@book{33005,
	author = {Norton, Mary E.},
	title = {Callen's ultrasonography in obstetrics and gynecology /},
	publisher = {Elsevier,},
	year = {[2017]},
	address = {Philadelphia, PA :},
	edition = {6th ed},
	note = {Preceded by Ultrasonography in obstetrics and gynecology / [edited by] Peter W. Callen. 5th ed. c2008.}
}