Depth-dependent fluence compensation without a priori knowledge of tissue composition for quantitative ultrasound-guided photoacoustic imaging.

Significance: Compensation for depth-dependent fluence without a priori knowledge of tissue composition is a crucial unmet need for quantitative photoacoustic imaging.

Aim: We developed a method for estimating the effective optical attenuation coefficient of bulk tissue with composition and optical properties that are not known in advance, through combined ultrasound/photoacoustic imaging during mechanical displacement of tissue.

Approach: Ultrasound/photoacoustic imaging was performed on a target embedded in biological media while applying tissue displacement to change the optical path. After compensation for geometry-dependent scattering of light from light source apertures, the change of photoacoustic amplitude against optical path length was used to estimate the effective optical attenuation coefficient.

Results: Using the developed approach, the estimation of the effective optical attenuation coefficient of tissue-mimicking (milk/water) phantoms and ex vivo porcine muscle and chicken breast was accurate compared with ground-truth literature values.

Conclusions: Regardless of the varying geometries used for light delivery in photoacoustic imaging, it is feasible to perform ultrasound-guided photoacoustic imaging with simultaneous mechanical displacement of tissue to determine the effective optical attenuation coefficient of bulk tissue along the light path to the target.