A 6-month-old infant is brought to the emergency department by her parents. The infant has been experiencing episodes of bilious vomiting for the past 24 hours. The parents also report that the child has been fussy and seems to be in pain, particularly during feeding. On physical examination, the infant appears to be in discomfort and has a mildly distended abdomen. The infant's medical history is unremarkable, and she has been developing normally. You order an abdominal ultrasound to further investigate the cause of the vomiting.