Which transducer will exhibit the least amount of volume averaging?

• A. 1.5D or multi-row array
• B. Mechanical single element
• C. Phased array
• D. Linear array

Answer: (A)

Volume averaging depends on how thick the imaging slice is in the elevational direction. If the beam samples a larger tissue volume, more different tissue echoes get mixed, increasing averaging. The transducer that minimizes this is the one that provides the thinnest elevational resolution, because a thinner slice means the ultrasound signal comes from a smaller, more localized tissue volume.

A 1.5D or multi-row array does this best by using multiple rows of elements to focus electronically in the elevational direction, producing a much thinner slice than a single-element, linear, or standard phased-array transducer. That narrower sampling volume means less tissue is averaged in the elevation dimension, so volume averaging is minimized. The other designs—mechanical single element, linear, and conventional phased arrays—have limited or no elevational focusing, resulting in thicker slices and more volume averaging.