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Exquisitely Sensitive Imaging

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Science Translational Medicine  28 Oct 2009:
Vol. 1, Issue 4, pp. 4ec14
DOI: 10.1126/scitranslmed.3000515

Blood vessels take center stage in sundry disease states, such as stroke and tumor metastasis. But currently available imaging methods like ultrasound, magnetic resonance imaging, positron emission tomography, and fluorescence microscopy, either are unable to resolve individual capillaries or necessitate the use of contrast materials to enhance resolution. Fluorescence is generally a powerful imaging method, but it relies on the tendency of molecules to emit light on their own when they're excited, and the components of blood don't cooperate. Now, Min et al. describe a method that employs stimulated emission in place of fluorescence. In this technique (which underlies the operation of lasers), excited molecules are given a push by a light beam, causing them to emit more light than they would otherwise. The authors exploit stimulated emission to achieve sensitive detection of light-absorbing moieties in biologically important molecules with undetectable fluorescence, such as hemoglobin. Indeed, they were able to visualize individual red blood cells within single capillaries. The authors anticipate that their method will reveal the three-dimensional distribution of oxygen in blood, a measure that will be valuable when interrogating a variety of disease states. They also suggest that the cost of the sophisticated instruments required for this method will be lowered if fiber lasers are adapted for use in this context.

W. Min et al., Imaging chromophores with undetectable fluorescence by stimulated emission microscopy. Nature 461, 1105–1109 (2009). [Abstract]

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