Bi-Exponential 3D UTE-T1 Relaxation Mapping of Ex Vivo Human Knee Patellar Tendon at 3T

Introduction: The objective of this study was to assess the bi-exponential relaxation times and fractions of the short and long components of the human patellar tendon ex vivo using three-dimensional ultrashort echo time T1 rho (3D UTE-T1 rho) imaging. Materials and Methods: Five cadaveric human knee specimens were scanned using a 3D UTE-T1 rho imaging sequence on a 3T MR scanner. A series of 3D UTE-T1 rho images were acquired and fitted using single-component and bi-component models. Single-component exponential fitting was performed to measure the UTE-T1 rho value of the patellar tendon. Bi-component analysis was performed to measure the short and long UTE-T1 rho values and fractions. Results: The single-component analysis showed a mean single-component UTE-T1 rho value of 8.4 +/- 1.7 ms for the five knee patellar tendon samples. Improved fitting was achieved with bi-component analysis, which showed a mean short UTE-T1 rho value of 5.5 +/- 0.8 ms with a fraction of 77.6 +/- 4.8%, and a mean long UTE-T1 rho value of 27.4 +/- 3.8 ms with a fraction of 22.4 +/- 4.8%. Conclusion: The 3D UTE-T1 rho sequence can detect the single- and bi-exponential decay in the patellar tendon. Bi-component fitting was superior to single-component fitting.