The goal is to develop non-radiative damage, high-resolution biological tissue imaging methods and techniques, and to be non-invasive, real-time, safe, economical, small, and capable of monitoring the chemical composition of living organisms. Features. At present, the research work mainly focuses on the following aspects:
1. Time-resolved imaging technology, which uses ultrashort pulsed laser as a light source, according to the time-resolved characteristics of light pulses propagating in tissue, using gated technology to separate the so-called early light that is not scattered in the diffuse reflection pulse for imaging. Typical time gates being studied are striped cameras, Kerrmen, electronic holography, and the like. This technology is the most important one in optical tomography (OT) imaging;
2. Coherent Resolution Imaging (OCT). It uses a weak coherent light source (eg, a weak coherent pulsed laser or a broadband incoherent light source) with a very short coherence length (eg, 20 μm). The low-coherence performance of the light source is utilized to achieve imaging through a scattering medium, and the means are interferometer, holography, etc.;
3. Diffuse photon density wave imaging technology. A large proportion of diffuse light through biological tissue can also be used for medical imaging. The high-frequency modulated light is incident on the biological tissue, and the diffused photons are periodically distributed inside the biological tissue to form a diffused photon density wave. The photon density wave propagates in the biological tissue with a certain phase velocity and amplitude attenuation coefficient, and is refracted, diffracted, dispersed, and scattered, so that the emitted light carries information of the internal structure of the biological tissue. The amplitude and phase are measured, and then processed by computer data to obtain images of biological tissues.
4. Image reconstruction technology. The structural characteristic information of the biological scattering medium is implicit in the diffused light. If it can be found to describe the migration law of light in the medium, by testing the relevant parameters of the diffused light, and retrospecting the scattering path of the eye, it should be able to reconstruct the structure image of the scattering medium. If a lock-type laser is used as the light source, the stripe camera tests the time-resolved parameters of the diffused light around the scatterer, and then uses the inverse problem algorithm for image reconstruction. At present, there are two types of inverse problem algorithms: one is Monte Carlo method, and the image reconstruction accuracy is high, but the calculation is complicated; the other is based on the light transmission equation, using the optimization algorithm, according to the test time The signal of the diffused light is reconstructed for image reconstruction.
In addition to the above four technologies, other biological tissue imaging techniques have been developed in recent years, such as spatial gate imaging, time-resolved fluorescence imaging, stimulated Raman scattering imaging, and photoacoustic medical imaging techniques. At present, the international optical medical imaging technology is still in the initial research stage, and there is still a considerable distance from the practical use, but people have already seen it dawn.
Medical semiconductor laser and its application technology Because semiconductor lasers have a series of significant advantages such as small size, high efficiency, and various wavelengths in life, it has gradually replaced other lasers in laser diagnostic medical technology. It is likely to become the most important source of laser medical instruments. The current situation is: low-power semiconductor lasers, with wavelengths from 800nm ​​to 900nm and power of 3~10mW, have gradually replaced He-Ne lasers for irradiation therapy and photo-needle therapy, as well as various indicator light sources; medium power devices, wavelength 652nm~ 690nm, power 1~5W, has gradually replaced dye laser for photodynamic therapy, can treat deeper tumors; high-power semiconductor lasers may also replace Nd:YAG laser treatment machines. For example, a high-power semiconductor laser with a wavelength of 800 nm to 900 and a power of 30 W has a deep penetrating depth and is suitable for most diseases that can be treated by Nd:YAG laser.
Other medical laser technology development trends In recent years, there are notable research trends: one is the development of new working wavelength laser medical instruments; the other is the Ho:YAG and Er:YAG laser scalpels are practical; the third is the cavity The development of fiberoptic endoscopic laser medical technology for internal treatment; the fourth is the realization of laser medical equipment.
Medical photonics technology is divided into two categories: photon diagnostic medical technology and photon therapy medical technology. The former uses photons as information carriers, while the latter uses photons as energy carriers. At present, whether it is light diagnosis or light therapy technology, laser is the light source. If you focus on human application, these two technologies belong to the field of laser medicine. Laser medicine is a unique and important application field of medical photonics technology, and it is also a new branch of discipline that has emerged rapidly in recent years.
According to international and domestic developments, the following points are the main research contents of medical photonics technology:
Medical spectroscopy
Laser spectroscopy has become an important research field in medical photonics with its high spectral and temporal resolution, sensitivity, accuracy, and non-destructive, safe, and fast advantages. With the in-depth research and application of laser spectroscopy in the medical field, a "medical spectroscopy" with development potential and application prospects has gradually formed.
1. Autofluorescence and drug fluorescence spectra of biological tissues. Preclinical studies have been conducted on laser-induced biological tissue autofluorescence and drug fluorescence diagnosis of atherosclerotic plaques and malignancies. The content involves the absorption spectrum of the photosensitizer, the excitation and emission fluorescence spectra, and the characteristic spectra of the endogenous fluorophores of normal tissues and diseased tissues under laser excitation at various wavelengths. Based on this, a real-time fluorescence image processing system for cancer diagnosis and localization was also studied.
The research of laser fluorescence spectroscopy for the diagnosis of tumor technology has been paid close attention. The sensitivity of the spectral test method is very high. If the characteristic fluorescent peak of tumor cells can be found to diagnose the presence of cancer cells, it will play an important role in the early diagnosis and treatment of tumors. . However, the technology has not been used 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. The so-called characteristic fluorescent peak is actually only the fluorescent peak of the porphyrin molecule. Objective and scientific judgment of laser fluorescence spectroscopy is essential for the diagnosis of tumors.
At present, the drug fluorescence diagnosis of some cancers has entered clinical trials, and the application of autofluorescence is still in the process of exploration. It is necessary to carry out research on the mechanism of laser excitation of biological tissues and intracellular substances, and to investigate the correlation between laser-induced tissue autofluorescence and pathological types of cancer tissues, as well as the fluorescence spectrum, fluorescence yield and optimal excitation wavelength of novel photosensitizers. Obtain extremely stable and reliable characteristic data and provide scientific basis for the development of diagnostic technology.
2. Raman spectra of biological tissues. In recent years, the application of Raman spectroscopy in medicine has shown its advantages in sensitivity, resolution, and no damage. Overcoming the fluorescence spectroscopy technique to distinguish diseased tissue is due to the wide and easy overlap of biological macromolecules. The impact of diagnosis. At present, this research field is still in its infancy, and the following research work should be intensified: First, the Raman spectroscopy of important medical substances is studied, and its spectral database (including the sensitive spectrum corresponding to molecular components and structures) is established. Line and its intensity, etc.) Second, study the Raman spectrum of disease, analyze the changes and pathogenesis of biological components from normal to disease; Third, develop small, efficient, suitable for body and body medical Man spectrometer and diagnostic instrument.
3. Ultrafast time-resolved spectra of biological tissues. Ultrafast time resolved spectra are technically more sensitive, more objective, and more selective than steady state spectra. Therefore, ultrashort laser pulse light sources with pulse widths of the order of ps and fs have been widely used in medicine. First, ultrafast time-resolved fluorescence spectroscopy should be developed to measure the fluorescence decay time of biological tissues and biomolecules. To analyze the molecular relaxation dynamics of cancer tissues, etc., to provide basic data for further study of autofluorescence to diagnose malignant tumors; secondly, ultrafast time-resolved diffuse reflectance (transmission) spectroscopy should be developed. The diffuse reflection of the tissue is measured at an angle in the time domain to indirectly determine the optical characteristics of the tissue. This is a new, non-destructive and real-time measurement method for living organisms. It opens a new path to the understanding of the interaction between light and biological tissues and solving the basic measurement problems in medical photonics. Research on principles and techniques should be carried out to obtain valuable living optical parameters, which will provide a basis for the development of photodiagnosis and phototherapy techniques.
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