Objective Fluid and fat accumulation can be observed in MRI images of patients with primary lower ex-tremity lymphedema;however,the distribution of components such as fat and fluid in the PLEL limb is currently unknown.The aim of this study was to apply the magnetic resonance STIR sequence-based threshold segmentation method to quantita-tively evaluate the different components of PLEL such as fat and liquid.Methods A retrospective analysis of 112 pa-tients diagnosed with unilateral primary lower limb lymphedema via the Department of Lymphatic Surgery at Beijing Shijitan Hospital between January 2018 and December 2021 was performed.The suprafascial and subfascial regions of the mid-calf were labeled using semi-automatic annotation via the Yizhun Artificial Intelligence Research Platform,and the suprafascial fat,fat-gap edema,and effusion components were extracted using the threshold segmentation method and their volumes were calculated(in number of pixels).Spearman's correlation was used to analyze the correlation between the content of the dif-ferent components and standard measures of lymphedema(segmental fat mass,BMI,extracellular water ratio of limb seg-ments,and multi-frequency bioelectrical impedance).Patients were categorized into stages Ⅰ,Ⅱ,and Ⅲ according to the International Society of Lymphology(ISL)clinical staging criteria,and non-parametric tests were used to compare the vol-umes of fat,fat-gap edema,and effusion components between the different clinical stages.Results Fat content was moder-ately negatively correlated with extracellular water ratio and moderately positively correlated with electrical impedance values at different frequencies.Adipoedema content showed a moderate positive correlation with BMI(r=0.453,P＜0.05),a strong positive correlation with extracellular water ratio(r=0.615,P＜0.05),and a strong and highly negative correlation with the electrical impedance values at 1 kHz,5 kHz,50 kHz,250 kHz,500 kHz,and 1000 kHz,with the highest correlation with electrical impedance at 1 kHz.The highest correlation was found with the correlation coefficient r=-0.730(P＜0.05);the fluid content showed a strong positive correlation with the extracellular water ratio(r=0.661,P＜0.05),and a strong negative correlation with the electrical impedance values at different kHz(r≥0.617).There were differences in lip-oedema and fluid content between different clinical stages(P＜0.05),and in a two-by-two comparison between the three stages,the lipoedema and fluid content was greater in ISL-Ⅱ and Ⅲ than in stage Ⅰ(P＜0.05).Both lipoedema and flu-id content were positively correlated with clinical stage,with the highest correlation between lipoedema content and clinical stage(r=0.510,P＜0.05).Conclusion PLEL compositional analysis based on the threshold segmentation method can assist clinicians in assessing the content of components such as fluid and fat in PLEL lesions and provide some diagnostic basis for clinical staging.
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