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Published March 6, 2006 | Published
Book Section - Chapter Open

Virtual-detector synthetic aperture focusing technique with application in in vivo photoacoustic microscopy


In this study, we introduce a synthetic aperture focusing technique which employs a virtual detector concept, combined with coherence weighting, to extend the depth of focus for an in-vivo photoacoustic microscopy system. This technique treats the transducer's focal point as a virtual point detector of photoacoustic signals, delays adjacent scan lines relative to the virtual detector, and then sums the delayed signals to achieve focusing in the out-of-focus region. In addition, a coherence factor among the delayed signals for each synthesized imaging point is used as a weighting factor to further improve the focusing quality. Images of an Intralipid phantom containing a carbon fiber show how this technique improves the -6 dB lateral resolution from 49-379 μm to 46-53 μm and increases the SNR by 0-29 dB, depending on the distance from the ultrasonic focal point. In vivo experiments show that this technique also provides a clearer tumorassociated angiogenesis in the mouse's scalp. The extended depth of focus for the photoacoustic microscopy system enables 3D reconstruction of the vascular network for the study of tumor angiogenesis.

Additional Information

© 2006 Society of Photo-optical Instrumentation Engineers (SPIE). We are grateful to Gina Lungu, Sergio Similache, and Ovidiu Cracium for assistance with cell culture and veterinary procedures. We also gratefully acknowledge funding from the National Institutes of Health, R01 EB000712 and R01 NS46214(BRP).

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