Influence Of Optical Fluence Distribution On Photoacoustic Imaging

Abstract

Photoacoustic imaging (PAI) is a non-invasive and<br> non-ionizing imaging modality that combines the absorption contrast<br> of light with ultrasound resolution. Laser is used to deposit optical<br> energy into a target (i.e., optical fluence). Consequently, the target<br> temperature rises, and then thermal expansion occurs that leads to<br> generating a PA signal. In general, most image reconstruction<br> algorithms for PAI assume uniform fluence within an imaging object.<br> However, it is known that optical fluence distribution within the<br> object is non-uniform. This could affect the reconstruction of PA<br> images. In this study, we have investigated the influence of optical<br> fluence distribution on PA back-propagation imaging using finite<br> element method. The uniform fluence was simulated as a triangular<br> waveform within the object of interest. The non-uniform fluence<br> distribution was estimated by solving light propagation within a<br> tissue model via Monte Carlo method. The results show that the PA<br> signal in the case of non-uniform fluence is wider than the uniform<br> case by 23%. The frequency spectrum of the PA signal due to the<br> non-uniform fluence has missed some high frequency components in<br> comparison to the uniform case. Consequently, the reconstructed<br> image with the non-uniform fluence exhibits a strong smoothing<br> effect.