Using frequency-sum beamforming in passive cavitation imaging

Abstract

Passive Cavitation Imaging (PCI) is a method for locating cavitation emissions to study biological effects of ultrasound on tissues. In this method, an image is formed by beamforming passively recorded acoustic emissions with an array. The image resolution depends on the ultrasound frequency and array geometry. Acoustic emissions can be scattered due to tissue inhomogeneity, which may degrade the image resolution. Emissions at higher frequencies are more susceptible to such degradation. Frequency-sum beamforming is a nonlinear technique that alters this sensitivity to scattering by manufacturing higher frequency information from lower frequency components via a quadratic product of complex signal amplitudes. This presentation evaluates the performance of frequency-sum beamforming in a scattering environment using simulations and experiments, conducted in the kHz and MHz frequency regimes. First, 50 and 100 kHz signals were broadcasted from a single source to an array of 16 hydrophones in a water tank with and without discrete scatterers. Second, a tissue-mimicking phantom perfused with microbubbles was insonified at 2 MHz, and the emissions were received by a 128-element linear array. The performance of frequency-sum beamforming was compared to conventional delay-and-sum and minimum variance beamforming in mild and strong scattering environments. [Work partially supported by NAVSEA through the NEEC.]