How is spatial pulse length (SPL) determined?

Spatial pulse length (SPL) is the physical length of one pulse of ultrasound and is determined by multiplying the wavelength of the ultrasound wave by the number of cycles contained within that pulse. Wavelength is the distance between successive peaks or troughs of a wave, and it is inversely related to frequency; that is, as frequency increases, wavelength decreases. By multiplying the wavelength by the number of cycles, you account for how many wavelengths fit into that pulse, ultimately giving you the length of the pulse in space.

Understanding SPL is essential in ultrasound imaging because it impacts the axial resolution, which defines the ability to distinguish between two closely spaced structures along the direction of the sound beam. A shorter SPL usually results in better axial resolution, allowing for clearer images.

Other calculations related to ultrasound, such as the number of cycles divided by frequency or frequency divided by wavelength, do not yield the spatial pulse length, as they pertain to different parameters of wave behavior.