Open-source full-waveform ultrasound computed tomography based on the angular spectrum method using linear arrays
Rehman Ali
Abstract
We present full-waveform ultrasound computed tomography (USCT) for sound speed reconstruction based on the angular spectrum method using linear transducer arrays. We first present a transmission scenario in which plane-waves are emitted by a transmitting array and received by an array on the opposite side of the object of interest. These arrays are rotated around the object of interest to interrogate the medium from di↵erent view angles. Waveform inversion reconstruction is demonstrated on a numerical breast phantom, in which sound speed is varied from 1486 to 1584 m/s. This example is used to isolate and examine the impact of each view angles and frequency used in the reconstruction process. We also examine cycle-skipping artifacts as well as optimization schemes that can be used to overcome them. The goal of this work is to provide an opensource example and implementation of the waveform inversion reconstruction algorithm on Github: https:// github.com/rehmanali1994/FullWaveformInversionUSCT (DOI: 10.5281/zenodo.4774394). Next, we extend the waveform inversion framework to perform sound speed tomography for pulse-echo ultrasound imaging with a single linear array that transmits pulsed waves and receives signals backscattered from the medium. We first demonstrate that B-mode image reconstructions can be achieved using the angular spectrum method; then, we derive an optimization framework for estimating the sound speed in the medium by optimizing B-mode images with respect to slowness, via the angular spectrum method. We demonstrate an initial proof of concept with point targets in a homogeneous medium to demonstrate the fundamental principles of this new technique.