UC San Diego

Purpose

To measure T₁ relaxations for the major tissues in whole knee joints on a clinical 3T scanner.

Methods

The 3D UTE-Cones actual flip angle imaging (AFI) method was used to map the transmission radiofrequency field (B₁ ) in both short and long T₂ tissues, which was then used to correct the 3D UTE-Cones variable flip angle (VFA) fitting to generate accurate T₁ maps. Numerical simulation was carried out to investigate the accuracy of T₁ measurement for a range of T₂ values, excitation pulse durations, and B₁ errors. Then, the 3D UTE-Cones AFI-VFA method was applied to healthy volunteers (N = 16) to quantify the T₁ of knee tissues including cartilage, meniscus, quadriceps tendon, patellar tendon, anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), marrow, and muscles at 3T.

Results

Numerical simulation showed that the 3D UTE-Cones AFI-VFA technique can provide accurate T₁ measurements (error <1%) when the tissue T₂ is longer than 1 ms and a 150 μs excitation RF pulse is used and therefore is suitable for most knee joint tissues. The proposed 3D UTE-Cones AFI-VFA method showed an average T₁ of 1098 ± 67 ms for cartilage, 833 ± 47 ms for meniscus, 800 ± 66 ms for quadriceps tendon, 656 ± 43 ms for patellar tendon, 873 ± 38 ms for ACL, 832 ± 49 ms for PCL, 379 ± 18 ms for marrow, and 1393 ± 46 ms for muscles.

Conclusion

The 3D UTE-Cones AFI-VFA method allows volumetric T₁ measurement of the major tissues in whole knee joints on a clinical 3T scanner.