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
Preferred method for obtaining dense nephrograms 
Select and explain. 
A. Increased concentration of contrast, B. Dehydration, C. Uretric compression, D. Rapid injection of contrast
D: Rapid injection of contrast
Answer: D: Rapid injection of contrast 
Explanation: Rapid (bolus) injection of contrast is preferred method.