Rapid beamforming of ultrasound chirp signals in frequency domain using the chirp scaling algorithm

Abstract

Linear frequency-modulated (chirp) transmits have been used successfully in the past to increase penetration depth of ultrasound signals in tissue and to improve the signal-to-noise ratio (SNR) in the resulting ultrasound images. However, beamforming chirp signals using delay-and-sum (DAS) can be slow on systems without a GPU. We propose using the chirp scaling algorithm (CSA), originally developed for synthetic aperture radar, as a faster alternative to DAS on CPU that results in similar image quality, especially at larger depths. To perform preliminary comparisons of the beamforming methods, we simulated in FIELD II monostatic synthetic aperture data containing point targets up to 300 mm in depth. The simulation accounted for average signal attenuation in soft tissue of 0.5 dB per MHz per cm. We analyzed the point spread functions and the runtimes of the methods in MATLAB with a single CPU. Beamformed point targets above 80 mm depth had almost identical sidelobe levels and full-width-at-half-maximum between the two methods, while the median runtime for CSA was 9.3 times faster than for DAS. We further extend CSA to multistatic acquisitions with chirp transmits and with curvilinear arrays for more clinical applicability and improved image quality.