This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fundamentals in Radiology, Subject name: Radiology
Ultrasonography transducer contain 
Select and explain. 
A. Sodium fluride, B. Lead Zirconate, C. Caesium fluoride, D. None
B: Lead Zirconate
Answer: B: Lead Zirconate 
Explanation: Some naturally occurring materials possess piezoelectric propeies (e.g., quaz) But most crystals used in medical ultra sound are man-made. This group of aificial piezoelectric materials are known as ferroelectrics. Barium titanate was the first of the ceramic ferroelectrics to be discovered. This has been largely replaced by lead zirconate titanate, commonly known as PZT. Now lead zirconate titanate is the most commonly used Several types of PZT are available, with slight variations in chemical additions and thermal treatment producing different propeies. Ref : Christensen's Physics of Diagnostic Radiology, 4/E,Pg no.329