B超原型机，图片来源：《Application of Echo-Ranging Techniques to the Determination of Structure of Biological Tissues》
这台设备和军方用的声纳有两个区别：分辨率更高，而且可以发出多束声波。每一束声波遇到人体组织后都可能折回，而折回的快慢、多寡，取决于组织的形态。
只要对折回的声波进行分析，就能得到一张二维的人体图象。因为是二维的，所以称之为B型超声图像。
总结
如今，超声机已经成为最常见的医疗设备。除了B超之外，还有多普勒超声、M型超声。利用它们，医生可以检查患者的甲状腺是否存在肿大、乳腺里有没有肿瘤、肝脏上的脂肪是不是太多了。
可以说，B超每年都挽救了数之不清的生命。而这一切，都要感谢众多前辈学者。_________________________________________________________
参考文献
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作者：赵言昌
