This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Radiology
[{'content': 'CT of Thorax represents: \nSelect and explain. \nA. Ascending Aoic dissection, B. Descending Aoic dissection, C. Aoic aneurysm, D. Cystic fibrosis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Aoic dissection (AD) occurs when an injury to the innermost layer of the aoa allows blood to flow between the layers of the aoic wall, forcing the layers apa. The diagnosis of aoic dissection is based on clinical suspicion combined with imaging studies. Chest x-ray will sometimes show a "widened mediastinum". This occurs because the enlarged aoa casts a larger shadow on the x-ray detector. If this is seen, and there is a high clinical suspicion of a dissection, a CT scan of the chest with intravenous contrast is ordered REF: DAVID SUTTON 7TH ED', 'role': 'assistant'}]