Photoacoustic flow measurements by use of laser-induced shape transitions of gold nanorods.
A quantitative technique for flow measurements based on a wash-in analysis is proposed. The technique makes use of the shape dependence of the optical absorption of gold nanorods and the transitions in their shape induced by pulsed laser irradiation. The photon-induced shape transition of gold nanorods involves mainly a rod-to-sphere conversion and a shift in the peak optical absorption wavelength. The application of a series of laser pulses will induce shape changes in gold nanorods as they flow through a region of interest, with quantitative flow information being derived from the photoacoustic signals from the irradiated gold nanorods measured as a function of time. To demonstrate the feasibility of the technique, a Nd:YAG laser operating at 1064 nm was used for irradiation and a 1 MHz ultrasonic transducer was used for acoustic detection. The flow velocity ranged from 0.35 to 2.83 mm/s. Excellent agreement between the measured velocities and the actual velocities was demonstrated, with a linear regression correlation coefficient of 0.93. This study is a pioneer work on wash-in flow estimation in photoacoustic imaging.
Li
Pai-Chi
PC
Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan. paichi@cc.ee.ntu.edu.tw
Huang
Sheng-Wen
SW
Wei
Chen-Wei
CW
Chiou
Ya-Chin
YC
Chen
Cheng-Dah
CD
Wang
Churng-Ren Chris
CR
D000162:Acoustics / Q000295:instrumentation*; D003287:Contrast Media; D006046:Gold / Q000737:chemistry* / Q000528:radiation effects; D017078:Laser-Doppler Flowmetry / Q000295:instrumentation* / Q000379:methods; D007834:Lasers; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000528:radiation effects / Q000648:ultrastructure; D014159:Transducers
D003287:Contrast Media; D006046:Gold