Ultrasound scan. Cancer Research UK. http://www.cancerresearchuk.org/about-cancer/cancers-in-general/tests/ultrasound-scan. Updated May 13, 2015. Accessed July 2016.
General ultrasound. RadiologyInfo.org. http://www.radiologyinfo.org/en/info.cfm?pg=genus. Updated June 23, 2014. Accessed June 2016.
US Department of Health and Human Services. US Food and Drug Administration. Ultrasound imaging. http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/ucm115357.htm. Updated December 16, 2014. Accessed June 2016.