Q. A 55-year-old woman presents to the gastroenterology clinic complaining of progressive difficulty swallowing both solids and liquids over the past three months. She denies any significant weight loss, vomiting, or history of gastroesophageal reflux disease (GERD). She has no history of smoking or excessive alcohol use. Her physical examination reveals that she is hemodynamically stable, and the patient does not exhibit signs of systemic disease. Routine blood tests, including complete blood count and metabolic panel, are normal. Given her symptoms and the absence of systemic findings, the most likely cause is a structural abnormality in the esophagus. Which diagnostic test is commonly used to evaluate dysphagia by visualizing the esophagus and assessing for structural abnormalities?