No abstract

Accurate inversion is vital for quantitative imaging, including ultrasonic guided wave tomography, where thickness maps of plate-like structures are reconstructed to quantify corrosion damage. The dispersive properties of guided waves are often exploited to enable thickness maps to be produced from wave speed reconstructions. Ray tomography, diffraction tomography and a hybrid algorithm combining their features were investigated to reconstruct wave speed. Test data produced from simple defects of different sizes using a realistic full elastic guided wave model and the equivalent idealized acoustic model were passed to the imaging algorithms, generating wave speed maps, and, from these, thickness maps. For both datasets, ray tomography exhibited poor resolution. Diffraction tomography performed better, but was limited to shallow, small defects. The hybrid algorithm achieved the best results, giving a resolution around 1.5-2 wavelengths from the realistic test data compared to half wavelength from the idealized case. These results were validated with experimental data, and also extended to a realistic corrosion patch confirming the trends demonstrated with simple defects. The resolution loss with realistic data compared with idealized data indicates the acoustic model cannot accurately capture guided wave scattering and an alternative approach is necessary for better resolution reconstructions.

-Finite Element modelling is a promising tool for further progressing the 1 development of ultrasonic NDE of polycrystalline materials. Yet its widespread adoption has 2 been held back due to a high computational cost, which has restricted current works to

High-resolution breast tomography 1 AbstractBreast ultrasound tomography has the potential to improve the cost, safety and reliability of breast cancer screening and diagnosis over the gold-standard of mammography. Vital to achieving this potential is the development of imaging algorithms to unravel the complex anatomy of the breast and its mechanical properties. The solution most commonly relied upon is Time-of-Flight Tomography but this exhibits low resolution due to the presence of diffraction effects. Iterative full-wave inversion methods present one solution to achieve higher resolution, but these are slow and are not guaranteed to converge to the cor-