Objective  To assess the value of quantitative parameters of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in determining tumor necrosis rates (TNRs) of osteosarcoma after neoadjuvant chemotherapy (NAC) based on MRI-pathological correlation.

  Methods  Patients with osteosarcoma that occurred around the knee from January 2019 to June 2020 were examined at The Third Affiliated Hospital of Kunming Medical University using conventional MRI and sagittal DCE-MRI before and after NAC. The whole tumor segment was obtained during surgery within 2 weeks after administering NAC. The tumor segments were cut along the median sagittal plane. Next, 5 mm-thick histopathological sections were sliced and divided into tissue blocks measuring 1 cm×1 cm in size and numbered as the specimens compared with the images. The lesion on DCE-MRI before and after NAC corresponding to the median sagittal histopathological section was also divided into the region of interest (ROI) measuring 1 cm×1 cm in size and matched with specimens. The quantitative parameters before (pre-K^trans, pre-K_ep, pre-V_e, pre-V_p) and after NAC (post-K^trans, post-K_ep, post-V_e, post-V_p) were measured using the Omni Kinetics software, and changes in parameters (∆K^trans, ∆K_ep, ∆V_e, ∆V_p) were also assessed. The tumor necrosis rate (TNR) of each specimen was determined using the Huvos grading system, and the patients were categorized into the responsive group (TNR ≥90%) and unresponsive group (TNR <90%). Mann-Whitney U test was used to compare quantitative parameters before and after NAC between the two groups. ROC curve analysis was performed to compare the efficiency of quantitative parameters of DCE-MRI to predict TNR.

  Results  Eleven patients with osteosarcoma were enrolled, and 304 specimens were obtained, including 59 (19.4%) in the responder group and 245 (80.6%) in the non-responder group. After NAC, K^trans, V_e, and V_p significantly decreased in both groups, and the parameters of the responder group were significantly lower than those of the non-responsive group (P<0.05). K_ep significantly increased in the responder group (P<0.05), with no significant difference in the non-responder group before and after NAC (P>0.05). There was no significant difference in the parameters ΔK^trans, ΔV_e, and ΔV_p between the two groups (P>0.05); however, ΔK_ep was significantly lower in the responder group than in the non-responder group (P<0.05). Receiver operating characteristic (ROC) curve analysis revealed that the efficacy of quantitative parameters after NAC was better than the changes in parameters, and post-K^trans had the highest diagnostic efficiency, with the most optimal cut-off of 0.663/min, AUC of 0.744, sensitivity of 89.83%, and specificity of 52.24% for predicting TNR of osteosarcomas after NAC.

  Conclusions  DCE-MRI parameters, especially K^trans, had a potential for evaluating TNR of osteosarcoma after NAC in a timely and non-invasive manner.