Differentiation of vein and lymphatic vessel by photoacoustic imaging system with parabolic array transducer and tunable laser

Recently, much attention is being paid to lymphatic circulation because intralymphatic immunotherapy and chemotherapy achieved significant clinical benefits. However, conventional ultrasound or photoacoustic (PA) imaging is hard to visualize lymphatic vessels. In the present study, real-time three-dimensional PA imaging system consisted of 256-ch parabolic array transducer with the central frequency of 10 MHz and tunable laser with the wavelength of 400-2100 nm was developed. Photoacoustic contrast agents such indocyanine green (ICG) or gold nanorods (AuNRs) were administrated to the lymphatic vessels of the ICR mouse. The vein was visualized at the wavelength of 490-600 nm without contrast agents. The lymphatic vessel was visualized at 670-770 nm with ICG and at 790-890 nm with AuNRs. The system is clinically applicable for detection of small lymphatic vessels to confirm successful drug delivery during intralymphatic chemotherapy.