Properties Of Various Biological Tissues Research Articles

Microwave Frequency Analysis of Dielectric Properties in Biological Tissues: Insights into Dielectric Constant, Conductivity, and Resistivity at 9.4 GHz

This study investigates the dielectric properties of various biological tissues at microwave frequencies, specifically focusing on their dielectric constant, conductivity, resistivity, and loss tangent. Using methods such as Von Hippel’s and Yadav Gandhi’s techniques, the dielectric characteristics of heart, liver, brain, and muscle of chicken tissues were analysed at 9.4 GHz. It is found that tissues with higher water content exhibit greater dielectric constants and conductivities, while those with higher solid content, like liver, display higher resistivity. It has also been observed that tissues with lower dielectric constants and conductivities are those with greater absorption indices, which are typically associated with increased energy dissipation as heat. An increasing amount of energy dissipation may result from tissues with higher absorption rates being less effective at transferring microwave energy, as suggested by this inverse connection, which also emphasizes the complexity of electromagnetic wave interaction within tissues. This work provides critical insights into the interaction of electromagnetic waves with biological tissues, which is essential for applications in medical diagnostics, therapeutic technologies, and electromagnetic exposure safety standards.

CT-based assessment of the stress state of dog spines

An urgent task of biomechanics is the study of the influence of external loads on the human musculoskeletal system, one of the main elements of which is the vertebral column. In this case, research involves considering the spine as a complex system consisting of vertebrae and the intervertebral discs that articulate them. At the moment, there are many works devoted to determining the causes of various abnormalities in the tissue fibers between the vertebrae, which leads to the development of discopathy. Dogs are the most susceptible to such changes due to their genetic predisposition. Thus, in this work, studies were carried out on the cervical spine of three animals: yorkshire terrier, russian toy terrier and half–breed. During the work, numerical modeling of samples was performed using computed tomography data. Computational experiments were carried out using the finite element method and made it possible to determine the stress state taking into account the distribution of the mechanical properties of the material. The tests corresponded to longitudinal compression of the samples. Based on the results obtained, the compressive stress field was determined, the reliability of the values was assessed according to the energy error, and the von Mises stress intensity and the rigidity of the resulting structure were calculated. Analysis of the results showed that the highest stress values are achieved between the vertebrae of the border sections of the cervical spine. On average, a sample of the Yorkshire Terrier breed is predisposed to experience greater stress compared to the results of other dogs in the experimental group. The highest rigidity corresponded to half–breed: twice as much as the average value for dwarf breeds. The distribution of the energy error showed that the areas with the highest values correspond to finite elements at the boundary between different phases of the medium. Thus, the results obtained in the framework of the study make it possible to establish the nature of the distribution of the stress state in the intervertebral discs, as well as to identify the strength indicators of the vertebral columns, taking into account the mechanical properties of various biological tissues.

Four-dimensional (4D) phase velocity optical coherence elastography in heterogeneous materials and biological tissue.

The variations of mechanical properties in soft tissues are biomarkers used for clinical diagnosis and disease monitoring. Optical coherence elastography (OCE) has been extensively developed to investigate mechanical properties of various biological tissues. These methods are generally based on time-domain data and measure the time-of-flight of the localized shear wave propagations to estimate the group velocity. However, there is considerable information that can be obtained from examining the mechanical properties such as wave propagation velocities at different frequencies. Here we propose a method to evaluate phase velocity, wave velocity at various frequencies, in four-dimensional space (x, y, z, f), called 4D-OCE phase velocity. The method enables local estimates of the phase velocity of propagating mechanical waves in a medium. We acquired and analyzed data with this method from a homogeneous reference phantom, a heterogeneous phantom material with four different excitation cases, and ex vivo porcine kidney tissue. The 3D-OCE group velocity was also estimated to compare with 4D-OCE phase velocity. Moreover, we performed numerical simulation of wave propagations to illustrate the boundary behavior of the propagating waves. The proposed 4D-OCE phase velocity is capable of providing further information in OCE to better understand the spatial variation of mechanical properties of various biological tissues with respect to frequency.

Measuring optical properties of human liver between 400 and 1000 nm

Laser diagnostics and treatment procedures are commonly performed for visible and near-IR wavelengths. The knowledge of the wavelength dependences for the optical properties of various biological tissues in this spectral range is useful for clinical applications. Since the optical properties of human liver have been previously known only for near-IR wavelengths, the aim is to estimate their wavelength dependences between 400 and 1000 nm. Using spectral measurements from liver samples in this range, we determine their optical properties with the inverse adding-doubling method. The obtained results indicate the presence of bile, oxyhaemoglobin and deoxyhaemoglobin in human liver. The combination of these biological components results in strong absorption for wavelengths between 400 and 600 nm, with peaks at unusual wavelengths. For wavelengths above 600 nm, the wavelength dependences for all optical properties present the typical behavior, but strong and shifted absorption observed for wavelengths below 600 nm has been previously unknown and can be useful for clinical procedures with lasers working in this range.

Stable gelatin-based phantom materials with tunable x-ray attenuation properties and 3D printability for x-ray imaging

We report a novel method for developing gelatin-based phantom materials for transmission x-ray imaging with high stability at room temperature and tunable x-ray attenuation properties. This is achieved by efficiently cross-linking gelatin in a glycerin solution with only 10% water by volume and systematically decreasing their x-ray attenuation coefficients by doping with microbubbles that are originally designed to be used as lightweight additives for paints and crack fillers. For demonstration, we mimic breast glandular and adipose tissues by using such gelatin materials and also study the feasibility of 3D printing them based on the extrusion-based technique. Results from x-ray spectroscopy (15–45 keV) show the materials to have stable x-ray attenuation properties of glandular and adipose tissues over a period of two months. Micro-CT analysis of independently prepared samples shows the materials to be uniform and easy to reproduce with minimum variability in attenuation values. These materials can be used to 3D print realistic phantoms that mimic x-ray properties of various biological tissues.

Optical properties measurement of highly diffusive tissue phantoms for biomedical applications

Extensive research in biomedical optics essentially requires the determination of optical properties of various biological tissues. Quantitative characterization of biological tissues in terms of optical properties is achieved with an integrating sphere. However, samples having significantly higher scattering and absorption coefficients such as malignant tissues potentially reduce the signal-to-noise ratio (SNR) and the accuracy of an integrating sphere. We describe the design, implementation and characterization of a modified sample holder (path length of up to 1 mm) for an integration sphere. Experiments conducted with various phantoms reveal significant improvement of the SNR for a wide range of optical properties. The alternative approach opens up potential applications in the measurement of optical properties of highly diffusive biological samples. For 20% intralipid µa = 0.112 ± 0.046 cm−1 and µs = 392.299 ± 10.090 cm−1 at 632.8 nm. For 1.0% Indian ink µa = 9.808 ± 0.490 cm−1 and µs = 1.258 ± 0.063 cm−1 at the same wavelength. The system shows good repeatability and reproducibility within a 4.9% error.

Characterization of Scattering Effects in Phantom Samples using Single and Two-Photon Excitation Light Sheet Microscopy

Scattering in thick biological samples plays a relevant role in imaging degradation and reduction of signal to noise ratio and contrast. Even if there are existing techniques that allow imaging of very thick samples, they can suffer from aberrations and distortions related to scattering properties of the sample. Recently, the capability of coupling light sheet techniques with Two Photon Excitation(TPE) (1,2,3) provided a powerful tool for deep imaging of biological samples. This has been proved to be a promising trend in thick-imaging microscopy, because it combines the advantages of light sheet techniques with the increased penetration depth intrinsic of TPE. For this reason, in this work a detailed characterization of the effects induced by scattering on the excitation profile of a light sheet based microscope is provided. In particular, different phantom samples, with different scattering coefficients mimicking the optical properties of various biological tissues, are used. Experiments were performed to investigate the shape distortions of the excitation intensity distribution provided by the light sheet, both in single and in two-photon excitation. This aspect represents a crucial point, since the effective light sheet intensity distribution is strictly related to the optical sectioning capability and image quality of the system. Results show that the light sheet intensity distribution is less affected by light-sample interactions and the shape is preserved in the case of TPE in comparison with single photon excitation regime. Furthermore, contrast measurements has been performed using fluorescent beads embedded in different scattering samples in both excitation modes. These experiments showed again the better performances of TPE compared to single photon excitation.(1) Cella Zanacchi et al. Proc. of SPIE, vol.7903 (2011)(2) Planchon et al. Nature Methods 8, 417-423, (2011)(3) Truong et al. Nature Methods 8,757-760, (2011)

OPTICAL PROPERTIES OF SKIN, SUBCUTANEOUS, AND MUSCLE TISSUES: A REVIEW

The development of optical methods in modern medicine in the areas of diagnostics, therapy, and surgery has stimulated the investigation of optical properties of various biological tissues, since the efficacy of laser treatment depends on the photon propagation and fluence rate distribution within irradiated tissues. In this work, an overview of published absorption and scattering properties of skin and subcutaneous tissues measured in wide wavelength range is presented. Basic principles of measurements of the tissue optical properties and techniques used for processing of the measured data are outlined.

An Auxiliary Differential Equation Method for FDTD Modeling of Wave Propagation in Cole-Cole Dispersive Media

A method for modeling time-domain wave propagation in dispersive Cole-Cole media is presented. The Cole-Cole model can describe the frequency dependence of the electromagnetic properties of various biological tissues with great accuracy over a wide frequency range and plays a key role in microwave medical imaging. The main difficulty in the time-domain modeling of Cole-Cole media is the appearance of fractional time derivatives. In the proposed method a Pade approximation is employed resulting in auxiliary differential equations of integer order. A finite-difference time-domain method is developed to solve the differential equations obtained. The comparison of analytical and calculated relative complex permittivity values over wideband frequency domain proves the validity of the method.

Tissue impedance: a historical overview

Over the past 150 years the study of the electrical properties of various biological tissues has been undertaken by researchers from a wide variety of scientific backgrounds. This has, unfortunately, led to the existing range of confusing and misunderstood terminology/concepts. Some of the most important are presented and explained.

Determination of reduced scattering and absorption coefficients by a single charge-coupled-device array measurement, part II: measurements on biological tissues

The optical properties of various biological tissues have been investigated by the measurement of the maximum intensity <i>M</i> and the full width at half maximum ( FWHM) of the intensity profile of a scattered light beam. These two quantities have turned out to be highly discriminating parameters for the different tissues under scrutiny: muscle, liver, adipose, and gray and white brain matter. The inverse problem, i.e., the computation of the absorption and reduced scattering coefficients from <i>M</i> and FWHM, has been solved in the domains where Monte Carlo simulations have yielded possible values for <i>M</i> and FWHM. The accuracy is typically 5% for the reduced scattering coefficient and 20% for the absorption coefficient. This method is judged to be reasonably good for application to biological materials: it allows a good overall characterization of tissues. A scanning technique has been developed to evaluate the variability of the optical parameters at different locations in biological tissues. Whereas Monte Carlo simulation works well for tissues such as muscle or liver, it appears to be inappropriate in describing the optical properties of adipose and brain tissues. The reasons are still unclear and are probably related to the particular structural properties of such tissues.