Digital Phantoms for Quantitative Ultrasound and Photoacoustic Characterization of Thrombosis

Venous thrombosis, or blood clot formation in veins, poses significant health risks, including pulmonary embolism if untreated. Ultrasound imaging is commonly used for diagnostic purposes due to its portability and safety. However, B-mode ultrasound alone is limited in its ability to quantitatively assess blood clot composition, which is crucial for effective treatment planning. Photoacoustic imaging, combining optical and acoustic methods, provides high molecular contrast and detailed tissue information based on the optical absorption properties of different tissues. In this study, we combined quantitative ultrasound and photoacoustic imaging to optimize thrombus characterization for improved diagnosis. We created a digital phantom representing a 3D heterogeneous blood vessel model, incorporating both optical and mechanical properties of blood clots and surrounding tissues by using the Monte Carlo and k-Wave toolboxes. We varied clot properties such as clot composition, size, and depth during the simulations. Quantitative parameters, including lag-one coherence (LOC), signal amplitude, spectral slope, and midband fit, were computed to assess their predictive relationships with collagen content in the clots. Results showed that photoacoustic signal amplitude strongly correlated with collagen content (R<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.94), significantly outperforming the ultrasound signal amplitude (R<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.38). The other quantitative parameters, such as spectral slope and midband fit, also demonstrated strong correlations with tissue microstructure in photoacoustic signals, with R<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> > 0.7. These results demonstrate the potential of a combined imaging approach as a non-invasive method for the quantitative monitoring of thrombosis, particularly in resource-limited settings.