Biological Tissue Phantoms Research Articles

Synchronous heating of two local regions of a biological tissue phantom using automated targeting of phase conjugate ultrasound beams

Synchronous heating of two local regions of an absorbing medium by phase conjugate ultrasound beams focused on them has been experimentally demonstrated. A polymeric biological tissue phantom with two small air cavities scattering sound has been used as the medium irradiated by a 5-MHz “probe” ultrasound beam. The scattered field is incident on a parametric device for ultrasonic wave phase conjugation. The conjugate and amplified field is self-adaptive focused on scatterers and heats the medium owing to the absorption of the ultrasonic energy. In this case, these regions are heated by about 5°C in 70 s. Only an insignificant increase in the temperature owing to the heat conduction effect is observed in the remaining volume of the phantom. The implemented effect can be used in medical applications of phase conjugate ultrasound beams.

Solution of Radiative Transfer Equation using Discrete Transfer Method for two-dimensional participating medium

The present work reports the development and application of a simplified numerical approach for solving the transient Radiative Transfer Equation (RTE) using Discrete Transfer Method (DTM) in two-dimensional coordinate system. The numerical formulation of the proposed scheme is discussed in detail and its application in the context of understanding light propagation phenomenon in laser-irradiated numerically simulated biological tissue phantoms has been demonstrated. The developed mathematical model has first been benchmarked against the results published in the literature for the same operating conditions. Thereafter, the results of a detailed parametric study have been presented to investigate the effects of optical properties of the biological phantom on the intensity distribution within the two-dimensional tissue phantom, net transmittance and reflectance, etc. The effect of anisotropy of the tissue medium has also been studied to understand the phenomenon of light propagation within the body of the sample. Based on the results of the study, it has been inferred that the developed numerical methodology for two-dimensional Discrete Transfer Method successfully predicts the physics of the phenomena of light propagation within the tissue phantom and compares well with the other conventionally employed numerical models for solving the Radiative Transfer Equation.

Sensitivity of coded aperture Raman spectroscopy to analytes beneath turbid biological tissue and tissue-simulating phantoms.

Traditional slit-based spectrometers have an inherent trade-off between spectral resolution and throughput that can limit their performance when measuring diffuse sources such as light returned from highly scattering biological tissue. Recently, multielement fiber bundles have been used to effectively measure diffuse sources, e.g., in the field of spatially offset Raman spectroscopy, by remapping the source (or some region of the source) into a slit shape for delivery to the spectrometer. Another approach is to change the nature of the instrument by using a coded entrance aperture, which can increase throughput without sacrificing spectral resolution.In this study, two spectrometers, one with a slit-based entrance aperture and the other with a coded aperture, were used to measure Raman spectra of an analyte as a function of the optical properties of an overlying scattering medium. Power-law fits reveal that the analyte signal is approximately proportional to the number of transport mean free paths of the scattering medium raised to a power of -0.47 (coded aperture instrument) or -1.09 (slit-based instrument). These results demonstrate that the attenuation in signal intensity is more pronounced for the slit-based instrument and highlight the scattering regimes where coded aperture instruments can provide an advantage over traditional slit-based spectrometers.

Numerical investigation of thermal response of laser irradiated tissue phantoms embedded with optical inhomogeneities

The present work is concerned with the numerical investigation of thermal response of biological tissue phantoms during laser-based photo-thermal therapy for destroying cancerous/abnormal cells with minimal damage to the surrounding normal cells. The synthetically generated two-dimensional tissue phantoms have been irradiated with a short pulse laser and light-tissue interaction has been modeled using transient radiative transport equation (RTE). Discrete ordinate method (DOM) has been employed to solve the complete transient radiative transport equation. Biological tissue phantoms with and without the presence of single and/or multiple inhomogeneities have been considered. Optical inhomogeneities of different nature and varying contrast levels (ratio of optical properties of the inhomogeneity and that of the background medium) have been considered to numerically simulate the abnormal cells embedded in an otherwise homogenous medium. In order to determine the two-dimensional temperature distribution inside the tissue medium, the RTE has been coupled with Penne’s bio-heat transfer equation which has been solved using finite volume method. The RTE-based numerical code developed in the present work has been benchmarked against the results published in the literature for the same operating parameters. Thereafter, the effects of varying contrast levels of the embedded inhomogeneity, nature of the inhomogeneity (absorbing/scattering), laser pulse amplitude, etc. on the resultant temperature distribution inside the tissue phantoms have been reported. Based on the primary findings of the study, safe laser parameters (e.g. amplitude of laser pulse) for a given set of absorption and scattering coefficients have been reported.

Anisotropic conductivity tensor imaging in MREIT using directional diffusion rate of water molecules

Magnetic resonance electrical impedance tomography (MREIT) is an emerging method to visualize electrical conductivity and/or current density images at low frequencies (below 1 KHz). Injecting currents into an imaging object, one component of the induced magnetic flux density is acquired using an MRI scanner for isotropic conductivity image reconstructions. Diffusion tensor MRI (DT-MRI) measures the intrinsic three-dimensional diffusion property of water molecules within a tissue. It characterizes the anisotropic water transport by the effective diffusion tensor. Combining the DT-MRI and MREIT techniques, we propose a novel direct method for absolute conductivity tensor image reconstructions based on a linear relationship between the water diffusion tensor and the electrical conductivity tensor. We first recover the projected current density, which is the best approximation of the internal current density one can obtain from the measured single component of the induced magnetic flux density. This enables us to estimate a scale factor between the diffusion tensor and the conductivity tensor. Combining these values at all pixels with the acquired diffusion tensor map, we can quantitatively recover the anisotropic conductivity tensor map. From numerical simulations and experimental verifications using a biological tissue phantom, we found that the new method overcomes the limitations of each method and successfully reconstructs both the direction and magnitude of the conductivity tensor for both the anisotropic and isotropic regions.

Needle Steering in Biological Tissue using Ultrasound-based Online Curvature Estimation.

Percutaneous needle insertions are commonly performed for diagnostic and therapeutic purposes. Accurate placement of the needle tip is important to the success of many needle procedures. The current needle steering systems depend on needle-tissue-specific data, such as maximum curvature, that is unavailable prior to an interventional procedure. In this paper, we present a novel three-dimensional adaptive steering method for flexible bevel-tipped needles that is capable of performing accurate tip placement without previous knowledge about needle curvature. The method steers the needle by integrating duty-cycled needle steering, online curvature estimation, ultrasound-based needle tracking, and sampling-based motion planning. The needle curvature estimation is performed online and used to adapt the path and duty cycling. We evaluated the method using experiments in a homogenous gelatin phantom, a two-layer gelatin phantom, and a biological tissue phantom composed of a gelatin layer and in vitro chicken tissue. In all experiments, virtual obstacles and targets move in order to represent the disturbances that might occur due to tissue deformation and physiological processes. The average targeting error using our new adaptive method is 40% lower than using the conventional non-adaptive duty-cycled needle steering method.

Experimental validations of in vivo human musculoskeletal tissue conductivity images using MR-based electrical impedance tomography.

Magnetic resonance (MR)-based electrical impedance tomography (MREIT) is a widely used imaging technique that provides high-resolution conductivity images at DC or below the 1 kHz frequency range. Using an MR scanner, this technique injects imaging currents into the human body and measures induced internal magnetic flux density data. By applying the recent progress of MREIT techniques, such as chemical shift artifact correction, multi-echo pulse sequence, and improved reconstruction algorithm, we can successfully reconstruct conductivity images of the human body. Meanwhile, numerous studies reported that the electrical conductivity of human tissues could be inferred from in vitro or ex vivo measurements of different species. However, in vivo tissues may differ from in vitro and/or ex vivo state due to the complicated tissue responses in living organs. In this study, we performed in vivo MREIT imaging of a human lower extremity and compared the resulting conductivity images with ex vivo biological tissue phantom images. The human conductivity images showed unique contrast between two different types of bones, muscles, subcutaneous adipose tissues, and conductive body fluids. Except for muscles and adipose tissues, the human conductivity images showed a similar pattern when compared with phantom results due to the anisotropic characteristic of muscle and the high conductive fluids in the adipose tissue.

Optical properties of mouse biotissues and their optical phantoms

Based on spectrophotometric measurements in the range of 700–1100 nm performed with the use of an integrating sphere, we have obtained absorption and scattering spectra of internal organs of mouse, as well as of aqueous solutions of India ink and Lipofundin, which are basic model media for creating optical phantoms of biological tissues. To retrieve the spectra of optical characteristics, we have used original formulas that relate the parameters of the medium with measured spectrophotometric characteristics and that are constructed based on classical analytical models of propagation of light in turbid media. As a result of comparison of spectra of biotissues and model media, we have developed a mixture of Lipofundin and India ink serving as mouse optical phantoms for problems of optical medical diagnostics.

Grooved conjugation ferrite element for ultrasound heating of a biological tissue phantom

A possibility of using a parametric ultrasound phase conjugation system with a grooved ferrite element for hyperthermal heating of a biological tissue phantom is experimentally investigated. The grooved surface of the ferrite element improves the quality of phase conjugation. With focused conjugate beams, this is supposed to lead to an increase in the ultrasound intensity and accordingly to more effective heating of the medium due to ultrasound absorption. The results of the investigation prove this supposition: ultrasound heating by 8.0°C in about 80 s is obtained for a sample with an inserted thermocouple placed between a focused piezoelectric transducer, which radiated a test wave with a frequency of 5.0MHz, and a system for phase conjugation and amplification of ultrasound.

Manufacture of Hydrogel-Based Phantoms of Biological Tissues and Research into Their Optical Properties

The goal of this work was to develop solid phantoms of biological tissues based on simple materials, such as water, gelatin, milk, and ink. Homogeneous and horizontal-layered phantoms are used in education and research purposes. The research into the phantoms manufactured using the technology suggested in this work was carried out using the Oxiplex TS spectrophotometer (ISS, Inc., USA), which monitors absolute optical parameters of the sample of interest (extinction coefficient and transport scattering coefficient).

Classification of Biological Spectrum Based on Principal Component Cluster Analysis

Spectrums of 17 biological tissue phantoms were measured using the fiber-optic spectrometer. Then, the spectrum was preprocessed by multiplicative scatter correction method to devoice the spectrum. Afterwards the features of the spectrum were extracted via principal component analysis. Ultimately, we applied cluster analysis for the spectral features. The results showed that the accumulated credibility of the first 12 spectral principal components was 99.86% for the spectrum after preprocessing; indicating that this spectrum feature extraction might be done in the case of losing no key information. And the results showed that the 17 biological tissue phantoms can be divided into four main categories according their optical features.

1706 採血技術訓練用ハプティツクデバイスの試作(OS2-2 ロボティクス・メカトロニクスII,OS2 ロボティクス・メカトロニクス)

Blood sampling is frequently performed in clinical inspections and blood donations. There are 2 ways to improve the skill of needle puncture: clinical experience and simulation training by using a human phantom. However trainee cannot practice positively in clinical site due to the subjects' burden. In addition, simulation training would not give difference of reaction force of venipuncturing between the subjects. In this study, a haptic device for novel venipuncture simulation training was prototyped. The device of human interface would reproduce various reaction forces of puncturing by using haptic technology. In addition, reaction force of puncturing against a biological tissue phantom has been measured with the device and represented as a restricted numerical model. As the results, the characteristic reaction force of puncturing was reproduced with the restricted numerical model. For the next step, viscoelastic characteristics of the tissue should be integrated to the numerical model to achieve further realistic reaction of needle puncture.

Effect of surface roughness on measurement of light distribution in intralipid suspension

Light distribution in the biological tissue phantom intralipid suspension with different interface roughness was measured for quantitative understanding of surface roughness effect. The results show that the surface roughness strongly affects light distribution inside the approximately semi-infinite biological tissue phantom. The phantom surface possesses a certain degree roughness and the effect of the surface roughness on measurement results of light distribution in tissue is substantial, so the measurement of light distribution in biological tissue needs to take surface roughness into account.

Polarimetry group theory analysis in biological tissue phantoms by Mueller coherency matrix

The characterization of biological tissues by optical techniques provides several advantages over other techniques. Optical techniques enable to perform high resolution and contrast imaging, in a non-invasive way and with no-contact. Biological tissues are turbid media that strongly scatter light. The ultrastructure of some tissues makes them present a certain degree of anisotropy. Both scattering and anisotropy affect light polarization. Some pathologies alter these characteristics of the tissue. As a consequence polarized light can be used to extract additional information and achieve a better diagnosis. In this work, Group Theory is applied to analyse the polarization behavior of several samples. Firstly, the Mueller matrix for each sample is measured. Then, the Mueller Coherency matrix is obtained by means of the SU(4)–O + (6) homomorphism. Finally, the target decomposition theorem is applied by analyzing the eigenvalues and eigenvectors, and subsequently the different polarimetric effects are separated. In this way, the contrast of tissue imaging can be increased. This analysis is applied to biological tissue phantoms, which consisted on glucose suspensions of polystyrene spheres with different scatterer concentrations. Their behaviour can be modeled by means of single or multiple scattering depending on the concentration, either in the Rayleigh or Mie regimes. The same procedure could be used in a wide range of applications, like the study of cancerous cells that grow without control in cell cultures, or erythrocytes monitoring in anemia. The technique also has a great potential to be applied in Polarization Sensitive Optical Coherence Tomography (PS-OCT).

Coaxial ultrasound-modulated optical spectroscopy in scattering medium

Ultrasound-modulated optical spectroscopy within a coaxial system capable of attaining submillimeter spatial resolution has been developed to investigate scattering media spectroscopic properties at depths of several centimeters. By using stroboscopic illumination methods, a broad spectral bandwidth pulsed laser and a focused ultrasound pulse simultaneously irradiated a biological tissue phantom containing oxyhemoglobin and deoxyhemoglobin absorbers. The ultrasound-modulated optical spectroscopic images were synchronously acquired by a fiber optic spectrometer scanning in two dimensions. We have obtained the wavelength dependent ultrasound-modulated optical signals produced by the ultrasound interactions changing the distribution of scattered light through several different mechanisms and evaluated the proposed system.

Analysis of recoverable current from one component of magnetic flux density in MREIT and MRCDI

Magnetic resonance current density imaging (MRCDI) provides a current density image by measuring the induced magnetic flux density within the subject with a magnetic resonance imaging (MRI) scanner. Magnetic resonance electrical impedance tomography (MREIT) has been focused on extracting some useful information of the current density and conductivity distribution in the subject Ω using measured Bz, one component of the magnetic flux density B. In this paper, we analyze the map from current density vector field J to one component of magnetic flux density Bz without any assumption on the conductivity. The map provides an orthogonal decomposition J = JP + JN of the current J where JN belongs to the null space of the map . We explicitly describe the projected current density JP from measured Bz. Based on the decomposition, we prove that Bz data due to one injection current guarantee a unique determination of the isotropic conductivity under assumptions that the current is two-dimensional and the conductivity value on the surface is known. For a two-dimensional dominating current case, the projected current density JP provides a good approximation of the true current J without accumulating noise effects. Numerical simulations show that JP from measured Bz is quite similar to the target J. Biological tissue phantom experiments compare JP with the reconstructed J via the reconstructed isotropic conductivity using the harmonic Bz algorithm.

Evaluation of the magneto-optical effect in biological tissue models using optical coherence tomography

For the first time to our knowledge, an experimental evaluation of the Faraday effect-induced polarization rotation in a biological tissue phantom is reported. The rotation of the polarization plane produced in the optical beam propagating through an Intralipid solution was evaluated using polarization-sensitive optical coherence tomography (PS-OCT), and the experimental results closely matched the theoretical values. The angle of rotation is proportional to the traversed path length along the magnetic field and can potentially be used to estimate the actual penetration depth.

Investigation of oscillations of biological tissues and their phantoms with model defects

The potential to create a remote, contactless, diagnostic method for biological tissues or materials with properties similar to those of biological tissues, so-called phantoms, is studied. The method is based on measurement of local oscillations of the surface of material under study under the action of acoustic and ultrasonic waves. The application of a laser-scanning vibrometer provides a means for visualization oscillations of a biological tissue phantom with model defects in the form of air bubbles, regions with higher density, and laminations, and allows determination of the positions of these defects.

Simulations of a spatially resolved reflectometry signal from a highly scattering three-layer medium applied to the problem of glucose sensing in human skin

The possibility of using spatially resolved reflectometry (SRR) at a wavelength of 820 nm to detect changes in the optical properties of a highly scattering layered random medium simulating a biological tissue caused by changes in the glucose level is analysed. Model signals from a three-layer biological tissue phantom consisting of two skin layers and a blood layer located between them are obtained by the Monte-Carlo method. It was assumed that variations in the glucose level induce variations in the optical parameters of the blood layer and the bottom skin layer. To analyse the trajectories of photons forming the SRR signal, their scattering maps are obtained. The ratio of the photon path in layers sensitive to the glucose level to the total path in the medium was used as a parameter characterising these trajectories. The relative change in the reflected signal caused by a change in the glucose concentration is analysed depending on the distance between a probe radiation source and a detector. It is shown that the maximum relative change in the signal (about 7%) takes place for the source — detector separation in the range from 0.3 to 0.5 mm depending on the model parameters.

Harmonic Decomposition in PDE-Based Denoising Technique for Magnetic Resonance Electrical Impedance Tomography

Recent progress in magnetic resonance electrical impedance tomography (MREIT) research via simulation and biological tissue phantom studies have shown that conductivity images with higher spatial resolution and accuracy are achievable. In order to apply MREIT to human subjects, one of the important remaining problems to be solved is to reduce the amount of the injection current such that it meets the electrical safety regulations. However, by limiting the amount of the injection current according to the safety regulations, the measured MR data such as the z-component of magnetic flux density Bz in MREIT tend to have low SNR and get usually degraded in their accuracy due to the nonideal data acquisition system of an MR scanner. Furthermore, numerical differentiations of the measured Bz required by the conductivity image reconstruction algorithms tend to further deteriorate the quality and accuracy of the reconstructed conductivity images. In this paper, we propose a denoising technique that incorporates a harmonic decomposition. The harmonic decomposition is especially suitable for MREIT due to the physical characteristics of Bz. It effectively removes systematic and random noises, while preserving important key features in the MR measurements, so that improved conductivity images can be obtained. The simulation and experimental results demonstrate that the proposed denoising technique is effective for MREIT, producing significantly improved quality of conductivity images. The denoising technique will be a valuable tool in MREIT to reduce the amount of the injection current when it is combined with an improved MREIT pulse sequence.