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

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          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/cm 2, which is 1/7 of the American National Standards Institute (ANSI) safety limit (20 mJ/cm 2). 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.

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          Most cited references 17

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          Optical coherence tomography.

          A technique called optical coherence tomography (OCT) has been developed for noninvasive cross-sectional imaging in biological systems. OCT uses low-coherence interferometry to produce a two-dimensional image of optical scattering from internal tissue microstructures in a way that is analogous to ultrasonic pulse-echo imaging. OCT has longitudinal and lateral spatial resolutions of a few micrometers and can detect reflected signals as small as approximately 10(-10) of the incident optical power. Tomographic imaging is demonstrated in vitro in the peripapillary area of the retina and in the coronary artery, two clinically relevant examples that are representative of transparent and turbid media, respectively.
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            In vivo photoacoustic tomography of chemicals: high-resolution functional and molecular optical imaging at new depths.

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              Surgical resection and radiolocalization of the sentinel lymph node in breast cancer using a gamma probe.

              We have recently reported on a technique of gamma probe localization of radiolabelled lymph nodes to identify the sentinel node in malignant melanoma. In order to determine whether this technique is applicable to assist in staging breast cancer, a pilot study was begun to address two questions: (i) can the sentinel lymph node draining a breast cancer be identified for selective resection; and (ii) is the sentinel lymph node predictive of the status of the entire axillary lymph nodes? One to four hours prior to axillary lymph node dissection, 22 consecutive patients had approximately 0.4 mCi of technetium sulfur colloid in 0.5 ml saline injected around the perimeter of the breast lesion. A hand-held gamma counter was used at surgery to locate the lymph node(s) receiving drainage from the breast. A sentinel lymph node was identified in 18 of 22 patients. Of these 18 patients, the sentinel lymph node was positive in seven of seven patients, with pathologically verified metastatic breast cancer to at least one lymph node. In three out of seven patients, the sentinel lymph node was the only lymph node with metastatic cancer. In this pilot study of breast cancer patients, we conclude that: (i) radiolocalization and selective resection of sentinel lymph nodes is possible; and (ii) the sentinel lymph node appears to predict correctly the status of the remaining axilla. These data justify a larger clinical trial to verify the value of this technique.

                Author and article information

                Biomed Opt Express
                Biomedical Optics Express
                Optical Society of America
                02 August 2010
                26 July 2010
                26 July 2010
                : 1
                : 1
                : 278-284
                [1 ]Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis, Campus Box 1097, One Brookings Dr. St. Louis, MO 63130-4899, USA
                [2 ]Philips Research North America, 345 Scarborough Rd. Briarcliff Manor, NY 10510, USA
                [3 ]These authors contributed equally to this work.
                Author notes
                ©2010 Optical Society of America

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 Unported License, which permits download and redistribution, provided that the original work is properly cited. This license restricts the article from being modified or used commercially.

                Funded by: National Institutes of Health
                Award ID: CA136398
                Photoacoustic Imaging and Spectroscopy
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