Comparative T2 and T1ρ mapping of patellofemoral cartilage under in situ mechanical loading with prospective motion correction

Purpose To demonstrate improved T2 and T1ρ mapping of patellofemoral cartilage with in situ loading by means of prospective motion correction and to assess load‐induced changes in healthy subjects. Materials and Methods Established T2 and T1ρ mapping sequences were augmented with prospective motion correction based on optical tracking. Protocols were optimized for robust imaging of the patellofemoral cartilage at a field strength of 3T. Subjects were positioned in the scanner with knee flexion and in situ loading of the patellofemoral joint was performed with a pneumatic loading device. In a pilot study on a cohort of 10 healthy subjects, load‐induced T2 and T1ρ changes were evaluated through measurements with axial loads of 0/20/40 kg. Results With prospective motion correction and additional lipid saturation, motion artifacts in patellofemoral cartilage magnetic resonance imaging (MRI) with in situ loading could be notably decreased, as demonstrated for T2 mapping. The acquired relaxation maps suggested a T2/T1ρ decrease in superficial cartilage and a T2/T1ρ increase in deep cartilage under loading. However, in the quantitative group evaluation of the lateral patellar facet, only T1ρ in superficial cartilage was significantly changed by loading (P ≤ 0.05), while no significant T2 differences for the three loading conditions were observed (P ≥ 0.3). Conclusion Prospective motion correction enables T2 and T1ρ mapping of patellofemoral cartilage with in situ loading and a comparison of the two contrasts in terms of their response to mechanical loading. T1ρ is a more sensitive marker for load‐induced patellar cartilage changes than T2. Level of Evidence: 3 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:452–460