 29.2 +/- 2.4ms for the posterior cruciate ligament, 79.0 +/- 9.3 and 52.0 +/- 3.1ms for the anterior cruciate ligament, 19.8 +/- 4.5 and 17.0 +/- 1.8ms for the patellar tendon, and 91.1 +/- 8.8 and 57.6 +/- 2.8ms for the muscle, respectively. Conclusion: The 3D PM-UTE-AdiabT(1 rho) sequence allows volumetric T-1 rho assessment for both short and long T2 tissues in the knee joint on a clinical 3 T scanner.