Increasing scanning depth automatically decreases which parameter to avoid range ambiguity?

Increasing scanning depth automatically decreases which parameter to avoid range ambiguity?

• A. Number of focal zones
• B. Sector width
• C. Pulse repetition frequency
• D. Pulse duration

Answer: (C)

The key idea is how depth affects the time window available to hear echoes before the next pulse is sent. When you image deeper, echoes take more time to travel to the deepest structures and back. If pulses are emitted very frequently, echoes from a deep pulse can still be returning when the next pulse is issued, making it hard to tell which echo came from which pulse—this is range ambiguity. Lowering the pulse repetition frequency gives more time between pulses (increasing the listening period). With a longer interval between pulses, all echoes from the deepest regions have time to return before the next pulse is transmitted, eliminating overlap and range ambiguity. That’s why increasing scanning depth automatically decreases pulse repetition frequency. The other settings don’t directly control this timing relationship. The number of focal zones affects focusing and resolution but not the timing window for echoes. Sector width changes the field of view and scanning speed, not the ambiguity issue. Pulse duration (the length of each transmitted pulse) influences axial resolution but isn’t the automatic adjustment used to prevent range ambiguity with depth.

The key idea is how depth affects the time window available to hear echoes before the next pulse is sent. When you image deeper, echoes take more time to travel to the deepest structures and back. If pulses are emitted very frequently, echoes from a deep pulse can still be returning when the next pulse is issued, making it hard to tell which echo came from which pulse—this is range ambiguity.

Lowering the pulse repetition frequency gives more time between pulses (increasing the listening period). With a longer interval between pulses, all echoes from the deepest regions have time to return before the next pulse is transmitted, eliminating overlap and range ambiguity. That’s why increasing scanning depth automatically decreases pulse repetition frequency.

The other settings don’t directly control this timing relationship. The number of focal zones affects focusing and resolution but not the timing window for echoes. Sector width changes the field of view and scanning speed, not the ambiguity issue. Pulse duration (the length of each transmitted pulse) influences axial resolution but isn’t the automatic adjustment used to prevent range ambiguity with depth.