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
A 50 year old male patient complains of reduced mouth opening. Patient gives h/o RTA 1 week back. A panoramic X-ray was taken using an intensifying screen containing gadolinium and lanthanum. When compared to calcium tungstate screen, the screen used in this patient decreases patient exposure by: 
Select and explain. 
A. 55%, B. 45%, C. 65%, D. 35%
A: 55%
Answer: A: 55% 
Explanation: Contemporary intensifying screens used in extraoral radiography use the rare earth elements gadolinium and lanthanum. These rare earth phosphors emit green light on interaction with X-rays. Compared with the older calcium tungstate screens, rare earth screens decrease patient exposure by 55% in panoramic and cephalometric radiography.
White and Pharoah, Oral radiology, ed 7th, pg-34