Quantitative interpretations of Visible-NIR reflectance spectra of blood

5-ALA induced PpIX fluorescence spectroscopy in neurosurgery: a review

The review begins with an overview of the fundamental principles/physics underlying light, fluorescence, and other light-matter interactions in biological tissues. It then focuses on 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX) fluorescence spectroscopy methods used in neurosurgery (e.g., intensity, time-resolved) and in so doing, describe their specific features (e.g., hardware requirements, main processing methods) as well as their strengths and limitations. Finally, we review current clinical applications and future directions of 5-ALA-induced protoporphyrin IX (PpIX) fluorescence spectroscopy in neurosurgery.

Non-invasive Reflectance Spectroscopy for Normal and Cancerous Skin Cells Refractive Index Determination: An In Vitro Study

BACKGROUND AND OBJECTIVE

Optical reflectance spectroscopy is a non-invasive technique for optical characterization of biological samples. Any alteration in a cell from normal or carcinogenic causes will change its refractive index. The aim of this study is to develop a computerized program for extraction of a refractive index of normal and cancerous skin cell lines, including melanoma, fibroblast, and adipose cells, using visible near-infrared reflectance spectra and the Kramers-Kronig (K-K) relations.

MATERIALS AND METHOD

A fiber optic reflectance spectrometer in visible near-infrared wavelength was used for spectrum acquisition in an in vitro study. Human skin cell lines for melanoma (A375), fibroblast, and adipose sample were cultured for optical spectroscopy. Following data acquisition, an analytical MATLAB code was developed to run the K-K relations. The program was validated for three biological samples using an Abbe refractometer.

RESULTS

The validation error (below 5%) and determination of changes in the refractive index of melanoma, normal fibroblasts, and adipose skin cells was carried out at wavelengths of 450-950 nm. The refractive index of melanoma was 1.59270 ± 0.0550 at 450 nm, the minimum amount of 1.27790 ± 0.0550 to 1.321 ± 0.0550 at 620 nm, and rose sharply to 1.44321 ± 0.0550 at 935 nm. The respective results for fibroblast and adipose tissue cells were 1.33282 ± 0.0134 and 1.28345 ± 0.0163 at 450 nm with an increasing trend to 1.30494 ± 0.0135 and 1.26716 ± 0.0163 at 935 nm.

CONCLUSION

Refractive index characteristics show potential for cancer screening and diagnosis. The results show that optical spectroscopy is a promising, non-invasive tool for assessment of the refractive index of living biological cells in in vitro settings. Tracking changes in the refractive index allows screening of normal and abnormal cells for probable alterations in a non-invasive label-free method. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Complex refractive index spectra of whole blood and aqueous solutions of anticoagulants, analgesics and buffers in the mid-infrared

Mid-infrared (MIR) spectroscopy is a powerful tool for characterising the vibrations of molecular bonds and is therefore ideal for label-free detection of chemical species. Recent research into thin-film deposition and etching techniques for mid-infrared materials shows potential for realising miniaturised bedside biosensors for clinical diagnostics exploiting MIR spectroscopy, to replace laboratory based-techniques. However, lack of refractive index information for commonly encountered biological media and analytes hampers optimisation of biosensor performance for maximum sensitivity, especially for devices exploiting evanescent spectroscopy. Here we present refractive index data for human whole blood and several aqueous solutions of general interest to the clinical community: anticoagulants, analgesics and buffers. The refractive indices are generally dominated by the water content of each sample and the whole blood spectra exhibit additional strong features due to protein content. Furthermore, we present a generalised method for extracting complex refractive indices of aqueous solutions in the mid-infrared region using conventional attenuated total reflection Fourier transform spectroscopy (ATR-FTIR) without the need for collimated or polarised incident light, as is required for existing methods.

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

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.

A novel first principles approach for the estimation of the sieve factor of blood samples

Light may traverse a turbid material, such as blood, without encountering any of its pigment containing structures, a phenomenon known as sieve effect. This phenomenon may result in a decrease in the amount of light absorbed by the material. Accordingly, the corresponding sieve factor needs to be accounted for in optical investigations aimed at the derivation of blood biophysical properties from light transmittance measurements. The existing procedures used for its estimation either lack the flexibility required for practical applications or are based on general formulas that incorporate other light and matter interaction phenomena such as detour (scattering) effects. In this paper, a ray optics framework is proposed to estimate the sieve factor for blood samples. It employs a first principles approach to account for the distribution, orientation and shape of the cells that contain hemoglobin, the essential (oxygen-carrying) pigment found in human blood. Within this framework, ray-casting techniques are used to determine the probability that light can traverse a blood sample without encountering any of these cells. The predictive capabilities of the proposed framework are demonstrated through a series of in silico experiments. Its effectiveness is further illustrated by visualizations depicting the different blood parameterizations considered in the simulations.

New method for the detection of micro-organisms in blood: application of quantitative interpretation model to aerobic blood cultures

The physical and chemical changes occurring in blood that has been inoculated into a blood culture bottle can be used as means to detect the presence of microorganisms in blood cultures. These changes include primarily the conversion of oxy- to deoxyhemoglobin within the red blood cells (RBCs) and changes in the cell number densities. These changes in the physical and chemical properties of blood can be readily detected using spectrophometric methods thus enabling the continuous monitoring of blood culture vials to provide quantitative information on the growth behavior of the microorganisms present. This paper reports on the application of spectrophotometric information obtained from diffuse reflectance measurements of aerobic blood cultures to detect microbial growth and compares the results to those obtained using the standard blood culture system.