Which factors can cause differences in signals from identical reflectors at different distances from the transducer?

• A. Material attenuation
• B. Beam divergence
• C. Near field
• D. All of the above

Answer: (D)

As you look at echoes from reflectors at different distances, the amount of energy that returns changes due to three real effects. First, material attenuation lowers the signal as it travels; more distance means more absorption and scattering, so the echo from a farther reflector is weaker. Second, beam divergence causes the ultrasound energy to spread out as it travels, so less energy is focused back toward the reflector at greater distances, reducing the reflected signal strength. Third, in the near field (the region close to the transducer), the beam isn’t yet fully formed and can be irregular in shape and intensity; this means the energy hitting identical reflectors can vary more with distance, altering the echo. Taken together, these factors can all cause differences in signals from identical reflectors at different distances, so all of them contribute.