Abstract： Objective:To explore the value of diffusion weighted imaging(DWI)for evaluating the early therapeutic efficacy of high intensity focused ultrasound(HIFU)in treating adenomyosis.Materials and Methods:The clinical and imaging data of 82 patients underwent HIFU treatment for adenomyosis were retrospectively analyzed.Contrast enhanced MRI(CE-MRI)with DWI were performed before treatment and within 48 hours post-treatment.DWI signal performance and change of ADC values of post-operative lesions were observed.The morphology of DWI signal change areas was evaluated and classified into three types:type I,spot-like or no obvious signal change;type Ⅱ,patchy signal change;type Ⅲ,ring-like signal change.The volume of DWI signal change areas and the nonperfused volume(NPV)on CE-MRI were evaluated and the difference and correlation between them were analyzed.Results:DWI showed that there were 3 cases of type I,4 cases of type Ⅱ,and 75 cases of type Ⅲ in the signal change areas of the necrotic lesions,and the kappa value of inter-observer reliability reached 0.848(P＜0.001).The volume of DWI signal variation zones was 41.24(25.63,85.21)cm3,and the statistical analysis revealed no significant difference in the inter-observer reliability(P=0.581).The NPV on CE-MRI was 41.71(20.72,87.03)cm3,which was not statistically significant difference in the concordance with the volume of signal change areas on DWI(P=0.932),and there was a significant positive correlation between them(r=0.975,P＜0.001).Whether the ablated necrotic area on DWI showed complete or incomplete signal ring,the volume measured on DWI was not significantly different from the NPV(P＞0.05).The post-operative ADC values were significantly higher compared with the pre-operative values(P＜0.001).Conclusions:DWI can effectively evaluate the early ablation effect of adenomyosis after HIFU,and it can make a reliable qualitative and quantitative evaluation of the occurrence and scope of ablation lesions.