Optical Parameters Of Biological Tissues Research Articles

Enhanced model iteration algorithm with graph neural network for diffuse optical tomography.

Diffuse optical tomography (DOT) employs near-infrared light to reveal the optical parameters of biological tissues. Due to the strong scattering of photons in tissues and the limited surface measurements, DOT reconstruction is severely ill-posed. The Levenberg-Marquardt (LM) is a popular iteration method for DOT, however, it is computationally expensive and its reconstruction accuracy needs improvement. In this study, we propose a neural model based iteration algorithm which combines the graph neural network with Levenberg-Marquardt (GNNLM), which utilizes a graph data structure to represent the finite element mesh. In order to verify the performance of the graph neural network, two GNN variants, namely graph convolutional neural network (GCN) and graph attention neural network (GAT) were employed in the experiments. The results showed that GCNLM performs best in the simulation experiments within the training data distribution. However, GATLM exhibits superior performance in the simulation experiments outside the training data distribution and real experiments with breast-like phantoms. It demonstrated that the GATLM trained with simulation data can generalize well to situations outside the training data distribution without transfer training. This offers the possibility to provide more accurate absorption coefficient distributions in clinical practice.

Skin cancer detection using effective optical parameters and the classification and regression tree algorithm: A novel framework

Early detection of skin cancer matters because diagnosis, prognosis and treatment plan differ for each skin cancer type at their stages. Medical imaging taking the advantages of the non-invasive and non-ionizing polarized light is emerging as a tool for the development of screening and diagnotic tests. In this work, we proposed a novel framework to classify human melanoma and nonmelanoma skin cancer using the Classification and Regression Tree algorithm (CART). The samples were prepared from twenty-four non-melanoma skin cancer samples (consisting of twelve squamous cell carcinoma and twelve basal cell carcinoma samples); and three melanoma skin cancer samples. We calculated ten optical parameters from anisotropic biological tissues, namely the LB orientation angle (α), the LB phase retardance (β), the CB optical rotation angle (γ), the LD orientation angle (θd), the linear dichroism (D), the circular dichroism (R), the degrees of linear depolarization (e1 and e2), the degree of circular depolarization (e3), and the depolarization index (∆) using Stokes-Mueller matrix formalism. All effective optical parameters of biological tissue were then input into the CART classifier as predictors. The model yielded an accuracy of 92.6%, which is desirable for any robust and interpretable classification model. The results showed that for biological tissue samples, linear polarization properties dominate over circular ones due to the cellular microstructural composition of tissue, especially under anomalous growth as seen in skin cancer. This novel framework can potentially assist physicians in making timely and well-informed medical decisions.

An optical parameter imaging system with profile information fusion

There is a shared problem in current optical imaging technologies of how to obtain the optical parameters of biological tissues with complex profiles. In this work, an imaging system for obtaining the optical parameters of biological tissues with complex profile was presented. Firstly, Fourier transformation profilometry was used for obtaining the profile information of biological tissues, and then the difference of incident light intensity at different positions on biological tissue surface was corrected with the laws of illumination, and lastly the optical parameters of biological tissues were achieved with the spatial frequency domain imaging technique. Experimental results indicated the proposed imaging system could obtain the profile information and the optical parameters of biological tissues accurately and quickly. For the slab phantoms with height variation less than 30 mm and angle variation less than 40º, the maximum relative errors of the profile uncorrected optical parameters were 46.27% and 72.18%, while the maximum relative errors of the profile corrected optical parameters were 6.89% and 10.26%. Imaging experiments of a face-like phantom and a human's prefrontal lobe were performed respectively, which demonstrated the proposed imaging system possesses clinical application value for the achievement of the optical parameters of biological tissues with complex profiles. Besides, the proposed profile corrected method can be used to combine with the current optical imaging technologies to reduce the influence of the profile information of biological tissues on imaging quality.

Estimating optical parameters of biological tissues with photon-counting micro-CT.

Wavelength-dependent absorption and scattering properties determine the fluorescence photon transport in biological tissues and image resolution of optical molecular tomography. Currently, these parameters are computed from optically measured data. For small animal imaging, estimation of optical parameters is a large-scale optimization problem, which is highly ill-posed. In this paper, we propose a new, to the best of our knowledge, approach to estimate optical parameters of biological tissues with photon-counting micro-computed tomography (micro-CT). From photon-counting x-ray data, multi-energy micro-CT images can be reconstructed to perform multi-organ segmentation and material decomposition in terms of tissue constituents. The concentration and characteristics of major tissue constituents can be utilized to calculate the optical absorption and scattering coefficients of the involved tissues. In our study, we perform numerical simulation, phantom experiments, and in vivo animal studies to calculate the optical parameters using our proposed approach. The results show that our approach can estimate optical parameters of tissues with a relative error of <10%, accurately mapping the optical parameter distributions in a small animal.

Use of Digital Image Correlation Method to Measure Bio-Tissue Deformation

Traditionally, strain gauge, extensometer, and reflection tracking markers have been used to measure the deformation of materials under loading. However, the anisotropy and inhomogeneity of most biological materials restricted the accessibility of the real strain field. Compared to the video extensometer, digital image correlation has the advantage of providing full-field displacement as well as strain information. In this study, a digital image correlation method (DIC) measurement system was employed for chicken breast bio-tissue deformation measurement. To increase the contrast for better correlation, a mixture of ground black pepper and white sesame was sprayed on the surface of samples. The first step was to correct the distorted image caused by the lens using the inverse distorted calibration method and then the influence of subset size and correlation criteria, sum of squared differences (SSD), and zero-normalized sum of squared differences (ZNSSD) were investigated experimentally for accurate measurement. Test results of the sample was translated along the horizontal direction from 0 mm to 3 mm, with an increment of 0.1 mm and the measurement result was compared, and the displacement set on the translation stage. The result shows that the error is less than 3%, and accurate measurement can be achieved with proper surface preparation, subset size, correlation criterion, and image correction. Detailed examination of the strain values show that the strain εx is proportional to the displacement of crosshead, but the strain εy indicates the viscoelastic behavior of tested bio-tissue. In addition, the tested bio-tissue’s linear birefringence extracted by a Mueller matrix polarimetry is for comparison and is in good agreement. As noted above, the integration of the optical parameter measurement system and the digital image correlation method is proposed in this paper to analyze the relationship between the strain changes and optical parameters of biological tissue, and thus the relative optic-stress coefficient can be significantly characterized if Young’s modulus of biological tissue is known.

Effect of purification, dehydration, and coagulation processes on the optical parameters of biological tissues

In this study, the effects of purification, dehydration, and coagulation processes on the absorption and reduced scattering coefficients of chicken liver tissues have been investigated by using a single integrating sphere system. The purification process performed on the tissue samples to remove blood residue has been found to cause a slight change in the optical parameters. Although the dehydration process brings about an increase in the absorption coefficient due to the water loss, no direct relationship has been observed between the reduced scattering coefficient and the dehydration level of the tissue. In addition, it has been observed that there was a relatively small increase in the absorption coefficient and a significant increase in the reduced scattering coefficient after the coagulation process. Therefore, it can be said that the optical penetration depth decreased significantly after dehydration and coagulation processes unlike blood purification. Moreover, fluence rate distributions inside the fresh, blood purified, dehydrated, and coagulated tissue models have been investigated by using the Monte Carlo modeling of photon transport in multilayered tissues simulation code.

Accurate Monte Carlo simulation of frequency-domain optical coherence tomography.

Optical coherence tomography (OCT) relies on optical interferometry to provide noninvasive imaging of living tissues. In addition to its 3D imaging capacity for medical diagnosis, its potential use for recovering optical parameters of biological tissues for biological and pathological analyses has also been explored by researchers, as pathological changes in tissue alter the microstructure of the tissue and therefore its optical properties. We aim to develop a new approach to OCT data analysis by estimating optical properties of tissues from OCT scans, which are invisible in the scans. This is an inverse problem. Solving an inverse problem involves a forward modeling step to simulate OCT scans of the tissues with hypothesized optical parameter values and an inverse step to estimate the real optical par1meters values by matching the simulated scans to real scans. In this paper, we present a Monte Carlo (MC)–based approach for simulating the frequency‐domain OCT. We incorporated a focusing Gaussian light beam rather than an infinitesimally thin light beam for accurate simulations. A new and more accurate photon detection scheme is also implemented. We compare our MC model to an analytical OCT model based on the extended Huygens‐Fresnel principle (EHF) to demonstrate the consistency between the two models. We show that the two models are in good agreement for tissues with high scattering and high anisotropy factors.

Optical parameters detection with multi-frequency modulation based on NIR DPDW

For measuring the optical parameters of biological tissues accurately and rapidly, this study built an optical parameters measurement system based on near-infrared (NIR) Diffuse Photon Density Waves (DPDW) technology using frequency sweep modulation. The transmitted swept optical amplitude and phase can be nonlinearly fitted according to the physical diffusive approximation equation then to obtain the absorption coefficient and reduced scattering coefficient of the tissue phantoms, respectively. The experimental results of the 20 Intralipid solutions show that the average absolute errors of μa and μs′ are 0.066 cm−1 and 0.716 cm−1, respectively, and the correlation coefficients between the measured and true values were 0.965 and 0.989, respectively. The experimental results of the 3 solid phantoms show that the average absolute errors of μa and μs′ are 0.1140 cm−1 and 0.0023 cm−1, respectively. Therefore, the DPDW technology with frequency sweep modulation can detect the optical parameters of the tissue phantoms accurately and quickly, and it would be optimized for tissue tomography imaging and blood components noninvasively detection in vivo.

Light transport in homogeneous tissue with m-dependent anisotropic scattering I: Case's singular eigenfunctions solution and Chandrasekhar polynomials.

This paper is the first of two deriving the analytical solutions for light transport in infinite homogeneous tissue with an azimuth-dependent (m-dependent) anisotropic scattering kernel by two approaches, Case’s singular eigenfuncions expansion and Fourier transform, as well as proving the consistence of the two solutions. In this paper, Case’s method was applied and extended to the general m-dependent anisotropic scattering case. The explicit Green’s function of radiance distributions, which was regarded as the comparative standard for the equivalent solution via Fourier transform and inversion in our second accompanying paper, was expanded into a complete set of the discrete and continuous eigenfunctions. Considering that the two kinds of m-dependent Chandrasekhar orthogonal polynomials that play vital roles in these analytical solutions are very sensitive to the typical optical parameters of biological tissue as well as the degrees or orders, four numerical evaluation methods were benchmarked to find the stable, reliable and feasible numerical evaluation methods in high degrees and high orders.

Estimation of optical parameters and fluence rate distribution in biological tissues via a single integrating sphere optical setup

Optical parameters of biological tissues play an important role in tissue characterization, including the absorption and scattering coefficients and the anisotropy factor. These parameters are high wavelength dependent and give functional information of the tissue such as total haemoglobin content, tissue oxygenation and water fraction. However, estimating the optical properties of any tissue requires measurements of diffuse reflectance, diffuse transmittance and collimated transmittance. Experimentally, these measurements can be obtained either by integrating spheres techniques or with methods that based on distant detectors array. In this work, total diffuse reflectance and transmittance of native and dry chicken breast skin were measured in vitro via a single integrating sphere optical setup at 660 and 808nm laser irradiation. Then, a combination between Kubellka-Munk model and Bouguer-Beer-Lambert law was used to estimate the three optical parameters from the collected data. The calculated optical parameters were then introduced to the diffusion equation to compute the optical fluence rate distribution at the boundary of the sample using the finite element method. The Monte-Carlo simulation method was implemented for validation showing absolute error of 0.002 and 0.009 at 660, 808nm respectively for normal skin, 0.0013, and 0.0078 in dry skin.

Research on Measurement System of Biological Tissue Parameters Based on Optical Coherence Tomography

In order to measure the optical parameters of biological tissue accurately and non-invasive, the measurement system based on optical coherence tomography was analyzed and designed from two aspects of hardware and software. The refractive index was calibrated by standard refractive index solutions, experiments were preformed to obtain refractive index of tissue samples and scattering coefficient of IntralipidTMsolution with different concentrations. Results show that the experimental values of refractive index agree with the standard values roughly and scattering coefficient linear relate with concentration in IntralipidTMsolution. The measurement system designed in our experiment is accurate and reliable, simple and feasible.

Technique for measuring laser radiation intensity in biological tissues

AbstractLaser methods, such as laser-induced fluorescence diagnostics, photodynamic therapy (PDT), and hyperthermia, are finding increasing use in medicine. Irradiation can be performed both with and without contact on the tissue surface. In the case of contact irradiation, especially when laser radiation is introduced into biological tissue through an optical fiber, it is important to know the processes taking place at the irradiation fiber end. These processes affect diffusely reflected radiation which returns to the fiber. By analyzing backscattered radiation, we can evaluate the quality of the radiation procedure and the state of the fiber end. The objectives of this study were to develop a method and device for measuring backscattered radiation power and using this method, to determine the time and temperature ranges realized in PDT and hyperthermia.Light propagation is discussed in bent optical fibers. A technique is proposed for measuring laser radiation intensity in the optical fiber bend. Based on this technique, a system was developed for monitoring the laser radiation dose absorbed in biological tissues. We studied samples of bovine liver, muscle and brain tissues. Experiments were performed using a 675 nm, 100–2200 mW continuous wave semi-conductor laser. Laser radiation was delivered through a silica/polymer optical fiber. Data concerning the temperature and transmitted radiation intensity was acquired.Modeling of the light propagation in a bent optical fiber showed that the sensitivity of the method depends on the position of the photodetectors, but is independent of the loop number of the optical fiber. The results of experiments are presented using different types of biological tissues. We obtained the experimental dependencies of backward and transmitted radiation intensities and the temperature of the tissue surface in the irradiated region on the irradiation time measured with a flat-end fiber. The characteristic ranges of tissue heating caused by irradiation were determined for use in clinical practice.The optical parameters of biological tissues change with increasing temperature. This affects the intensity of transmitting radiation and diffuse radiation entering the fiber. The change in the backscattered radiation intensity greatly depend on the temperature of the irradiated area. The control of the irradiation of biological objects provides an efficient delivery of laser radiation to biological tissues and increases hyperthermia and PDT treatment effect.

Sensitivity of delta-P1 approximation model to the reduced scattering parameter

For spatial-resolved diffuse reflectance, the sensitivity expression to the reduced scattering parameter μs' is derived and numerically analyzed in the two-point-source delta-P1 approximation of transport theory, and the influences of the scattering parameter μs' on the delta-P1 approximation reflectance, hybrid diffuse approximation reflectance, and diffusion approximation reflectance are also compared. The results show that the optical properties of biological tissue can be better described by the delta-P1 approxiamate model in relatively high scattering and absorbing medium for a short souce-detector separation; the optimum probe spacing ρopt is obtained and approximately equal to 2.7-4 transport mean free path for the reduced albedo a'&gt;0.83, at which a variable reduced scattering coefficient has the smallest effect on the measurement of optical absorption in the turbid medium and ρopt reduces with the scattering parameter μs' increasing. The study is of great significance for optimizing the probe geometry and measuring the optical parameters of biological tissues.

Research on Non-Invasive Measurement of Optical Parameters of the Tissues by Support Vector Machine

To measure optical parameters of biological tissues, support vector machine was adopted. The diffuse reflected light on the surface of the biological tissue corresponding to optical characteristic parameters of human tissue were obtained by Monte Carlo simulation. The nonlinear relationship model had been established between the diffuse reflected light and the optical parameters. The optical parameters were obtained by the support vector machine and the diffuse reflected light. That were compared with the given values of the same sample, and they were coherent basically. It was shown that support vector machine used to measure optical parameters had a high accuracy.

Retrieving the optical parameters of biological tissues using diffuse reflectance spectroscopy and Fourier series expansions I theory and application

The determination of optical parameters of biological tissues is essential for the application of optical techniques in the diagnosis and treatment of diseases. Diffuse Reflection Spectroscopy is a widely used technique to analyze the optical characteristics of biological tissues. In this paper we show that by using diffuse reflectance spectra and a new mathematical model we can retrieve the optical parameters by applying an adjustment of the data with nonlinear least squares. In our model we represent the spectra using a Fourier series expansion finding mathematical relations between the polynomial coefficients and the optical parameters. In this first paper we use spectra generated by the Monte Carlo Multilayered Technique to simulate the propagation of photons in turbid media. Using these spectra we determine the behavior of Fourier series coefficients when varying the optical parameters of the medium under study. With this procedure we find mathematical relations between Fourier series coefficients and optical parameters. Finally, the results show that our method can retrieve the optical parameters of biological tissues with accuracy that is adequate for medical applications.

Research on the Photography Measurement of the Optical Parameters of the Vegetable Tissues

To measure the optical parameters of biological tissue, the laser imaging system of the diffusing reflection and the transmission measurements based on CCD was designed. The absorption coefficient (μa) and the reduced scattering coefficient (μ's) of the biological tissue simulating liquid (Intralipid-20% diluents) were derived from nonlinear regression of the diffusion equation with spatially resolved steady-state diffuse reflectance which was measured by CCD. At the same time, the reduced scattering coefficient (μ's) of the biological tissue simulating liquid (Intralipid-20% diluents) was also derived from linear regression of the Beer-Lambert equation with transmission light intensity of the biological tissue simulating liquid (Intralipid-20% diluents) which was measured by CCD for the different titer, which is used as the calibration of the non-invasively method. The optical parameters of the same sample measured by CCD diffusing reflection and transmission measurements were compared. The results of the two methods were approximately consistent. Furthermore, the optical parameters of Eggplant and Murphy were measured by CCD diffusing reflection measurements. So the technique of laser scattering imaging analysis is useful for measuring the optical properties of the vegetable tissues.

Optical characteristics of cartilage at a wavelength of 1560 nm and their dynamic behavior under laser heating conditions

A double-integrating-sphere system was used to measure the diffuse transmittance, diffuse reflectance, and collimated transmittance of cartilage and polyacrylamide hydrogel samples as a function of temperature under 1560-nm laser heating conditions. The dynamic behavior of the absorption and scattering coefficients and scattering anisotropy of the biomaterials was calculated by the inverse Monte Carlo method. The absorption coefficient of the cartilage and hydrogel samples proved to be linear in temperature. Raising the temperature of the cartilage samples to 80°C caused their absorption coefficient to decrease by some 25%. The temperature-induced change of the absorption spectrum of the interstitial water was found to be responsible for the clarification of the cartilage tissue observed to occur under 1560-nm laser heating conditions. The temperature field produced in the tissue by the laser energy deposited therein was calculated using a bioheat transfer equation with temperature-dependent parameters. The calculation results demonstrated that the temperature-induced changes of the optical parameters of biological tissues should be taken into account to make their 1560-nm laser treatment effective and safe.

Multiple scattering effects on optical characterization of biological tissue using spectroscopic scattering parameters

Spectroscopic optical parameters measured from biological tissue have been used to estimate the size distribution and density of subcellular particles. The calculations are usually performed under an independent scattering assumption, where scattering of a particle ensemble is assumed to be the linear summation of individual particle scattering. We use rigorous numerical solutions of Maxwell's equations to investigate the validity of this independent scattering assumption and find that interparticle scattering can have significant contributions to the optical parameters of biological tissue. In addition, we find that the reduced scattering coefficient is less affected by multiple scattering compared to the scattering coefficient and thus in general produces better results for the inverse calculation. These observations may be useful in improving the characterization of biological tissues based on their spectroscopic light scattering measurements.

Non-invasive imaging of optical parameters of biological tissues.

The normalised back-scattered intensity (NBI) profiles at various locations on the forearms of ten human subjects were obtained by moving the multi-probe of a laser reflectometer. The statistical analysis of the NBI data showed that the variation in the NBI was significantly higher at the ulnar region compared with that at other regions. For determination of the scattering (mus) and absorption (mus) coefficients and the anisotropy parameter g at each location on the forearm, these profiles were matched with the NBI profiles simulated by a Monte Carlo procedure (chi(2)0.99). For the reconstruction of images of variation of these parameters, the averaged values of mua, mus, and g at all locations on the forearms of the subjects were determined. The absorption coefficient had a minimum (1.92 cm(-1)) and maximum (2.21cm(-1)) at the wrist and the lateral region of the forearm, respectively. The scattering coefficient had a maximum (194 cm(-1)) at the medial side and near the elbow, and a minimum (186 cm(-1)) at the lateral side of the forearm. Similar changes in the anisotropy parameter were also observed. By interpolation of the data of each parameter on a 100 x 100 image matrix and after median filtering, colour-coded images of the variation in the optical parameters were constructed. These images could be useful for diagnostic and therapeutic applications of lasers.

The effect of preparation technique on the optical parameters of biological tissue

The absorption coefficient μa, the scattering coefficient μs, and the scattering anisotropy factor g of porcine liver were studied in vitro using the integrating sphere technique and inverse Monte Carlo simulation in the wavelength range 450 to 700 nm. A reference preparation technique was developed using a dermatome providing specimens of 200 to 800 μm thickness without pre-freezing the tissue. The optical parameters as measured applying the reference preparation were compared to those measured after cryo-homogenisation. We found significant deviations of the scattering coefficient and the anisotropy factor which were compensated when the reduced scattering coefficient μs ′ was calculated. We also compared the effects of freezing reference specimens at -20 °C and at 77 K without homogenisation. For both freezing protocols noticeable deviations were found in all three optical parameters as well as in μs ′. The impact of tissue storage at 4 °C was measured in the range 4 to 48 h post mortem and showed a clear reduction of μa and a significant increase of μs even after 24 h of storage. Short-time storage of the specimens in saline solution reduced all three optical parameters significantly. In conclusion, the tissue preparation must be controlled in order to provide in vitro optical parameters that sufficiently mimic the in vivo situation.