Waveform inversion with calibrated source-time functions for improving in-vivo ultrasound computed tomography

We present a full-waveform inversion (FWI) of an in-vivo data set acquired with a transmission-reflection optoacoustic ultrasound imaging platform containing a cross-sectional slice through a mouse. FWI is a high-resolution reconstruction method that provides quantitative images of tissue properties such as the speed of sound. As an iterative data-fitting procedure, FWI relies on the ability to accurately predict the physics of wave propagation in heterogeneous media to account for the non-linear relationship between the ultrasonic wavefield and the tissue properties. A key component to accurately predict the ultrasonic field numerically is a precise knowledge of the source characteristics. For realistic problems, however, the source-time function is generally unknown, which necessitates an auxiliary inversion that recovers the time series for each transducer. This study presents an updated sound speed reconstruction of a cross-section through a mouse using source wavelets that are inverted individually per transducer. These source wavelets have been estimated from a set of observed data by application of a source-wavelet correction filter, which is equivalent to a water-level deconvolution. Compared to previous results, the spatial resolution of anatomical features such as the vertebral column is increased whilst artefacts are suppressed.