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Published November 28, 2011 | public
Journal Article

Performance benchmarks of an array-based hand-held photoacoustic probe adapted from a clinical ultrasound system for non-invasive sentinel lymph node imaging


Clinical translation of photoacoustic (PA) imaging can be facilitated by integration with commercial ultrasound (US) scanners to enable dual-modality imaging. An array-based US scanner was modified for hand-held PA imaging. The performance was benchmarked in terms of signal-to-noise ratio (SNR), axial spatial resolution and sensitivity. PA images of a tube, filled with methylene blue (MB; approx. 30 mM) and placed at various depths in chicken tissue, were acquired. A 5 cm penetration depth was achieved with an 18.6 dB SNR using a laser fluence of 3 mJ cm^(−2), only one-seventh of the safety limit (20 mJ cm^(−2)). An axial resolution of approximately 400 μm was maintained at all imaging depths. The PA sensitivity to MB placed 2.3 cm deep in chicken tissue was less than 100 μM. Further, after intradermal injection of MB (approx. 30 mM), a rat sentinel lymph node was clearly identified in vivo, beneath a 3.8 cm thick layer of chicken breast. The accumulated concentration of MB in the node was estimated to be approximately 7 mM. The noise-equivalent sensitivities (approx. 2 cm depth) were 17 and 85 μM, ex vivo and in vivo, respectively. These results support the use of this PA system for non-invasive mapping and image-guided needle biopsy of sentinel nodes in breast cancer patients.

Additional Information

© 2011 The Royal Society. Published 17 October 2011. This work was supported in part by grants from the National Institutes of Health (R01 EB000712, R01 EB008085, R01 CA134539, U54 CA136398, R01 EB010049 and 5P60 DK02057933). 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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