[1] Univ Hosp Geneva, Dept Pediat Radiol, Geneva, Switzerland
[2] Univ Hosp Geneva, Div Clin Pathol, Geneva, Switzerland
[3] Univ Geneva, Div Clin Epidemiol, Geneva, Switzerland
[4] Harvard Univ, Dept Psychol, Cambridge, MA 02138 USA
[5] Univ Hosp Geneva, Dept Pediat Gastroenterol, Geneva, Switzerland
[6] Hop Univ Enfants, Unite Radiopediat, CH-1211 Geneva 14, Switzerland