Final answer:
A barium swallow can be used to visualize pyloric stenosis if the ultrasound is nondiagnostic.
Step-by-step explanation:
If the ultrasound is nondiagnostic of pyloric stenosis, then a barium swallow can be used to visualize the condition. A barium swallow involves drinking a liquid containing barium sulfate, which coats the gastrointestinal tract and provides greater visual detail than a traditional x-ray. This procedure can help identify any abnormalities or obstructions in the stomach or intestines, including pyloric stenosis.