Ultrasound transmits high-frequency, but low-energy sound beams into the human body. The returning 'echoes' are converted into an electrical signal, thence into images which are meaningful to the operators to detect diseases. 

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Ultrasound scanning is made famous by the media depicting it as a tool to examine the unborn baby. However, technology has progressed so far that almost every organ in the body can be examined.

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Contrary to CT or MRI, the cross section images produced by ultrasound is only limited to a very small window (area), which is in contact with the ultrasound transducer (probe). Hence studies using ultrasound are frequently more targeted and may not be as comprehensive as studies using  CT or MRI. Nonetheless, its portability, lower costs and ease of use are still extremely valuable as part of the disease workup process, even for the screening of healthy population.