RT Journal Article SR Electronic T1 Abdominal pain duration impacts the accuracy of ultrasound for diagnosing paediatric appendicitis JF Evidence Based Medicine JO Evid Based Med FD BMJ Publishing Group Ltd SP 224 OP 225 DO 10.1136/eb-2012-101170 VO 18 IS 6 A1 Andrea S Doria YR 2013 UL http://ebm.bmj.com/content/18/6/224.abstract AB