Working with mini text
Read text No. 2 and complete tasks A6-A11.
(I)... (2) They are durable and take root well, have the chemical and mechanical properties of bone. (3) Such implants are used in neurosurgery, allowing the restoration of joints and bones of the skull, damaged vertebrae, and even the implantation of “living teeth”. (4) Employees of the biotechnology laboratory of the Russian Chemical-Technological University named after D.I. Mendeleev have been struggling to create artificial prostheses for more than ten years. (5)... which in their structure and mineral composition resemble bone and will not be rejected by a living organism. (6) Group B.I. Beletsky developed a new material for implants, the so-called BAC, the use of which made it possible to reduce the number of amputations by a third.
A6. Which of the following sentences should come first in this text?
1) Russian scientists are developing and producing bioactive bone substitutes.
2) Interestingly, the latest development of a bioactive bone substitute is used in neurosurgery.
3) Here is the chin, the bridge of the nose, here are the cheekbones, and here are the vertebrae.
4) Statistics show a decrease in the number of amputations.
A7. Which of the following words (combinations of words) should be in the gap in the fifth sentence?
1) First of all 2) And such 3) Besides such 4) But not such
A8. What words are the grammatical basis in the fifth (5) sentence of the text?
1) which remind and will not be rejected 2) which remind and will not be rejected
3) resemble bone 4) which will not be rejected
A9. Indicate the correct characteristic of the sixth (6) sentence of the text.
1) complex with non-union and union coordinating connections 2) complex
3) complex with non-union connection 4) complex
A10. Indicate the correct morphological characteristic of the word DURABLE from the second (2) sentence of the text.
3) short adjective.
A11. State the meaning of the word IMPLANT in sentence 3.
1) an artificially created substance intended for implantation into the human body
2) a substance obtained as a result of complex chemical experiments
3) strain of beneficial bacteria 4) technical device
Working with mini text
Read text No. 3 and complete tasks A6-A11.
(1)... (2) The answer to this question depends on how far ahead a person is able to look. (3) We take all the benefits of civilization for granted. (4)... all of them, like the successes of medicine, were the result of many decades and centuries of work by scientists engaged in activities that seemed trivial to the average person, like observing the stars or the lives of some boogers. (5) The application of the results of science, uncontrolled by scientists, has brought many difficult problems, but now only the further development of science can save us from them, as well as give us new sources of energy, save us from the challenges of the future, such as new epidemics or natural disasters.
1) Doesn't science lead to even greater dangers?
2) Does modern science solve global problems of everyday life?
3) Does fundamental science solve the problems facing humanity or does it only lead to new dangers?
4) Can’t science get rid of dangers?
A7. Which of the following words (combinations of words) should be in place of the gap in the fourth sentence?
1) First of all 2) However " 3) In addition 4) In other words
1) the scientists involved 2) were the result of the work
3) they were the result of 4) they were the result of decades.
A9. Indicate the correct characteristic of the fourth (4) sentence of the text.
1) complex with non-union and union coordinating connections 2) complex
3) simple 4) complex with non-union and allied subordination
A10. Indicate the correct morphological characteristic of the word CAPABLE from the second (2) sentence of the text.
4) perfect participle
A11. Indicate the meaning of the word CATACLYSM in sentence 5.
1) natural disaster 2) annual river flood
3) the influence of man on nature 4) the influence of nature on man
Working with mini text
Read text No. 4 and complete tasks A6-A11.
(1)... (2) Alternative research methods include computational biology. (3) This is a kind of border area that is rapidly developing and branching out, using the capabilities of computers and digital photo and video equipment. (4) This includes mathematical modeling of biological processes and work with computer databases. (5) There are also various biological collections on the Internet - electronic versions of traditional zoo museums, herbariums or identification books, where “portraits” of fixed, dried and prepared plants and animals are presented. (6) ...such an Internet resource can become an information base for a new science about a living organism - physionomics.
A6. Which of the following sentences should come first in this text?
1) The virtual biological museum that will be discussed is fundamentally different from such online biological collections.
2) The general opinion was expressed by Academician of the Russian Academy of Sciences and Russian Academy of Medical Sciences Natalia Bekhtereva.
3) Today in biology, alternative research methods are preferable.
4) The idea of its creation belongs to the candidate of biological sciences, senior researcher at the Institute of Theoretical and Experimental Biophysics of the Russian Academy of Sciences (ITEB RAS) Kharlampiy Tiras.
1) So 2) However 3) In addition 4) In other words
A8. What words are the grammatical basis in the sixth (6) sentence of the text?
1) An Internet resource can 2) Can become a base 3) An Internet resource can become a base 4) Become a base
A9. Indicate the correct characteristic of the fifth (5) sentence of the text.
1) simple 2) complex 3) complex non-union 4) complex
A10. Indicate the correct morphological characteristic of the word USING from the third (3) sentence of the text.
1) active participle 2) passive participle
A11. State the meaning of the word MODELING in sentence 4.
1) creating an approximate model of an existing or future
2) copying an existing or future
3) recreation of an existing or future
4) imitation of what already exists or the future
Working with mini text
Read text No. 5 and complete tasks A6-A11.
(1)... (2) It is clear, you say, that, when passing by, people should pay tribute of respect and gratitude to the object of worship. (3) On the pedestal of the new monument, built near St. Petersburg University, sits importantly... a cat. (4) University scientists, and they were supported by colleagues from the Institutes of Physiology named after I.P. Pavlov, evolutionary physiology and biochemistry named after I.M. Sechenov, the human brain, bioregulation and gerontology, and other world-famous scientific institutions, decided that it was time to repent to the animals who gave their lives in the name of Science by the thousands. (5) Animals, without which there would not have been many discoveries in biology. (b) ... the cat Vasily is already the third monument to a laboratory animal in the world - after the frog at the Sorbonne and the “Pavlovian” dog near the Institute of Experimental Medicine in St. Petersburg.
A6. Which of the following sentences should come first in this text?
1) Have you seen the new monument? 2) Why are monuments erected?
3) What is this monument dedicated to? 4) How to get to the new monument?
A7. Which of the following words (combinations of words) should be in place of the gap in the sixth sentence?
1) First of all 2) However 3) What is characteristic 4) In other words
A8. What words are the grammatical basis in the third (3) sentence of the text? .
1) the cat is sitting important 2) the cat is sitting important 3) the cat is sitting on a pedestal 4) the cat is sitting
A9. Indicate the correct characteristic of the fifth (5) sentence of the text.
1) complex with subordinating and coordinating connections 2) complex
3) complex 4) simple
A10. Indicate the correct morphological characteristic of the word PASSING from the second (2) sentence of the text.
1) active participle 2) passive participle
3) imperfective participle 4) perfect participle
A11. Indicate the meaning of the word EXPERIMENTAL in sentence 6.
1) based on the search for new methods 2) using classical methods
3) old 4) new
Working with mini text
Read text No. 6 and complete tasks A6-A11.
(1)... (2) It is called a laser optical-acoustic tomograph, and it will be used to examine tumors in the mammary glands. (3) The device, using radiation of one wavelength, helps to find an inhomogeneity the size of a match head in the patient’s chest, and another to determine whether the tumor is benign or not. (4) With the amazing accuracy of the method, the procedure is completely painless and takes only a few minutes. (5) ... the laser makes the tumor sing, and the acoustic microscope finds and determines its nature by the sound timbre.
A6. Which of the following sentences should come first in this text?
1) The device is based on two methods.
2) The authors were able to carry out the work thanks to the support of the Russian Foundation for Basic Research.
3) A unique device was designed by physicists from the International Scientific and Educational Laser Center of Moscow State University. M.V. Lomonosov.
4) It allows you to obtain an optical image of a tumor hidden at a depth of up to 7 cm and accurately find its location.
A7. Which of the following words (combinations of words) should be in the gap in the fifth sentence?
1) First of all 2) Figuratively speaking 3) In addition 4) However
A8. What words are the grammatical basis in the fourth (4) sentence of the text?
1) the procedure is painless and takes a few minutes
2) the procedure takes a few minutes
3) the procedure is painless
4) takes only a few minutes
A9. Indicate the correct characteristic of the fifth (5) sentence of the text.
1) complex with non-union and union coordinating connections 2) complex
3) complex non-union 4) complex with non-union and allied subordination
A10. Indicate the correct morphological characteristics of the word THIS from the third (3) sentence of the text.
1) personal pronoun 2) demonstrative pronoun
3) attributive pronoun 4) relative pronoun
A11. Indicate the meaning of the word TUMOR in sentence 5.
1) neoplasm 2) swelling from impact
3) only benign neoplasm 4) only malignant neoplasm
Answers
Job No.
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Literature used
Tekucheva I.V. Russian language: 500 educational and training tasks to prepare for the Unified State Exam. – M.: AST: Astrel, 2010.
The device was created by physicists at the International Scientific and Educational Laser Center of Moscow State University. M.V. Lomonosov based on two long-known phenomena. First, a cancerous tumor absorbs light and heat more intensely than healthy tissue, which has lower blood concentrations and more oxygen.
In addition, it is known that when heated, all bodies not only expand, but also emit sound. Let us remember, for example, how a boiling kettle whistles. Moreover, slow heating produces a weak sound. Faster - stronger. And instantaneous gives a powerful acoustic wave.
So, the “singing tomograph” almost instantly heats the tissue being examined with its laser beam: in a hundredth of a microsecond - by one tenth of a degree. Since any tumor contains more blood than healthy tissue, it heats up more. And the sound coming from it is two to three times more powerful. It is detected by the ultra-sensitive acoustic system of the tomograph. This "electronic ear" pinpoints the location of the tumor.
The sound signal on the computer screen turns into a picture. A bright yellow spot in a blood-red frame on a black background looks like a cosmic landscape. You can even admire it, if you don’t know that it’s a picture of a cancerous tumor. It is hundreds of times more contrasting than any image of her made by already known methods.
This is the general operating principle of the device,” explains project manager, Doctor of Physical and Mathematical Sciences Alexander Karabutov. - In reality, tomography takes place in two steps. First, a laser beam of a certain wavelength scans the patient's chest. For now, this is just a search for inhomogeneities. If the tomograph “hears” a sharp increase in sound, it means that a suspicious place has been found. But what is it? Malignant or benign formation? We switch the device to another wave, which checks the blood in the found tumor for oxygen levels. If it is less than normal, it is cancer. This is what the tomograph reports. He “sings” again, but this time “not in his own voice”: the timbre changes significantly. But if the oxygen concentration is higher than normal, then the timbre of the sound is completely different. This is most likely just mastopathy.
An ordinary laboratory assistant can process acoustic signals. And within a few minutes you will receive on the computer screen an image of a tumor - if it exists, of course - ranging in size from 2 millimeters at a depth of up to 7 centimeters. And also find out whether it is benign or not. All this is completely without harm to the patient. And painless. This “four in one” is where the uniqueness of the “singing tomograph” lies.
For comparison, the same X-ray or neutron capture diagnostic technologies, like any radioactive irradiation, are not harmless even for a healthy person. And modern means, for example, optical diagnostics, make it possible to detect a tumor of at least five millimeters. Moreover, breast cancer, which has not yet metastasized, is only three millimeters. It is even more difficult to distinguish such a “grain of sand” using the optical method if it lies at a depth of, for example, six centimeters. After all, the beam must pass through the entire female breast - back and forth. And this is a medium that scatters light. On the way there it scatters a million times, and back - also a million times. But the sound does not undergo any serious distortion. Therefore, an optical signal converted into an acoustic signal provides much higher diagnostic accuracy.
Just awarded the Nobel Prize, nuclear magnetic tomography, with absolute harmlessness, provides a three-dimensional image of a tumor located at any depth. But it also has a very significant drawback: what is good for brain research fails with mammography. The NMT study lasts twenty minutes: the patient breathes, the blood pulsates, and both its concentration and oxygen levels change. The picture is obtained with significant distortion. It happens that a nuclear magnetic tomogram is used to diagnose cancer, but then a biopsy gives a negative conclusion.
Yes, we get only a two-dimensional image, says Alexander Karabutov, but practically without distortion. After all, in a third of a second too strong physiological changes in the tissue under study do not occur. Our tomograph does not replace all known ones, it complements them.
So far, the “singing tomograph” exists only in a laboratory version. And yet, two dozen volunteers with suspected malignant tumors have already been tested on it. The device never made a mistake. And the following story came out with one of the women. Various tests indicated that she had cancer. But where he was hiding could not be revealed by any known means. It turned out to be behind a silicone implant. This is what the laser optical-acoustic tomograph reported.
Laser tomography as a method for diagnosing diseases
Tomography (Greek tomos layer, piece + graphiō to write, depict) is a method of non-destructive layer-by-layer study of the internal structure of an object through repeated exposure to it in various intersecting directions (the so-called scanning transmission).
γ-quantum511 keV |
tomography |
Types of tomography
Today, organs inside the body are diagnosed mainly by X-ray (X-ray), magnetic resonance (MRI) and ultrasound (UT) methods. These methods have high spatial resolution, providing precise structural information. However, they have one common drawback: they cannot determine whether a certain spot is a tumor, and, if so, then is it malignant?. In addition, X-ray tomography cannot be used before the age of 30.
MULTIMODALITY! Combined use of different methods - one with good spatial resolution
Electron beam CT – 5th generation
Frontal CT (left), PET (center) and Combined PET/CT
(right), shows the distribution of positrons emitted by 18 F-fluorodioxide glucose superimposed on the CT
Laser Optical Tomography
Optical, and primarily interference measurements, have made a significant contribution to the development of physical and instrumental optics, as well as to the improvement of measurement technology and metrology. These measurements have exceptionally high accuracy over a wide range of measured quantities, thanks to their use of light wavelength as a measure and technically easy to reproduce in laboratory and production conditions. The use of lasers not only provided new functional and metrological capabilities for optical interferometry, but also led to the development of fundamentally new methods of interference measurements, such as interferometry using low-coherence optical radiation, which ensures the formation of an interference signal only at small differences in the wave paths in the interferometer.
Low-coherence interference systems operate in the mode of the so-called correlation radar, which determines the distance to the target by the position of the correlation pulse signal, which is the interference signal in the interferometer. The shorter the coherence (correlation) length, the shorter the duration of the correlation pulse and the more accurately the distance to the target is determined, in other words, the higher the spatial resolution of the radar. Achievable values of the coherence length of optical radiation in units of micrometers, accordingly, provide micron resolution of the optical radar. Optical interference radars have found particularly wide practical application in biomedical diagnostic technology (optical tomographs) for monitoring the parameters of the internal structure of biological tissue.
Luminescent optical tomography is one variation of this idea. The light reflected from the tumor (Fig. 1.11a) differs from the light reflected from normal tissue, and the luminescent characteristics also differ (Fig. 1.11b) due to differences in the degree of oxygenation. To reduce false-negative diagnoses, an IR laser irradiates the tumor through a probe, and then the radiation reflected from the tumor is recorded.
Optical-acoustic tomography uses differences in the absorption of short laser pulses by tissue, their subsequent heating and extremely rapid thermal expansion, to produce ultrasonic waves detected by piezoelectrics. Useful primarily for studying blood perfusion.
Confocal scanning laser tomography (SLO) - used to obtain non-invasive three-dimensional images of the posterior segment of the eye (optic disc and surrounding retinal surface) The laser beam is focused at some depth inside the eye, and is scanned in a two-dimensional plane. Receiver
light reaches only from this focal plane. Subsequence |
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such flat 2D patterns obtained by increasing the focal depth |
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plane, resulting in a 3D topographic image of the disk |
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optic nerve and peripapillary retinal layer nerve |
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fibers (comparable to standard stereo fundus photography) |
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Fig.1.10. This approach is useful not only for direct |
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anomaly detection, but also to track minor |
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temporary changes. Less than 2 seconds required to do |
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sequentially 64 scans (frames) of the retina on a field of 15°x15°, |
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670 nm laser radiation reflected from different depths. Edge shape |
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pit highlighted by a curved green line indicates a defect |
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layer of nerve fibers on the rim of the optic nerve. |
Fig.1.10 Confocal scanning laser |
optic disc tomography |
Confocal microscope
Axial Resolution LimitationsSLO |
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Longitudinal resolution |
SLO and, |
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respectively, |
confocal z |
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microscope depends on |
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sharpness is inversely proportional to the square of the numerical aperture (NA=d/2f) of the microlens. Since the thickness of the eyeball, which plays the role of a microscope lens, is ~2 cm for an undilated pupil N.A. <0,1. Таким образом,
retinal image depth of field for laser scanning confocal ophthalmoscopy is limited to >0.3 mm due to the combined effect of low numerical aperture and anterior chamber aberrations.
Optical coherence tomography (OCT)
OCT, a new medical diagnostic developed in 1991, is attractive to biomedical research and the clinic for several reasons. OST Allows real-time imaging with µm resolution of cell dynamics, without the need for conventional biopsy and histology, providing images of tissues, incl. with strong scattering, such as skin, collagen, dentin and enamel, at a depth of 1-3 µm.
What dissipates in fabric?
penetration of radiation into |
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biological tissue depends on both absorption and |
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scattering. Scattering is associated with different |
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refractive indices of different cells and |
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cell cells. |
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Scattering of light on tissue structures |
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Scattering depends on wavelength |
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Dispersion into tissue occurs at the lipid-water interface in cell membranes (especially |
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laser beam |
(Rice.). Radiation with length |
mitochondrial membranes (a)), nuclei and protein fibers (collagen or actin-myosin (b)) |
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waves much larger than the diameter of the cellular structures (>10 µm) are weakly scattered.
UV excimer laser radiation (193, 248, 308 and 351 µm), as well as IR radiation of 2.9 µm erbium (Er:YAG) laser caused by absorption by water, and 10.6 µm CO2 laser have a penetration depth of 1 to 20 microns. Due to the shallow depth of penetration, scattering in the layers of keratinocytes and fibrocytes, as well as on red blood cells in blood vessels, plays a subordinate role.
For light with a wavelength of 450-590 nm, which corresponds to the lines of argon, KTP/Nd lasers and diode lasers in the visible range, the penetration depth averages from 0.5 to 3 mm. Just like absorption in specific chromophores, scattering plays a significant role here. The laser beam of these wavelengths, although remains collimated at the center, is surrounded by a zone of high collateral scattering.
In the spectral region between 590–800 nm and up to 1320 nm, scattering also dominates with relatively weak absorption. Most IR diode and well-studied Nd:YAG lasers fall into this spectrum. The radiation penetration depth is 8-10 mm.
Small tissue structures, such as mitochondrial membranes, or the periodicity of collagen fibers, much smaller than the wavelengths of light (λ), lead to isotropic Rayleigh scattering (stronger at short wavelengths, ~λ-4). Large structures, such as whole mitochondria or bundles of collagen fibers, much longer wavelengths of light, lead to anisotropic (forward) Mie scattering (~λ-0.5 ÷ λ-1.5).
Optical diagnostics involves the study of biological tissue using ballistic Coherent tomography (the time of flight of a photon to the target is detected), or Diffuse tomography (the signal is detected after multiple photon scattering). An object hidden within a biological environment must be detected and localized, providing both structural and optical information, preferably in real time and without changing the environment.
Diffuse optical tomography (DOT).
In a typical DOT, tissue is probed with near-infrared light transmitted through a multimode fiber applied to the tissue surface. Light scattered by tissue is collected from various locations by fibers coupled to optical detectors, similar to CT or MRI. But practical
the use of DOT is limited by the strong absorption and scattering of light by tissue, which results in low resolution compared to standard clinical techniques, X-ray and MRI.
Laser detection of an object in a scattering medium, incl. ommethod of average photon trajectories (APT).
In addition, the sensitivity of the method decreases with increasing depth, leading to a non-linear dependence across the image area, making it even more difficult to recover large volumes of tissue. There is also a relatively low contrast between the optical characteristics of healthy and abnormal tissues, even with the use of exogenous chromophores (Indocyanine ICG leakage into tumor vasculature increases its concentration relative to normal tissue), is critical for clinical use.
Principle of ballistic coherence tomography (BCT)
A beam scattered by an object in a Michelson interferometer (the mirror in the object arm of the interferometer is replaced by biological tissue) interferes with the reference beam (the reference arm has a precision-movable retromirror). By changing the delay between beams, it is possible to obtain interference with a signal from different depths. The delay is continuously scanned, causing the frequency of the light in one of the beams (the reference) to shift due to the Doppler effect. This makes it possible to isolate the interference signal from a strong background caused by scattering. A pair of computer-controlled mirrors scan a beam across the surface of the sample, creating a tomographic image that is processed in real time.
Block diagram and operating principle of OST
Spatial depth resolution is determined by the temporal coherence of the light source: below
coherence, less than the minimum slice thickness of the image of the object under study. With multiple scattering, optical radiation loses coherence, so you can use
broadband, low coherence, incl. femtosecond lasers for studying relatively transparent media.True, even in this case, the strong scattering of light in biological tissues does not allow one to obtain an image from depth>2-3 mm.
Axial Resolution Limitations
For Gaussian beams d is the size of the beam on a focusing lens with focal length f
Axial resolution of the OCT ∆z depending on the width of the laser radiation spectrum ∆λ and the central wavelength λ
(Assumptions: Gaussian spectrum, non-dispersive medium)
Depth of field
b - confocal parameter = twice the Rayleigh length
In contrast to confocal microscopy, OCT achieves very high longitudinal image resolution regardless of focusing conditions, because longitudinal and transverse resolution are determined independently.
Lateral resolution as well as depth of field depend on the size of the focal spot
(as in microscopy), while longitudinal
the resolution depends mainly on the coherence length of the light source ∆z = IC /2 (a
not from the depth of field, as in microscopy).
The coherence length is the spatial width of the autocorrelation field measured by the interferometer. The envelope of the correlation field is equivalent to the Fourier transform of the power spectral density. Therefore longitudinal
resolution is inversely proportional to the spectral bandwidth of the light source
For a central wavelength of 800 nm and a beam diameter of 2-3 mm, neglecting the chromatic aberration of the eye, the depth of field is ~450 µm, which is comparable to the depth of formation of a retinal image. However, the low numerical aperture NA of the focusing optics (NA=0.1÷0.07) is the low longitudinal resolution of a conventional microscope. The largest pupil size, for which a diffraction resolution of ~3 mm is still preserved, gives a retinal spot size of 10-15 µm.
Reduction of spots on the retina, and, accordingly,
increased lateral resolution of OCT by an order of magnitude, can be achieved by correcting eye aberrations using adaptive optics
Limitations of OCT axial resolution
Distortion of the shape of an ultra-wide band spectrum of a light source
Chromatic aberration of optics
Group velocity dispersion
Chromatic aberration of optics
Achromatic lens (670-1020nm 1:1, DL)
Chromatic aberrations as a function of interferometer focusing length for conventional and parabolic reflex lenses
Group velocity dispersion
Group velocity dispersion reduces resolution
OST (left) is more than an order of magnitude (right).
Group velocity dispersion correction Retina OC Thickness of fused silica or BK7 in reference
leverage varies to compensate for dispersion
(a) spectral width of Ti:sapphire laser and SLD (dashed line)
(b) axial resolution of OCT
High resolution optical coherence tomograph
IN Unlike X-ray (CT) or MRI tomography, OCT can be designed into a compact, portable
And relatively inexpensive device. Standard resolution of OCT(~5-7 µm), determined by the lasing bandwidth, is ten times better than that of CT or MRI; ultrasound resolution at the optimal transducer frequency ~10
MHz ≈150 µm, at 50 MHz ~30 µm. The main disadvantage of OCT is its limited penetration into opaque biological tissue. The maximum imaging depth in most tissues (except the eyes!) ~1-2 mm is limited by optical absorption and scattering. This depth of OCT imaging is superficial compared to other techniques; however, it is sufficient to work on the retina. It is comparable to a biopsy and is therefore sufficient to evaluate most early changes in neoplasms, which very often occur in the most superficial layers, for example, in the epidermis of human skin, mucosa or submucosa of internal organs.
In OCT, in comparison with the classical design of an interference microscope, sources with higher power and better spatial coherence (usually superluminescent diodes) and objectives with a small numerical aperture (NA) are used<0,15), что обеспечивает большую глубину фокусировки, в пределах которой селекция слоев осуществляется за счет малой длины когерентности излучения. Поскольку ОСТ основан на волоконной оптике, офтальмологический ОСТ легко встраивается в щелевую лампу биомикроскопа или фундус-камеру, которые передают изображения луча в глаз.
Let us consider λ=1 µm as the central wavelength (the laser can have Δλ< 0,01нм), и в этом случае l c ≈ 9см. Для сравнения, типичный SLD имеет полосу пропускания Δλ ≥50 нм, т.е. l c <18 мкм и т.к l c определяется для двойного прохода, это приводит к разрешению по глубине 9 мкмв воздухе, которое в тканях, учитывая показатель преломления n ≈1.4, дает 6 мкм. Недорогой компактный широкополосный SLD с центральной длиной волны 890 нм и шириной полосы 150 нм (D-890, Superlum ),
allows you to image the retina with an axial resolution in air of ~3 μm.
Interference requires a strict phase relationship between the interfering waves. With multiple scatterings, phase information disappears, and only singly scattered photons contribute to interference. Thus, the maximum penetration depth in the OCT is determined by the depth of single photon scattering.
Photodetection at the interferometer output involves the multiplication of two optical waves, so that a weak signal in the target arm, reflected or transmitted through tissue, is amplified by a strong signal in the reference arm. This explains the higher sensitivity of OCT compared to confocal microscopy, which, for example, in the skin can only image down to a depth of 0.5 mm.
Since all OC systems are based on a confocal microscope, the lateral resolution is determined by diffraction. To obtain 3D information, imaging devices are equipped with two orthogonal scanners, one for scanning an object in depth, the other for scanning an object in the transverse direction.
A new generation of OST is being developed both in the direction of increasing the longitudinal resolution ∆ z= 2ln(2)λ 2 /(π∆λ) ,
by expanding the generation band ∆λ and increasing |
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depth of radiation penetration into tissue. |
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Solid State |
lasers show ultra-high |
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OST resolution. Based on broadband Ti:Al2 O3 |
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laser (λ = 800 nm, τ = 5.4 fsec, bandwidth Δλ up to 350 |
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nm) an OCT with ultra-high (~1 µm) axial |
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resolution, an order of magnitude higher than standard |
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OCT level using superluminescent diodes |
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(SLD). As a result, it was possible to obtain in vivo from the depths |
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highly scattering tissue image of biological |
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cells with a spatial resolution close to |
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diffraction limit of optical microscopy, which |
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allows for |
tissue biopsy directly |
Level of development of femtosecond lasers: |
operation time. |
duration<4fs, частота 100 MГц |
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Since scattering depends strongly on wavelength, decreasing as it increases, greater penetration depth into opaque tissue can be achieved with longer wavelength radiation, compared to λ=0.8 µm. The optimal wavelengths for imaging the structure of opaque biological tissues are in the range of 1.04÷1.5 µm. Today, a broadband Cr:forsterite laser (λ=1250 nm) makes it possible to obtain an OCT image of a cell with an axial resolution of ~ 6 μm from a depth of up to 2-3 mm. A compact Er fiber laser (supercontinuum 1100-1800 nm) provides a longitudinal resolution of 1.4 μm and a transverse resolution of 3 μm at λ = 1375 nm.
Phononic crystal highly nonlinear fibers (PCFs) have been used to generate an even wider spectral continuum.
Broadband solid-state lasers and superluminescent diodes cover almost the entire visible and near-IR region of the spectrum, which is most interesting for the formation of OCT images.
But I like this conversation, guys! In fact!
I am very lazy and in order to make the routine easier, I am inserting a fragment from an official newsletter. If there are any substantive questions, I will be happy to answer. Just let's be tolerant and replace emotions with logic. And, skeptics, understand - sometimes it is difficult to prove to a convinced colorblind person that in addition to white and black, there is a red-yellow-blue color.
"Dear colleagues!
You may find this information useful.
At the Research Laboratory of Technical Design “VEGA” at LLC«
Center for Scientific and Applied Research on Energy Information Security “Veles”[email protected]
a UNIQUE, superior to world-known analogs, has been created, the “VEGA-11” device, which can become your indispensable assistant. The device"VEGA-11" was developed primarily for identifying geophysical anomalies and identifying geopathogenic zones both indoors and in the field. Moreover, weather conditions (rain, dampness) do not affect the operation of the device.
This device has unique properties, surpassing the Russian type"IGA-1" due to the fact that it is based on new scientific approaches. Their essence is that in a normal electromagnetic field, at the interface between two media with different conductivities, a double electric layer appears, which creates a weak electric (electromagnetic) field. That is, if there is an object underground that contrasts with the natural (continuous) field of the Earth, then by recording these changes on the surface (intensities, polarization ellipses, frequencies, etc.), this object can be recorded. Using the high-frequency field illumination method, we excite this weak electromagnetic field, which allows us to more confidently identify anomalies in the natural electromagnetic field.
In practice, this makes it possible to detect centuries-old burials, foundations of destroyed buildings, voids in the ground (tunnels, caches, filled-in dugouts, underground passages up to 20 meters deep, etc.). The device also registers human remains, metal objects, metal and plastic pipelines, communication lines, etc. The device is quite successful in registering a person’s aura, which the device is able to detect at distances of about five meters through brickwork up to a meter thick, which can be used to determine the presence of people inside (outside) the premises (hostages, criminals, etc.).
The device was also tested in terms of energy information survey of the area near Lake Bolduc. The work was carried out at the request of the Chairman of the ICCC, Ph.D. Romanenko Galina Grigorievna and Deputy Chairman of the Presidium of the International Non-Governmental Educational Institution MAIT, Doctor of Technical Sciences, Professor, Academician of the BAN Sychik V.A. during our stay in Belarus at a scientific and practical conference"GIS-Naroch_2014".
More detailed information about the devices can be found on our website oooveles.com
We hope that our development will help you in your research."
And not about the 20-meter deep dungeon - we ourselves are in shock. The search engine guys sent this information as a thank you. The device showed that they drilled a well, and... the result is obvious.
ASSESSMENT OF THE POTENTIAL OF OPTICAL-ACOUSTIC TOMOGRAPHY IN THE DIAGNOSTICS OF BIO-TISSUE
T.D. Khokhlova, I.M. Pelivanov, A.A. Karabutov
Moscow State University named after. M.V. Lomonosov, Faculty of Physics
t khokhlova@ ilc.edu.ru
In optical-acoustic tomography, broadband ultrasonic signals are generated in the medium under study due to the absorption of pulsed laser radiation. Registration of these signals with high time resolution by an antenna array of piezoelectric receivers makes it possible to reconstruct the distribution of absorbing inhomogeneities in the medium. In this work, we carry out numerical modeling of the direct and inverse problems of optical-acoustic tomography to determine the capabilities of this diagnostic method (probing depth, image contrast) in the problem of visualizing light-absorbing inhomogeneities 1-10 mm in size located in a scattering medium at a depth of several centimeters. Such tasks include, for example, diagnosing human breast cancer in the early stages and monitoring high-intensity ultrasound therapy of tumors.
Optical-acoustic tomography is a hybrid laser-ultrasound method for diagnosing objects that absorb optical radiation, including biological tissues. This method is based on the thermoelastic effect: when pulsed laser radiation is absorbed in a medium, its non-stationary heating occurs, which leads, due to thermal expansion of the medium, to the generation of ultrasonic (opto-acoustic, OA) pulses. The pressure profile of an OA pulse carries information about the distribution of heat sources in the medium, therefore, from the recorded OA signals one can judge the distribution of absorbing inhomogeneities in the medium under study.
OA tomography is applicable to any task that requires visualization of an object with an increased light absorption coefficient relative to the environment. Such tasks include, first of all, the visualization of blood vessels, since blood is the main chromophore among other biological tissues in the near-IR range. An increased content of blood vessels is characteristic of malignant neoplasms, starting from an early stage of their development, therefore OA tomography allows for their detection and diagnosis.
The most important area of application of OA tomography is the diagnosis of human breast cancer in the early stages, namely, when the tumor size does not exceed 1 cm. In this task, it is necessary to visualize an object measuring ~1-10 mm located at a depth of several centimeters. The OA method has already been used in vivo to visualize tumors 1-2 cm in size; the method was shown to be promising, but images of smaller tumors were not obtained due to the insufficient development of OA signal recording systems. The development of such systems, as well as image construction algorithms, are today the most pressing problems in OA tomography.
Rice. 1 Multi-element antenna of focused piezoelectric receivers for two-dimensional OA tomography
Registration of OA signals is usually carried out by antenna arrays of receivers, the design of which is determined by the characteristics
specific diagnostic task. In this work, a new numerical model has been developed that makes it possible to calculate the output signal of a piezoelectric element of complex shape when recording OA signals excited by an arbitrary distribution of thermal sources (for example, an absorbing inhomogeneity located in a light-scattering medium). This model was used to estimate and optimize the parameters of the antenna array in the problem of OA diagnostics of human breast cancer. The results of numerical calculations showed that the new design of the antenna array, consisting of focused piezoelements (Fig. 1), can significantly improve the spatial resolution and contrast of the resulting OA images, as well as increase the probing depth. To confirm the correctness of the calculations, a model experiment was carried out, during which OA images of an absorbing inhomogeneity 3 mm in size located at a depth of 4 cm in a light-scattering medium were obtained (see Fig. 2). The optical properties of the model media were close to the values characteristic of healthy and tumor human breast tissue.
The inverse problem of OA tomography is to calculate the distribution of heat sources from the recorded pressure signals. In all studies on OA tomography to date, the brightness of the resulting images has been measured in relative units. Quantitative construction algorithm
two-dimensional OA images,
proposed in this work, allows us to obtain information about the distribution of thermal sources in absolute values, which is necessary in many diagnostic and therapeutic tasks.
One of the possible areas of application of OA tomography is monitoring of high-intensity
ultrasound therapy (in English literature - high intensity focused ultrasound, HIFU) of tumors. In HIFU therapy, powerful ultrasound waves are focused into the human body, which leads to heating and subsequent destruction of tissue in the focal area of the emitter due to ultrasound absorption. Typically, a single fracture caused by HIFU is approximately 0.5-1 cm in length and 2-3 mm in cross section. For
Rice. 2 OA image of a model absorbing object (pork liver, size 3 mm) located at a depth of 4 cm in a light-scattering medium (milk).
destruction of a large mass of tissue, the focus of the emitter is scanned over the required area. HIFU therapy has already been used in vivo for non-invasive removal of tumors in the mammary gland, prostate gland, liver, kidney and pancreas, however, the main factor preventing the mass use of this technology in the clinic is the insufficient development of methods for controlling the exposure procedure - visualization of the destroyed area, targeting. The possibility of using OA tomography in this area depends, first of all, on the ratio of light absorption coefficients in the original and coagulated biological tissues. The measurements carried out in this work showed that this ratio at a wavelength of 1064 μm is no less than 1.8. The OA method was used to detect the destruction created inside a biological tissue sample by HIFU.
1. V.G. Andreev, A.A. Karabutov, S.V. Solomatin, E.V. Savateeva, V.L. Aleynikov, Y.V. Z^Um, R.D. Fleming, A.A. Oraevsky, "Opto-acoustic tomography of breast cancer with arc-array transducer", Proc. SPIE 3916, pp. 36-46 (2003).
2. T. D. Khokhlova, I. M. Pelivanov, V. V. Kozhushko, A. N. Zharinov, V. S. Solomatin, A. A. Karabutov “Optoacoustic imaging of absorbing objects in a turbid medium: ultimate sensitivity and application to cancer breast diagnostics,” Applied Optics 46(2), pp. 262-272 (2007).
3. T.D. Khokhlova, I.M. Pelivanov., O.A. Sapozhnikov, V.S. Solomatin, A.A. Karabutov, “Optical-acoustic diagnostics of the thermal effect of high-intensity focused ultrasound on biological tissues: assessment of capabilities and model experiments,” Quantum Electronics 36(12), p. 10971102 (2006).
THE POTENTIAL OF OPTO-ACOUSTIC TOMOGRAPHY IN DIAGNOSTICS OF BIOLOGICAL TISSUES
T.D. Khokhlova, I.M. Pelivanov, A.A. Karabutov Moscow State University, Faculty of Physics t [email protected]
In optoacoustic tomography wideband ultrasonic signals are generated due to absorption of pulsed laser radiation in the medium under study. The detection of these signals with high temporal resolution by an array of piezodetectors allows to reconstruct the distribution of light absorbing inclusions in the medium. In present work numerical modeling of direct and inverse problems of opto-acoustic tomography is performed in order to evaluate the potential of this diagnostic method (maximum imaging depth, image contrast) in visualization of millimeter-sized light absorbing inclusions located within a scattering medium at the depth of several centimeters. The corresponding applied problems include the detection of breast tumors at early stages and visualization of thermal lesions induced in tissue by high intensity focused ultrasound therapy.
