Abstract
There is a need for cost effective, quantitative tissue spectroscopy and imaging systems in clinical diagnostics and pre-clinical biomedical research. A platform that utilizes a commercially available light-emitting diode (LED) based projector, cameras, and scaled Monte Carlo model for calculating tissue optical properties is presented. These components are put together to perform spatial frequency domain imaging (SFDI), a model-based reflectance technique that measures and maps absorption coefficients (μa) and reduced scattering coefficients (μs') in thick tissue such as skin or brain. We validate the performance of the flexible LED and modulation element (FLaME) system at 460, 530, and 632 nm across a range of physiologically relevant μa values (0.07 to 1.5 mm-1) in tissue-simulating intralipid phantoms, showing an overall accuracy within 11% of spectrophotometer values for μa and 3% for μs'. Comparison of oxy- and total hemoglobin fits between the FLaME system and a spectrophotometer (450 to 1000 nm) is differed by 3%. Finally, we acquire optical property maps of a mouse brain in vivo with and without an overlying saline well. These results demonstrate the potential of FLaME to perform tissue optical property mapping in visible spectral regions and highlight how the optical clearing effect of saline is correlated to a decrease in μs' of the skull.
Highlights
Spatial frequency domain imaging (SFDI) is a reflectance-based technique that can measure and map absorption and scattering coefficients in tissue on a pixel-by-pixel basis
We present a low cost, three-wavelength SFDI system that operates in the visible spectral regime using three light-emitting diodes (LEDs) (460, 530, and 632 nm)
While there is a natural variation in Intralipid batches,[20] we show in Fig. 4(c) that flexible LED and modulation element (FLaME)-fitted scattering values are within the range of the Mie theorypredicted scattering for 1% Intralipid,[21] with a mean error of 3% Æ 0.3%
Summary
Spatial frequency domain imaging (SFDI) is a reflectance-based technique that can measure and map absorption (μa) and scattering (μs0) coefficients in tissue on a pixel-by-pixel basis. Recent applications of SFDI to skin imaging include in vivo monitoring of burn wounds,[3,4] determining flap perfusion during surgical procedures,[5,6] and assessing cutaneous vascular abnormalities.[7] SFDI has been used for characterizing brain in small animal models of stroke,[8] glioblastoma,[9] and Alzheimer’s disease.[10] In each example, multispectral maps of tissue scattering are separately constructed from tissue absorption This allows formation of chromophore images such as oxyhemoglobin (HbO2), deoxy-hemoglobin (Hb), lipid, and water using the Beer–Lambert law. The inverse relationship between spatial frequency and average photon pathlength[11] facilitates SFDI depth sectioning and tomography of absorbing and fluorescent inhomogeneities.[12,13,14]
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