Although the baby is exposed to radiation, an upper GI series (x-rays taken after the baby drinks a special contrast agent) can be diagnostic by showing the pylorus with elongated, narrow lumen and a dent in the duodenal bulb. A "string sign" or the "railroad track sign". For either type of study, there are specific measurement criteria used to identify the abnormal results. Plain x-rays of the abdomen sometimes shows a dilated stomach.Although UGI endoscopy would demonstrate pyloric obstruction, physicians would find it difficult to differentiate accurately between hypertrophic pyloric stenosis and pylorospasm.