Frequency selection for compounding synthetic aperture ultrasound images

In ultrasound imaging range resolution is proportional to the bandwidth of the transmitted pulse; however, noise also increases with frequency and forces a compromise in imaging accuracy. By compounding multiple synthetic aperture ultrasound images from different frequencies, both the resolution and signal-to-noise ratio (SNR) can be improved, unlike when averaging multiple scans at a single frequency, which would only increase SNR. This paper describes a technique for frequency compounding of synthetic aperture ultrasound images and a practical test setup is introduced for frequency selection for imaging systems consisting of a single piezoelectric transducer and a variable-frequency pulser. An example is provided in which point-scatterers in water are scanned along a linear path at frequencies of 16 to 21 MHz. The resulting multi-frequency imaging increases peak SNR by 13% more than single-frequency averaging with the same number of scans and reduces the range-domain support of the point-spread function by 30%.