A 67-year-old female presents to the emergency room with a complaint of sudden, severe abdominal pain, described as “all over her belly.” Her medical history includes peptic ulcer disease, hypertension, and vitamin D deficiency. Her temperature is 101 °F (38.3 °C), heart rate is 108 beats/min, blood pressure is 88/68 mm Hg, respirations are 19 breaths/min, and oxygen saturation is 94% on room air. On examination, the patient appears severely distressed, lying quietly with knees drawn up, breathing shallowly. Her abdomen is rigid and quiet with rebound tenderness. After intravenous fluids, the patient reports significant improvement in abdominal pain. Suspecting a perforated peptic ulcer, which of the following tests has the greatest sensitivity to detect the location of the perforation?
