Axial resolution measures the ability to display two structures very close together when the structures are ______.

Axial resolution measures the ability to display two structures very close together when the structures are ______.

• A. Perpendicular to the sound beam's main axis
• B. Parallel to the sound beam's main axis
• C. Along the lateral width of the image
• D. At the surface of the skin

Answer: (B)

Axial resolution measures how well two reflectors that lie along the direction the ultrasound wave travels—that is, parallel to the beam’s main axis (the depth direction)—can be seen as separate. This depends on the spatial pulse length: shorter pulses provide better axial resolution, because echoes from closely spaced structures along the beam path don’t blend together. Shorter spatial pulse length comes from using a higher frequency transducer or fewer cycles per pulse. This is different from lateral resolution, which concerns structures side-to-side across the image width and depends on beam width and focusing.

Axial resolution measures how well two reflectors that lie along the direction the ultrasound wave travels—that is, parallel to the beam’s main axis (the depth direction)—can be seen as separate. This depends on the spatial pulse length: shorter pulses provide better axial resolution, because echoes from closely spaced structures along the beam path don’t blend together. Shorter spatial pulse length comes from using a higher frequency transducer or fewer cycles per pulse. This is different from lateral resolution, which concerns structures side-to-side across the image width and depends on beam width and focusing.