Imaging light fluence distribution in blood vessels with combined photoacoustic fluctuation imaging and ultrasound power doppler

Spatial light distribution prediction is highly useful but challenging; no imaging method is currently capable of measuring it at different depths. This study introduces a novel technique for fluence quantification within blood vessels through the ratio of photoacoustic fluctuation imaging (PAFI) and ultrasound power Doppler (USPD). However, their direct coupling fails in accurately estimating the fluence due to differences in the Point Spread Functions (PSFs), leading to varying image resolution and amplitude dependence over vessel sizes. To address this, we propose a model-based matrix approach to apply a non-stationary PSF filter to USPD. Validation through 3D simulations and experiments with tissue-mimicking phantoms demonstrates accurate fluence recovery. Results indicate a robust correlation with the Monte Carlo-simulated ground truth, even in unresolved vessels. This direct imaging technique uniquely offers precise measurement of light distribution in ubiquitous blood vessels, showing great potential for clinical applications and quantitative photoacoustic inverse problems.