Self-healing and repair of old Achilles tendon (AT) rupture is difficult, and tendon allograft was often used to repair the old AT rupture (1). The conventional clinical MRI sequences are useful for visualizing the tissues with relatively long transversal T2 relaxation times (2). However, AT mainly consists of collagen fibers (mostly type I collagen) which results in extremely short relaxation parameters, a short echo time (TE) must be used to acquire signal from the AT. Three-dimensional ultrashort time echo (3D-UTE) sequence can provide ability of T2*-mapping in AT in several previous studies (3). By now, no studies on T2* quantification in patients after tendon allograft reconstruction for old AT rupture were published. Therefore, the aim of this study was to investigate T2* value in AT after tendon allograft reconstruction surgery (AT-R) using 3D-UTE and analyze the correlation between the T2* value and American Orthopaedic Foot and Ankle Society (AOFAS) score.The study was approved by the health sciences institutional review board of our hospital, and written consent was obtained from all participants before participation. Six patients (6 males, mean age of 34.6 years, BMI≤24kg/m2, a time between surgery and MRI scan was more than 24 months and mean was 29.2 months) and 6 volunteers (6 males, mean age of 32.8 years, free of any pain or abnormalities in the AT) were included in the study. The control participants were sex, age, and BMI matched to the patients with AT-R. Four different TEs (0.032, 7.5, 20.5, and 28ms) were used for monoexponential UTE. The AT was segmented and divided into insertion (INS), middle (MID), muscle-tendon junction (MTJ) and all bulk of AT regions (Fig. 1). These four ROIs on the each echo UTE image were drawn to get the mean MR signal and then T2* value were calculated for each region. For clinical evaluation, AOFAS scoring system was used to evaluate the patients’ clinical outcome. An independent sample t-test was used to compare the differences of MRI and clinical score between two groups. Pearson's correlation coefficient was used to analyze correlations between them.There were no significant differences in age, sex or BMI between patients and control subjects. The T2* values of MID and MTJ regions in AT-R patients were statistically lower compared with the matched regions of controls (MID: 10.598±0.815ms vs 11.516±0.550ms, P=0.045; MTJ: 11.070±1.645ms vs 13.151±1.493ms, P=0.045), while there were no significant differences in T2* values of INS and all bulk regions between the two groups (P>0.05). (Table 1) The mean AOFAS of AT-R patients was 84.5±6.3. The T2* value of MID region was negatively correlated with AOFAS score (r=0.-0.814, P=0.049) (Fig. 2), while the T2* value of MTJ region was not correlated with AOFAS score.UTE-T2* mapping is a novel quantitative technique with the potential short-T2* relaxations from AT that are not well captured by standard T2 mapping (4). It is sensitive to degeneration changes in AT. These degenerative changes consist of loss of collagen structure, increase of proteoglycan and water content (5). The results of this study suggest that the MID and MTJ regional variability of AT after AT-R can be quantified by UTE-T2*. After AT-R more than 24 months, the mean T2* values of MID and MTJ in AT-R patients were lower than healthy controls, which means the allograft would be mature in a long-term follow-up and it might consisted of much fiberized tissue. Additionally, T2* value of MID region was correlated with AOFAS score, which indicates the T2* of MID could give a more precise guidance to patients’ clinical outcome after AT-R. Finally, as the preliminary patient data suggest, T2* may be a promising marker for the detection of matrix changes in AT after AT-R. Further investigation in larger cohort of patients, different terms follow-up are required to define the exact role of UTE-T2* for monitoring maturation process of AT-R.