Photoacoustic Imaging Quantitative Analysis of Elastic andAbsorption Contrast of the k-Wave PseudospectralSimulation Framework

Photoacoustic imaging takes advantage of optical absorption difference to create ultrasonic waves that can be used to create high-resolution biomedical imaging. Although the method is mainly sensitive to optical absorption, recent theoretical studies have also indicated that mechanical elastic characteristics could be relevant in the early increase in pressure. This paper will demonstrate a strict quantitative comparison between absorption-based and elasticity-based contrast mechanisms through the use of the k-Wave pseudospectral simulation framework. We modeled two circular disc targets of the same geometry, but with different physical properties, absorption coefficients of 1 cm -1 and 2 cm -1, and young moduli of 94 KPa and 202 KPa. The forward acoustic propagation was modeled with the help of the kspaceFirstOrder2D, and the elastic waves dynamics was calculated through pstdElastic2D. To restore source distributions, time reversal reconstruction was done. Experiments prove that the elastic contrast produces preliminary pressures that are about four orders of magnitude less than absorption contrast although the Young’s modulus varies 2.15 times compared to an absorption coefficient variation of two. Quantitative analysis of reconstructed pressure profiles ensures faithful recovery of the source positions in both instances, but the small amplitude of the elastic signals confirms that photoacoustic imaging is still an optical absorbance-based modality. Such results elucidate the relative role of optical and mechanical properties in the generation of photoacoustic signals and confirm the use of k-Wave toolbox in the comparative study of contrast mechanisms.