• Anne-Sofie Agergaard, Nikolaj M Malmgaard-Clausen, Rene B Svensson, Janus D Nybing, Mikael Boesen, Michael Kjaer, S Peter Magnusson, and Philip Hansen.
• Institute of Sports Medicine Copenhagen, Department of Orthopedic Surgery, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark.
• Acta Radiol. 2021 Feb 1; 62 (2): 215-224.

BackgroundThere is currently a lack of imaging modalities that can be used as a sensitive measure in tendinopathy. Recent findings suggest the applicability of ultra-short echo time (UTE) magnetic resonance imaging (MRI) T2* mapping in tendons, but the reproducibility remains unknown.PurposeTo evaluate test-retest reproducibility of UTE MRI T2* mapping of tendinopathic patellar tendons and to evaluate the intra- and inter-observer reproducibility of the measurement.Material And MethodsFifteen patients with chronic patellar tendinopathy were evaluated with UTE MRI twice in a 3.0-T scanner on the same day. Manual segmentation of the patellar tendon was performed by two blinded investigators and automated T2*map reconstruction was performed in custom-made software.ResultsThere was a significant and numerically small difference in test-retest T2* values (T2*meandiff = 0.06 ± 0.07 ms ≈ 3.7%; P = 0.006) with an ICC = 0.91 (95% confidence interval [CI] 0.58-0.98; typical error of 3.0%). The intra- and inter-observer reproducibility showed no significant bias (P = 0.493 and P = 0.052), and generally substantial reproducibility was demonstrated for T2* (intra-observer ICC = 0.99; 95% CI 0.98-1.00 and inter-observer ICC = 0.99; 95% CI 0.96-1.00, and typical error 1.3% and 1.3%, respectively).ConclusionThese data demonstrate a small bias between repeated measurements for UTE T2*, but with a very low associated mean difference (3.7%) between the two tests. The high ICC values and low typical error % demonstrate reproducibility of repeated T2*-mapping sessions. Further, the method showed substantial intra- and inter-observer reproducibility for T2* values proving feasibility for use of UTE T2* mapping in research and clinical practice.

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