The range equation describes the relationship between:

The range equation describes the relationship between:

• A. Acoustic impedance of two media
• B. Side lobe intensity between two crystals
• C. Round-trip pulse travel time and distance to the reflector
• D. Bandwidth and transducer frequency

Answer: (C)

The main idea here is how the round-trip travel time of an ultrasound pulse translates into depth. The pulse travels to a reflector and back, so the total time t is twice the one-way travel time. Using the speed of sound in the medium, the distance to the reflector is d = (speed × round-trip time) / 2. In soft tissue, that speed is about 1540 m/s, so a round-trip time of 13 microseconds corresponds to roughly 1 centimeter in depth. This range relationship is what you use to convert time measurements into spatial locations in imaging. Acoustic impedance tells you how much of the wave reflects at a boundary, not how far away the reflector is. Side-lobe intensity is about the beam’s off-axis energy, not travel time to depth. Bandwidth and transducer frequency affect resolution and frequency content, not the fundamental time-to-depth conversion.

The main idea here is how the round-trip travel time of an ultrasound pulse translates into depth. The pulse travels to a reflector and back, so the total time t is twice the one-way travel time. Using the speed of sound in the medium, the distance to the reflector is d = (speed × round-trip time) / 2. In soft tissue, that speed is about 1540 m/s, so a round-trip time of 13 microseconds corresponds to roughly 1 centimeter in depth. This range relationship is what you use to convert time measurements into spatial locations in imaging.

Acoustic impedance tells you how much of the wave reflects at a boundary, not how far away the reflector is. Side-lobe intensity is about the beam’s off-axis energy, not travel time to depth. Bandwidth and transducer frequency affect resolution and frequency content, not the fundamental time-to-depth conversion.