第4题: [单项选择]背向散射回声强度的射频测定在超声造影技术上有什么用途() A. 用以定量评价超声造影效果 B. 加速血流速度 C. 增大血流量 D. 增强超声造影效果 E. 消除超声造影的副作用 参考答案:A 答案解析:超声在组织内传播过程中,遇到比发射超声波长小的界面如微气泡、细胞、微细血管、胶原纤维、小的异物等,产生散射信号,散射如为朝向探头与入射超声方向成180°时称为背向散射,相关散射区域的回声信号强度即背向散射回声强度。背向散射回声强度的射频测定在超声造影技术上是用以定量评价超声造影效果。
第15题: [单项选择]Questions 33 to 35 are based on the passage you have just heard.A. They were educators themselves. B. They had high credibility. C. They had made an investigation. D. They had brought the idea into practice. 参考答案:B 答案解析:[解析] Q: Why did many educators accept the two presidents’ belief