Quantification of infrapatellar fat pad fibrosis using magnetic resonance imaging-derived proton density fat fraction: a pathology-controlled study.

Background: Knee osteoarthritis (KOA) is a degenerative joint disease leading to disability in the elderly. Fibrosis of the infrapatellar fat pad (IPFP) impacts knee joint function and disease progression. Accurate assessment of IPFP fibrosis aids early intervention and treatment. The aim of this study was to evaluate the diagnostic efficacy of proton density fat fraction (PDFF) and T2* measurements using mDixon-Quant technology in assessing IPFP fibrosis in KOA.

Methods: A total of 47 patients were included in this study (23 patients without fibrosis, 17 with mild fibrosis, and 7 with severe fibrosis). Knee magnetic resonance (MR) scans were performed on a 3.0 T MR system. MR sequences included 3.0 T, sagittal T2-weighted images, proton density-weighted spectral adiabatic inversion recovery (PDW-SPAIR), and three-dimensional (3D) six-echo gradient recalled echo sequence (mDixon-Quant). Two radiologists performed PDFF, T2* measurements, and the hypointense signal grade of the IPFP. Measurements were compared among the three subgroups, and correlations of the three parameters with pathology-derived IPFP fibrosis degree and diagnostic efficacy were evaluated. Intraclass correlation coefficient (ICC), one-way analysis of variance (ANOVA), and Spearman correlation analysis were used. The diagnostic performance was assessed using the area under the receiver operating characteristic (ROC) curve (AUC) and linear regression with leave-one-out cross validation. Statistical significance was set at P<0.05.

Results: MR measurements demonstrated good inter-observer reproducibility (ICC for PDFF =0.901, ICC for T2* =0.902). The PDFF and T2* values in the normal and mild fibrosis groups were higher than those in the severe fibrosis group. PDFF and T2* measurements were strongly correlated with IPFP fibrosis (ρ=-0.7083, -0.6028, respectively). PDFF and T2* showed good diagnostic performance for IPFP fibrosis (AUC =0.9529, 0.8098, respectively). Adjusted R indicated similar results (PDFF 0.6682, T2* 0.538, hypointense 0.1437). Using PDFF and T2* together showed good diagnostic performance for IPFP fibrosis (AUC =0.9601) and had the best R of 0.6995.

Conclusions: PDFF and T2* measurements based on mDixon technology provide a non-invasive and quantitative assessment of IPFP fibrosis, especially PDFF.