Objective:To explore the value of synthetic MRI in quantitative monitoring of knee joint structural and cartilage changes of amateur marathon runners before and after the whole marathon.Methods:Totally 26 amateur marathon enthusiasts from Zhuhai City, Guangdong Province were recruited from October 2019 to January 2020. The right knee joints were scanned 1 week before the race and within 48 h after the race. The scanning sequence included the three-dimensional proton density weighted image with isotropic (3D-CUBE-PD) sequence and synthetic MRI sequence. The conventional contrast weighted images T 1WI, T 2WI, proton density (PD) weighted imaging, short-T 1 inversion recovery (STIR) and T 1, T 2, PD mapping were obtained by the latter scans. The 3D-CUBE-PD sequence was used as a reference to evaluate the detection of knee joint lesions. The knee articular cartilage was divided into 8 subregions: central medial femoral condyle (CMFC), posterior medial femoral condyle (PMFC), central lateral femoral condyle (CLFC), posterior lateral femoral condyle (PLFC), medial tibia plateau (MTP), lateral tibia plateau (LTP), patella and trochlear. Based on the synthetic MRI quantitative mapping, the T 1, T 2 and PD values of each cartilage subregion were measured independently by 2 radiologists. The ICC was used to evaluate the consistency of the measurement between observers. The T 1, T 2 and PD values of knee cartilage before and after marathon exercise were compared by Wilcoxon signed rank test. Results:The 2 radiologists had good consistency in the measurement of T 1, T 2 and PD values of knee articular cartilage with the ICC values of 0.912, 0.933 and 0.954, respectively. The synthetic MRI quantitative mapping sequence can detect all cartilage damage ( n=3) and joint effusion ( n=15), and 7 of 9 meniscus injuries were detected. The T 1, T 2 and PD values of the knee cartilage as a whole before the race were higher than those after race, and the differences were statistically significant (all P<0.05). The T 1 values were statistically significant except patellar cartilage and trochlear cartilage, and T 2 values were significantly different in the CMFC, LTP, MTP ( P<0.05). Conclusion:Synthetic MRI has a good display of knee joint structural lesions, and its quantitative parameters T 1, T 2 and PD can detect the changes of knee cartilage before and after marathon.

Objective:To explore the value of ultra-short echo time magnetization transfer (UTE-MT) techniques for quantitatively dynamic monitoring of anterior patellar tendon (patellar tendon, quadriceps tendon) changes in amateur marathon runners before and after competition.Methods:Between October 2020 and January 2021, 23 amateur marathoners in Zhuhai, aged 28-50 (40±6) years, were prospectively recruited. Three-dimensional UTE-MT and dual-echo UTE-T 2* sequence scans of bilateral knee joints were performed before, 48 hours and 4 weeks after the marathon running, respectively. Another 5 non-running volunteers were recruited for verification of sequence stability. UTE-magnetization transfer ratio (MTR) and UTE-T 2* value of the patellar tendon, quadriceps tendon, and 3 tendon-bone insertion points (patellar tendon-tibial insertion point, patellar tendon-patellar insertion point, and quadriceps tendon-patellar insertion point) were measured independently on sagittal images of the knee joint by 2 radiologists. The stability of the 2 serial measurements and consistency tests between the 2 radiologists were assessed with a two-way mixed intraclass correlation coefficient (ICC). Repeated-measures analysis of variance was used to compare the differences in UTE-MTR and UTE-T 2* values of the prepatellar tendon before and after the marathon running. Results:Both UTE-MT and dual-echo UTE-T 2* sequence measurements had good stability, with ICC values of 0.98 and 0.92, respectively. Measurements of UTE-MTR and UTE-T 2* value of the patellar tendon, quadriceps tendon, and the 3 tendon-bone insertion points by the 2 radiologists were in good agreement (ICC>0.80). Forty-eight hours after the marathon running, the UTE-MTR of the patellar tendon, quadriceps tendon, and the 3 tendon-bone insertion points decreased, and UTE-MTR of the patellar tendon continued to decrease 4 weeks after the race, while UTE-MTR of other regions increased. Only the difference in UTE-MTR for the patellar tendon was statistically significant ( F=7.46, P=0.001) among pre-marathon (0.34±0.04), 48 h after the race (0.32±0.04), and 4 weeks after the race (0.31±0.04). UTE-T 2* value was mildly elevated in all regions at 48 h after the marathon running, but the differences among the three points were not statistically significant ( P>0.05). Conclusion:The UTE-MT has better reproducibility and inter-rater reliability. The UTE-MT can be used to monitor the dynamic changes of the prepatellar tendon before and after marathon exercise, where the UTE-MTR of the patellar tendon consistently decreases after marathon exercise.