Axial resolution is determined by spatial pulse length. Which option correctly identifies spatial pulse length?

Axial resolution is determined by spatial pulse length. Which option correctly identifies spatial pulse length?

• A. Transmission frequency
• B. Lateral beam width
• C. Spatial pulse length
• D. Aperture size

Answer: (C)

Axial resolution depends on how long the ultrasound pulse occupies space along the beam. This length is called the spatial pulse length, the physical length of one pulse in tissue. It’s calculated as the number of cycles in the pulse times the wavelength (SPL = n × λ), or equivalently the speed of sound times the pulse duration. Shorter spatial pulse length means echoes from two closely spaced interfaces along the beam return in closer time, making them easier to distinguish. The quantity asked for is spatial pulse length itself, not other factors. Transmission frequency can influence SPL indirectly (higher frequency gives a shorter wavelength and can shorten SPL for the same number of cycles), but the key idea is that axial resolution is governed by the spatial pulse length. Lateral resolution is affected by beam width and aperture, not by SPL.

Axial resolution depends on how long the ultrasound pulse occupies space along the beam. This length is called the spatial pulse length, the physical length of one pulse in tissue. It’s calculated as the number of cycles in the pulse times the wavelength (SPL = n × λ), or equivalently the speed of sound times the pulse duration. Shorter spatial pulse length means echoes from two closely spaced interfaces along the beam return in closer time, making them easier to distinguish. The quantity asked for is spatial pulse length itself, not other factors. Transmission frequency can influence SPL indirectly (higher frequency gives a shorter wavelength and can shorten SPL for the same number of cycles), but the key idea is that axial resolution is governed by the spatial pulse length. Lateral resolution is affected by beam width and aperture, not by SPL.