Spatial pulse length is inversely proportional to which factor?

Spatial pulse length is inversely proportional to which factor?

• A. Wavelength
• B. Amplitude
• C. Frequency
• D. Time

Answer: (C)

Spatial pulse length is the distance the ultrasound pulse occupies in space, which depends on how many cycles are in the pulse and the length of each cycle (the wavelength). The wavelength is determined by the speed of sound in the medium divided by the frequency: λ = c/f. If you keep the number of cycles in the pulse constant, the spatial pulse length becomes SPL = (number of cycles) × λ = (number of cycles) × (c/f), so SPL is inversely proportional to frequency. In practice, higher frequency shrinks the wavelength, so the same pulse occupies less space. Amplitude changes how strong the signal is, not how long it spans in space, and time relates to how long the pulse lasts, which is not the factor SPL is testing.

Spatial pulse length is the distance the ultrasound pulse occupies in space, which depends on how many cycles are in the pulse and the length of each cycle (the wavelength). The wavelength is determined by the speed of sound in the medium divided by the frequency: λ = c/f. If you keep the number of cycles in the pulse constant, the spatial pulse length becomes SPL = (number of cycles) × λ = (number of cycles) × (c/f), so SPL is inversely proportional to frequency. In practice, higher frequency shrinks the wavelength, so the same pulse occupies less space. Amplitude changes how strong the signal is, not how long it spans in space, and time relates to how long the pulse lasts, which is not the factor SPL is testing.