Magic angle effect on adiabatic T imaging of the Achilles tendon using 3D ultrashort echo time cones trajectory.

The protons in collagen-rich musculoskeletal (MSK) tissues such as the Achilles tendon are subject to strong dipolar interactions which are modulated by the term (3cos θ-1) where θ is the angle between the fiber orientation and the static magnetic field B . The purpose of this study was to investigate the magic angle effect in three-dimensional ultrashort echo time Cones Adiabatic T (3D UTE Cones-AdiabT ) imaging of the Achilles tendon using a clinical 3 T scanner. The magic angle effect was investigated by Cones-AdiabT imaging of five cadaveric human Achilles tendon samples at five angular orientations ranging from 0° to 90° relative to the B field. Conventional Cones continuous wave T (Cones-CW-T ) and Cones T * (Cones-T ) sequences were also applied for comparison. On average, Cones-AdiabT increased 3.6-fold from 13.6 ± 1.5 ms at 0° to 48.4 ± 5.4 ms at 55°, Cones-CW-T increased 6.1-fold from 7.0 ± 1.1 ms at 0° to 42.6 ± 5.2 ms at 55°, and Cones-T2 increased 12.3-fold from 2.9 ± 0.5 ms at 0° to 35.8 ± 6.4 ms at 55°. Although Cones-AdiabT is still subject to significant angular dependence, it shows a much-reduced magic angle effect compared to Cones-CW-T and Cones-T *, and may be used as a novel and potentially more effective approach for quantitative evaluation of the Achilles tendon and other MSK tissues.