Quantitative MRI analysis of menisci using biexponential T ₂* fitting with a variable echo time sequence

Purpose The goal of this study was to differentiate between normal, degenerative meniscus, and meniscal tears using monoexponentially and biexponentially calculated T₂*. Meniscal disease, characterized by an altered collagen fiber matrix, might be detectable in vivo using quantitative T₂* mapping. Methods A 3D Cartesian spoiled gradient echo technique was adapted to enable the use of a variable echo time approach in combination with a highly asymmetric readout. T₂* was calculated monoexponentially and biexponentially using three- and five-parametric non-linear fits, respectively. Results From a total of 68 evaluated menisci, 48 were normal, 12 were degenerated, and eight had tears. Mean values for the short (T₂*_s) and long (T ₂*_l) T₂* components were as follows: in normal menisci, 0.82 ± 0.38/15.0 ± 5.4 ms, respectively; in degenerated menisci, 1.29 ± 0.53/19.97 ± 5.59 ms, respectively; and, in meniscal tears, 2.05 ± 0.73 and 26.83 ± 7.72 ms, respectively. Biexponentially fitted T₂* demonstrated a greater ability to distinguish normal and degenerated menisci using receiver operating characteristic (ROC) analysis (higher area under curve as well as higher specificity and sensitivity). Conclusion This study suggests that biexponential fitting, used for T₂* calculation in the menisci, provides better results compared to monoexponential fitting. Observed changes in T₂* result from the matrix reorganization in degenerative processes in the menisci, which affects the collagen fiber orientation, as well as content.