Life science is one of the biggest hot spots in the development of science and technology in the world today. At present, almost all science and technology will focus on people and human development issues, seeking their own meaningful growth points and development aspects, and the key research objects of life sciences are directed at some major issues of higher living organisms and the human body itself. In recent years, a new branch of the discipline that intersects photonics and life sciences—Biomedical Photonics—has been formed. Research work in this area is very active and developing very rapidly. It will open up a new field of life sciences. Nearly two-thirds of the papers published at the American Optical Annual Meeting in the past two years were related to life sciences. Specialized research institutions and magazines have also emerged internationally. For example, Japan has established a biomedical photonics research center, and several universities in the United States have also established several research groups. Laurin Publishing Company launches a new magazine "Bio-Photonics" in 1991. For many years, SPIE (Society for International Optical Engineering) has held a very large-scale international academic conference on "Biomedical Optics" at the beginning of each year, and published a new journal, Journal of Biomedical Optics, in 1996. "Applied Optics", one of the important journals of the Optical Society of America, also changed its "Optical Technology" column to "Optical Technology and Biomedical Optics" in 1996. Biomedical photonics includes biophotonics and medical photonics. There is still no clear boundary between the fields of photonics and photonic technology, which belong to biology or medicine, and there is overlap between the two. Among them, medical photonics has developed rapidly and has taken shape. At present, biomedical photonics mainly includes the following research contents: First, photons generated in biological systems and the life processes they reflect, as well as the importance of such photons in biological research, medical diagnosis, agriculture, environment, and even food quality inspection application. The detection, treatment, processing and transformation of biological systems using photons and their technologies is also an important task. The second is the foundation and technology of medical photonics, including research on tissue optics, medical spectroscopy technology, medical imaging, novel laser diagnosis and laser medical mechanisms and their mechanisms of action.
Biophotonics As early as the early days of photonics, the dynamic biological sciences and photonics have intertwined with each other, prompting the quiet rise of biophotonics, a marginal subject. In the early 1980s, this emerging field was proposed based on the discovery and research results of ultra-weak photon radiation (BPE) in biological systems. So far, people have gained some preliminary understanding of BPE. For example, they believe that BPE is a ubiquitous phenomenon in nature and an inherent function of living organisms. It is a reflection of the comprehensive information of organisms under different physiological and biochemical conditions. Except for a few lower organisms such as some protists and algae, most animals and plants can produce BPE. Moreover, the higher the degree of biological evolution, the greater the BPE value. The spectrum of BPE ranges from ultraviolet, visible to infrared bands. In addition, the higher the level of biological evolution, the more the wavelength of radiation expands toward infrared. BPE is highly coherent and has the characteristics of a Poisson coherent field. It is a low-level chemiluminescence with extremely low quantum efficiency in living organisms. If photonics is a technology that generates and utilizes radiation with photons as quantified units, and its application scope extends from energy generation and detection to information extraction, transmission and processing, then biophotonics involves biological systems using photons. The form releases energy and detects photons from biological systems, as well as the structural and functional information carried by these photons about biological systems, and also includes the use of photons to process and transform biological systems.
Photon emission of biological systems
The spontaneous ultra-weak luminescence of biological systems can be detected by living organisms, as small as bacteria, microorganisms and various animal and plant cells, as large as plants, animals and even humans. , there is spontaneous photon radiation. Usually, this photon emission is extremely weak, only a few to several thousand photons/second per square centimeter, so it is called the spontaneous ultra-weak luminescence of the system. Its spectral range is quite wide, extending from ultraviolet to near-infrared, and must be detected with sensitive photodetectors. Research in the past 30 years has shown that biological ultra-weak luminescence is intrinsically linked to many basic life processes such as biological oxidative metabolism, cell division and death, photosynthesis, canceration and growth regulation, and it is precisely because it is closely related to living things. The biochemical processes occurring in living organisms and the physiological and pathological states of living organisms are closely related, so they have potential diagnostic value in many aspects such as medicine, agriculture, and the environment.
The nature of ultra-weak luminescence in biological systems. The source of ultra-weak luminescence in biological systems has always been the focus of researchers. It is currently believed to come from the following aspects: 1. Continuously produced due to oxidative metabolism in biological systems Reactive oxygen free radicals, which produce singlet oxygen and excited carbon radicals, are affected by the antioxidant defense system and immune system in organisms; 2. Excited molecules formed by enzymatic reactions in organisms; 3. Due to the collective effect The formed excited states and excited state complexes of important biological macromolecules (such as DNA and its carboxyl groups) have their energy level distribution far away from the Boltzmann distribution, which puts the biological system in a highly inverted state of energy levels, and interacts with each other. Emit photons with a certain degree of coherence. Its degree of coherence may be a characteristic of life. Does ultraweak photon radiation from biological systems carry information, and does it constitute a pathway for communication between biological systems and between cells within them? These are important issues of concern. Deeply understanding the nature of ultra-weak biological luminescence and developing its application potential are one of the basic tasks of biophotonics.
Important applications of ultra-weak luminescence in biological systems Ultra-weak luminescence in biological systems has important applications in clinical diagnosis, crop genetic diagnosis and environmental monitoring functions. Because ultra-weak luminescence is related to the physiological and pathological conditions of organisms, it has potential application value in clinical diagnosis. For example, studies have shown that compared with healthy people, tumor patients have increased ultra-weak luminescence in their blood and many organs and tissues. In addition, the study also found that the dependence of the ultra-weak luminescence of seeds and sprouts on temperature, humidity, and salinity reflects the cold, drought, and salt-alkali resistance of crops to a certain extent, showing that ultra-weak organisms Luminescence has important application prospects in agricultural selection and breeding. Environmental monitoring using physical and chemical methods can only give the degree of pollution measured at that time. Since the ultra-weak luminescence of biological systems is extremely sensitive to chemical pollution in environmental water sources and the atmosphere, it can be used as a biological indicator of environmental pollution, providing a new and simple method for environmental monitoring.
The imaging of biological ultra-weak luminescence uses highly sensitive photon detection and imaging technology, combined with photon statistics and photon correlation measurement technology, to obtain two-dimensional images of ultra-weak luminescence of organisms in the visible or near-infrared band. , used to measure the body's metabolic function and anti-oxidation and anti-aging body defense functions. Therefore, it is expected to have important applications in disease and clinical diagnosis.
Optical communication between biological systems and cells It is generally believed that "communication" between cells is always achieved with the help of some special "messenger molecules". "Messenger molecules" include hormones, antibodies, growth factors and neurotransmitters, as well as certain inorganic ions. This kind of communication is essentially "chemical communication" achieved through intermolecular interactions (such as the interaction between messengers and receptor proteins on the cell membrane). Is there "physical communication" between cells? That is, is there modern information transmission between cells through electromagnetic fields or photon interactions? There is experimental evidence that it is possible to transmit information between cells, tissues and even organisms through the emission and reception of photons. The study of optical communication between cells will reveal a little-known aspect of life phenomena and may have important applications in many aspects such as medicine, fitness and agriculture.
Induced luminescence of biological systems Short-term strong light irradiation from the outside can induce photon divergence in biological systems. The intensity of this induced luminescence is usually much higher than the intensity of spontaneous luminescence, and it decays over time. The spectrum and intensity of induced luminescence depend on the type and content of excitable molecules that make up the biological system, as well as on the interaction and energy transfer between molecules. Therefore, induced luminescence will be able to provide information about the structure of the biological system. This kind of luminescence It has long been used in the study of plant photosynthesis. Recent studies have shown that this induced luminescence has very attractive application prospects in the diagnosis of diseases and the detection of food quality.
The application of photon technology in biological sciences With the rapid development of laser technology, spectroscopy technology, microscopy technology and optical fiber technology, their application in biological science research and medical diagnosis is closely related to the application of photon technology in biological science. The applications are becoming more and more in-depth and extensive, and it has become an important tool in modern life sciences and brought revolutionary changes to it.
Fluorescent probes and laser scanning focal microscopy The basic principle of laser scanning focal microscopy is to focus a laser beam at an arbitrarily selected depth within the cell into a line close to a single molecule. Very small spots are scanned at a certain depth within the cell. Through the optical system, a clear image of one level of the cell can be obtained. Continuously change the focus depth of the laser, scan at a series of levels, and finally obtain a three-dimensional image of the entire cell. Using currently thousands of fluorescent probes that specifically bind to different molecules (or ions) in cells, people can directly observe the position, movement, and interactions with other molecules of various important biomolecules in living cells. For example, you can observe microtubules, microfilaments and intermediate fibers on the cytoskeleton, observe various important enzymes and messenger molecules on the signal transduction pathway, and use genetic recombination technology to introduce existing fluorescent proteins into cells and scan them with lasers. ***Focal microscopy studies gene expression, intracellular protein interactions and intracellular "traffic", etc. The combination of fluorescent probes and fluorescent proteins with laser focus microscopy allows people to see a complex and colorful world inside cells.
Multiphoton fluorescence imaging technology Currently, focal microscopy uses argon ion lasers in the visible light band, which may cause damage to living cells. Using multi-photons, such as multi-photon excitation, has at least the following three advantages: First, due to near-infrared light excitation, the damage to living cells is greatly reduced; second, in tissues, since near-infrared light has a higher transmittance than visible light , so deeper fluorescence imaging in the sample can be observed; third, many fluorescent probes used in the visible region and even the purple region can still be used. This technology mainly uses high-intensity infrared lasers to make the excitation efficiency of two-photons equivalent to that of short-wavelength single photons. There are already some lasers that meet this requirement.
Optical tweezer and single-molecule manipulation Optical tweezer technology was born in the 1980s and developed in the 1990s. The basic principle is: when a particle (such as a silicon bead combined with a biological macromolecule) is in a laser beam with a Gaussian distribution of intensity, the beam will produce a gradient pressure on the particle due to the spatial variation of the light field intensity. Driving it toward the center of the beam and stabilizing it there. In this way, the laser beam acts like a "pincer" to tightly clamp the particles and allow them to move artificially with the beam. The pressure exerted by the optical clamp on the particles depends on the wavelength of the light, the width and power of the beam, etc. When the power of the laser is several milliwatts to several watts, the force exerted on micron-sized particles is approximately several to several hundred picoNewtons (10-10). In order to prevent the laser from being strongly absorbed by biological tissues, optical forceps generally use near-infrared laser light sources. An important application of optical clamp technology is to study and observe a type of protein-molecular motors that are closely related to muscle contraction, cell division, protein synthesis, etc. During research, a micron-sized silicon bead or polystyrene bead is connected to these molecular motors, the bead is clamped with optical clamps under a microscope, and the molecular motor is started, and the force generated by the movement of the molecular motor can be measured.
German scholars have used lasers to drill holes in the egg cell membrane and used optical forceps to capture sperm and send it into the egg cell, greatly improving the success rate of in vitro fertilization. In the future, a new generation of optical clamps will be equipped with a force feedback mechanism, so that the force exerted by the optical clamp on the captured ions can change their size, thereby studying various factors that affect molecular motors. Optical forceps can also be used to perform various processing on cells. Therefore, -----optical clamps will play an important role in cell engineering technology.
Medical Photonics
Today, medicine is in a period of major change. The focus of medicine is changing from the traditional symptom-based treatment model to an information-based treatment model. People have realized that symptoms are just delayed and crude abnormal reactions of the body to the disease. Research on some major medical topics today focuses from the beginning on exploring the biological information patterns that cause disease, in order to control biological logic information in a healthy state, and then achieve the purpose of treating diseases. To this end, new methods of medical diagnosis and treatment are explored from various disciplines (magnetism, acoustics, chemistry, optics, etc.). Photonics are currently thought to have the potential to play an important role in today's major revolution in medicine. Understanding the propagation laws of light in biological tissues, and the successful development of high-performance light sources and high-sensitivity optical detectors represented by lasers are the theoretical basis and material basis of this cognition respectively. The combination of emerging photonics and modern medicine has formed a new interdisciplinary growth point: Medical photonics. The development motivation of medical photonics mainly comes from the urgent needs of medicine. Many specific applications of clinical light therapy and light diagnosis, such as photometrics in laser medicine, optical imaging diagnostics, tumor diagnosis and treatment, etc., raise various questions that urgently need satisfactory answers from medical photonics. This has greatly promoted the rapid development of medical photonics. The direct object of medical photonics research is biological tissue, especially living biological tissue. Its research results will directly serve human medicine and may create new high-tech industries and contribute to human civilization and social progress. Medical photonics is in the emerging stage. Although our country's research foundation and conditions are relatively backward, we have many advantages in practice and are on the same starting line as foreign countries. Therefore, as long as we are well organized and choose the topic appropriately, we will definitely achieve success in the field after hard work. Breakthroughs have been made in certain aspects, such as theory, calculation and clinical aspects, and have taken an international leading position.
Basics of Medical Photonics The laws and knowledge about the interaction between light, especially lasers, and biological tissues have attracted international attention and have become the foundation and prerequisite for the application of laser biomedicine, which is booming. For example, one of the key issues in photodynamic treatment and diagnosis of tumors, which is currently on the verge of clinical application, is how to design and confirm the light distribution in human tissues. This involves theoretical and experimental issues in many disciplines, including The most important ones include the special way that light propagates in tissues, the description of the optical properties of tissues, and the development and improvement of relevant experimental techniques, etc. All new problems arising from these research efforts must be solved with new thinking and methods. Although a preliminary model of light propagation in biological tissues has been established, a unified optical theory of biological tissues is far from mature. In this context, "Tissue optics" emerged as a specialized discipline to study the optical properties of biological tissues. It involves the most basic theoretical issues in medical photonics and is an important step in the further development of photomedicine (including photodiagnosis and photonics). treatment). Tissue optics is the theoretical basis of medical photonic technology. The kinematics (such as the propagation of light) and dynamics (such as the detection of light) problems of light in biological tissues are the main contents of the research. The current main research tasks are: studying the optical properties of biological tissues and determining the light energy flow rate per unit area of ??a certain target. The former involves determining the basic optical parameters of the tissue from the measured light distribution and a certain light propagation model, which is called the "positive" problem; the latter derives the light distribution in the tissue based on the basic optical parameters of the tissue and the light propagation model, which is a "positive" problem. "Inverse" problem.
At present, taking into account the possibilities provided by international development trends and domestic reality, research work should be carried out in the following aspects:
Theoretical research on light transmission in biological tissues is currently based on the neutron transmission theory. The model of light propagation in biological tissues is still far from establishing a unified theoretical architecture system for tissue optics. The optical theory of biological tissues is far from mature, and there are many theoretical gaps to be filled. The reason for this situation naturally stems from the diversity and complexity of the biological tissue structure itself. On the other hand, it is also the result of insufficient theoretical tools. There is a need for more sophisticated and accurate theories to replace the oversimplified existing models, that is, more complex theories to describe the optical properties of biological tissues and the propagation behavior of light in them. The first thing that needs to be done is to establish an accurate optical model of tissue so that it can reflect the spatial structure and size distribution of biological tissue, the scattering and absorption characteristics of various parts of the tissue, and the changes in refractive index under certain conditions; the other The second is: transform the transmission equation to adapt to new conditions, and be able to find out the basic properties of light transmission in biological tissues under certain circumstances.
Monte Carlo simulation calculation of light transmission Monte Carlo calculation simulation method has played an irreplaceable role in many fields. There are already some relatively successful algorithms, but new and more effective algorithms should continue to be developed to adapt to the requirements of the diversity and complexity of biological tissues. In addition to understanding the distribution of light in tissues, we are also exploring the empirical relationship between the macroscopic distribution of light in biological tissues and the basic parameters of its optical properties from a large number of digital simulations. In addition, the development of Monte Carlo simulation methods for unsteady-state light transmission is also an important research direction, from which more information can be obtained than under steady-state conditions.
Measurement methods and techniques for tissue optical parameters. After the theory of light transmission in tissues is established, a key task is to determine the basic parameters of the optical properties of the tissue, especially the human body, namely the absorption coefficient, scattering coefficient and Scattering phase function or average scattering cosine g and refractive index n, etc. Once these interaction parameters between light and tissue are known, under given illumination methods and boundary conditions, the distribution of light energy flow rate or other parameters, total reflectance R, total transmittance T, etc., can be uniquely determined by the relevant transmission model. . At present, the measurement methods of optical properties of biological tissues need to be further developed and improved, among which non-destructive testing of living bodies is particularly important. In this regard, the measurement methods of time resolution and frequency resolution are interesting.
Relationship between refractive index of biological tissue and dispersion People use assumed refractive index data (1.33-1.38) in various situations, but the research on the refractive index of biological tissue has been ignored to some extent. So far, people have not made an in-depth conceptual analysis of the refractive index of biological tissues, nor have they fully mastered the precise measurement method of the refractive index of living or even isolated tissues. In addition, accurate measurement is difficult due to the strong scattering of tissues. Reliable experimental data on various tissues of the human body have not yet been obtained. It has been proven that the refractive index and dispersion parameters of biological tissues are very important for in-depth study of tissue optics, both theoretically and experimentally. In view of this, the measurement and methods of refractive index and dispersion parameters of biological tissues should be studied as one of the focuses.
Some thoughts on the theoretical work of tissue optics
In summary, as the tissue optics part of medical photonics, in addition to developing measurement technology and establishing a tissue optical parameter database, In theory, we can focus on the following issues: A. Continue to improve the biological tissue light transmission model. First, we must develop a model with fewer restrictions, fast and accurate; second, we must refine the tissue optical model to make it consistent with biological tissue, especially The state of living tissue is similar; B. Study the propagation behavior of short pulse light in tissues and the time changing characteristics of diffuse scattered light to make sufficient theoretical preparations for optical imaging; C. Study the propagation characteristics of modulated light in biological tissues, For example, irradiating amplitude-modulated light onto tissue will produce slow-scattering photon density waves, which will also produce reflection, refraction, diffraction, scattering, dispersion, etc. It can detect the optical property parameters of the tissue non-destructively, and can also be used for imaging; D. Study the influence of the optical properties of scattering and absorption of biological tissues on the measurement of fluorescence and its spectrum. Numerical simulation research has initially shown that this effect cannot be ignored. E. Carry out computer simulations of the transmission process of light in complex tissue structures, and through a large number of simulations, find simple and effective rules to explain the basic principles of light transmission in tissues. properties, and establish connections between various parameters to provide a basis for the measurement of tissue optical properties; F. Unify the description of optical property parameters of biological tissues and establish a complete tissue optical theoretical system.
Medical photon technology
Medical photon technology is divided into two categories: photon diagnostic medical technology and photon treatment medical technology. The former uses photons as information carriers, while the latter uses photons as information carriers. energy carrier. At present, whether it is light diagnosis or light treatment technology, most of them use laser as the light source. If we focus on human body applications, these two technologies belong to the category of laser medicine. Laser medicine is a unique and important application field of medical photonic technology, and it is also a new subject branch that has emerged rapidly in recent years (see point 3 of this section for details).
According to the international and domestic development situation, the following points are the main research contents of medical photonic technology:
Medical spectroscopy technology laser spectroscopy, with its extremely high spectral and time resolution, It has become an important research field in medical photonics due to its advantages of sensitivity, accuracy, losslessness, safety and speed. With the in-depth research on the application of laser spectroscopy technology in the medical field, a "medical spectroscopy" with development potential and application prospects has gradually taken shape.
1. Autofluorescence and drug fluorescence spectra of biological tissues. Preclinical research has been conducted on laser-induced autofluorescence of biological tissues and drug fluorescence for the diagnosis of atherosclerotic plaques and malignant tumors. The content involves the absorption spectra, excitation and emission fluorescence spectra of photosensitizers, and the characteristic spectra of endogenous fluorescent groups in normal tissues and diseased tissues under laser excitation of various wavelengths. On this basis, a real-time fluorescence image processing system for cancer diagnosis and localization was also studied.
The research on laser fluorescence spectroscopy tumor diagnosis technology has always attracted much attention. The sensitivity of spectral testing method is very high. If the characteristic fluorescence peaks of tumor cells can be found to diagnose the existence of cancer cells, it will be helpful for the early stage of tumors. Diagnosis and treatment will play a huge role. But so far, this technology cannot be used alone as a basis for cancer cell detection in clinical practice. The key reason is that the true characteristic fluorescence peak of cancer cells has not yet been found. What people now call characteristic fluorescence peaks are actually just the fluorescence peaks of porphyrin molecules. It is very necessary to objectively and scientifically judge the diagnostic criteria of laser fluorescence spectrum for tumors. At present, drug fluorescence diagnosis of some cancer tumors has entered clinical trials, and the application of autofluorescence is still being explored. It is necessary to carry out research on the mechanism of laser excitation of biological tissues and intracellular substances, to explore the correlation between laser-induced tissue autofluorescence and the pathological types of cancer tissue, as well as research on the fluorescence spectrum, fluorescence yield and optimal excitation wavelength of new photosensitizers, in order to Obtain extremely stable and reliable characteristic data to provide scientific basis for the development of diagnostic technology. 2. Raman spectrum of biological tissues. In recent years, the application of Raman spectroscopy technology in medicine has shown its advantages in terms of sensitivity, resolution, and non-destruction. It overcomes the difficulty of fluorescence spectroscopy technology in distinguishing diseased tissues because the fluorescence bands of biological macromolecules are wide and easy to overlap. Impact of diagnosis.
At present, this research field is still in its infancy, and the following research work should be stepped up: First, study the Raman spectra of important medical substances and establish its spectral database (including sensitive characteristic spectra corresponding to molecular components and structures) lines and their intensity, etc.); second, study the Raman spectrum of diseases, and analyze the changes in biological components and pathogenesis from normal to disease; third, develop small, efficient, and medical Raman spectrometers suitable for use on the body surface and inside the body. Man spectrometers and diagnostics. 3. Ultrafast time-resolved spectroscopy of biological tissues. Ultrafast time-resolved spectroscopy is technically more sensitive, objective, and selective than steady-state spectroscopy. Therefore, the use of ultrashort laser pulse light sources with pulse widths of the order of ps and fs in medicine has received widespread attention. First, ultrafast time-resolved fluorescence spectroscopy technology should be developed to measure the fluorescence decay time of biological tissues and biomolecules. Analyze the molecular relaxation dynamics properties of cancer tissue to provide basic data for further research on autofluorescence diagnosis of malignant tumors; secondly, ultrafast time-resolved diffuse reflection (transmission) spectroscopy technology should be developed. The diffuse reflectance of the tissue is measured in the time domain to indirectly determine the optical characteristics of the tissue. This is a brand-new, non-destructive and real-time measurement method suitable for living bodies. It opens up a new way to determine the interaction between light and biological tissues and solve basic measurement problems in medical photonics. Research on principles and techniques should be carried out as soon as possible to obtain valuable in vivo optical parameters and provide a basis for the development of photodiagnosis and phototherapy technology.
The goal of medical imaging technology is to develop non-radiation damage, high-resolution optical imaging methods and technologies for biological tissues, which should be non-invasive, real-time, safe, economical, small, and capable. Monitor the characteristics of the chemical composition of living tissue in its natural state. Current research work mainly focuses on the following aspects:
1. Time-resolved imaging technology, which uses ultrashort pulse laser as the light source and uses gating based on the time-resolved characteristics of the light pulse propagating in the tissue. The technology separates out the so-called early light that is not scattered in the diffuse reflection pulse and performs imaging. Typical time gates being studied include streak cameras, Kerr gates, electronic holography, etc. This technology is the most important type of optical tomography (OT) technology; 2. Coherent resolution imaging technology (OCT). It uses a weakly coherent light source (such as a weakly coherent pulsed laser or a broadband incoherent light source), and its coherence length is very short (such as 20 μm). Utilizing the low coherence performance of the light source to achieve imaging through scattering media, the methods include interferometers, holography, etc.; 3. Diffuse photon density wave imaging technology. Diffuse light that passes through biological tissue accounts for a considerable proportion, and it can also be used for medical imaging. High-frequency modulated light is injected into biological tissue, and the diffused photons are periodically distributed inside the biological tissue to form diffuse photon density waves. This photon density wave propagates in biological tissues with a certain phase velocity and amplitude attenuation coefficient, and is refracted, diffracted, dispersed, and scattered, so that the emitted light carries information about the internal structure of biological tissues. By measuring its amplitude and phase, and then through computer data processing, relevant images of biological tissues can be obtained. 4. Image reconstruction technology. Information about the structural characteristics of biological scattering media is implicit in diffuse light. If we can find the rules describing the migration of light in the medium, by testing the relevant parameters of the diffuse light and tracing the scattering path of the eye backwards, we should be able to reconstruct the structure image of the scattering medium. For example, a locking laser is used as the light source, a stripe camera tests the time-resolved parameters of the diffuse light around the scatterer, and then the inverse problem algorithm is used to reconstruct the image. At present, there are generally two types of inverse problem algorithms: one is the Monte Carlo method, using this method, the image reconstruction accuracy is high, but the calculation is complicated; the other is based on the light transmission equation, using an optimization algorithm, according to the test surrounding time Resolution of diffuse light signals for image reconstruction.
In addition to the above four technologies, other biological tissue imaging technologies have also been developed in recent years, such as spatial gate imaging technology, time-resolved fluorescence imaging, stimulated Raman scattering imaging and photoacoustic medical imaging. Technology etc. At present, optical medical imaging technology is still in its initial research stage internationally and is still far from practical use, but people have already seen its beginnings.
Medical semiconductor laser and its application technology. Because semiconductor lasers have a series of significant advantages such as small size, high efficiency, and multiple wavelength options for life, they have gradually replaced other laser diagnostic medical technologies. The trend of multiple lasers may become the main light source for laser medical instruments. The current situation is: low-power semiconductor lasers, with a wavelength of 800nm~900nm and a power of 3~10mW, have gradually replaced He-Ne lasers for irradiation therapy and photoacupuncture therapy, as well as various indicating light sources; medium-power devices, with a wavelength of 652nm~ 690nm, power 1~5W, has gradually replaced dye lasers for photodynamic therapy and can treat deeper tumors; high-power semiconductor lasers may also replace Nd:YAG laser therapy machines. For example, a high-power semiconductor laser with a wavelength of 800nm~900 and a power of 30W can penetrate deep into tissue and is suitable for most diseases that can be treated by Nd:YAG laser.
Other development trends in medical laser technology. In recent years, noteworthy research trends include: one is the development of new working wavelength laser medical instruments; the other is the trend of Ho:YAG and Er:YAG laser scalpels. Practicalization; the third is the development of fiber-optic endoscopic laser medical technology suitable for intracavity treatment; the fourth is the realization of intelligent laser medical equipment.
Laser Medicine
Photodiagnosis and phototherapy technology using laser as light source and focusing on human application has opened up an important new field of laser medicine. Over the years, laser technology has become an effective means of clinical treatment and a key technology in the development of medical diagnosis. It solves many difficult problems in medicine and contributes to the development of medicine. Now, we maintain a sustained and strong momentum of development in many aspects such as basic research, new technology development, and new equipment development and production. The current outstanding application research of laser medicine is mainly reflected in the following aspects:
1. Photodynamic therapy (PDT) for cancer treatment Photodynamic tumor therapy is a major topic of widespread concern around the world. After the body is injected with a photosensitizer that can accumulate in tumors, it is irradiated by laser and produces a photochemical effect, which can selectively kill tumor cells. There are two main problems at present: First, the skin has severe photosensitivity side effects and needs to be protected from light for a long time; but the depth of the laser penetrating into the human body is too shallow, and deep-seated tumors cannot undergo actinization, so the possibility of recurrence is very high. We are now actively researching and developing photosensitizers with excellent performance and lasers that can penetrate deep into tissues and interact well with photosensitizers. The prospects for this therapy remain very promising.
2. Laser treatment of cardiovascular diseases The technology of percutaneous laser coronary angioplasty to treat coronary artery stenosis and obstructive lesions has made great progress. Coronary angioplasty with the excimer laser has become the method of choice. However, due to problems such as restenosis of the lumen that need to be further solved, this technology is still difficult to effectively promote. In addition to the above-mentioned coronary angioplasty, myocardial vascular reconstruction, laser direct ablation of abnormal cardiac rhythm points, and treatment of severe arrhythmias are also current research hotspots