FoCUS: Fourier-Based Coded Ultrasound

Modern imaging systems typically use single-carrier short pulses for transducer excitation. Coded signals together with pulse compression are successfully used in radar and communication to increase the amount of transmitted energy. Previous research verified significant improvement in signal-to-noise ratio (SNR) and imaging depth for ultrasound imaging with coded signals. Since pulse compression needs to be applied at each transducer element, the implementation of coded excitation (CE) in array imaging is computationally complex. Applying pulse compression on the beamformer output reduces the computational load but degrades both the axial and lateral point spread function, compromising image quality. In this paper, we present an approach for efficient implementation of pulse compression by integrating it into frequency domain beamforming. This method leads to significant reduction in the amount of computations without affecting axial resolution. The lateral resolution is dictated by the factor of savings in computational load. We verify the performance of our method on a Verasonics imaging system and compare the resulting images to time-domain processing. The computational savings are evaluated for a minimal sampling rate of four times the central frequency. We show that from 4- to 33-fold reduction is achieved as a function of the resulting lateral resolution, with no degradation of axial resolution. For an imaging system operating at a higher sampling rate, e.g., 10 times the central frequency, the savings can be as high as 77-fold. The efficient implementation makes CE a feasible approach in array imaging with the potential to enhance SNR as well as improve imaging depth and frame rate.