We introduced several approaches of terahertz wavefront phase retrieval from intensity measured in a volumetric grid. Our developments include several experimental solutions for the registration of multiple intensity distributions spaced along the optical axis for two types of terahertz sources, namely Gunn diode with frequency multiplication chain and quantum cascade laser. We implemented several measurement modes: (i) sequential raster scanning by single Schottky diode with two lock-in amplifiers, complimentary tuned to different sensitivities for high dynamic range recording; (ii) step by step registration on matrix photodetectors, with averaging over several images for every measurement plane; (iii) continuous measurement during the displacement of the motorized translation stage. The high dynamic range data acquisition allowed us to successfully implement single-beam terahertz surface profilometry in the reflection, while the on-the-go recording ensures the shortest measurement times. In addition, we experimentally appraised two matrix detectors (INO and I2S) and applied several phase retrieval algorithms which proved their effectiveness in various experimental conditions, namely for the intensity registration in various diffraction zones and axial measurement plane allocations.
Terahertz (THz) radiation in the frequency range 0.1 - 10 THz began to be used for the analysis of artwork in 2006. Terahertz images of paintings require computer processing in order to optimize the process of detecting defects and their visualization. In this work, an algorithm for solving this problem is proposed in relation to the terahertz analysis of paintings. A program is written in Python that searches, group and highlight defects in an image. To work with images, the methods of the OpenCV library is used, designed to solve computer vision problems. They are used to binarize images and search the defect contours on them, as well as to isolate defects when visualizing the results. The grouping of defects is carried out by the method of agglomerative hierarchical clustering. Scientific analysis of the materials used in art items allows to determine the period in which they were created, how they were preserved over the centuries and how they were restored. As part of the study, in this work, a 3D-model of the crystal structure of the red pigment was created. For this, the terahertz spectrum of the pigment was modeled by the density functional method. To experimentally study the optical characteristics of the pigment, measurements are carried out on a TeraView-4000 instrument in transmission mode. The pigment is measured in powder and tableted form.
Significance. One of the modern trends in medical diagnostics is based on metabolomics, an approach allowing determination of metabolites which can be the specific features of disease. High-resolution gas spectroscopy allows investigation of the gas metabolite content of samples of biological origin. We present the elaboration of a method of studying diabetic and non-diabetic biological samples, prepared as pellets, by terahertz (THz) high-resolution spectroscopy.
Aim: The main idea of the work is studying the content of thermal decomposition gas products of diabetic and non-diabetic dried blood plasma and kidney tissues for revealing the set of gas-markers that characterized the diabetes by the THz high-resolution spectroscopy method.
Approach: We present an approach to study the diabetic and non-diabetic blood plasma (human and rats) and kidney tissues (rats), using high-resolution spectroscopy based on the non-stationary effect of THz frequency range. The methods of preparing the blood and kidney tissue samples as pellets and of vaporizing the samples were developed.
Results: The measurements of rotational absorption spectra of vapors at heating the pellets prepared from blood and kidney tissue were carried out in 118 to 178 GHz frequency range. The absorption lines appearing in spectra of the sample vapors were detected and identified. The molecular contents of thermal decomposition products differed for non-diabetic and diabetic samples; e.g., main marker is acetone appearing in the diabetic blood (human and rats) and in the diabetic kidney tissue.
Conclusions: Our paper illustrates the potential ability for determining the metabolite content of biological samples for diagnostics and prognosis of diseases for clinical medicine.
Significance: The creation of fundamentally new approaches to storing various biomaterial and estimation parameters, without irreversible loss of any biomaterial, is a pressing challenge in clinical practice. We present a technology for studying samples of diabetic and non-diabetic human blood plasma in the terahertz (THz) frequency range.
Aim: The main idea of our study is to propose a method for diagnosis and storing the samples of diabetic and non-diabetic human blood plasma and to study these samples in the THz frequency range.
Approach: Venous blood from patients with type 2 diabetes mellitus and conditionally healthy participants was collected. To limit the impact of water in the THz spectra, lyophilization of liquid samples and their pressing into a pellet were performed. These pellets were analyzed using THz time-domain spectroscopy. The differentiation between the THz spectral data was conducted using multivariate statistics to classify non-diabetic and diabetic groups’ spectra.
Results: We present the density-normalized absorption and refractive index for diabetic and non-diabetic pellets in the range 0.2 to 1.4 THz. Over the entire THz frequency range, the normalized index of refraction of diabetes pellets exceeds this indicator of non-diabetic pellet on average by 9% to 12%. The non-diabetic and diabetic groups of the THz spectra are spatially separated in the principal component space.
Conclusion: We illustrate the potential ability in clinical medicine to construct a predictive rule by supervised learning algorithms after collecting enough experimental data.
We performed the transmission-mode terahertz (THz) pulsed spectroscopy of several THz-wave penetration- enhancing agents (PEAs): glycerol, propylene glycol, ethylene glycol, and polyethylene glycol, featuring the molecular weight of 200, 300 and 400. We vacuumized the THz beam path in order to reduce an impact of water vapor on measured data. We reconstructed optical properties and dielectric constants of the abovementioned PEAs in the spectral range of 0.1 to 2.5 THz. We analyzed measured THz optical properties along with the literature data for coefficients of PEAs' diffusion into tissues in order to objectively uncover strength and weaknesses of their use in the immersion optical clearing of tissues at THz frequencies.
Drag-laden magnetic nanoparticles can deliver drugs to a zone of ischemic damage for various purposes of clinical medicine. THz spectroscopy of nanoparticles with adsorbed organic and biological molecules could enable estimation of drug delivery efficiency of the nanoparticles sample and curative effect of delivering chemical substance. The first task of this work was to simulate the contribution of nanoparticles and the shell of organic molecules (glycose) to the dielectric properties of the pressed pellets, consisting of the polyethylene and nanoparticles. The second task of this paper was to study experimentally the possibility of using terahertz radiation for spectral diagnosis of NPs based on iron oxide in a biologically inert shell of silicon dioxide drug-laden with a glycose.
Pulse holographic imaging along with time-domain spectroscopy scan and tomographic techniques are of great interest. Since the advantages of holography are the lack of focusing optics and high spatial resolution, and, comparing with tomography, less computation cost for numerical reconstruction, this technique is preferable for the analysis of thin histological samples. In this work we have created the experimental scheme that involves measurement of diffraction pattern of the collimated THz pulse field spatial distribution at some distance behind the object in the time-domain mode, thus allowing reconstruction of amplitude and phase distribution at the object plane by numerical backpropagation of the wavefront in the spectral domain. In our experiment, we used a breast biopsy sample containing cancer tissues, we also performed numerical simulations accounting for experimental conditions to confirm the conceptual applicability of the reconstruction method.
We have developed a method of the terahertz (THz) solid immersion microscopy for the reflection-mode imaging of soft biological tissues. It relies on the use of the solid immersion lens (SIL), which employs the electromagnetic wave focusing into the evanescent-field volume (i.e. at a small distance behind the medium possessing high refractive index) and yields reduction in the dimensions of the THz beam caustic. We have assembled an experimental setup using a backward-wave oscillator, as a source of the continuous-wave THz radiation featuring λ= 500 μm, a Golay cell, as a detector of the THz wave intensity, and a THz SIL comprised of a wide-aperture aspherical singlet, a truncated sphere and a thin scanning windows. The truncated sphere and the scanning window are made of high-resistivity float-zone silicon and form a unitary optical element mounted in front of the object plane for the resolution enhancement. The truncated sphere is rigidly fixed, while the scanning window moves in lateral directions, allowing for handling and visualizing the soft tissues. We have applied the experimental setup for imaging of a razor blade to demonstrate the advanced 0:2λ resolution of the proposed imaging arrangement. Finally, we have performed imaging of sub-wavelength-scale tissue spheroids to highlight potential of the THz solid immersion microscopy in biology and medicine.
The optical properties of normal fibroblasts and fibroblasts cultured with cancer cells were studied in the frequency range of 0.2 - 1.0 THz. The results show the possibility to distinguish healthy cells from corrupted ones using their optical parameters.
We revealed that after exposure of scarified cornea of rabbits to low-intensity pulsed terahertz radiation 0.1 to 1.8 THz a positive effect on epithelization triggered within the first hours was higher compared to non-irradiated cornea. However, while elevating power of terahertz radiation up to 60.8 nW it resulted in retarding epithelialization process. At that, irradiation did not affect timeframe of complete corneal epithelialization. During experiments it was found that terahertz radiation was well tolerated, exhibited no toxic and allergic reactions or resulted in pathohistological changes in the eye tissues. Also, low-intensity terahertz radiation did not affect normal physiological functions of the eyes and facilitated to re-epithelialization of scarified eyes in rabbits.
It was revealed correlation between the optical density of the lens’s nucleus in terahertz range with its density,
determined according to the L. Buratti classification. Consolidation of the lens fibers caused by senile cataract, increases the reflectivity of the lens in the THz range. The temporal structure of reflected THz signals allows to determine the spatial distribution of density in the lens.
Application of terahertz radiation for the creation of medical equipment and solving of biological problems has become
widely spread. From this point of view, the influence of THz radiation on the nerve fibers is of primary concern. In
addition, several studies indicated both stimulating and depressive effects on nerve cells. However, the mechanism of
this effect has not yet been studied, including the dose and exposure time. Our research was devoted to the impact of
broadband pulsed THz radiation in the frequency range of 0.05 to 2 THz on the neurite growth in the sensory ganglia of
10-12-day chicken embryos. Dependence of changes in functional responses of cells on the average output power has
been found. An increase in the stimulating effect was observed at the lowest power density used (0.5 μW/cm2). Through
non-destructive process and choosing the correct parameters of THz radiation, potential control of neural response
becomes possible, which can subsequently lead to new medical treatments.
In the present paper research results of broadband THz radiation influence in a range 0.1÷2 THz on some biological tissues
are presented. Theoretical modeling of THz radiation propagation through the fat sample is performed. Experimental
absorption spectra of samples of vegetable oil, nail tissue, skin tissue and blood are obtained. Spectra of these tissues differ
in a range of 0.1 ÷ 2 THz. Also they depend on water content. From these samples vegetable oil has the best transmission.
The study of thermoinduced changes of optical properties of adipose tissue is very actual problem. We made the optical
model of thermo-sensitive heterophase medium (adipose tissue). Here the elementary adipose cell will consist of a cube
which basic volume will contain a adipose ball, everything else- water. The adipose ball will contain liquid and crystal
phases. Has been created the experimental scheme for research of angular distribution of the light passed through the
adipose tissue sample. The same model has been created in program Tracepro - General Raytracing. It is presented the
good coordination of calculated and experimental curves for temperatures 5, 26 and 40 °C. We have made a calculated
curve of dependence of intensity transmitted through the multyphase medium (adipose tissue) from a ratio of volume of
liquid phase to total volume. Experimentally knowing also, that intensity of transmitted light depends on temperature,
we have made the dependence of a ratio of volume of a liquid phase to total volume of a cell from temperature. Also we
have put the experiment. We have keep the sample of adipose tissue at temperature 20, 30 and 39 °C in drying box. And
we have received a ratio of hard and liquid phases in the sample. Thus the dependence of observed in experiment
intensity on temperature can be caused by dependence of a ratio of volume of liquid and hard phases in the medium on
temperature.
The goal of the present paper is to find a connection between time-point of fat tissue removal out of a human organism, rotation angle of polarization plane and optical transmission as well. The authors determined experimentally that in vitro fat tissue rotates polarization plane of linearly polarized light at temperature of 24 °C. At that as left- and right-rotation of polarization plane is observed. Value of rotation angle rises proportionally in time of in vitro specimen keeping up. The authors defined a connection of this phenomenon to features of polymorphous structure of a fat tissue.
One of the most attractive perspectives for modern medicine is to solve a problem of a superfluous weight. Method of solving the problem by means of a light source initiates to study optical characteristics of fatty tissue in details. This paper studies temperature dynamic of IR, NIR and visible spectrum of fatty tissue. It refers to temperature, spectra absorption bands and aggregation state of fatty tissue. Character of spectrum changes close to temperatures complying with the change of in-vitro fatty tissue condition is a subject of author’s particular attention.
The problem of a superfluous weight is extremely exciting for a modern cosmetology. The solution of the problem by application of light sources is quite difficult if no optical characteristic of a fat tissue is known. This paper studies a temperature dynamics of full, collimated and diffuse and scattering flows of non-coherent polychromatic light came through an in vitro lard sample. On experimenting the authors found a sharp degradation of in vitro lard sample scattering properties at a temperature of 25±1°C.
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