Which transducer will exhibit the least amount of volume averaging?

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

Answer: (B)

Volume averaging is minimized when the ultrasound beam is narrow in the elevational (thickness) direction, so echoes are sampled from a thinner slice of tissue rather than a whole thick slab. A mechanical single-element transducer can’t focus in the elevational direction, so its beam is relatively thick and more of the volume is averaged. Linear and phased arrays mainly provide steering and focusing in the imaging plane; their elevational thickness remains relatively large, leading to more volume averaging. A 1.5D or multi-row array, with multiple rows of elements and elevational focusing, can produce a much thinner beam in the elevational direction, sharply reducing the sampled volume and thus exhibiting the least volume averaging.