Which term describes the fraction of time the machine is emitting a pulse?

• A. Period
• B. Duty factor
• C. Pulse duration
• D. Frame rate

Answer: (B)

The fraction of time the machine is emitting a pulse is described by the duty factor. In pulsed ultrasound, energy is turned on for a short interval (the pulse duration) and then off for the rest of the cycle. The duty factor is the on-time divided by the total cycle time (the period), often expressed as a percentage. So it specifically measures how much of the cycle the transducer is actively emitting.

To see why the other terms don’t fit: the period is the total time for one complete cycle, not the fraction itself. The pulse duration is the length of the actual pulse on, not the proportion of time. Frame rate refers to how many frames are produced per second, which relates to temporal resolution rather than the on/off time ratio of emission.