Why does deeper ultrasound require higher transmit power or longer acquisition?

• A. Tissue reflect more at depth.
• B. Deeper ultrasound requires more line rate.
• C. Attenuation increases with depth.
• D. Depth reduces speed.

Answer: (C)

The main idea is that attenuation increases with depth. As ultrasound travels through tissue, part of its energy is absorbed and scattered along the way. The farther the beam goes, the more energy is lost, so the echoes returning from deep structures are weaker. To keep the image bright enough and maintain good signal-to-noise ratio, you compensate by increasing the transmitted power or by listening longer to collect more echoes (longer acquisition). The speed of sound in tissue stays roughly constant with depth, so depth doesn’t change speed. Reflection isn’t inherently greater at deeper depths—it's about impedance contrasts—so depth itself isn’t making more echoes. Line rate affects how fast you can acquire data, not the energy loss that requires compensation.