Spectral distortion in diffuse molecular luminescence tomography in turbid media

Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755, USA
Journal of Applied Physics (Impact Factor: 2.18). 06/2009; 105(10):102024 - 102024-8. DOI: 10.1063/1.3116130
Source: IEEE Xplore


The influence of tissue optical properties on the shape of near-infrared (NIR) fluorescence emission spectra propagating through multiple centimeters of tissue-like media was investigated. Fluorescence emission spectra measured from 6 cm homogeneous tissue-simulating phantoms show dramatic spectral distortion which results in emission peak shifts of up to 60 nm in wavelength. Measured spectral shapes are highly dependent on the photon path length and the scattered photon field in the NIR amplifies the wavelength-dependent absorption of the fluorescence spectra. Simulations of the peak propagation using diffusion modeling describe the experimental observations and confirm the path length dependence of fluorescence emission spectra. Spectral changes are largest for long path length measurements and thus will be most important in human tomography studies in the NIR. Spectrally resolved detection strategies are required to detect and interpret these effects which may otherwise produce erroneous intensity measurements. This observed phenomenon is analogous to beam hardening in x-ray tomography, which can lead to image artifacts without appropriate compensation. The peak shift toward longer wavelengths, and therefore lower energy photons, observed for NIR luminescent signals propagating through tissue may readily be described as a beam softening phenomenon.

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    • "The main advantage in the presented methodology is the acquisition of the fluorescence spectra in situ with the same device and under the same conditions as the fluorescence tomography data acquisition. This innovation can account for any spectral distortions due to the propagation of the fluorescence light through tissue with different optical properties and different pathlengths, thus improving significantly the localization of the object of interest at varying depths [34,35]. Furthermore, this feature could prove very important for accurate reconstruction and quantification in reflection geometry since autofluorescence could be accounted for as one additional fluorescence contributor and could then be efficiently subtracted [23]. "
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