18F-FDG PET/MRI中棕色脂肪组织摄取的影像学表现和规律分析

目的 研究并分析18F-氟脱氧葡萄糖（FDG）PET/MRI中棕色脂肪组织（BAT）摄取的影像学表现和规律。 方法 回顾性分析2017年7月至2020年1月于空军军医大学第二附属医院行18F-FDG PET/MRI检查的1 529名受检者的影像学资料和临床资料，其中男性836名、女性693名，年龄14~93（53.6±13.2）岁；BAT摄取18F-FDG阳性者31名，其中男性13名、女性18名，年龄16~61（33.3±11.6）岁。分析BAT摄取18F-FDG的PET/MRI影像学表现，选取18F-FDG摄取增高部位以周围肌肉组织的最大标准化摄取值（SUV_max）为临界值]，采用三维勾画法勾画感兴趣区，计算SUV_max和平均标准化摄取值（SUV_mean）。SUV_max和SUV_mean与性别及摄取部位数目的相关性采用Spearman相关性分析，与年龄、体重指数（BMI）、检查当日平均气温的相关性采用Pearson相关性分析。组间计数资料的比较采用χ2检验；计量资料的比较采用独立样本t检验。 结果 （1）BAT摄取18F-FDG阳性者的PET/MRI图像表现为颈部、锁骨上区、纵隔、脊柱两旁及肾上区等部位呈对称性分布的片状、结节状及串珠状的18F-FDG高摄取灶，MRI图像的T1加权成像（WI）、T2WI均呈高信号，频率衰减反转恢复序列呈低信号，弥散加权成像未见高信号。（2）BAT摄取多发生于寒冷的季节，男性和女性BAT摄取18F-FDG的阳性率差异无统计学意义（χ2=2.07，P=0.15）；BAT摄取18F-FDG阳性者的年龄、BMI和检查当日气温均明显低于阴性者（33.3±11.7）岁对（ 54.1±13.5）岁、（21.89±2.79） kg/m2对（24.01±3.26） kg/m2、（7.5±6.5）℃对（16.5±11.9）℃]，且差异均有统计学意义（t=?12.03、?5.15、?8.97，均P<0.001）。（3）BAT摄取的SUV_max和SUV_mean均与年龄、BMI呈负相关（r=?0.45~?0.36，均P<0.05），与摄取BAT部位数量呈正相关（r=0.61、0.59，均P<0.001），与性别和检查当日平均气温均无明显相关性（r=0.01~0.29，均P>0.05）。 结论 在18F-FDG PET/MRI显像中，BAT摄取存在特定的影像学表现和规律性，大多发生在寒冷的季节，年轻、偏瘦者较易出现。

Imaging characteristics and patterns of brown adipose tissues by 18F-FDG PET/MRI

Objective To investigate and analyze the imaging manifestations and rules of brown adipose tissue (BAT) uptake in 18F-fluorodeoxyglucose (FDG) PET/MRI. Methods The imaging and clinical data of 1 529 subjects (836 males and 693 females, aged 14–93(53.6±13.2) years) who underwent 18F-FDG PET/MRI examination in the Second Affiliated Hospital of Air Force Medical University from July 2017 to January 2020 were analyzed retrospectively. Thirty-one subjects, including 13 males and 18 females aged 16–61 (33.3±11.6) years, had positive BAT uptake of 18F-FDG. The PET/MRI imaging features of 18F-FDG uptake of BAT were analyzed, and three-dimensional sketching was adopted to select sites with increased 18F-FDG uptake to delineate the region of interest (with the maximum standardized uptake value (SUV_max) of surrounding muscles as the boundary value). SUV_max and the mean standardized uptake value (SUV_mean) were calculated automatically by the software program. The correlation between SUV_max and SUV_mean with variable factors(eg. gender, age, body mass index (BMI), mean temperature on the examination day and number of ingestion sites) were evaluated by Spearman or Pearson correlation analysis. Count data between groups was compared by χ2 test. Measurement data were compared by independent sample t test. Results (1) The PET/MRI images of subjects with positive BAT uptake of 18F-FDG showed symmetrical flaky, nodular and bead uptake in sucravicula, cervical regions, and paravertebral, mediastinal, and perirenal mediastinum. T1-weighted imaging (WI) and T2WI of the MRI images showed high signal. The frequency attenuation inversion recovery sequence showed low signal. The diffusion weighted imaging showed no high signal. (2) Most BAT uptake occurred in cold periods, and no significant difference was found in the positive rate of BAT uptake between males and females (χ2=2.07, P=0.15). The age, BMI, and the temperature on the day of examination of the subjects with positive uptake of BAT were significantly lower than those with negative uptake ((33.3±11.7) years vs. (54.1±13.5) years, (21.89±2.79) kg/m2 vs. (24.01±3.26) kg/m2, (7.5±6.5)℃ vs. (16.5±11.9)℃), and the differences were statistically significant (t=?12.03, ?5.15, ?8.97; all P<0.001). (3) SUV_max and SUV_mean of BAT were negatively correlated with age and BMI (r=?0.45 to ?0.36; all P<0.05) but positively correlated with the number of BAT depots (r=0.61, 0.59; both P<0.001). SUV_max and SUV_mean of BAT had no significant correlation with gender or the average temperature on the day of examination (r=0.01?0.29; all P>0.05). Conclusion In 18F-FDG PET/MRI imaging, BAT uptake has specific imaging manifestations and regularity, which mostly occurs in cold season and is more likely to occur in young and low-BMI subjects.