Diffusion as Sound Propagation: Physics-inspired Model for Ultrasound Image Generation
MICCAI 2024 (Oral Presentation)
Marina Domínguez*1,2
Yordanka Velikova*1,2
Nassir Navab1,2
Mohammad Farid Azampour1,2,3
1Technical University of Munich
2Munich Center for Machine Learning
3Sharif University of Technology
[Paper]
[Code]
[Bibtex]

Abstract

Deep learning (DL) methods typically require large datasets to effectively learn data distributions. However, in the medical field, data is often limited in quantity, and acquiring labeled data can be costly. To mitigate this data scarcity, data augmentation techniques are commonly employed. Among these techniques, generative models play a pivotal role in expanding datasets. However, when it comes to ultrasound (US) imaging, the authenticity of generated data often diminishes due to the oversight of ultrasound physics. We propose a novel approach to improve the quality of generated US images by introducing a physics-based diffusion model that is specifically designed for this image modality. The proposed model incorporates an US-specific scheduler scheme that mimics the natural behavior of sound wave propagation in ultrasound imaging. Our analysis demonstrates how the proposed method aids in modeling the attenuation dynamics in US imaging. We present both qualitative and quantitative results based on standard generative model metrics, showing that our proposed method results in overall more plausible images.


Forward Process

Forward Pass with Bmaps

Forward pass: Noise addition from bottom to top. Linearly-scheduled coneshaped B-Maps on the top row and the visualization of the noising process of the US image in the bottom row. B-Maps are applied at each step, making the gaussian distribution converge earlier on the bottom than on the top.

Bmaps Definition

Bmaps

Evolution of B-maps across time-steps. In every timestep, the values in the B-Maps decrease top-to-bottom from 1 to a number, y. As the timestep increases, γ goes from 1 to 1 − ϵ, with ϵ being a small fixed value in the interval (0, 1).

Reverse Process

Reverse Pass with Bmaps

Reverse Process: denoising the image. Initially focusing on the area near the probe, the model progresses to denoise the image toward the bottom, mimicking the way US images are traditionally generated.

Results

Qualitative Results

Qualitative comparison: The top row displays the label maps used for SegThy and CAMUS datasets. For the liver dataset, no labels were used. The bottom row shows the US images generated with B-Maps (left) versus without B-Maps (right) for each dataset.


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