Although optical absorption is strongly associated with the physiological status of biological tissue, existing high-resolution optical imaging modalities, including confocal microscopy1,2, two-photon microscopy3,4 and optical coherence tomography5, do not sense optical absorption directly. Furthermore, optical scattering prevents these methods from imaging deeper than ∼1 mm below the tissue surface. Here we report functional photoacoustic microscopy (fPAM), which provides multiwavelength imaging of optical absorption and permits high spatial resolution beyond this depth limit with a ratio of maximum imaging depth to depth resolution greater than 100. Reflection mode, rather than orthogonal or transmission mode, is adopted because it is applicable to more anatomical sites than the others. fPAM is demonstrated with in vivo imaging of angiogenesis, melanoma, hemoglobin oxygen saturation (sO2) of single vessels in animals and total hemoglobin concentration in humans.
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We thank O. Craciun, J. Oh, G. Ku, M.L. Li and G. Lungu for experimental assistance. This work was sponsored by National Institutes of Health grants R01 EB000712 and R01 NS46214.
The authors declare no competing financial interests.
An illustrative example showing the penetration depth of fPAM in tissue. (PDF 69 kb)
Images of vasculature in a rat acquired in vivo by fPAM at the isosbestic optical wavelength of 584 nm before, two days post, and five days post subcutaneous inoculation of BR7C5 tumor cells. (PDF 76 kb)
Comparison among the modern high-resolution microscopic imaging techniques, whose depth-to-resolution ratios are all greater than 100. (PDF 15 kb)
(1.7 MB) Movie for the composite volumetric visualization of a melanoma in the skin acquired in vivo. (AVI 1774 kb)
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Zhang, H., Maslov, K., Stoica, G. et al. Functional photoacoustic microscopy for high-resolution and noninvasive in vivo imaging. Nat Biotechnol 24, 848–851 (2006). https://doi.org/10.1038/nbt1220
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