A 52-year-old man with a history of gastroesophageal reflux disease (GERD) and obesity (BMI 34 kg/m²) is scheduled for emergency repair of a perforated duodenal ulcer. He consumed a heavy meal 2 hours ago. During pre-anesthetic evaluation, you suspect delayed gastric emptying and high aspiration risk. Which investigation is most appropriate to confirm the diagnosis before induction of anesthesia?