Which statement is true about the relationship between duty factor and imaging depth?

• A. It is directly proportional
• B. It is independent
• C. It is inversely related
• D. It depends on color Doppler

Answer: (C)

Duty factor is the fraction of time the transducer is actively transmitting during each ultrasound cycle. The transmit time stays essentially fixed for a given probe and frequency, but the time spent listening for echoes—the receive window—grows as you image deeper because echoes have more distance to return. Since the total cycle time is transmit time plus listen time, increasing depth lengthens the cycle while the transmit time stays the same, causing the duty factor to decrease. So deeper imaging leads to a smaller duty factor—in other words, an inverse relationship. This isn’t a direct proportionality, it isn’t independent of depth, and it isn’t determined by color Doppler.