A 4-week-old male infant presents with projectile, non-bilio…

A 4-week-old male infant presents with projectile, non-bilious vomiting after nearly every feeding. On exam, he appears dehydrated, and an “olive-shaped” mass is palpated in the epigastric region. The pediatric APRN suspects pyloric stenosis. Which of the following is the diagnostic study of choice to confirm this condition?