This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: ULTRASOUND, Subject name: Radiology
[{'content': 'Pulse echo principle is used by which modality? \nSelect and explain. \nA. USG, B. CT, C. X-ray, D. MRI', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Pulse Echo Technique is used in Ultrasound, which sho-duration Ultrasound pulses are transmitted into the region to be studied, and Echo signals resulting from scattering and reflection are detected and displayed. The depth of a reflective structure is inferred from the delay between pulse transmission and echo reception. CT scan is based on Linear Attenuation of X Rays. MRI is based on Gyromagnetic propey of H+ ions.', 'role': 'assistant'}]