In ultrasound physics, which property of a transducer determines axial resolution (ability to distinguish two structures along the beam axis)?

• A Transducer footprint size
• B Focus depth
• C Pulse duration (spatial pulse length) — shorter pulse = better axial resolution ✓
• D Frame rate of the B-mode image

Explanation

Axial resolution in ultrasound is the ability to distinguish two structures lying along the direction of sound propagation. Axial resolution = half the spatial pulse length (SPL) = half of (number of cycles × wavelength). A shorter pulse duration (fewer cycles per pulse, higher frequency) produces better axial resolution. Higher frequency transducers have shorter wavelengths and hence better axial resolution but less depth penetration. Lateral resolution depends on beam width at the focal zone. Frame rate affects temporal resolution, not axial resolution. Transducer footprint affects the field of view.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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