Non-transparent Objects Research Articles

Реконструктивные методы визуализации тепловых флуктуаций в тканях человека с использованием ультразвуковой томографии

Thermal therapy is an emerging non-invasive method used for cancer treatment. Implementation of this method requires non-invasive temperature monitoring during the treatment process and through-transmission ultrasonic tomography is a potential technique for such monitoring. The technique allows internal cross-sectional images of acoustic properties to be obtained. These properties change with temperature and the technique therefore allows the temperature field in the tissue to be measured non-invasively. The accuracy of this technique is significantly reduced, however, for regions of tissue which contain acoustically non-transparent objects such as medical devices or implants, because these cause missing parts in the projection data. The heated lesion itself may also distort ultrasonic rays. The present work considers and compares different methods of solving the inverse problem for ultrasonic tomographical reconstruction. A special method, which is a modification of the expectation maximization (EM) method for temperature distribution reconstruction from noisy projections with missing data, has been developed for through-transmission fan-beam tomography. The accuracy of the developed method was investigated by computer modeling and compared with the conventional EM method. It was shown that the developed method gives higher accuracy and less distortion after reconstruction than the conventional EM methods.

Optical coherence tomography and its applications in experimental mechanics: A review

Optical coherence tomography (OCT) is a low-coherence interferometry based optical technique capable of imaging internal structures of transparent/semitransparent objects with micrometer resolution and millimeter range. It features distinct advantages of non-invasive and fast-imaging, and has been widely applied in biology, medicine, and material science. After combining with digital image/volume correlation (DIC/DVC) or phase-contrast, OCT can also be used as an elastography method, known as OCT elastography, for measuring full-field displacements and strains inside objects. Recently, OCT elastography has already been developed as an effective tool for investigating mechanical behaviors of inside bio-tissues and materials, such as cornea, skin, tumor, polymer, and polymer composite. In this work, we introduce the basic principles of OCT elastography, summarize the typical experimental mechanics applications of OCT elastography, and finally discuss the remaining problems and limitations of the technique. OCT was originally developed by D. Huang et al. in 1991. The early OCT technique detects depth information of a specimen by means of mechanical scanning, and therefore it is also called time-domain OCT (TD-OCT). Owing to the limitation of mechanical scanning manner, the imaging speed and signal-to-noise (SNR) of this first-generation OCT is relatively low, which makes it unable to meet the requirements of most measurement situations. In 1995, A. F. Fercher et al. developed another type of OCT, called Fourier-domain OCT (FD-OCT). This second-generation OCT uses parallel detection instead of mechanical scanning to improve the imaging speed and SNR, and greatly accelerated the extension of OCT application. Recently, OCT has also been combined with some other techniques and forms a lot of functional OCT methods, including Doppler OCT, polarization-sensitive OCT, OCT elastography, and spectroscopic OCT. Among them, OCT elastography can realize displacement and strain fields measurement inside objects, which is a promising technique in the field of experimental mechanics. The development of OCT elastography can be traced back to 1998, J. M. Schmitt et al. measured the in-plane and out-of-plane displacement fields inside specimens by using the combination of OCT and DIC. However, owing to the low resolution and poor SNR of the early OCT systems, the imaging quality of the method is unsatisfactory. In addition, the displacement sensitivity of the method is at sub-pixel level (micrometer or sub-micrometer level), which is insufficient for most measurement scenarios. For these reasons, DIC-based OCT elastography hasn’t been widely accepted by the researchers. In 2006, R. K. Wang et al. proposed an alternative method that combines OCT and phase-contrast for achieving OCT elastography. The method uses phase sensitive characteristic of OCT for measuring displacements, and makes the displacement sensitivity reach to nanometer level or even higher. Benefiting from the significant improved displacement sensitivity, OCT elastography has received increasing attention in the last decade. Though OCT elastography developed rapidly in recent years, there still remain some problems: (1) Current OCT elastography is only available of measuring transparent and semitransparent objects. For measuring non-transparent objects, it is helpless. Therefore, in the future work, improving penetrating capability is required for OCT elastography. (2) Despite the fact that the development of FD-OCT greatly improved the imaging speed of OCT elastography, it is still insufficient for measuring full-field deformations of inside objects dynamically. Therefore, improving the imaging speed of OCT elastography is also on demand. (3) The employment of phase-contrast can significantly improve the displacement measurement sensitivity of OCT elastography, but it also makes the method lose its in-plane displacement measurement capability. Therefore, developing a novel OCT elastography enabling both in-plane and out-of-plane displacement measurements with high sensitivity is required in the further research.

Graffiti saves birds: A year-round pattern of bird collisions with glass bus shelters

The increase in the human population is bringing with it a concomitant rise in the number of novel man-made structures appearing in different environments, which may affect wildlife. Glass shelters at bus stops create surfaces invisible to many animals like birds and may increase their mortality; evidence for this is rare, however. The main aim of the study was to analyse the temporal variation and frequency of the risk of birds colliding with small, man-made, glass structures. A year-round survey investigating the frequency of bird collisions with 81 glass bus shelters was performed in south-western Poland. A total of 2467 visits to these bus stops yielded evidence of 155 collisions at 40 of them (mean: 1.9 per shelter, range 0–18). The bird carcasses most often found were of passerines, principally blackbirds Turdus merula. The traces left on the glass included feather remains (70%) and whole bird contours (30%). The probability of finding, during a single visit to a bus stop, that a bird had collided with the glass shelter tended to be higher in rural than in urban areas. Both dust and graffiti covering the glass panels of a bus shelter reduced the likelihood of collision. The occurrence of collisions was the highest in July-August and the lowest from November to February. Our study is the first in Europe and the first year-round study worldwide to demonstrate that such small man-made objects can cause death and injuries to birds. We suggest covering such shelters with non-transparent objects, e.g. city maps, paintings or other forms of artwork, in order to reduce the negative impact of these structures on local birds.

Imaging the unimaginable: Medical imaging in the realm of photography

There is an almost innate urge in human beings to represent reality in a visual form. From rock art in the Paleolithic to images of galaxies, the quotidian and the extraordinary have been visually represented through the ages. Medical and scientific disciplines are no exception. Accurate representation of the human body structures and anatomy based on cadaver dissections was almost not possible up to the Renaissance due to ethical, social, and religious beliefs and objections. The works of Leonardo da Vinci (1452-1519) and others and, later, Andreas Vesalius (1514-1564), who produced De Humanis Corporis Fabrica, are considered landmarks in the history of medicine. During the following centuries medical and scientific illustration relied upon the expertise of physician-artists and scientist-artists until a new paradigm appeared in the realm of scientific (medical) illustration: the invention of photography in the 19th century. Two of the medical disciplines most rapidly influenced by photography were dermatology and pathology, both macro- and microscopic. Physicians rapidly started to use photographs as a tool for consultation, documentation, and education, and large collections of images were amassed by individuals and institutions for these purposes. Photographic images are produced by visible light impressing a light-sensitive material such as a silver halide plate, and nowadays a silicon chip. But photons are reflected by nontransparent objects, including the human skin. Developments in science and technology allowed the use of other types of radiation to reveal internal structures in the human body and, most interestingly, noninvasively. Thus today much of the medical diagnosis and treatment is guided by the so-called medical imaging with the use of these techniques, that is, medical photography, endoscopy, x-ray radiography, computer-aided tomography, magnetic resonance imaging, ultrasonography, thermography, and nuclear medicine functional imaging techniques as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Some of these techniques are being applied at the microscopic level to study cell structure and even functional changes in real time. All these advancements in science and technology applied to medicine and other disciplines pose the question as to what extent physicians are trading their capabilities as clinicians. Ethics issues add to the complexity of this new era governed by constant changes in scientific paradigms.

Light Propagation Through Composite Heterophase Objects with Liquid Crystal Material

We simulate LC director distribution and optical transmission of heterophase systems with different LC boundary conditions. The first type is a transparent isotropic material with spherical or cylindrical objects. The second type is an LC incorporating an isotropic transparent or non-transparent object. Systems parameters influence on LCD performances are discussed.

Visible Surface Detection Algorithms: A Review

In computer graphics, there are many surface detection algorithms. When we view a picture containing non-transparent objects and surfaces, then we cannot see those objects from view which is behind from objects closer to eye. We must remove these hidden surfaces to get a realistic screen image. The identification and removal of these surfaces is called Hidden-surface problem. In this paper I review some visible surface detection algorithms like Z buffer method, Area subdivision method, Scan line method etc.

P-136: Light Propagation through Composite Heterophase Objects with Liquid Crystal Material

We simulate LC director distribution and optical transmission of heterophase systems with different LC boundary conditions. The first type is a transparent isotropic material with spherical or cylindrical objects. The second type is an LC layer incorporating an isotropic transparent or non-transparent object. Systems parameters' influence on LCD performances is discussed.

Segmentation of multi-phase X-ray computed tomography images

X-ray computed tomography (CT) is useful for non-destructively visualising internal features of non-transparent objects. In addition, it provides quantitative information about the geometry and spatial distribution of an object’s constituent materials. However, X-ray CT images include blurs and noises. Herein, the authors focus on the partial volume effect that causes blurs depending on image resolution. Artificial materials (e.g., thin wire and threads) and natural materials (e.g., oil sand) were observed using a microfocus X-ray CT scanner. A maximum likelihood thresholding method considering the partial volume effect based on histogram data was applied for segmenting two- and three-phase X-ray CT images. Relative errors in measured cross-sectional areas of aluminium wires and nylon threads were evaluated for verifying the segmentation method. Occupancy ratios of each phase of oil sand to its bulk volume were quantified. The introduced segmentation method estimates the volume of each constituent of two- and three-phase porous materials with reasonable accuracy.

3P1-J05 三次元距離画像の不観測データパターンを利用した物体の存在位置推定(3次元計測/センサフュージョン)

This paper describes an object detection method. Depth images obtained from 3D range camera are used, object detection with classification into three types are performed. We focus on image region where measurement data does not obtained, and analyze the reason how such region is produced. It enables us to reduce uncertain region of an input depth image and to provide information for viewpoint changing to obtain more advanced object information. We implemented an application to classify above three types of objects. Non-transparent objects and partly-transparent objects were classified from a single depth image, and multi-view measurements were used to reduce uncertainty data and to narrow down the existing area of transparent objects.

3D imaging of biofilms on implants by detection of scattered light with a scanning laser optical tomograph

Biofilms – communities of microorganisms attached to surfaces – are a constant threat for long-term success in modern implantology. The application of laser scanning microscopy (LSM) has increased the knowledge about microscopic properties of biofilms, whereas a 3D imaging technique for the large scale visualization of bacterial growth and migration on curved and non-transparent surfaces is not realized so far.Towards this goal, we built a scanning laser optical tomography (SLOT) setup detecting scattered laser light to image biofilm on dental implant surfaces. SLOT enables the visualization of living biofilms in 3D by detecting the wavelength-dependent absorption of non-fluorescent stains like e.g. reduced triphenyltetrazolium chloride (TTC) accumulated within metabolically active bacterial cells. Thus, the presented system allows the large scale investigation of vital biofilm structure and in vitro development on cylindrical and non-transparent objects without the need for fluorescent vital staining. We suggest SLOT to be a valuable tool for the structural and volumetric investigation of biofilm formation on implants with sizes up to several millimeters.

Measurement of micro-motions within non-transparent objects using gray scale information in x-ray stereo projection imaging

We propose a new technique to measure the 3D motion of marker points along a straight path within an object using x-ray stereo projections. From recordings of two x-ray projections at different angles, the 3D coordinates of marker points can be determined. By synchronizing the x-ray exposure time to the motion event, a moving marker leaves a trace in the image of which the gray scale is linearly proportional to the marker velocity. By measuring the marker gray scale along the motion path, the velocity at each point is determined and the position as a function of time is obtained by integration. In combination with the 3D information from two stereo recordings, the full 3D motion is obtained. The difference in position between the new method and laser vibrometry was less than 5 µm. The 3D motion measurement is performed within seconds, making the method ideal for applications in biomechanics. In combination with a full CT-scan of the object, the motion information on the marker points can be used to measure and visualize how an internal rigid 3D structure moves. We demonstrate the method on the malleus ossicle motion in the gerbil middle ear as a function of pressure on the eardrum.

Optically trapped probes with nanometer-scale tips for femto-Newton force measurement

We describe the development of a novel force probe, controlled by multiple optical traps, with a nanometer-scale tip that protrudes outside the direct laser radiation field. We have measured forces to an accuracy of 240 fN, which enables future experiments that probe photo-sensitive components (such as biological cells) and non-transparent objects. The probes were produced using two methods, electron beam lithography and two-photon polymerization, with the latter providing approximately twice as much trapping stiffness.

Quadri-stable percepts for a rotating non-transparent object

Continuous viewing of a rotating transparent object with an axis inside of the object may lead to perceptual alternation between two opposite rotations. The current consensus maintains that the bi-stable phenomenon depends on simultaneous stimulation by multiple depths defined by elements moving in different directions (1). By using a single specifically designed non-transparent object with a rotation axis outside of the object, this abstract shows that for perceiving rotation alternation the requirement for simultaneous stimulation by the elements in different depth moving in different directions is not necessary. If the rotation axis is outside, the object when moving rightward does not appear simultaneously with the same object when moving leftward at a different time, or vice versa, regardless of the real rotation leftward or rightward. Our experiments demonstrate that continuous viewing of the rotation leads to perceptual alternation also. In addition to the commonly perceived two opposite rotations, two new stable percepts occur as well. In other words, total four different stable percepts may occur (a quadri-stable phenomenon): rightward rotation; leftward rotation; two rotations following the infinite symbol ∞-like tracks: &uArr∞ &uArr and ⇓∞⇓. The arrow symbol indicates the moving direction of the object towards to the viewer (⇓) or away from the viewer (⇑) at the both ends of the ∞-like track. Because the elements of different depth moving in different directions do not appear simultaneously, the quadri-stable phenomenon signifies that some kinds of perceptual memory facilitate perceptual alternation. It is interesting to note that the perceptual memory, on the contrary, also stabilize percepts in perceptual rivalry (2). The quadri-stable phenomenon also suggests that using depth ambiguity to explain depth reversal is not completely satisfactory (2). (1). Blake Nawrot. Science 244, 716-718 (1989). (2). Leopold, etal. Nature Neuroscience. 5, 605-609> (2002).

Russian avant-garde experiments with light

The leaders of the photographic avant-garde in Russia were engaged primarily in experiments in photographic form, seeking maximal abstraction and employing a limited number of elements, avoiding pictorialism in the same way that happened earlier with painting, sculpture, and graphics. Characteristic features of Futurism and Dadaism, such as visual shock, montage, and alogism, were also found in experimental photography, the difference being that it did not occur within the traditional genres of landscape, portraiture, or reportage but in the one-step photographic process of the photogram, an image created by light falling on photographic paper, on the surface of which transparent and non-transparent objects are placed. Light and shadow are the main means of expression in this camera-less form of the photographic process.

Quantitative analysis of reservoir rocks by microfocus X-ray computerised tomography

Abstract Microfocus Computer Tomography (μCT) is a non-destructive imaging technique that allows visualisation of internal features within non-transparent objects such as sedimentary rocks. With resolution as good as 10 μm in three dimensions, this technique is highly superior to medical CT widely used in geology and material sciences. Superior resolution is achieved by decreasing the X-ray spot size, which allows a decrease in the penumbra effect and an increase in primary magnification by placing the sample close to the X-ray source. Since polychromatic X-ray sources are used, the technique is not free of artefacts. Application of filtering techniques is recommended to circumvent these artefacts and to achieve good quality images for quantitative analysis. Application of a dual energy approach allows quantification of density as well as effective atomic number distribution of internal features. As the technique acquires data in 3D, μCT provides an ideal tool to link 2D thin-section petrography to 3D petrophysical measurements or to be used within an upscaling approach. A number of applications and the use of dual energy density and effective atomic number characterisations are presented. Attention is also paid to some of the limitations of this technique.

Depth Illusion by Delayed 3-D Perception (‘Delayed Stereopsis Illusion’): A Novel Way to Determine Computation Times in Human Vision by Depth Reversal in Partially Occluded Moving Objects

Viewed through depth-reversing spectacles, nontransparent objects appear to cut ‘gaps’ into a patterned background. In moving objects this gap is seen to extend beyond the occluded area (‘delayed stereopsis illusion’, DSI): Its trailing border appears to lag behind by a precisely measurable distance, indicating a processing time of approximately 0.13 s to accomplish stereopsis [cf Morgan and Castet, 1995 Nature (London)378 380 – 383]. Other than in thigmaesthesia, there is no correction by antedating. Why is this delay not perceived in normal stereopsis? If an object is moving before some background, the background usually maintains its position; it may be occluded, or not. Depth information thus might be extrapolated to the continuously uncovered regions of the patterned background. Depth reversal demands that the occluded region of the background must jump behind the moving, occluding object. As this object is perceived to retain its distance, the background, as it is getting uncovered, must jump back into the foreground, where it can be perceived only after renewed calculation of binocular depth. The dependence of DSI on eye movements, disparity, velocity, motion direction, surface texture, illuminance, spatial frequency, and fractal dimension of the objects involved is currently being investigated in model systems which allow us to determine processing times of human stereopsis under well-defined conditions.

Visual events' identification of solids of revolution from perspective views

An algorithm is presented for identifying the visual events of solids of revolution from a perspective point of view. The object representation model comprises of these different visual events (or aspects) which can be applied for object identification. Algorithms have been developed to handle general polyhedral objects from either orthographic or perspective views, or to compute the aspect graph of solids of revolution using the orthographic projection. The orthographic view aims to find the aspects of the solid of revolution which are purely object-oriented, the theory of differential geometry can be applied sufficiently to find the aspects without referring to the distance of the viewer. In the real case, the distance effect, that may influence the aspect dramatically when the viewer is close to the object, has to be considered. For instance, to generate the same aspect, the viewer may have to change his viewing directions when he is at a different distance from the object. Firstly, this paper uses the constraint of contour generator to identify the aspects of solids of revolution under perspective projection. The difference between our approach and the others is the distance effect. The present method combines the object-oriented and viewer-oriented aspect finding. Secondly, a method is developed to find the limb termination point of the non-transparent object from a certain perspective viewpoint. Many aspect finding methods are developed for transparent objects (i.e. objects made of glass) of which the projection contour (limb) is continuous. For non-transparent objects, the self-occlusion may induce the limb termination phenomena.

Photoacoustical Spectroscopy Investigation of Cellular Polymers

Abstract Optical non-transparent biological objects were investigated by photoacoustic spectroscopy method. The dynamics of structural changes both in the peel and in the pulp in the process of fruit maturing was studied. The change of intensity of absorption bands of fruits in the process of maturing as well as the appearance of new bands in the process of rotting provides monitoring both the terms of maturing and storage of such objects.

A fringe-compensation technique for stress analysis by reflection holographic interferometry

The use of holographic interferometry for stress analysis of nontransparent objects is limited by rigid-body displacements of the object. These displacements can alter the fringe patterns and often cause the fringes to disappear completely. A technique of compensation for this deterioration of the fringe pattern forreal-time holographic interferometry is described in this paper. It is especially designed to permit the accurate measurement of the out-of-plane component of strain near regions of stress concentration in plates that are subjected to in-plane loading. It is first shown that the fringes caused by a pure rigid-body displacement can be eliminated almost completely by translations of the hologram and rotation of the illumination wave. This procedure is first described when the displacement is known; then when it is unknown. A method to estimate the error made in the correction is presented.