Exposing humans to potentially dangerous levels of radiation as used x-rays can be fatal. X-rays are able to denature and mutate genetic molecules such as DNA and RNA, hence it can be described as a mutagen. An ultrasound scan however uses sound to create an image - this involves no radiation and is hence far safer. It is one of the reasons why it is used to examine foetuses and babies when in the uturus. The ultrasound also allows the kidney's topography and underlying structures to be observed.