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: Radiology
Ideal imaging modality to diagnose hydrocephalus in a one month old baby is: 
Select and explain. 
A. Plain X-ray, B. Ultrasound, C. Computerised tomography, D. Magnetic Resonance Imaging
B: Ultrasound
Answer: B: Ultrasound 
Explanation: Ans. Ultrasound