This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Magnetic Resonance Imaging, Subject name: Radiology
[{'content': 'Contrast used for MRI \nSelect and explain. \nA. Gadolinium, B. Radium, C. Iridium, D. TDT', 'role': 'user'}, {'content': 'Answer: A \nExplanation: MRI Contrast Agents : Are contrast agents used to improve the visibility of internal body structures in magnetic resonance imaging(MRI). The most commonly used compounds for contrast enhancement are Gadolinium-based.', 'role': 'assistant'}]