Spatial pulse length is defined as the product of the number of cycles in a pulse and the wavelength.

Spatial pulse length is defined as the product of the number of cycles in a pulse and the wavelength.

• A. Wavelength multiplied by cycles per pulse
• B. Wavelength multiplied by the number of cycles in a pulse
• C. PRF multiplied by pulse duration
• D. Frequency multiplied by wavelength

Answer: (B)

Spatial pulse length is the distance the ultrasound pulse occupies in space. Each cycle travels one wavelength in space, so the total length is the number of cycles contained in the pulse times the wavelength. Therefore, spatial pulse length = (number of cycles in the pulse) × (wavelength). This makes the option stating wavelength multiplied by the number of cycles in a pulse the exact expression for SPL. The other ideas don’t describe a length: multiplying PRF by pulse duration gives a duty-factor-like value, not a physical length; multiplying frequency by wavelength yields speed (the wave’s propagation velocity), not length; and while “cycles per pulse” would amount to the same count, the standard description uses the phrase “number of cycles in a pulse” for clarity.

Spatial pulse length is the distance the ultrasound pulse occupies in space. Each cycle travels one wavelength in space, so the total length is the number of cycles contained in the pulse times the wavelength. Therefore, spatial pulse length = (number of cycles in the pulse) × (wavelength). This makes the option stating wavelength multiplied by the number of cycles in a pulse the exact expression for SPL. The other ideas don’t describe a length: multiplying PRF by pulse duration gives a duty-factor-like value, not a physical length; multiplying frequency by wavelength yields speed (the wave’s propagation velocity), not length; and while “cycles per pulse” would amount to the same count, the standard description uses the phrase “number of cycles in a pulse” for clarity.