If the PRP increases while the pulse duration remains constant, what happens to the duty factor?

If the PRP increases while the pulse duration remains constant, what happens to the duty factor?

• A. Increases
• B. Decreases
• C. Stays the same
• D. Becomes negative

Answer: (B)

Duty factor is the fraction of time the ultrasound is on during one cycle, defined as pulse duration divided by pulse repetition period (DF = PD / PRP). If the pulse repetition period increases while the pulse duration stays the same, the denominator grows while the numerator stays constant, so the ratio decreases. In other words, the beam is emitting for the same short time but with a longer gap between pulses, reducing the fraction of time it's active. This cannot become negative since both times are positive, so the duty factor must decrease.

Duty factor is the fraction of time the ultrasound is on during one cycle, defined as pulse duration divided by pulse repetition period (DF = PD / PRP). If the pulse repetition period increases while the pulse duration stays the same, the denominator grows while the numerator stays constant, so the ratio decreases. In other words, the beam is emitting for the same short time but with a longer gap between pulses, reducing the fraction of time it's active. This cannot become negative since both times are positive, so the duty factor must decrease.