SPL is defined as the product of the number of cycles in the pulse and which parameter?

• A. Wavelength
• B. Pulse duration
• C. Frequency
• D. Beam width

Answer: (A)

Spatial pulse length is how far the ultrasound pulse extends in tissue, and it is found by multiplying how many cycles are in the pulse by the physical length of one cycle, which is the wavelength. So SPL = number of cycles × wavelength. Since wavelength equals speed of sound divided by frequency (λ = c/f), SPL = N × c / f. This means about the same pulse becomes shorter in space at higher frequency, while more cycles also increase SPL. The other options don’t define a spatial length: pulse duration is a temporal measure (time), frequency is the inverse of period but doesn’t directly give distance, and beam width is a lateral dimension, not the axial length of the pulse. Therefore, wavelength is the parameter in the product.