Spatial mapping of fluorophore quantum yield in diffusive media.

Fluorescence quantum yield (QY) indicates the efficiency of the fluorescence process. The QY of many fluorophores is sensitive to local tissue environments, highlighting the possibility of using QY as an indicator of important parameters such as pH or temperature. QY is commonly measured by comparison to a well-known standard in nonscattering media. We propose a new imaging method, called quantum yield imaging (QYI), to spatially map the QY of a fluorophore within an optically diffusive media. QYI utilizes the wide-field diffuse optical technique spatial frequency domain imaging (SFDI) as well as planar fluorescence imaging. SFDI is used to measure the optical properties of the background media and the absorption contributed by the fluorophore. The unknown QY is then calculated by combining information from both modalities. A fluorescent sample with known QY is used to account for instrument response. To demonstrate QYI, rhodamine B and SNARF-5 were imaged in liquid phantoms with different background optical properties. The methanol:water ratio and pH were changed for rhodamine B and SNARF-5 solvents, respectively, altering the QY of each through a wide range. QY was determined with an agreement of 0.021 and 0.012 for rhodamine B and SNARF-5, respectively.