To investigate influence of different contrast agent injection doses of sulphur hexafluoride microbubbles (SHM) through fetal rats′ umbilical veins and different mechanical indexes (MI) setting on imaging quality of contrast-enhanced ultrasound (CEUS) in placental fetal surface of SD rats in late pregnancy.

Forty SD rats in late pregnancy were selected as study subjects. According to random number table method, they were divided into A, B, C and D groups each group with 10 rats, and doses of SHM were 0.03, 0.06, 0.09 and 0.12 mL/kg, respectively during CEUS. Meanwhile, contrast pulse sequence (CPS) imaging technology was used and MI were set as 0.10, 0.15, 0.20, 0.25 and 0.30 in each group. The quantitative analysis was conducted by time-intensity curve (TIC) method for CEUS imaging quality, and 3 indexes measured by TIC for this study included arrival time (AT), time to peak (TTP) and peak intensity (PI) after SHM was injected. One-way ANOVA and least significant difference (LSD)-t test were used for overall comparison and further comparison between each two groups of above 3 indexes when adjusted different SHM doses and set different MI.

① Results of CEUS in placental fetal surface of pregnant rats in C group: when MI setting increased from 0.10 to 0.30, there were no significant differences in AT and TTP (P>0.05). When MI setting increased from 0.10 to 0.20, PI increased with increased of MI (P<0.05), and PI reached the maximum when MI setting was 0.20. When MI setting increased from 0.20 to 0.30, PI showed no significant difference (P>0.05). ② CEUS results of placental fetal surface of pregnant rats in 4 groups when MI setting was 0.20: AT, TTP and PI of C group were (0.95±0.45) s, (7.9±3.0) s and (30.6±4.2) dB, which were significantly different from (1.67±0.83) s, (12.5±2.8) s and (25.5±4.8) dB of those in A group, and the differences were statistically significant (P=0.004, 0.001, 0.004). There were no significant differences between C group and B group, also between C group and D group in those 3 indexes (P>0.05). There were significant differences between B group and D group in AT and TTP (P<0.05); However, there were no significant differences between B group and A group in those 3 indexes, and between B group and D group in PI (P>0.05). There were significant differences between D group and A group in those 3 indexes (P<0.05). With contrast agent dose increased, AT and TTP shorten, while PI increased.

When CEUS was performed on the placental fetal surface of SD rats in late pregnancy, SHM dose was 0.09 mL/kg and MI setting was 0.20 that CEUS may had best imaging quality.