Whole knee joint mapping using a phase modulated UTE adiabatic T_1ρ (PM-UTE-AdiabT_1ρ ) sequence

Area of Science:

• Biomedical Engineering
• Magnetic Resonance Imaging
• Musculoskeletal Imaging

Background:

• T1ρ (longitudinal relaxation time in rotating frame) MRI is sensitive to tissue composition.
• Accurate T1ρ mapping of the knee joint is challenging due to the complexity of tissues and motion.

Purpose of the Study:

• To develop and validate a novel 3D phase modulated UTE adiabatic T1ρ (PM-UTE-AdiabT1ρ) sequence.
• To enable whole knee joint volumetric T1ρ mapping on a clinical 3T scanner.

Main Methods:

• The PM-UTE-AdiabT1ρ sequence incorporates magnetization reset, adiabatic pulses, phase modulation, fat saturation, variable flip angles, and 3D UTE Cones acquisition.
• T1ρ quantification was performed using simple exponential fitting.
• Phantom studies assessed sensitivity, reproducibility, and correlation with continuous wave-T1ρ.
• The sequence was applied to ex vivo and in vivo normal knees.

Main Results:

• Phantom studies showed high sensitivity to compositional changes, excellent reproducibility, and strong correlation with continuous wave-T1ρ.
• In vivo T1ρ values were obtained for femoral cartilage (77.9 ± 3.9 ms), meniscus (30.1 ± 2.2 ms), ACL (52.0 ± 3.1 ms), PCL (29.2 ± 2.4 ms), patellar tendon (17.0 ± 1.8 ms), and muscle (57.6 ± 2.8 ms).

Conclusions:

• The developed 3D PM-UTE-AdiabT1ρ sequence is suitable for volumetric T1ρ assessment of the knee joint.
• This technique can map both short and long T2 tissues within the knee on a clinical 3T scanner.