Acceleration of Phase‐Modulated Ultrashort Echo Time Sequence for Fast T ₂ and Adiabatic T 1ρ Mapping of the Knee Joints

Purpose To develop and validate an accelerated phase‐modulated ultrashort echo time (PM‐UTE) sequence for volumetric T 2 and adiabatic T 1ρ (AdiabT 1ρ ) mapping of both short‐ and long‐T 2 tissues in the knee joint. Methods The proposed method estimates and removes the T 1 ‐dependent component from a single reference acquisition, eliminating repeated phase‐cycled scans. PM‐UTE‐T 2 and PM‐UTE‐AdiabT 1ρ sequences were implemented on a 3T scanner. Four agarose phantoms, five ex vivo human knees, and five in vivo healthy knees were imaged. Single‐exponential fitting was applied to compute T 2 and T 1ρ values in cartilage, meniscus, muscle, patellar tendon, anterior cruciate ligament (ACL), and posterior cruciate ligament (PCL). Agreement between accelerated and conventional PM‐UTE methods was evaluated using Pearson correlation and voxel‐wise difference maps. Results In phantoms, accelerated and conventional mapping showed excellent agreement (T 2 : R = 0.99; T 1ρ : R = 0.99). Ex vivo studies demonstrated strong correlations (T 2 : R = 0.97; T 1ρ : R = 0.97) across all tissues with minimal voxel‐wise differences. In vivo measurements correlated strongly (T 2 : R = 0.96; T 1ρ : R = 0.96), with reliable visualization of short‐ and long‐T 2 structures. Across all tissues, T 2 and T 1ρ relaxation times from accelerated method closely matched conventional values, with differences smaller than their respective standard deviations. The acceleration reduced total scan time by ∼1.6‐fold across phantom, ex vivo and in vivo experiments. Conclusion The accelerated PM‐UTE technique enables accurate, efficient whole‐knee T 2 and T 1ρ mapping, providing comprehensive multi‐tissue characterization within a clinically feasible timeframe. This technique shows promise for early osteoarthritis detection and longitudinal monitoring.