Which statement about duty factor is true?

Which statement about duty factor is true?

• A. It can exceed 100%
• B. It is always zero for pulsed ultrasound
• C. It is the ratio of transmit time to total cycle length
• D. It is independent of pulse duration

Answer: (C)

Duty factor describes how much of the time the transducer is actively emitting. It’s defined as the transmit time divided by the total cycle length (the entire time from the start of one pulse to the start of the next). This ratio is between 0 and 1, so in diagnostic ultrasound it’s usually a small percentage, well under 100%. This is why the statement is true: the duty factor equals transmit time over the full cycle, capturing the fraction of time the system is radiating. It can’t exceed 100% because the transmit time can’t be longer than the total cycle length; if the emission were continuous, it would be 100%, but never more. It isn’t always zero for pulsed ultrasound because there is a finite pulse duration in every cycle, so there is nonzero transmit time. And it depends on pulse duration: longer pulses increase the duty factor, shorter pulses decrease it.

Duty factor describes how much of the time the transducer is actively emitting. It’s defined as the transmit time divided by the total cycle length (the entire time from the start of one pulse to the start of the next). This ratio is between 0 and 1, so in diagnostic ultrasound it’s usually a small percentage, well under 100%.

This is why the statement is true: the duty factor equals transmit time over the full cycle, capturing the fraction of time the system is radiating. It can’t exceed 100% because the transmit time can’t be longer than the total cycle length; if the emission were continuous, it would be 100%, but never more. It isn’t always zero for pulsed ultrasound because there is a finite pulse duration in every cycle, so there is nonzero transmit time. And it depends on pulse duration: longer pulses increase the duty factor, shorter pulses decrease it.