The PRF is reduced when systems image to a _____ depth.

The PRF is reduced when systems image to a _____ depth.

• A. Shallower
• B. Greater
• C. Deeper
• D. Moderate

Answer: (B)

In pulsed imaging, PRF must be lowered as imaging depth increases. The echoes from the deepest target take longer to return, so you need a longer listening time between pulses to avoid overlapping a new transmitted pulse with returning echoes. The relationship can be written as depth roughly equals c divided by twice the PRF (depth ≈ c / (2·PRF)), where c is the wave speed in the medium. So imaging to a greater depth means you must reduce PRF. The option that matches this is greater depth, i.e., deeper imaging requires a lower PRF.

In pulsed imaging, PRF must be lowered as imaging depth increases. The echoes from the deepest target take longer to return, so you need a longer listening time between pulses to avoid overlapping a new transmitted pulse with returning echoes. The relationship can be written as depth roughly equals c divided by twice the PRF (depth ≈ c / (2·PRF)), where c is the wave speed in the medium. So imaging to a greater depth means you must reduce PRF. The option that matches this is greater depth, i.e., deeper imaging requires a lower PRF.