Photoacoustic Imaging Using Array Transducer Suhyun Park, Srivalleesha Mallidi, Andrei B. Karpiouk, Salavat Aglyamov, and Stanislav Y. Emelianov Department of Biomedical Engineering University of Texas at Austin, Austin, TX USA 78712 ABSTRACT To perform ultrasound imaging using an array transducer, a focused ultrasound beam is transmitted in a particular direction within the tissue and the received backscattered ultrasound wave is then dynamically focused at every position along the beam. The ultrasound beam is scanned over the desired region to form an image. The photoacoustic imaging, however, is distinct from conventional ultrasound imaging. In photoacoustic imaging the acoustic transients are generated simultaneously in the entire volume of the irradiated tissue – no transmit focusing is possible due to light scattering in the tissue. The photoacoustic waves are then recorded on every element of the ultrasound transducer array at once and processed to form an image. Therefore, compared to ultrasound imaging, photoacoustic imaging can utilize dynamic receive focusing only. In this paper, we describe the image formation algorithms of the array-based photoacoustic and ultrasound imaging system and present methods to improve the quality of photoacoustic images. To evaluate the performance of photoacoustic imaging using an array transducer, numerical simulations and phantom experiments were performed. First, to evaluate spatial resolution, a point source was imaged using a combined ultrasound and photoacoustic imaging system. Next, image quality was assessed by imaging tissue imaging phantoms containing a circular inclusion. Finally, the photoacoustic and ultrasound images from the combined imaging system were analyzed. Keywords: Photoacoustic imaging, ultrasound imaging, array transducer, beamforming, image formation, image reconstruction, delay and sum 1. INTRODUCTION Ultrasound imaging can visualize the morphology of the tissue but histopathological information is limited. Photoacoustic imaging can be used to identify different functional activity of tissues that may be indistinguishable in ultrasound imaging. Since these imaging methods are complementary, combined photoacoustic and ultrasound imaging can take full advantage of the many synergistic features of these systems 1 . Integrated together, the combined imaging system can be used in many fundamental and applied, biomedical and clinical applications. Imaging sample Transducer Scan Convert Ultrasound Imaging Rectification Low-pass filter Log/Gamma compression Photoacoustic Imaging Pre- processing Filter Post- processing Pulsed Laser Ultrasound Pulser Receiver Receive Beamformer Memory Trigger Display Fig. 1. Combined ultrasound and photoacoustic imaging system. Photons Plus Ultrasound: Imaging and Sensing 2007: The Eighth Conference on Biomedical Thermoacoustics, Optoacoustics, and Acousto-optics, edited by Alexander A. Oraevsky, Lihong V. Wang, Proc. of SPIE Vol. 6437, 643714, (2007) · 1605-7422/07/$18 · doi: 10.1117/12.704240 Proc. of SPIE Vol. 6437 643714-1