Biocompatible astaxanthin as novel contrast agent for biomedical imaging.

Photoacoustic imaging (PAI) is a hybrid imaging modality with high resolution and sensitivity that can be beneficial for cancer staging. Due to insufficient endogenous photoacoustic (PA) contrast, the development of exogenous agents is critical in targeting cancerous tumors. The current study demonstrates the feasibility of marine-oriented material, astaxanthin, as a biocompatible PA contrast agent. Both silicon tubing phantoms and ex vivo bladder tissues are tested at various concentrations (up to 5 mg/ml) of astaxanthin to quantitatively explore variations in PA responses. A Q-switched Nd : YAG laser (λ = 532 nm) in conjunction with a 5 MHz ultrasound transducer is employed to generate and acquire PA signals from the samples. The phantom results presented that the PA signal amplitudes increase linearly with the astaxanthin concentrations (threshold detection = 0.31 mg/ml). The tissue injected with astaxanthin yields up to 16-fold higher PA signals, compared with that with saline. Due to distribution of the injected astaxanthin, PAI can image the margin of astaxanthin boles as well as quantify their volume in 3D reconstruction. Further investigations on selective tumor targeting are required to validate astaxanthin as a potential biocompatible contrast agent for PAI-assisted bladder cancer detection.