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Published August 2, 2010 | Published
Journal Article Open

Deeply penetrating in vivo photoacoustic imaging using a clinical ultrasound array system


Using a hand-held photoacoustic probe integrated with a clinical ultrasound array system, we successfully imaged objects deeply positioned in biological tissues. The optical contrasts were enhanced by methylene blue with a concentration of ~30 mM. The penetration depth reached ~5.2 cm in chicken breast tissue by using 650-nm wavelength, which is ~4.7 times the 1/e optical penetration depth. This imaging depth was achieved using a laser fluence on the tissue surface of only 3 mJ/cm2, which is 1/7 of the American National Standards Institute (ANSI) safety limit (20 mJ/cm2). The noise equivalent sensitivity at this depth was ~11 mM. Further, after intradermal injection of methylene blue in a rat, a sentinel lymph node was easily detected in vivo, beneath a 2-cm thick layer of chicken breast. Also, blood located 3.5 cm deep in the rat was clearly imaged with intrinsic contrast. We have photoacoustically guided insertion of a needle into a rat sentinel lymph node with accumulated methylene blue. These results highlight the clinical potential of photoacoustic image-guided identification and needle biopsy of sentinel lymph nodes for axillary staging in breast cancer patients.

Additional Information

© 2010 Optical Society of America. Received 15 Jun 2010; revised 20 Jul 2010; accepted 20 Jul 2010; published 26 Jul 2010. This work was supported in part by grants from the National Institutes of Health (Network for Translational Research U54 CA136398, R01 EB008085, and R01 EB000712). L.V.W. has a financial interest in Microphotoacoustics, Inc. and in Endra, Inc., which, however, did not support this work.

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