Which factors contribute to improved axial resolution?

• A. Increased bandwidth
• B. Shorter pulse length
• C. Shorter wavelength
• D. All of the above

Answer: (D)

Axial resolution depends on how short the sound pulse is along the beam. The shorter the spatial pulse length, the better you can distinguish two reflectors that lie on the beam axis. Spatial pulse length equals the number of cycles in the pulse times the wavelength, so factors that shorten the pulse length improve axial resolution. Increasing bandwidth allows the emitted pulse to be shorter in time (fewer cycles or a shorter duration), which reduces spatial pulse length. A shorter wavelength (higher frequency) also shortens the distance a cycle travels, so for the same number of cycles the spatial pulse length is smaller. Since a smaller spatial pulse length directly enhances axial resolution, all of these factors contribute to better axial resolution.