A 50-year-old male presents to the emergency department with sudden onset severe chest pain after an episode of forceful vomiting following a heavy meal. He describes the pain as sharp and radiating to his back. On physical examination, there is subcutaneous crepitus over the neck and diminished breath sounds on the left side. Chest X-ray shows pneumomediastinum and left-sided pleural effusion. Which of the following investigations is the most definitive for diagnosing Boerhaave syndrome in this patient?
