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5. Diagram of fiber optic system for CW R(r) measurements applied in Paper III. (1) Probe head with source and detector optical fibers. (2) Handheld box with photo diodes and amplifier electronics. (3) Stationary box containing a digital signal processing board and diode lasers. (4) External temperature controller. (5) Laptop PC to analyze, display, and store the acquired R(r) data.
Source publication
The main topic of this thesis is real-time quantification of relevant
chromophores and light scattering elements in biological media. The
presented methods and instrumentation are based on continuous wave
(steady- state) optical measurements of (a)spatially- resolved diffuse
reflectance from bulk media and (b)combined spatially-resolved and
goniome...
Citations
... In the visible spectrum, melanin and haemoglobin have most effect on absorption. Oxyhaemoglobin has peaks at 418 nm, 542 nm and 577 nm, while deoxyhaemoglobin has peak absorption at 430 nm and 555 nm [41,42]. Melanin absorption peaks at 335 nm but this reduces steadily with increasing wavelength. ...
... The absorption of skin chromophores in the wavelength range 300 nm -1500 nm with respect to their skin volume fraction (Reprinted with permission from Ref.[42],Fig. 2.4). ...
Imaging non-invasively into the human body is currently limited by cost (MRI and CT scan), image resolution (ultrasound), exposure to ionising radiation (CT scan and X-ray), and the requirement for exogenous contrast agents (CT scan and PET scan). Optical imaging has the potential to overcome all these issues but is currently limited by imaging depth due to the scattering and absorption properties of human tissue. Skin is the first barrier encountered by light when imaging non-invasively, and therefore a clear understanding of the way that light interacts with skin is required for progress on optical medical imaging to be made. Here we present a thorough review of the optical properties of human skin measured in-vivo and compare these to the previously collated ex-vivo measurements. Both in-vivo and ex-vivo published data show high inter- and intra-publication variability making definitive answers regarding optical properties at given wavelengths challenging. Overall, variability is highest for ex-vivo absorption measurements with differences of up to 77-fold compared with 9.6-fold for the in-vivo absorption case. The impact of this variation on optical penetration depth and transport mean free path is presented and potential causes of these inconsistencies are discussed. We propose a set of experimental controls and reporting requirements for future measurements. We conclude that a robust in-vivo dataset, measured across a broad spectrum of wavelengths, is required for the development of future technologies that significantly increase the depth of optical imaging.
... Biomedical optics has evolved in medical area as a new interdisciplinary field covering a wide range of therapeutic and diagnostic techniques [1]. One main advantage of optical techniques is the use of non-harmful radiation (excepted when UV radiation is used). ...
... In particular optical biopsy is a non or minimally invasive spectroscopic analysis of biological tissue without cutting or removed tissues. In vitro diffuse spectroscopy requires relatively small samples and provides fast analysis [1]. Diffuse reflectance spectroscopy analyses and characterizes biological tissues in order to study and determine their optical properties [3]. ...
A multispectral imaging system enabling biological tissue identifying
and differentiation is presented. The measurement of β(λ)
spectral radiance factor cube for four tissue types (beef muscle, pork
muscle, turkey muscle and beef liver) present in the same scene was
carried out. Three methods for tissue identification are proposed and
their relevance evaluated. The first method correlates the scene
spectral radiance factor with tissue database characteristics. This
method gives detection rates ranging from 63.5 % to 85 %. The second
method correlates the scene spectral radiance factor derivatives with a
database of tissue β(λ) derivatives. This method is more
efficient than the first one because it gives detection rates ranging
from 79 % to 89 % with over-detection rates smaller than 0.2 %. The
third method uses the biological tissue spectral signature. It enhances
contrast in order to afford tissue differentiation and identification.
... Biomedical optics has evolved in medical area as a new interdisciplinary field covering a wide range of therapeutic and diagnostic techniques [1]. One main advantage of optical techniques is the use of non-harmful radiation (excepted when UV radiation is used). ...
... In particular optical biopsy is a non or minimally invasive spectroscopic analysis of biological tissue without cutting or removed tissues. In vitro diffuse spectroscopy requires relatively small samples and provides fast analysis [1]. Diffuse reflectance spectroscopy analyses and characterizes biological tissues in order to study and determine their optical properties [3]. ...
In order to build biological tissues spectral characteristics database
to be used in a multispectral imaging system a tissues optical
characterization bench is developed and validated. Several biological
tissue types have been characterized in vitro and ex vivo with our
device such as beef, turkey and pork muscle and beef liver.
Multispectral images obtained have been analyzed in order to study the
dispersion of biological tissues spectral luminance factor. Tissue
internal structure inhomogeneity was identified as a phenomenon
contributing to the dispersion of spectral luminance factor. This
dispersion of spectral luminance factor could be a characteristic of the
tissue. A method based on envelope technique has been developed to
identify and differentiate biological tissues in the same scene. This
method applied to pork tissues containing muscle and fat gives detection
rates of 59% for pork muscle and 14% for pork fat.
... During PDT treatment a photosensitiser (PS) is administered to the patient. Figure 1: Absorption features of different parameters in skin [1]. ...
Science real and relevant: 2nd CSIR Biennial Conference, CSIR International Convention Centre Pretoria, 17&18 November 2008 For effective laser treatment it is very important to provide the correct dose at the required treatment depth. In South Africa we have a richness of ethnic groups contributing to a large variety in skin tones. Effective laser treatment of skin requires calculations that take into account the skin tone. Results from the modelling work presented show that darker skin can absorb as much as 3 times more laser light in the epidermis than very light skins
A method of noninvasive determination of optical and microphysical parameters of skin is developed. Errors in the retrieval of these parameters in terms of their general variance are estimated. It is shown that simultaneous interpretation of the results of spectral and spatial measurements of diffuse reflection from skin enables us to significantly increase the accuracy of retrieval of these parameters in comparison with cases of their separate interpretation.
We have developed a method for online determination of biophysical parameters of mucous membranes (MMs) of a human body (transport scattering coefficient, scattering anisotropy factor, haemoglobin concentration, degrees of blood oxygenation, average diameter of capillaries with blood) from measurements of spectral and spatial characteristics of diffuse reflection. The method is based on regression relationships between linearly independent components of the measured light signals and the unknown parameters of MMs, obtained by simulation of the radiation transfer in the MM under conditions of its general variability. We have proposed and justified the calibration-free fibre-optic method for determining the concentration of haemoglobin in MMs by measuring the light signals diffusely reflected by the tissue in four spectral regions at two different distances from the illumination spot. We have selected the optimal wavelengths of optical probing for the implementation of the method.
We have developed a simple and efficient method for determining the hemoglobin concentration in biological tissues, based on spatially resolved measurements of the diffuse reflectance of the tissue at λ = 524, 578, and 662 nm (or 773 nm) using multiple regressions between the measured parameters and the hemoglobin concentrations. The method takes into account the presence in the blood of the major hemoglobin derivatives (oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin, and methemoglobin) and eliminates the effect of the parameters of the top layer of the biological tissue (for example, the epidermis of the skin) and the bulk scattering coefficient of the tissue on the measurement results. Based on numerical Monte Carlo experiments, we have estimated the uncertainties in determining the hemoglobin concentration in skin tissues when its structural and biochemical parameters are all variable.
Sensitivity analyses are valuable tools for identifying important model parameters, testing the model conceptualization, and improving the model structure. They help to apply the model efficiently and to enable a focussed planning of future research and field measurement. Two different methods were used for sensitivity analyses of the complex process-oriented model TACD (tracer aided catchment model, distributed) that was applied to the meso-scale Brugga basin (40km2) and the sub-basin St Wilhelmer Talbach (15.2km2). Five simulations periods were investigated: two summer events, two snow melt induced events and one summer low flow period. The model was applied using 400 different parameter sets, which were generated by Monte Carlo simulations using latin hypercube sampling. The regional sensitivity analysis (RSA) allowed determining the most significant parameters for the complete simulation periods using a graphical method. The results of the regression-based sensitivity analysis were more detailed and complex. The temporal variability of the simulation sensitivity could be observed continuously and the significance of the parameters could be determined in a quantitative way. A dependency of the simulation sensitivity on initial- and boundary conditions and the temporal and spatial variability of the sensitivity to some model parameters was revealed by the regression-based sensitivity analysis. Thus, the difficulty of transferring the results to different time periods or model applications in other catchments became obvious. The analysis of the temporal course of the simulation sensitivity to parameter values in conjunction with simulated and measured additional data sets (precipitation, temperature, reservoir volumes etc.) gave further insight into the internal model behaviour and demonstrated the plausibility of the model structure and process conceptionalizations.
In any laser skin treatment, the optical properties (absorption and scattering coefficients) are important parameters. The melanin content of skin influences the absorption of light in the skin. The spread in the values of the absorption coefficients for the South African skin phototypes are not known. A diffuse reflectance probe consisting of a ring of six light delivery fibers and a central collecting fiber was used to measure the diffused reflected light from the arms of 30 volunteers with skin phototypes I-V (on the Fitzpatrick scale). The absorption coefficient was calculated from these measurements. This real-time in vivo technique was used to determine the absorption coefficient of sun-exposed and -protected areas on the arm. The range of typical absorption coefficients for the South African skin phototypes is reported. The values for the darker South African skin types were much higher than was previously reported for darker skin phototypes. In the analysis, the contributions of the eumelanin and pheomelanin were separated, which resulted in improved curve fitting for volunteers of southern Asian ethnicity without compromising the other groups.
