Blood interference in fluorescence spectrum – Experiment, analysis and comparison with intra- operative measurements on brain tumor (original) (raw)

A literature review and novel theoretical approach on the optical properties of whole blood

Lasers in Medical Science, 2014

Optical property measurements on blood are influenced by a large variety of factors of both physical and methodological origin. The aim of this review is to list these factors of influence and to provide the reader with optical property spectra (250-2,500 nm) for whole blood that can be used in the practice of biomedical optics (tabulated in the appendix). Hereto, we perform a critical examination and selection of the available optical property spectra of blood in literature, from which we compile average spectra for the absorption coefficient (μ a ), scattering coefficient (μ s ) and scattering anisotropy (g). From this, we calculate the reduced scattering coefficient (μ s ′) and the effective attenuation coefficient (μ eff ). In the compilation of μ a and μ s , we incorporate the influences of absorption flattening and dependent scattering (i.e. spatial correlations between positions of red blood cells), respectively. For the influence of dependent scattering on μ s , we present a novel, theoretically derived formula that can be used for practical rescaling of μ s to other haematocrits. Since the measurement of the scattering properties of blood has been proven to be challenging, we apply an alternative, theoretical approach to calculate spectra for μ s and g. Hereto, we combine Kramers-Kronig analysis with analytical scattering theory, extended with Percus-Yevick structure factors that take into account the effect of dependent scattering in whole blood. We argue that our calculated spectra may provide a better estimation for μ s and g (and hence μ s ′ and μ eff ) than the compiled spectra from literature for wavelengths between 300 and 600 nm.

Fluorescent strip-lights as a source of error in tissue reflectance spectroscopy

Medical Engineering & Physics, 1999

Tissue reflectance spectroscopy is a widely used technique for measuring the blood content of the skin. Fluorescent strip-lighting of a type in widespread use (Osram L36 W/23 Gelbweiss-white) is a potential source of misleading artefacts in tissue reflectance spectroscopy. The fluorescent light signal has successive peaks and troughs in the 520-580 nm range which closely emulate the inverse of the reflected signal of white light modulated by blood. The presence of fluorescent light in the reflected signal cancels some of the blood signature. Conversely, the presence of fluorescent light in the white reference augments the true blood reflected signal. The marked similarity of the resultant artefact blood spectrum to the true blood spectrum is a hazard, as the presence of the artefact may go undetected.

Determining the optical properties of blood using He-Ne laser and double integrating sphere set-up

2019

The behaviour of light interaction with biological tissue is determined by micro-optical parameters: refractive index (n), absorption coefficient (µ a), scattering coefficient (µ s), and anisotropy (g). The goal of this study is to measure the optical properties of normal whole blood using He-Ne laser (wavelength 632.8 nm). The refractive index is measured using the traveller microscope. The integrating sphere method is used to measure the macro-optical parameters: total diffusive reflectance, transmittance, and collimated transmittance at wavelength 632.8 nm. The macro-optical parameters are fed to Inverse Adding Doubling (IAD) theoretical technique, to estimate the micro-optical parameters (µ s , µ a , g). An alternative practical method is used to measure the g value based on utilising the goniometric table. The study reveals that the refractive index (n) equals 1.395±0.0547, absorption coefficient (µ a) equals 2.37 mm-1 , scattering coefficient (µ s) equals 55.69 mm-1 , and anisotropy (g) equals 0.82. In conclusion, these findings approved, in general, the applicability of the suggested experimental set up. The set up depend on using three devices: the integrating sphere method to estimate (µ s , µ a , g), traveller microscope (n) and goniometer (g).

Non-contact spectroscopic determination of large blood volume fractions in turbid media

Biomedical Optics Express, 2011

We report on a non-contact method to quantitatively determine blood volume fractions in turbid media by reflectance spectroscopy in the VIS/NIR spectral wavelength range. This method will be used for spectral analysis of tissue with large absorption coefficients and assist in age determination of bruises and bloodstains. First, a phantom set was constructed to determine the effective photon path length as a function of μ a and μ s ′ on phantoms with an albedo range: 0.02-0.99. Based on these measurements, an empirical model of the path length was established for phantoms with an albedo > 0.1. Next, this model was validated on whole blood mimicking phantoms, to determine the blood volume fractions ρ = 0.12-0.84 within the phantoms (r = 0.993; error < 10%). Finally, the model was proved applicable on cotton fabric phantoms.

Hemoglobin parameters from diffuse reflectance data

Journal of Biomedical Optics, 2014

Tissue vasculature is altered when cancer develops. Consequently, noninvasive methods of monitoring blood vessel size, density, and oxygenation would be valuable. Simple spectroscopy employing fiber optic probes to measure backscattering can potentially determine hemoglobin parameters. However, heterogeneity of blood distribution, the dependence of the tissue-volume-sampled on scattering and absorption, and the potential compression of tissue all hinder the accurate determination of hemoglobin parameters. We address each of these issues. A simple derivation of a correction factor for the absorption coefficient, μ a , is presented. This correction factor depends not only on the vessel size, as others have shown, but also on the density of blood vessels. Monte Carlo simulations were used to determine the dependence of an effective pathlength of light through tissue which is parameterized as a ninth-order polynomial function of μ a. The hemoglobin bands of backscattering spectra of cervical tissue are fit using these expressions to obtain effective blood vessel size and density, tissue hemoglobin concentration, and oxygenation. Hemoglobin concentration and vessel density were found to depend on the pressure applied during in vivo acquisition of the spectra. It is also shown that determined vessel size depends on the blood hemoglobin concentration used.

FluoRa - a System for Combined Fluorescence and Microcirculation Measurements in Brain Tumor Surgery

2021 43rd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), 2021

In brain tumor surgery it is difficult to distinguish the marginal zone with the naked eye. Fluorescence techniques can help identifying tumor tissue in the zone during resection and biopsy procedures. In this paper a novel system for combined real-time measurements of PpIX-fluorescence, microcirculation and tissue grey-whiteness is presented and experimentally evaluated. The system consists of a fluorescence hardware with a sensitive CCD spectrometer for PpIX peak detection, a laser Doppler system, optical probes, and a LabView software. System evaluation was done on static fluorescing material, human skin, and brain tumor tissue. The static material indicates reproducibility, the skin measurements exemplify simultaneous fluorescence and microcirculation measurement in real-time, and the tumor tissue showed PpIX peaks. These decreased over time, as expected, due to photo bleaching. In addition, the system was prepared for clinical use and thus laser-and electrical safety issues were considered. In summary, a system for multiparameter measurements during neurosurgery was successfully evaluated in an experimental environment. As a next step the system will be applied in clinical brain tumor biopsies and resections.

Optical transmission of blood: effect of erythrocyte aggregation

IEEE Transactions on Biomedical Engineering, 2003

The influence of red blood cell (RBC) aggregation on transparency of blood in the red-near infrared spectral range is investigated. We argue that for relatively thin blood layers the light diffraction on aggregates becomes the dominant phenomenon. The nature of pulsatile changes of blood transparency is explained by pulsations of RBC aggregate size. For another case of over-systolic vessel occlusion the following time evolution of blood transparency strongly depends on light wavelength. This dependence may serve as a basis for an alternative approach to noninvasive blood tests: occlusion spectroscopy. Theoretical results well correspond to both in vivo and in vitro measurements reproducing pulsatile blood flow and long occlusion as well.

Optical quantification of hemolysis, icterus, and lipemia in human serum

2014

In order to increase the automation and efficiency for a national reference laboratory, the ability to quantify interferences like Hemolysis, Icterus, and Lipemia in serum samples is investigated. The system is intended as a screening step prior to clinical analysis of medical samples to prevent false results caused by the interferences. The system is based on selective absorption of transmitted light by the interferences that cause loss of light at specific wavelengths. The absorption spectra of interferences are analyzed to identify the appropriate wavelengths, resulting in a mathematical formulation between the absorbance and concentrations. An absorption wavelength is selected so that the transmitted power of light through a tube with the sample significantly decreased due to the presence of condition of interest, while the reference wavelength is selected so that the transmitted light varies mostly due to the presence of tube material and labels and does not vary due to the presence of interference. A computational model is formulated using a commercial software package, ANSYS FLUENT, in order to understand the absorption and scattering effects, the thermal effects of higher power irradiation on the biological samples, as well as to determine the radiant power of transmitted light through the sample for different power levels. The Discrete Ordinates Method is used to model the radiation through a participating medium. The temperature distribution and spectral power of transmitted radiation are determined for water in a tube for different wavelengths used in the current system.