10A-4 In Vitro Blood Flow Mean Velocity Estimation Using a Fast Photoacoustic Imaging System

We previously proposed a quantitative flow estimation method for photoacoustic imaging and verified its performance with phantom measurements. In this study, we continue to experimentally evaluate its performance using real tissue and a fast photoacoustic imaging system. The estimation method requires the use of gold nanorods and wash-in time-intensity analysis. In addition, shape transition of gold nanorods is induced by laser and it results in changes in the optical absorption spectrum. By monitoring temporal concentration changes of the injected gold nanorods, the time-intensity curve (TIC) is calculated and curve-fitted to estimate the mean flow velocity. The fast imaging system consisted of a Q-switched Nd:YAG laser system, an ultrasonic digital phased array system, and a custom- design photoacoustic probe. The effective frame rate of the system in this case is limited by the pulse repetition frequency (PRF) of the laser to 15 Hz. An in vitro flow model consisted of chicken breast tissue in which a polyethylene tubing was embedded. Human blood mixed with gold nanorods was injected into the tubing by using a syringe pump. In the results, flow rates ranging from 0.125 to 2 mm/s can be measured, with an average normalized standard deviation of 31.3%. The correlation coefficient between the measured flow velocities and their linear regression fit was 0.83. Therefore, the proposed method is proven effective for relative mean velocity measurements.