Design and Development of Photoacoustic Spectroscopy System for Contrast Agent Characterisation

Abstract

Photoacoustic imaging (PAI) is a hybrid biomedical imaging technique that combines high optical-absorption contrast with the deep-penetration and resolution capabilities of ultrasound. This combination enables the detailed visualisation of tissue structures at greater depths than conventional optical imaging. While endogenous chromophores such as haemoglobin provide inherent contrast, introducing exogenous contrast agents further enhances sensitivity, specificity, and molecular targeting. However, current PAI methods lack standardised quantitative approaches to relate dye concentration to signal amplitude, which limits their clinical translation. In response to this gap, we designed and developed an integrated and calibrated experimental system to build a systematic framework for analysing the relationship between contrast-agent concentration and photoacoustic signal amplitude. The system comprises a tunable nanosecond-pulsed laser, a high-frequency needle hydrophone, and a LabVIEW-based acquisition interface to ensure precise synchronisation, signal integrity, and real-time control. To build the setup, custom 3D-printed components were fabricated to optimise optical and acoustic performance, and the system was verified using simulated signals before laser implementation. This work establishes the technical basis for generating calibration curves and developing standardised imaging protocols. Ultimately, the system provides a foundational tool for advancing the quantitative capabilities of PAI using exogenous contrast dyes in biomedical applications.