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
[{'content': "Compared to round collimator, use of rectangular collimator reduces the patient's skin surface exposed by: \nSelect and explain. \nA. 15%, B. 30%, C. 45%, D. 60%", 'role': 'user'}, {'content': "Answer: D \nExplanation: Use of a rectangular PID having\xa0an\xa0exit\xa0opening\xa0of\xa03.5 cm\xa0×\xa04.4 cm\xa0(1.38\xa0 inches\xa0×\xa01.34 inches) reduces the area of the patient’s skin surface exposed by 60% over that of a round (7 cm) PID.\xa0\nReference: White and Pharoah's Oral Radiology Principles and Interpretation 7th edition page no 34", 'role': 'assistant'}]