PET serves as one of the most advanced imaging modalities,and its development depends on the improvement of radiotracers.Among numerous positron isotopes,18 F appears to be the best radionuclide candidate for PET radiotracers by virtue of its favorable physical characteristics.18 F-labeled aromatic radiotracers have been widely investigated by researchers due to its special metabolic stability.However, the development and application of 18 F-labeled aromatic radiotracers have been limited due to lacking of radiochemical methods to obtain products with high selectivity,high radioactivity and high purity.This review focuses on the new labeling methods of 18 F-labeled aromatic radiotracers from the aspects of electrophilic and nucleophilic substitution reactions.

OBJECTIVE: To retrospectively analyze non-invasive prenatal screening (NIPS) data from two centers. METHODS: The NIPS results of 10 840 samples were analyzed, including 21/18/13 trisomies (T21/T18/T13), sex chromosome and other autosomal aneuploidies, and copy number variants (CNVs). The maternal age, gestational week, body mass index and concentration of free fetal DNA (cffDNA) were also analyzed. RESULTS: The average gestational age of the 10 840 pregnant women was (32.34±5.04) year old, and the average gestational week for NIPS was (17.60±3.55) week. The overall false positive rate for T21/T18/T13 was 0.11%, sensitivity was 100%, specificity was 99.89%, and positive predictive value was 81.5%. The positive predictive values for sex chromosome and other autosomal aneuploidies and CNVs were 56.67%, 11.76% and 83.33%, respectively. The incidence of T21/T18 in the elder women (35 years or elder) was 2.12 times(P<0.01) and 1.81 times (P> 0.05) that of young women. cffDNA was in proportion to gestational week (r = 0.207) and in inverse proportion to body mass index (r = -0.177). It has increased slowly before 15 weeks of gestation and thereafter at a rate of 0.5% per week after the 16th week. CONCLUSION The performance of NIPS in this study is by large close to the reported in the literature, and the results can provide a reference for further study.