Measurement of absorption in scattering media using objective laser speckle: application to blood oximetry

Abstract

Multi-spectral imaging enables non-invasive sensing of chemical concentrations in biological tissue based on measurement of optical absorption, but invariably in the presence of high levels of scatter. Absorption is normally inferred from measurement of contrast of biological features, such as the vasculature, and so accuracy is degraded by the poorly characterized modulation-transfer function of the imaging optics and overlying tissue. We report how experimental characterization of the spectral variation of the tissue point-spread function and associated objective speckle pattern can be used to characterize the absorption spectrum and chromophore concentration, with a particular emphasis on determination of the ratio of oxygenated to deoxygenated hemoglobin within blood. Absorption measurements are determined purely by the geometry of the experiment, without degradation due to optical aberrations and associated light scatter. The technique offers enhanced and low-cost determination of in vitro or in vivo chromophore characterizations, including blood-gas analysis.

Computational Optical Sensing and Imaging 2021: introduction to the feature issue

“…Junek et al report the exploitation of the rapid temporal fluctuations of speckles produced by a rotating speckle plate to provide a low-cost alternative excitation source for fluorescence-lifetime imaging [19]. Carles et al exploit variations in the tissue-point spread function and associated spatial-frequency spectrum of objective speckle to enable calculation of chromophore absorption in turbid media (such as partially oxygenated blood), without the degradations and practicalities of lens-based imaging [20]. Temporal correlations in speckle can also be exploited to extract polarimetric phase of an object obscured behind scattering media as described by Chen et al [21].…”