What is the most appropriate initial radiographic study for a 2-week-old male infant presenting with abdominal pain and bilious emesis?

In the case of a 2-week-old male infant presenting with abdominal pain and bilious emesis, the most appropriate initial radiographic study is the Upper GI series. This choice is particularly relevant in the evaluation of potential gastrointestinal obstruction or malrotation, conditions that can present with these symptoms in young infants.

An Upper GI series involves the administration of a contrast material that outlines the gastrointestinal tract, allowing visualization of the anatomy and any abnormalities, such as improper positioning of the intestines or blockages. This study can also provide information on the presence of conditions like duodenal atresia and volvulus, which are critical to diagnose early in the setting of acute abdominal symptoms.

While other imaging modalities like ultrasound and X-rays can provide valuable information, they are often less specific for gastrointestinal issues in infants or may not adequately show the abnormalities that an Upper GI series can highlight. CT scans are typically avoided in very young patients unless necessary due to their higher radiation exposure and the potential need for sedation, which is more complicated in neonates.

Thus, the Upper GI series is the most effective and appropriate initial study to investigate the cause of the infant's symptoms, emphasizing the importance of selecting the right imaging technique based on the clinical scenario presented.