History of medical laser
With the development of laser technology, a brand-new applied discipline, laser medicine, has been gradually formed. The unique advantages of laser, which solves many difficult problems that cannot be solved by the traditional medical science in the basic research and Linchuan application, has attracted the attention of the domestic and foreign medical circles.
After Maiman researched the first ruby laser in 1960, it was used for welding technology for ophthalmic retinal peeling in 1961 Zaret, 1963 Campbell, 1964 Zweng, followed by Goodman in 1964, and Stern in 1964 for the field of stomatology. In ophthalmology, where lasers were first used and are also the most established discipline, laser therapy is cited as the first choice in certain ophthalmic diseases. For example, in fundopathy, retinal tears, central plasma retinopathy, diabetic retinopathy Coats disease, retinal schwannoma, retinal hemangioma, as well as primary glaucoma, laser keratoplasty treatment of myopia, this treatment is a computer technology applied to refractive medicine, a new technology, refractive cornea in the field of a revolution. There are laser keratomileusis (PRK), laser in situ keratomileusis and laser subepithelial keratomileusis, the last of which is the newest form of surgery.
The development of laser in other departments is also rapid, such as transurethral laser prostatectomy coagulation, laser myocardial hemodialysis, laser lithotripsy and so on.
Laser can be operated through a variety of endoscopes, such as holmium laser through the arthroscope for meniscectomy, cholecystectomy through laparoscopy, endometriosis, through the gastroscope, bronchoscopy on the digestive tract disorders, such as bleeding interest, polyps benign and malignant tumors, etc., the respiratory tract, scarring stenosis, inflammatory granulation and polyps, benign and malignant tumors, etc., laser treatment, through the enteroscopy likewise Can treat bleeding, polyps, benign and malignant tumors of the rectum, sigmoid colon and colon.
Laser pharyngoplasty has become a routine treatment for obstructive sleep apnea syndrome.
Laser transmission tools, such as rotating light-guided articulating arms and optical fibers to the rapid development, such as in 1971, West Germany, Nath can be made to transmit high-energy Ar + laser single quartz optical fiber, 1973, the first with the fiber-optic transmission of laser endoscopy, has developed into a variety of shapes made of fiber optic head (spherical, granular, etc.) for the laser to enter the inner lumen opens the way. In 1977, the United States developed into a thallium bromide and other multi-crystalline core of the new far-infrared fiber, in 1981, Japan also developed a successful CO2 laser fiber used in clinical applications.
Particularly photodynamic therapy, that is, photosensitive drugs with laser irradiation therapy, laser light source from a single He-Ne laser (no longer in common use) to the development of dye lasers, gold vapor lasers, krypton (Kr +) lasers and semiconductor lasers.
Photosensitizers have been developed from hematoporphyrin derivatives (HPD) into a wide variety of more effective laser photosensitizers, such as hematoporphyrin but monomethylhexylamine (HMME), synthetic fuel phthalocyanine in the sulfonated zinc phthalocyanine (ZR-PeS4). Sulfonated phthalocyanines (SPs), dihydroporphyrin derivatives of L-monoaspartyl dihydroporphyrin (Npe6) and chlorophyll derivative 4 (CPD4) and 5-amino ketoglutaric acid (ALA)
Photodynamic therapy ranges from the treatment of malignant tumors, such as skin, lung, gastrointestinal tract tumors, bladder cancer, etc., and also extends to the treatment of benign pathologies such as nevus erythematosus, age-related macular degeneration. age-related macular degeneration, etc.
Laser cosmetology used to be limited to skin pigmented nevus, vascular lesions, etc., has developed into cosmetic laser medicine, which is mainly due to the 1980s Anderson's "selective photothermal effect" theory, that is, according to the biological characteristics of different tissues, select the appropriate wavelength, energy, pulse duration, to ensure effective treatment of diseased tissues. In order to ensure that the lesions of the tissue for effective treatment at the same time, as far as possible to avoid damage to the surrounding normal tissue.
In the early 1980s, argon ions were used to treat vascular lesions, and yellow pulsed fuel laser (PDL) was developed in the late 1980s, and in the mid-1990s, the 532nm green light produced by YAG frequency doubling was used to treat nevus erythematosus, and the dilatation of small blood vessels was significantly improved; for melanin lesions, Q-switching ruby laser treatment was used in the 1980s. Nevus of Ota achieved better results in the 90's also developed to dual-frequency Q-switched Nd: YAG laser treatment of pigmented diseases obtained near-perfect results, in the removal of wrinkles, also by the development of pulsed CO2 laser to the super-pulsed CO2 laser treatment in 1994 (in the white better), in 1996 and developed to 2940nm bait laser treatment, so that the yellow skin with laser Wrinkle removal can be realized, hair removal from the early 90's ruby laser, Nd: YAG began, has developed to the late 90's semiconductor laser hair removal, to achieve better results.
The above talked about is the development of high-intensity laser, the patient lesion vaporization, cutting, coagulation and cauterization, the development of selective lesion destruction, without damaging the normal tissues, to achieve the therapeutic purpose.
In the laser treatment machine, but also supporting the production of special optical fiber, laser endoscopy and interventional therapy of various types of catheters. Laser with the slit lamp, laser operating microscope, etc., as well as various types of laser medical equipment required by the supporting equipment, there are special production of manufacturers supply.
In addition, the basic research on biomedical and clinical diagnostic laser equipment is also a key area of development at home and abroad, such as laser fluorescence technology, laser Raman technology, laser cell analysis technology, laser micro-beam technology, etc., and its corresponding laser equipment, some of which have been formed into a product, and some have been applied in the laboratory.
Laser performance parameters
1. Laser energy and output power. There are two aspects necessarily involved in laser bioeffects, the properties of the laser and the properties of biological tissues. There are many parameters that characterize the laser, but the most directly relevant to biomedicine are: laser wavelength, output energy or output power, irradiation energy density or irradiation power density, irradiation spot size, irradiation duration or pulse width. Among them, the most commonly used parameter is irradiation power density or irradiation energy density, that is, irradiation power (energy) divided by the area of the spot, the former is called "irradiance" [W/cm2 (watts/cm2)], and the latter is called "irradiation" [J/cm2 (Joule/cm2)], and the latter is called "irradiation" [J/cm2 (Joule/cm2)], and the latter is called "irradiation" [J/cm2 (Joule/cm2)], and the latter is called "irradiation". The latter is called "irradiance" [J/cm2 (J/cm2)], which is the main parameter for evaluating any biological effect, as well as for evaluating the effectiveness of clinical treatment. The formula is:
Power density= Irradiation power/spot area=P/πr2
Energy density= Irradiation energy/spot area=E/πr2
In this formula, P is the irradiation power in watts (W); π is the periphery of the circle (about 3.14); R is the radius of the spot; and E is the irradiation energy in joules (J), i.e., irradiation power × pulse width. ).
Generally continuous laser is expressed in terms of power density, pulsed laser is expressed in terms of energy density.
Laser irradiation to the human body of different dosage sizes, causing biological effects are also different, generally speaking, so that the destruction of tissue to achieve the purpose of healing, such as cauterization, coagulation, cutting, vaporization of the approach, we call it a strong laser, or high-powered laser; non-invasive treatment, that is, the laser effect on biological tissues, does not cause irreversible damage to the biological tissues, but stimulate the body to produce a series of response reactions To play a regulatory function of enhancement or inhibition, so as to achieve the purpose of curing the disease, this kind of laser we call low-intensity laser, or low-power laser, low-intensity laser, low-energy laser. Low-intensity laser is divided into large, medium and small doses, small doses can play a stimulating effect, large doses play a suppressive effect.
2. Laser oscillation mode. These include continuous, pulsed and Q-tuned. The main effect of continuous laser on the organism is thermal effect, while the effect of pulsed laser on the organism in the thermal effect at the same time, there is a non-negligible pressure effect, if you use the laser with Q tuning, you can improve the peak pulse power.
3. Laser wavelength. Different wavelengths on the body of the role of different, such as infrared laser on the role of the body is the thermal effect; red and near-infrared light can be more y transmitted to the depths of the organization, the role of the body of the ultraviolet wavelengths is the role of photochemistry, a variety of different wavelengths of the laser on the role of the organism has a distinctly different effect.
Laser mode: laser has a multi-mode and single-mode points, the power density of the cross-section belongs to the Gaussian type, that is, the power density of the middle of the spot than the edge of the edge of the power density is much larger, this mode has the best coherence, and has the best directional, so it can be used as a laser scalpel and holographic photography. Multi-mode lasers are easy to manufacture due to the process, so the machine is manufactured with higher power, and it is only used for localized irradiation in medical treatment.
4. Laser polarization. Because the light wave is a kind of electromagnetic wave, the light vibration vector to favor some direction of the phenomenon called polarization, with the polarization phenomenon of light called polarized light, the laser emitted by the laser, because of its light-emitting mechanism of the specificity of the light emitted by the light may be polarized light, generally with the Brewster window (Brewster window) of the laser emitted by the laser is completely polarized light, can be used to diagnose tumors on medical treatment, because the cancer cells and normal cells, the laser is used for local irradiation. The laser light emitted by a laser with a Brewster window is fully polarized, which can be used to diagnose tumors in medical treatment, and can distinguish between cancerous and normal cells because of the different polarization angles of these cells. In addition, Mester proved that as long as the light is polarized, regardless of whether it is coherent or not, it has a stimulating effect on living things, which is due to the intensity of the polarized electric field changes the conformation of the lipid bilayer of the cell membrane. This affects membrane surface properties such as changes in charge distribution, which in turn may affect every process related to the cell membrane, such as changes in cellular energy, immunity and enzymes.
5. Duration of action. Generally speaking, the longer the irradiation time of the laser on the organism, the stronger the reaction of the organism, the shorter the irradiation time, the less chance of heat transfer to the surrounding area, the smaller the heated volume, and the smaller the effect on the surrounding tissues.
Laser biological effects
(1) the mechanical properties of biological tissues (density, elasticity, etc.): high density of the tissue, the intensity of the laser effect on it is reduced.
(2) Thermal properties (specific heat, thermal conductivity, thermal diffusivity): the higher the thermal conductivity of the tissue, the greater the effect of the laser on it; the higher the thermal diffusivity of the tissue, the smaller the laser damage to it; the greater the electric capacity, the slower the rise in skin temperature.
(3) Electrical properties: impedance, polarization rate.
(4) Optical properties (reflectance, absorbance, transmission, scattering): the higher the absorbance of the laser on the tissue, the greater the response; the higher the reflectance and transmission, the less effect on the tissue.
(5) Acoustic properties: acoustic resistance, acoustic absorption rate.
(6) Biological properties: tissue pigmentation, water content, blood flow, inhomogeneity, hierarchical structure. The more pigmented the tissue, the stronger the effect of the laser on it.
It can be seen that the effect of laser on biological tissues is determined by many complex factors, especially the hierarchical structure of biological tissues, which makes the factors more complex. However, the main factors affecting the degree of biological response to laser irradiation in biological tissues are: the wavelength of the laser; the intensity of the incident light and the size of the laser divergence angle; the area and duration of radiation; the absorption characteristics of the target tissue; the water content and pigment content.
Ultraviolet light cannot be absorbed or stored by molecules because the photon energy is too high, but it can destroy enzymes and induce genetic mutations. For infrared light, on the other hand, because the photon energy is too small, can only make the molecules vibrate, rotate, and heat biological tissues. In the case of near-ultraviolet light, visible light up to near-infrared light can cause most of the photochemical processes that are essential in the life process. The most important aspect of the action of lasers on intracellular biochemical processes is the clarification of the actual value of *** vibrational absorption and the selective damage that occurs when the maximum absorption of intracellular metabolites coincides with the wavelength of the laser used, which is not described in detail here.
When the laser irradiation of the body surface and soft tissues, from the ultraviolet to the near-infrared wavelength, the longer the wavelength, the deeper the penetration, in the red and the near-infrared when the depth of penetration reaches its maximum value, the consideration of the biological role of the laser, the absorption system of biological tissues and the actual depth of penetration of the laser there are two parameters that need to be taken into account, according to a number of experiments, the following conclusions can be made: ① colored tissues than the absorption of colorless tissues large; ② colored The absorption of colored tissue is selective; ③ laser through soft tissue is easy to pass through the skin.