Which of the following will NOT improve axial resolution?

• A. Increased focusing
• B. Increased damping
• C. Increased transducer frequency
• D. Increased bandwidth

Answer: (A)

Axial resolution is determined by the spatial pulse length along the beam, which depends on how long the pulse is and how long its wavelength is. Shorter pulses or shorter wavelengths yield better axial resolution because two reflectors along the beam path can be distinguished more clearly.

Increasing transducer frequency shortens the wavelength, so axial resolution improves. Increasing damping reduces ringing and shortens the actual pulse length, also improving axial resolution. Increasing bandwidth allows a shorter effective pulse length by broadening the spectral content, which improves axial resolution.

Increasing focusing, on the other hand, mainly sharpens the beam laterally by concentrating energy at a focal depth. It does not reduce the pulse length along the axis, so it does not improve axial resolution.