Spectral distortion in diffuse molecular luminescence tomography in turbid media

Abstract

The influence of tissue optical properties on the shape of near-infrared ͑NIR͒ 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.

Poly(N-isopropyl acrylamide)-block-poly(n-butyl acrylate) thermoresponsive amphiphilic copolymers: Synthesis, characterization and self-assembly behavior in aqueous solutions

“…More surprisingly, the emission maximum of ANS also does not exhibit any significant shifts with temperature and is about 470 nm for both copolymers, close to the value reported for PNIPAm homopolymer above the LCST [24], indicating that the inner part of the shell is dehydrated already at the room temperature. (The observed broadening of the emission bands at 318 K can be ascribed to the spectral distortion induced by increased photon path lengths in turbid solutions above the LCST [25].) It is noteworthy that the ANS emission maximum in PNIPAm 360 -b-PnBA 32 aggregates is slightly flattened which suggests that the ANS binding sites in PNIPAm 360 -b-PnBA 32 micelles have a broader distribution of local polarities as compared with PNIPAm 360 -b-PnBA 32 .…”

Implicit and explicit prior information in near-infrared spectral imaging: accuracy, quantification and diagnostic value

“…Additionally, a large body of work has been produced to either correct for or exploit the distortion of luminescent spectra by the absorbing spectra of the tissue. This can correct quantification of signals that would otherwise be incorrect [75][76][77] or be used to make an intractable problem solvable, such as in the case of bioluminescence tomography where spectral constraints are used to reduce the ill-posedness of the problem [77][78][79][80][81][82]. However, an inherent limitation of such approaches is that quantification improvements heavily rely on prior knowledge not only of the absorption spectra of the tissue chromophores but also of the magnitude of their relative contributions.…”

Mathematical model to interpret localized reflectance spectra measured in the presence of a strong fluorescence marker

“…While the magnitude of the emission peak increases with FS concentrations in the range of 0 to 125 μg∕mL, the relationship does not hold for higher concentrations where the peak exhibits both a decrease in magnitude and a subtle shift toward longer wavelengths-distortions that are consistent with self-absorption and re-emission by FS. 23 Characterization of the FS absorption and emission effects embedded within the spectra are complicated by the overlap with the distinctive absorption bands of oxy-and deoxyhemoglobin, shown in Fig. 1(c) for comparison.…”

“…These effects can be characterized by observing spectral distortions to the emission bands. 23 The data presented in the current study represent a first step toward quantitative optical spectroscopic guidance of neurosurgery in the presence of FS.…”