MRI is currently the most reliable modality for preoperative staging of EC, and DWI is regarded as the most convenient, rapid, and non-invasive MRI technique [8, 12]. Meanwhile, DWI is also considered as an imaging biomarker of tumors and has been extensively used in the diagnosis of gynecologic tumors [2, 17, 18]. However, the option of b-value has a considerable impact on the visual assessment of DWI image and the calculation of ADC value [19]. There have been many studies exploring the optimal b-value for pelvic tumors such as prostate cancer, rectal cancer, and cervical cancer. and some researchers have found that the DWI with b = 1000 s/mm2 has better performance in pelvic scans [20, 21]. The use of an optimized b-value may be an important step in the optimization of DWI. This retrospective study compared the diagnostic performance of DWI, the ADCmean and ADCmin values with b = 1000 s/mm2 and b = 800 s/mm2 for the diagnosis and staging of EC. The results demonstrated that the protocol of DWI and ADC values with b = 1000 s/mm2 had all slightly higher performance than those of b = 800 s/mm2 for the assessment of EC diagnosis and staging. However, the improvement was only slightly higher, and b = 800 s/mm2 could still be used as an alternative, especially in clinical settings where b = 1000 s/mm2 is not available or feasible. It is worth noting that other studies have used multiple b-values, such as 50, 500, and 1000 s/mm2, for DWI in similar contexts [8]. The use of multiple b-values can potentially provide more comprehensive information about the diffusion characteristics of tissues. However, our study focused on comparing the two commonly used b-values (800 and 1000 s/mm2) to determine their relative diagnostic performance. The results suggest that while b = 1000 s/mm2 provides slightly better diagnostic accuracy and stability, b = 800 s/mm2 remains a viable option, especially considering that the differences in performance were not statistically significant in all parameters. And the ADC values with b = 1000 s/mm2 had higher accuracies and better stabilities. The better stabilities of the b = 1000 s/mm2 protocol can be attributed to several factors. First, higher b-values (such as b = 1000 s/mm2) provide greater sensitivity to diffusion, which enhances the contrast between tissues with different diffusion properties. This increased contrast allows for more accurate differentiation between benign and malignant endometrial lesions, as well as more precise assessment of myometrial invasion, cervical stromal invasion, and lymph node metastasis. Second, the ADC values derived from higher b-values tend to be more stable and less influenced by T2 shine-through effects, which can interfere with the accuracy of ADC measurements at lower b-values [2, 18]. In our study, the cutoff values for ADCmean and ADCmin at b = 1000 s/mm2 were more consistent and had a narrower range compared to those at b = 800 s/mm2 (Fig. 4). This suggests that the b = 1000 s/mm2 protocol provides more reliable and reproducible ADC values, which are crucial for accurate diagnosis and staging.

Regarding the cutoff value for ADC in the diagnosis of lymph node metastases, our study found that the ADCmean values with b = 1000 s/mm2 had a cutoff value of 0.777 × 10 − 3 mm2/s, while the ADCmin values had a cutoff value of 0.692 × 10 − 3 mm2/s. These cutoff values were determined based on the ROC analysis and were found to be highly effective in differentiating between metastatic and non-metastatic lymph nodes. The use of these cutoff values in conjunction with established morphological, criteria such as lymph node size and shape, can significantly enhance the diagnostic accuracy for lymph node metastases. Specifically, lymph nodes with a short diameter greater than 1 cm are typically considered suspicious for metastasis, but the inclusion of ADC values can provide additional quantitative evidence to support the diagnosis, especially for smaller lymph nodes with a short diameter greater than 0.8 cm that exhibit rounded or irregular shapes, hairy margins, or low signal on ADC maps [7]. Our findings suggest that incorporating ADC values into the diagnostic workflow can complement morphological criteria and improve the sensitivity and specificity of lymph node metastasis detection in patients with endometrial carcinoma.

Most guidelines for assessing the female pelvis, such as those by the ESUR, advise a high b-value of >800–1000 s/mm2 for female pelvic imaging [13]. This recommendation is based on the improved sensitivity and specificity of DWI at higher b-values, which can better delineate the diffusion characteristics of lesions and reduce the T2 shine-through effect. Our study supports this guideline by demonstrating that DWI with b = 1000 s/mm2 outperforms b = 800 s/mm2in both qualitative and quantitative assessments for EC diagnosis and staging.

The study of Basaran et al. [17] with 88 patients (36 malignant cases and 52 benign cases) reported the accuracy, sensitivity and specificity of EC diagnosis with visual evaluation on DWI with b = 1000 s/mm2 were 74%, 81% and 69% and 69% respectively. In our study, the accuracy and sensitivity were relatively higher compared to the study. Which might be related to the increase in the number of malignant tumors.Rechichi et al. found the accuracy, sensitivity and specificity of assessment myometrial invasion on DWI were 75%, 85% and 71% respectively. With the increase of b-value, DWI images could provide higher contrast, minimizing T2-weighted and perfusion effects [22, 23]. The sharp contrast between the hyperintense EC and the hypointense myometrium on DWI significantly facilitates assessment of myometrial invasion depth. Meanwhile, we found that the protocol of DWI with b = 1000 s/mm2 had higher performance than those of b = 800 s/mm2 for detecting deep myometrial invasion. In addition, the findings of this study were similar with the previous study [24]. They demonstrated that DWI had superior diagnostic efficiency in the evaluation of cervical stromal invasion of EC (the accuracy, sensitivity, and specificity respectively for reader 1/reader 2 were 95.2%, 91.6%, 91.7%/100%, and 95.8%/90.1%). In our results, the sensitivity was lower for the detection of cervical stromal invasion. We only evaluated axial DWI. It may be beneficial to increase sagittal DWI for improving the sensitivity [7]. Our results showed that DWI with b = 1000 s/mm2 had a high accuracy and specificity for the assessment of lymph node metastasis. The results of this study support previously published studies that DWI showed low sensitivity and high specificity for detecting lymph node metastases [25].

This study showed that the AUCs and accuracies of ADCmean values with b = 1000 s/mm2 were higher than those of b = 800 s/mm2 for EC diagnosis and staging. Since the ADC values are a quantitative analysis and not easily affected by T2 penetration effects, it has a higher accuracy than the visual assessment. Our findings supported the results of previous studies [], in which the AUC of the ADCmean for distinguishing malignant from benign lesions was 0.985 and the cutoff values of ADCmean was 1.007 × 10−3 mm2/s. Our results were also in this range. According to the study of Koh et al. [23], the estimation of ADC values became more accurate as b-values increases. Although high b-values can highlight the area of lesions, signal-to-noise ratios and an increased susceptibility artifact of the images also need to be considered [2].

Reyes et al. [] demonstrated the AUCs of ADCmean and ADCmin for assessment myometrial invasion were 0.90 and 0.88 respectively, which was similar to our results. They also found that ADCmean and ADCmin values of EC with deep myometrial invasion were lower than those with superficial or no myometrial invasion, which suggested ADC values might be a useful indicator to evaluate the local invasiveness of EC . Cao et al. [9] found that the ADCmin values were correlated with cervical stromal invasion, and the AUC was 0.83. Our results supported the findings and showed that using ADCmean and ADCmin values to detect cervical stromal invasion had a higher sensitivity than visual evaluation. Many studies found that ADCmean and ADCmin values could be used to estimate the lymph node metastasis [27, 27,28,29]. Quan et al. [29] demonstrated the AUCs of ADCmean and ADCmin to assess lymph node metastasis were 0.737 and 0.643 respectively. They believe that pretreatment ADC values may be a potential biomarker to predict prognosis factors of patients with EC. Our results also showed that the ADC values have the ability to assess lymph node metastasis, and can provide better diagnostic efficacy with b = 1000 s/mm2. As a consequence, the accuracy of staging may be improved by the addition of ADC values in clinical practice.

There are some limitations in our study. First, this was a single-center retrospective study. The sample size was not very large and only two b-values were studied. And this retrospective design is that each DWI acquisition was performed with a single, clinically dictated b-value; therefore, paired images of the same lesion at two different b-values from the same patient are not available. Next, we will include a larger sample with multiple centers and more b-values to further validate our findings. Second, we only studied the staging and identification of EC, the pathological subtype and grade of EC need to be further explored. Third, in order to further validate the efficiency of DWI in staging EC, we should enroll more patients with advanced EC. Finally, it is worth noting that we focused solely on DWI for the assessment of EC. While DWI has shown promising results in our study, it is important to recognize that combining DWI with other MRI sequences, such as T2-weighted imaging (T2WI), might provide more comprehensive diagnostic information. T2WI is known for its excellent soft tissue contrast and is often used in conjunction with DWI in clinical practice to improve the accuracy of lesion characterization and staging. Future studies should consider incorporating T2WI to better understand the complementary roles of these imaging modalities in the diagnosis and staging of endometrial carcinoma.