Study on the imaging technique of fluorescent marker and reporter to extract biological function and gene expression base on the ultrasound tagging fluorescence detection method

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We have studied on the development of tomographic imaging technique of fluorescence in biological tissue for assays of biological function. Ultrasonic modulation of light based on the acousto-optic effect (so called ultrasound 'tagging') is applied for imaging of fluorescence distribution in the light-scattering media. Sound-field characteristics that affect the light by modulating its amplitude through variation of the refractive index in the medium were determined. With using focused ultrasound, selectively modulated fluorescence on a depth-axis of the medium can be detected. Ultrasound tagging technique applied measuring the optical absorption in light scattering media is well known, and it is principally based on the modulation of speckle pattern. On the contrary, in the case of fluorescence, displacement of scattering particles and variation of the refractive index that is induced by density distribution in a sound field might produce the intensity modulation of scattered light. We have experimentally shown that ultrasound tagging technique is also available for fluorescence measurement. In this paper, we demonstrate the result of tomographic images of fluorescence in dense scattering media using biological tissue, porcine muscle and bovine adipose. Tissue samples had the dimension of 40 × 40 mm in section and fluorescent region which had the 3mm size was embedded in the center of the tissue. The image of the fluorophore was determined with the spatial resolution of focus size of the ultrasound, suggesting the applicability of this technique for visualization of fluorescent probes in deep portion of living body for clinical application. We continue the research aiming to development of a novel diagnostic imaging system.