How can Ultrasound be used for Medical Uses?

-Ultrasound can simply Pass through the Body, but some of it can be Reflected back -Knowing the Speed of Ultrasounds, and the Time it took to come Back [And divide that by 2 because you only care for the Distance THERE] you can see the Distance to that Tissue, or Festus -And then the Reflections can be Computerised to make an Image -Examples of Useful images being made is Foetus, Soft Tissues and Organs -And, Ultrasound as of now is Completely Safe