This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: FMGE 2017, Subject name: Radiology
[{'content': 'Which of the following is a gold standard investigation for diagnosis of renal stone? \nSelect and explain. \nA. USG, B. Helical CT with Non - contrast, C. Helical CT with contrast, D. MRI', 'role': 'user'}, {'content': 'Answer: B \nExplanation: USG is the IOC for gall stones and not renal stones. Helical CT without contrast is the IOC for all type of renal stones Helical CT with contrast is not preferred for looking calcifications like renal stones MRI is not preferred for renal stones', 'role': 'assistant'}]