Comparative T₂ and T_1ρ mapping of patellofemoral cartilage under in situ mechanical loading with prospective motion...

To demonstrate improved T₂ and T_1ρ mapping of patellofemoral cartilage with in situ loading by means of prospective motion correction and to assess load-induced changes in healthy subjects.

Established T₂ and T_1ρ 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 T_1ρ changes were evaluated through measurements with axial loads of 0/20/40 kg.

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 /T_1ρ decrease in superficial cartilage and a T₂ /T_1ρ increase in deep cartilage under loading. However, in the quantitative group evaluation of the lateral patellar facet, only T_1ρ 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).

Prospective motion correction enables T₂ and T_1ρ mapping of patellofemoral cartilage with in situ loading and a comparison of the two contrasts in terms of their response to mechanical loading. T_1ρ is a more sensitive marker for load-induced patellar cartilage changes than T₂ .

3 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:452-460.