2D full waveform inversion for a full 3D ultrasound tomography setup

We present one of the first applications of full waveform inversion (FWI) to data from a 3D Ultrasound Computed Tomography system, using a two-dimensional projection of the 3D aperture. This approach enables rapid assessment of FWI’s sensitivity to data quality, preprocessing, and initial models, serving as a practical intermediate step toward full 3D FWI. Based on a frequency-domain FWI framework, we incorporate a phase shift correction to partially compensate for out-of-plane wave propagation. The method is evaluated using both simulated and experimental datasets. Results demonstrate that FWI can successfully recover sound speed distributions in 3D USCT data and reveal inclusions not present in the ray-based initial model. Key insights include the importance of low-frequency starting points and reliable initializations to prevent cycle skipping. The approach is extensible to multiple planes, enabling future 3D reconstructions from stacked 2D slices.