[Analysis of the application value of 18F-FDG PET-CT in differentiating physiological uptake in the endometrium from stage IA endometrial carcinoma].

Objective: To investigate the uptake patterns of 18F-fluorodeoxy glucose (¹⁸F-FDG) in the endometrium using positron emission tomography (PET) imaging and to differentiate these from stage IA endometrial cancer. Methods: From September 2022 to April 2024, a prospective inclusion of 354 women without gynecological diseases and no hormone usage who underwent ¹⁸F-FDG PET-CT examinations at the affiliated hospital of Qingdao University were set as the physiological group, while a group containing 42 cases of Stage IA endometrial carcinoma was also set. The physiological group was divided into five groups based on the menstrual cycle: menstrual period, proliferative phase, ovulatory phase, secretory phase, and menopausal phase. The images were analyzed using visual and quantitative measurements; quantitative analysis indicators were standardized uptake value maximum (SUVmax) and the region of interest/liver ratio (R/L value). Receiver operating characteristic (ROCs) curve was used to determine the optimal cutoff values for SUVmax and R/L value. A clinical model was established using binary logistic regression, and ROC curves were drawn to evaluate the predictive performance of the model. Results: The uptake of ¹⁸F-FDG in the endometrium exhibited cyclical variations throughout different physiological phases, with higher uptakes observed during the menstrual and ovulation phases (SUVmax values of 6.66±3.26 and 3.89±1.21, respectively), which are significantly higher than those in the proliferative phase [median SUVmax of 2.54 (2.02, 3.47)], secretory phase (SUVmax of 2.55±0.86), and menopausal phase [SUVmax median of 2.04 (1.69, 2.29)]. During the menstrual and ovulation phases, the radiotracer accumulation patterns were triangular in 105 cases, oval in 32 cases, and round-like in 2 cases. All 42 cases of endometrial cancer showed ¹⁸F-FDG uptake, with radiotracer accumulation patterns being round-like in 17 cases, oval in 10 cases, triangular in 9 cases, and irregular in 6 cases. There were statistically significant differences in the shapes of radiotracer concentration between the menstrual, ovulatory periods, and endometrial carcinoma (both P＜0.001). The SUVmax and R/L values in menstrual period and ovulatory period were significantly lower than that in endometrial carcinoma group (P＜0.001). During the menstrual phase, the optimal cutoff values for SUVmax and R/L in distinguishing between endometrial and endometrial cancer were 12.59 and 3.81, respectively, with corresponding AUCs of 0.885 and 0.842. After incorporating endometrial uptake morphology into the model, the AUCs was improved to 0.969 and 0.948, respectively. During the ovulatory phase, the optimal cutoff values for SUVmax and R/L were 5.96 and 2.85, respectively, with AUCs of 0.984 and 0.968. After integrating endometrial uptake morphology into the model, the AUCs were increased to 0.999 and 0.998, respectively. Conclusions: The ¹⁸F-FDG PET imaging of the endometrium shows higher uptake during the menstrual and ovulatory periods, primarily triangular in shape; endometrial carcinoma uptake is significantly higher than the physiological uptake during the menstrual and ovulatory periods, mainly in circular, oval, and irregular shapes. When SUVmax≥5.96, R/L≥2.85, combined with the physiological cycle of the subjects and the morphological characteristics of the radiotracer concentration, it is possible to effectively differentiate between physiological uptake and Stage IA endometrial carcinoma.