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This study investigates the effectiveness of different U-Net variants for suppressing ring artefacts in high-resolution X-ray microtomography (XMT) images of basalt from triaxial rock deformation experiment. Ring artefacts, due to electronic noise in detector diodes, distort greyvalue distributions, impair feature segmentation and digital volume correlation (DVC) accuracy. To overcome limited availability of XMT data, a custom Ring Artefact Generator (RAG) was developed to simulate artefacts of varying frequency and amplitude in sinograms, producing over 130,000 pairs of noisy and clean overlapping image patches for training. Three machine learning models: (a) U-Net (baseUNET), (b) Residual U-Net (ResUNET), and (c) Attention-Guided ResUNET (AG-ResUNET)—were trained and evaluated using PSNR and SSIM metrics.
Results show that all models effectively suppressed ring artefacts, with ResUNET achieving the highest PSNR improvement (57.5%) with comparable SSIM scores (0.99) across all models. The inclusion of residual connections accelerated convergence and improved denoising compared to the baseUNET, while attention mechanisms increased computational cost without significant performance gains due to limited data. The findings highlight that residual learning offers the best balance between denoising performance, model complexity, and efficiency, without impacting XMT images for downstream tasks like pore segmentation and DVC.