Quantitative Characterization of the Achilles Tendon in Cadaveric Specimens: T1 and T2*Measurements Using Ultrashort-TE MRI at 3 T

OBJECTIVE. The objective of our study was to provide a quantitative means of evaluating the intrinsic T1 and T2* values of the Achilles tendon through the measurement of T1 recovery and T2* relaxation times, respectively, using ultrashort-TE (UTE) MRI at 3 T with histologic correlation. MATERIALS AND METHODS. Six cadaveric specimens underwent MRI at 3 T. The MRI protocol included standard MRI and UTE pulse sequences. For T1 measurement, a saturation recovery time method was applied (saturation recovery time range, 10-1,600 milliseconds), and for T2* measurements, a constant TR-varying TE method was used (TE, 100 microseconds-15 milliseconds). An analysis algorithm written in Matlab was executed off-line on axial DICOM images for the T1 and T2* measurements in areas of normal tendon. The cadaveric specimens were subsequently frozen to -40 degrees C. They were sectioned with the slice thickness corresponding to the MR images. Anatomic sections were photographed and visually inspected. Specimens were then processed for histology. MR images, specimen photographs, and histology results were reviewed by two musculoskeletal radiologists and one pathologist. RESULTS. Compared with histology results, the combination of UTE and standard MRI provided an accurate means of identifying normal tendon. The mean T1 measurement was 621 milliseconds and the mean T2* measurement was 2.18 milliseconds in histologically proven regions of normal tendon. CONCLUSION. The UTE MR sequence offers structural information about and allows reproducible quantitative evaluation of tissues with short T2 components, such as tendons, that are inaccessible on conventional MRI. This technique showed T1 and T2* measurements in the normal Achilles tendon and allowed correlation with structural status by histology. Because of the small number of specimens, this is considered a feasibility study.