Frontiers of Photoacoustic Imaging

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The long-term objective of our proposed research is to develop photoacoustic imaging technologies that push new frontiers of biomedical imaging. Photoacoustic imaging is an emerging biomedical imaging modality that uses pulsed lasers to excite tissues. When light is absorbed, sound waves are created and used to form images of the optical properties inside the body. We have made considerable progress photoacoustic imaging, however, we perceive some areas where PA imaging needs further development: (1) Aside from blood & melanin-based pigment, until recently little has been done to explore other naturally-occuring contrast mechanisms in the body. We propose a number of techniques to image into tissues to attain information about specific chemical bonds without the need for contrast agents. The proposed methods will also provide information about the time chemical species are in an excited state after being interrogated by a laser pulse. (2) Quantitation has been difficult in photoacoustic imaging. Ideally we would like to create quantitative images of optical absorption, scattering coefficients (important because cell nuclei are often enlarged in cancers and pre-cancers, affecting scattering), and concentrations of chromophores. A large number of methods have been proposed to algorithmically solve this non-trivial inverse problem, however, each has its own set of problems. More work is needed to develop a useful & robust method for improved quantitation and we propose key algorithms and methods to do this. (3) Improved ultrasound transducer technology is needed. Photoacoustic signals can be weak & sensitivity and frequency response should be maximized. Ultrabroadband & ultrasensitive transducers are proposed to improve the quality, resolution, and penetration depth of photoacoustic imaging. Our proposed research aims to address present limitations to bring PA imaging to new frontiers.