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
USG velocity 
Select and explain. 
A. Increases in frequency in a medium, B. Equal to Ultrasound frequency, C. Equal to Ultrasound wavelength, D. Is lower in tissues with a higher fat or water content
D: Is lower in tissues with a higher fat or water content
Answer: D: Is lower in tissues with a higher fat or water content 
Explanation: Answer: d) Is lower in tissues with a higher fat or water contentUltrasound velocity:It is a product of the frequency and wavelengthIt is inversely proportional to the square root of the material densityUltrasound travels faster in stiff, non-compressible mediaVelocity in a given medium is virtually independent of the frequency. With velocity being constant, an increase in the frequency causes a proportional decrease in wavelengthThe velocity of ultrasound in fat and water is lower than in an average soft tissue.