With the presence of which phenomenon do we see more boundaries than there are reflecting surfaces?

• A. shadowing
• B. enhancement
• C. arrays
• D. reverberations

Answer: (D)

Reverberation is the phenomenon at play. It happens when the ultrasound pulse keeps bouncing back and forth between two strong reflectors. Each bounce sends another echo back to the transducer, and the system displays that echo as a boundary at a greater depth. Because there can be many back-and-forth reflections, you end up with a chain of echoes that appear as more boundaries on the image than there are actual surfaces in the tissue. The boundaries are typically equally spaced, reflecting the round-trip travel time between the two reflectors. This is different from shadowing, where signal is lost behind an attenuating object, or enhancement, where brightness increases behind a weakly attenuating area, and it’s not related to the transducer being a certain type of array.