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A three-dimensional laser optoacoustic imaging system was developed, which combines the advantages of optical
spectroscopy and high resolution ultrasonic detection, to produce high contrast maps of optical absorbance in tissues.
This system was tested in a nude mouse model of breast cancer and produced tissue images of tumors and vasculature.
The imaging can utilize either optical properties of hemoglobin and oxyhemoglobin, which are the main endogenous
tissue chromophores in the red and near-infrared spectral ranges, or exogenous contrast agent based on gold nanorods.
Visualization of tissue molecules targeted by the contrast agent provides molecular information. Visulization of blood at
multiple colors of light provides functional information on blood concentration and oxygen saturation. Optoacoustic
imaging, using two or more laser illumination wavelengths, permits an assessment of the angiogenesis-related
microvasculature, and thereby, an evaluation of the tumor stage and its metastatic potential.
The optoacoustic imaging system was also used to generate molecular images of the malignancy-related receptors
induced by the xenografts of BT474 mammary adenocarcinoma cells in nude mice. The development of the latter images
was facilitated by the use of an optoacoustic contrast agent that utilizes gold nanorods conjugated to monoclonal
antibody raised against HER2/neu antigens. These nanorods possess a very strong optical absorption peak that can be
tuned in the near-infrared by changing their aspect ratio. The effective conversion of the optical energy into heat by the
gold nanorods, followed by the thermal expansion of the surrounding water, makes these nanoparticles an effective
optoacoustic contrast agent. Optical scattering methods and x-ray tomography may also benefit from the application of
this contrast agent. Administration of the gold nanorod bioconjugates to mice resulted in an enhanced contrast of breast
tumors relative the background of normal tissues in the nude mouse model. The combination of this novel contrast agent
and optoacoustic imaging has the potential to become a useful imaging modality, for preclinical research in murine
models of cancer and other human diseases.
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