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
Which one of the following is the investigation of choice for evaluation of suspected Perthes' disease? 
Select and explain. 
A. Plain X-ray, B. Ultrasonography (US), C. Computed Tomography (CT), D. Magnetic Resonance Imaging (MRI)
D: Magnetic Resonance Imaging (MRI)
Answer: D: Magnetic Resonance Imaging (MRI) 
Explanation: MRI is the investigation of choice as it can diagnose Perthes disease in early stages when X-ray is normal.