This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: CT SCAN, Subject name: Radiology
CT SCAN is based on? 
Select and explain. 
A. piezoelectric effect, B. linear attenuation of xrays, C. Coincidence Imaging, D. Pulse Echo principle
B: linear attenuation of xrays
Answer: B: linear attenuation of xrays 
Explanation: CT scan is based on Linear attenuation of Xrays/stopping power of various tissues, which is based on its density and is measured in Hounsfield Units. Pulse-Echo principle and Piezoelectric effect are used in USG. Coincidence imaging is used in PET scan.