Fluorescence spectra provide information on the depth of fluorescent lesions in tissue

Abstract

The fluorescence spectrum measured from a fluorophore in tissue is affected by the absorption and scattering properties of the tissue, as well as by the measurement geometry. We analyze this effect with Monte Carlo simulations and by measurements on phantoms. The spectral changes can be used to estimate the depth of a fluorescent lesion embedded in the tissue by measurement of the fluorescence signal in different wavelength bands. By taking the ratio between the signals at two wavelengths, we show that it is possible to determine the depth of the lesion. Simulations were performed and validated by measurements on a phantom in the wavelength range 815-930 nm. The depth of a fluorescing layer could be determined with 0.6-mm accuracy down to at least a depth of 10 mm. Monte Carlo simulations were also performed for different tissue types of various composition. The results indicate that depth estimation of a lesion should be possible with 2-3-mm accuracy, with no assumptions made about the optical properties, for a wide range of tissues.

Modeling of spectral changes for depth localization of fluorescent inclusion

“…In a previous study, we demonstrated a method to determine the depth of an embedded inclusion marked with a fluorescent probe [11]. As the depth, size of inclusion, and concentration are parameters that can be difficult to evaluate independently with fluorescence imaging [4], independent information on any of these parameters will make the determination and localization of the object more accurate.…”

“…The deeper a fluorescent lesion is located in the tissue, the greater the change in intensity between different fluorescence wavelengths. In our previous study [11], the depth of a fluorescent layer was determined with both Monte Carlo simulations and experiments on a liquid phantom, by studying the fluorescence emitted in the 800−900 nm range in reflection geometry. The depth of a fluorescent layer could be determined with an accuracy of 0.6 mm down to a depth of 10 mm.…”

Prior information in fluorescence molecular tomography based on multispectral fluorescence emission

“…It has previously been reported that the intensity ratio of two fluorescence spectral bands is dependent on the fluorescent inclusion position 7 .…”

Time-of-flight laser spectroscopy in biomedical diagnostics

“…The multispectral information provided in fluorescence measurements of lesions located at a certain depth in tissue would, in addition to the diagnostic information that there exist a lesion, also provide depth information useful for reconstruction of fluorescent inclusions in tissue [15,16]. This is one possible concept to improving the robustness and accuracy of the fluorescence tomography reconstructions.…”