http://www.radiologyinfo.org/en/info.cfm?pg=genus

http://www.ob-ultrasound.net/

http://en.wikipedia.org/wiki/Ultrasound

http://www.nlm.nih.gov/medlineplus/ency/article/003336.htm

http://www.webmd.com/baby/guide/ultrasound

http://www.ehow.com/how_5054485_information-ultrasound-techs.html

http://www.ardms.org/default.asp?ContentID=236&order=1

http://www.childrenshospital.org/az/Site1663/mainpageS1663P0.html

http://www.healthline.com/adamcontent/ultrasound

http://www.medicinenet.com/ultrasound/article.htm