Which would increase the spatial pulse length?

Which would increase the spatial pulse length?

• A. Increased PRF
• B. Decreased number of transmit pulses per frame
• C. Increased number of transmit pulses per line
• D. Increased number of cycles per pulse

Answer: (D)

Spatial pulse length is the physical length of the ultrasound pulse in tissue during one emitted burst. It scales with how long the pulse lasts, which can be expressed as the number of cycles in the pulse times the wavelength (SPL = n × λ). So increasing the number of cycles per pulse makes the pulse endure longer and travel a greater distance in tissue, enlarging the spatial pulse length. The other adjustments affect how often pulses are sent or how many pulses are used per frame, not the length of a single pulse, so they don’t change SPL. (Note: a longer SPL can degrade axial resolution, since a longer pulse blurs closely spaced reflectors.)

Spatial pulse length is the physical length of the ultrasound pulse in tissue during one emitted burst. It scales with how long the pulse lasts, which can be expressed as the number of cycles in the pulse times the wavelength (SPL = n × λ). So increasing the number of cycles per pulse makes the pulse endure longer and travel a greater distance in tissue, enlarging the spatial pulse length. The other adjustments affect how often pulses are sent or how many pulses are used per frame, not the length of a single pulse, so they don’t change SPL. (Note: a longer SPL can degrade axial resolution, since a longer pulse blurs closely spaced reflectors.)