An in-silico simulation study to generate computed tomography images from ultrasound data by using deep learning...

Ultrasound has low sensitivity in parenchymal lesion detection compared to contrast-enhanced computed tomography (CT). In this proof-of-concept-study, we investigate whether raw ultrasound data can be used to generate CT-like images using deep learning models in order to enhance lesion detection.

The k-wave ultrasound and Astra CT simulation toolkits were used to generate 2 datasets (1000 samples each) from simulated phantoms with up to 3 inclusions. The pix2pix conditional Generative adversarial network (cGAN) was trained on 800 samples per dataset, reserving the remainder for testing. Outputs were evaluated using generalized contrast-to-noise ratio (gCNR) and Structural Similarity Index (SSIM). Segmentation of B-mode alone versus B-mode with model-generated CT overlay was performed by 2 radiologists (1 board-certified and 1 resident) and both their performance and inter-observer agreement were evaluated using the Jaccard Index.

Model-generated CT-like images exhibited significantly improved gCNR ( $0.574\pm 0.210$ to $0.873\pm 0.163$ ) and SSIM ( $0.808\pm 0.092$ to $0.912\pm 0.062$ ) depending on phantom and inclusion type. Computed tomography-like images sometimes highlighted lesions otherwise undetectable in B-mode. The Jaccard index for 100 test samples improved significantly when segmenting Machine-Learning-augmented B-Mode compared with B-Mode images alone ( $0.58\pm 0.18$ to $0.69\pm 0.16$ ), depending on dataset and radiologist. Inter-observer agreement also improved significantly ( $0.74\pm 0.18$ to $0.85\pm 0.07$ for 1 dataset).

Deep learning models can effectively translate ultrasound data into CT-like images, improving quality and inter-observer agreement, and enhancing lesion detectability, for example, by alleviating shadowing artefacts.

Generating CT-like images using raw ultrasound RF data as input to a cGAN model results in a significant improvement in lesion detectability by, for example, alleviating acoustic shadowing. With a cGAN architecture, even relatively small datasets can successfully generate CT-like images that improve lesion detectability.