A photoacoustic imager with infrared illumination through the CMUT chip

This paper describes the design and preliminary experimental results of a novel photoacoustic imaging system which cascades a light source behind a near infrared (NIR) transparent ultrasonic transducer array and illuminates the image target through the transducer chip. With this in-line arrangement between the light source and the ultrasonic transducer, no time-consuming light-to-ultrasound alignment is needed in the image acquisition process, and better illumination uniformity on the target area can be achieved. Taking advantage of low infrared absorption coefficient of silicon in the near infrared spectrum, a surface-micromachined capacitive micromachined ultrasonic transducer (CMUT) array with a center acoustic frequency of 3.5 MHz is used for ultrasound reception in this system. Preliminary imaging results on a wire phantom using this cascaded PAI setup have been demonstrated.