This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Orthopaedics
[{'content': "Which one of the following is the investigation of choice for evaluation of suspected Perthes' disease? \nSelect and explain. \nA. Plain X-ray, B. Ultrasonography (US), C. Computed Tomography (CT), D. Magnetic Resonance Imaging (MRI)", 'role': 'user'}, {'content': 'Answer: D \nExplanation: MRI is the investigation of choice as it can diagnose Perthes disease in early stages when X-ray is normal.', 'role': 'assistant'}]