Full name: Positron Emission Computed Tomography (Positron Emission Computed Tomography), is a relatively advanced clinical examination imaging technology in the field of nuclear medicine. The general method is to label a certain substance, which is generally necessary in the metabolism of biological life, such as glucose, protein, nucleic acid, fatty acid, with short-lived radionuclides (such as F18, Carbon 11, etc.), and inject it into the human body, and then reflect the metabolic activity of life through the aggregation of the substance in metabolism, so as to achieve the diagnostic purpose. Recently, the main substance used in hospitals is fluorodeoxyglucose, FDG for short, the mechanism is that the metabolic state of different tissues of the body is different, and glucose metabolism is exuberant and aggregates more in the tissues of malignant tumors with high metabolism, and these characteristics can be reflected in the image, so that the lesion can be diagnosed and analyzed.
1 Principle of PET Examiner
Some short-lived substances, in the process of decay, release a positron, which travels 1 to 3 centimeters and encounters an electron and then undergoes annihilation, thus generating a pair of 511KeV of energy in basically opposite directions. This information, captured by a highly sensitive camera and corrected by a computer for scattering and random information, allows us to obtain a three-dimensional image of the situation of aggregation in an organism.
2 Advantages of PET examination
PET is currently the only new imaging technology that can display the metabolism of biomolecules, receptors and neuromediators' activities in the living body, and it is now widely used in the diagnosis and differential diagnosis of a variety of diseases, judgment of the condition, evaluation of the efficacy of treatment, research on the function of the organ, and the development of new drugs. (1) High sensitivity: PET is a kind of imaging reflecting molecular metabolism, when the disease is in the early stage of molecular level changes, the morphology and structure of the lesion area has not yet presented abnormalities, MRI, CT examination can not be a clear diagnosis, PET examination can be found where the lesion is, and can be obtained from three-dimensional images, but also can be quantitatively analyzed, to achieve an early diagnosis, which is currently incomparable to other imaging examinations. (2) High specificity: It is difficult to judge whether a tumor is benign or malignant when it is found in organs by MRI or CT examination, but PET examination can diagnose malignant tumors according to their high metabolic characteristics. (3) Whole-body imaging: PET can obtain images of all areas of the body in one-time whole-body imaging. (4) Good safety: The nuclide needed for PET examination has a certain degree of radioactivity, but the amount of nuclide used is very small, and the half-life is very short (the short one is about 12 minutes, and the long one is about 120 minutes), and after physical attenuation and biological metabolism, it will remain in the body of the examined person for a short period of time. The radiation exposure dose of a PET whole-body examination is much smaller than that of a conventional CT examination of a part of the body, and is therefore safe and reliable.
3 Who is a good candidate for PET?
(1) Tumor patients. At present, 85% of PET examination is used for tumor examination, because most of the malignant tumors have high glucose metabolism, and FDG, as a compound with similar structure to glucose, will accumulate in malignant tumor cells after intravenous injection, so PET can identify malignant tumors with benign tumors and normal tissues, and also distinguish recurrent tumors from the surrounding necrotic and scar tissues, which is now mostly used for lung cancer, breast cancer, colorectal cancer, ovarian cancer and other cancers, as well as other cancers, Now it is mostly used for the examination of lung cancer, breast cancer, colon cancer, ovarian cancer, lymphoma, melanoma and so on, and its diagnostic accuracy is more than 90%. This kind of examination can show at a glance whether the malignant tumor disease has metastasis and the site of metastasis, which plays an important guiding role in the staging of tumor diagnosis, whether surgery is needed and the scope of surgical resection. According to foreign data, nearly one-third of tumor patients need to change the original surgical plan after PET examination before surgery. In the early stage of tumor chemotherapy and radiotherapy, PET examination can find out whether the tumor treatment has been effective and provide help for determining the next treatment plan. Some data show that PET can detect the metabolic changes of tumor cells as early as 24 hours after tumor chemotherapy and radiotherapy. (2) Neurological diseases and psychiatric patients. It can be used for localization of epileptic foci, early diagnosis and differentiation of Alzheimer's disease, evaluation of Parkinson's disease, and judgment of tissue damage and survival after cerebral infarction.PET examination has shown unique advantages in the pathological diagnosis of psychiatric diseases and evaluation of treatment effects, and is expected to make breakthrough progress in the near future. PET examination has shown unique advantages in the pathologic diagnosis of psychosis and evaluation of treatment effects, and is expected to make breakthroughs in the near future. It has an important role in guiding the development of new drugs in the treatment of AIDS encephalopathy and drug addiction treatment. (3) Patients with cardiovascular diseases. It can check the location and scope of myocardial ischemia in coronary heart disease and accurately evaluate myocardial vitality to determine whether thrombolytic therapy, coronary stenting or coronary artery bypass grafting surgery is needed. It is capable of evaluating the therapeutic effect of coronary artery disease by analyzing myocardial blood flow and determining coronary artery reserve capacity in conjunction with drug loading.
4, PET/CT and MR/PET
Due to the characteristics of nuclear medicine technology, PET has some limitations in terms of precision and some limitations in terms of localization. For this reason, we consider the results of this device in combination with the results of radiology. However, if the scanning time is different and the state of the less dense tissue is unstable, the results of fusing the images of the two devices are often less precise. Since 2000, the industry has solved the problem of integrating PET and CT equipment for simultaneous scanning.PET/CT not only solves the problem of simultaneous scanning, but at the same time, the density map obtained from CT scanning, which is used for scatter correction, can greatly improve the precision and diagnostic accuracy. Currently, the most advanced equipment can reach 52-ring PET with 64-slice CT summing (e.g., Siemens Biograph64), which can be used for precise localization of cardiac function and malignant lesions through synchronization with ECG (the term is called gating) and manual ECG editing and reconstruction to take into account heart rate irregularities. Currently, a company is experimenting with an integrated MR/PET device called MR/PET, which fully integrates MR's ability to detect soft tissue density and PET's ability to detect molecules at a molecular level, and will have a very important performance for the diagnosis of brain and neurological disorders, which is worthy of anticipation. Although PET has the above advantages, it still has the following shortcomings: (1) There are still some limitations in the diagnosis of the pathological nature of tumors, for example, the specificity for inflammation is not good. (2) The examiners need to have rich experience, especially in what kind of examination position and how much nuclide should be injected into patients with different diagnostic needs of different body shapes, and sometimes the readers have to have the knowledge of both radiology and nuclear medicine at the same time. (3) The cost of the examination is expensive, and a whole-body PET examination currently costs about 10,000 yuan, which is not easy to promote.
Source:/view/67860.htm#6
Thermoplastic elastomers (TPEs) have the physical and mechanical properties of vulcanized rubber and the processability of thermoplastics. Since there is no need for hot vulcanization, the use of general-purpose plastics processing equipment can complete the production of products. This feature makes the rubber industry production process shortened by 1/4, saving 25% to 40% of energy consumption, improve efficiency 10 times to 20 times, known as the rubber industry and a material and process technology revolution. This year, with the increasing frequency of domestic and international exchanges, some domestic TPE/TPR manufacturers have begun to halogen-free flame retardant development in this area, which is a more far-reaching impact on China and even the world.
The advantages of TPE
1. general thermoplastic molding machine processing, do not need special processing equipment. 2. 2. Production efficiency is greatly improved. Can be directly vulcanized with rubber injection molding machine, the time from the original 20min or so, shortened to less than 1min; due to the need for vulcanization time is very short, so it has been available for direct vulcanization of the extruder, the production efficiency has increased dramatically. 3. Easy to recycle, reduce costs. Waste generated in the production process (escaping burrs, extrusion waste rubber) and the final appearance of the waste products can be directly returned to reuse; used TPE old products can be recycled after a simple regeneration, reduce environmental pollution, expanding the source of renewable resources. 4. Energy saving. Most of the thermoplastic elastomers do not need vulcanization or vulcanization time is very short, can effectively save energy. Take high pressure hose production energy consumption as an example: rubber is 188MJ/kg, TPE is 144MJ/kg, energy saving of more than 25%. 5. Wider application areas. Because TPE has the advantages of both rubber and plastic, it opens up new application fields for the rubber industry. 6. It can be used for the reinforcement and toughening modification of plastics. Self-reinforcement, simplified formula, with the influence of the agent on the polymer constraints are small, the quality of performance easier to grasp. However, the heat resistance of TPE is not as good as rubber, with the temperature rise and the physical properties of a larger decline, thus limiting the scope of application. At the same time, compression deformation, elastic recovery, durability and other comparisons with rubber is poor, the price is often higher than similar rubber. Nevertheless, the advantages of TPE are still very prominent, and a variety of new TPE products have been developed. As an energy-saving and environmentally friendly new rubber raw material, the development prospect is very favorable. Transparency series Application scope: ordinary transparent toys, sports equipment, etc.. Product performance: better transparency, elasticity and lower prices, with a wide range of design space. Transparency series Applications: high-grade, highly transparent toys, adult products, suction cups, sports equipment and seals. Product Performance: Wide range of hardness, from super soft to 90 A. Excellent transparency, gloss, and comfortable hand feeling, widely used in adult products. Good UV resistance, weather resistance, high temperature resistance, long-term use in outdoor.
Applications: appliance shells, handles, grips, etc. Product properties: excellent hand feel, bonded firmly to hard rubber ABS, PC, PC/ABS, PA6, PA66, etc.. Anti-slip and labor-saving, and easy to color and process, with a wide range of design space Oil-coated series Application: all kinds of oiled toys, daily necessities, etc., widely replace PVC. Product performance: low price, the first choice to replace PVC, health, safety, environmental protection, easy to oil. General Series Application: stationery, sports equipment, seals, handles, etc. Product performance: excellent feel, good UV resistance, chemical resistance and easy to color and processing, with a wide range of design space. Functional Series Application: sealing rings, automobile parts, handles, gears, etc. Product properties: good shock absorption, compression resistance, electrical insulation, steel, etc. ② U.S.-China Trans-Pacific Direct International Fiber Optic Cable (TPE) The U.S.-China Trans-Pacific Direct International Fiber Optic Cable (TPE) has recently begun construction, according to the Associated Press, the undersea fiber optic cable will be named "Trans-Pacific Express" (Trans-Pacific Express), up to 11,000 miles long, capable of handling the equivalent of 62 million simultaneous calls. handle the equivalent of 62 million simultaneous calls. The cable will be completed in July 2008 and will be able to transmit data at speeds of up to 10 gigabits per second for individual users. The 26,000-kilometer TPE cable, with a total investment of US$500 million, is being built by China Netcom, China Telecom, China Unicom, China Telecom, Korea Telecom and Verizon***, and is the largest, longest and most technologically advanced submarine cable system in China. As the second submarine fiber optic cable between China and the U.S., TPE is also the world's first submarine high-speed direct fiber optic cable. Upon completion, the fiber optic cable will significantly increase the trans-Pacific transmission bandwidth to meet the growth of broadband communications services from the Asian region to the United States.
Thermoplastic elastomers are currently divided into the following categories:
1. Styrene-based TPE Styrene-based TPE, also known as TPS, is butadiene or isoprene and styrene block-type **** polymer, whose performance is closest to SBR rubber. At present, the world production of TPS has reached more than 700,000 tons, accounting for about half of all TPE. Representative varieties of styrene-butadiene-styrene block **** polymer (SBS), widely used in the footwear industry, has mostly replaced the rubber; at the same time in the tape, rubber sheet and other industrial rubber products in the use of the expanding. SBS is also used in large quantities as a PS plastic impact modifiers, but also asphalt paving asphalt pavement wear-resistant, anti-cracking, anti-floppy and skidding modifiers of excellence. PS plastic modified with SBS, not only can greatly improve the impact resistance like rubber, but also very good transparency. SBS-modified asphalt pavement is easier to dissolve in asphalt than SBR rubber or WRP rubber powder. Therefore, although it is more expensive, it is still used in large quantities. Nowadays, more waterproofing membrane to further promote to the building roof, subway, tunnels, trenches, etc., waterproof, moisture above. SBS and S-SBR, NP rubber and sponge manufacturing, than the original PVC, EVA plastic sponge is more rich in rubber touch, and lighter than vulcanized rubber, bright colors, clear pattern. Therefore, not only suitable for the manufacture of rubber shoes midsole sponge, but also travel shoes, sports shoes, fashion shoes and other disposable outsole of the ideal material. In recent years, isoprene instead of butadiene segmented styrene polymer (SIS) is developing rapidly, and its output has accounted for about 1 / 3 of the amount of TPS, about 90% of which is used in adhesives. Made of SIS hot melt adhesive is not only superior viscosity, and heat resistance is also good, has become the United States, Europe and Japan hot melt adhesive of the main materials. SBS and SIS is the biggest problem is not heat-resistant, the use of temperature generally can not exceed 80 ℃. At the same time, its strong stretch, weather resistance, oil resistance, abrasion resistance, etc. can not be compared with rubber. For this reason, in recent years, the United States and Europe, it has carried out a series of performance improvements, has appeared in SBS and SIS by saturated hydrogenation of SEBS and SEPS. SEBS (to BR hydrogenated as a soft chain segment) and SEPS (to IR hydrogenated as a soft chain segment) can be made to greatly improve the impact strength, weathering and heat aging resistance is also good. Japan's Mitsubishi Chemical in 1984 and SEBS, SEPS as the base material made of better performance of the mixture, and this saturated TPS named "Rubberron" on the market. Therefore, SEBS and SEPS are not only general-purpose, but also engineering plastics to improve weather resistance, abrasion resistance and heat aging **** mixing materials, and therefore quickly developed into nylon (PA), polycarbonate (PC) and other engineering plastics such as "alloys" of the capacitance of the agent. In addition, we have developed many new varieties such as highly transparent TPS for epoxy resins and non-toxic TPS for medical and healthcare applications. SBS or SEBS and PP plastic melt **** mixing, but also the formation of IPN-type TPS. the so-called IPN, in fact, two networks running through each other in the polymer, so also known as the interpenetrating network compounds. Although most of them belong to the thermosetting resin class, but there are also many like TPE's to cross-continuous phase form performance of thermoplastic elastomers. IPN-TPS formed with SBS or SES as the base material and other engineering plastics can be coated directly without pretreatment. The coating is not easy to scratch and has a certain degree of oil resistance, and the elastic coefficient has little change in a wide temperature range at low temperatures; it greatly improves the cold- and heat-resistant properties of engineering plastics. Styrene compounds and rubber joint technology **** polymerization can also become a thermoplastic TPE, has developed EPDM / styrene, BR / styrene, CI - IIR / styrene, NP / styrene. 2. olefin TPE olefin TPE Department of PP for the hard chain segment and EPDM for the soft chain segment **** mixture, referred to as TPO, because it is lighter than the other TPE specific gravity (only O.88), heat resistance up to 100 ℃, weather resistance and ozone resistance is also good, and thus become a TPE in the development of a very fast varieties. Since 1972 in the United States by the UniroyaI company to the TPR trade name first listed since many years to double-digit growth in 2000, the production volume has reached 3.5 million t, to 2002 is estimated to be up to 400,000 t. Now, the TPO has become the United States, Japan and Europe, such as automobiles and home appliances in the field of the main rubber and plastic materials. Especially in the car has accounted for its total 3 / 4, with its manufacture of car bumpers, has basically replaced the original metal and PU. In 1973, the emergence of dynamic part of the vulcanization of TPO, especially in the United States in 1981, Mansanto company developed the success of the Santoprere named after the complete dynamic vulcanization type of TPO, the performance and greatly improved, the highest temperature of up to 120℃. This dynamic vulcanization type of TPO referred to as TPV, mainly on the TPO in the PP and EPDM mixture in the melt **** mixing, adding the crosslinking agent that can make its vulcanization, the use of refiners, screw machines and other mechanical high shear force, so that the full vulcanization of the micro-fine EPDM crosslinked rubber particles, fully dispersed in the PP matrix. Through this cross-linked rubber "particle effect", resulting in TPO compression deformation resistance, heat aging resistance, oil resistance, etc. have been significantly improved, and even reached the level of CR rubber, which is also known as thermoplastic vulcanized rubber. 3. Diallyl TPE Diallyl TPE is mainly isomers of natural rubber, it is also known as thermoplastic trans natural rubber (1-NR). As early as 400 years ago, people as natural rubber that is found in this material, but because of its production from different and three-leaf rubber tree Guttabo and Barata and other wild trees, and therefore called Guttabo rubber, Barata rubber. Although T-NR has been used as undersea cables and golf ball skins for more than 100 years, its use has not been expanded for a long time due to its thermoplastic state, strong crystallinity, and limited availability. Organometallic catalyst made of synthetic T-NR - trans polyisoprene rubber, called TPI, its microstructure with isoprene rubber (IR) just the opposite, trans binding 99%, crystallinity of 40%, melting point of 67 ℃, with the natural production of Guttabo and Balata rubber is very similar. Therefore, has begun to gradually replace the natural products, and further development to the orthopedic appliances, plaster substitutes and sports protection equipment. In recent years, using TPI's excellent crystallinity and temperature sensitivity, it has been successfully developed as a shape memory rubber material, which is much favored by people. Structurally, TPI is a thermoplastic rubber that is formed by combining the crystallinity formed by the high trans structure as a hard chain segment with the remaining soft chain segments that are in an elastic phase state in an arbitrary shape. Compared with other TPEs, it has the advantage of good mechanical strength and wound resistance, and can be vulcanized, but the disadvantage is that the softening temperature is very low, generally only 40-70 ℃, and the use is limited. BR rubber (cis-1,4 polybutadiene) isomer - between the same l, 2 polybutadiene, referred to as TPB, which is more than 90% of the l, 2-position combination of between the same polybutadiene rubber, trade name RB. microstructure by the hard chain segments of the same structure of the crystalline part of the soft chain segments of the soft part of the arbitrarily shaped soft part of the composition of the block polymer each other. The microstructure is a block polymer consisting of a crystalline part between hard chain segments and a soft part of soft chain segments. Although its heat resistance and mechanical strength are not as good as that of rubber, it is widely used in shoes, sponges, optical films, and other industrial rubber products for its good transparency, weather resistance, electrical insulation, and photodegradability. The biggest difference between TPB Lee TPI and other TPE is that it can be vulcanized. Solve the general TPE can not use sulfur, peroxide vulcanization. And must use electronic waves, radiation and other special devices. Can improve the quality of the modified problem, thus improving the TPE heat resistance, oil resistance and durability shortcomings such as poor TPB can be in the 75-1 10 ℃ melting point within the range of arbitrary processing, can be used for the production of non-vulcanized injection molding slippers, shoes, can also be used in the manufacture of vulcanized foam sports shoes, shoes and other tourist midsole. It is not easy to collapse and deformation of the EVA sponge midsole, comfortable to wear, conducive to improving the effect of sports.TPB film, with good air permeability, waterproof and transparency, easy to decompose light, very safe, especially for the family and vegetables, fruits, freshness of the packaging used. 4. vinyl chloride TPE is divided into two categories of thermoplastic PVC and thermoplastic CPE, the former known as TPVC, the latter known as TCPE. TPVC is mainly elasticized PVC modifier, which is divided into chemical polymerization and mechanical **** mixing of two forms. Mechanical **** mixing is mainly part of the crosslinked NBR mixed into PVC to form **** mix (PVC / NBR). TPVC is actually said to be a soft PVC resin extensions, just because the compression deformation has been greatly improved, resulting in the formation of a class of rubbery PVC. this TPVC can be regarded as a modification of PVC and rubber substitutes, mainly used in the manufacture of rubber hose, rubber sheet, rubber cloth and part of the rubber parts. It is mainly used to make hose, rubber sheet, rubber cloth and some rubber parts. At present, more than 70% of the consumption in the automotive field, such as car steering wheel, wiper strips and so on. For other uses, electric wires account for about 75%, and construction waterproof film accounts for about 10%. In recent years, and began to expand to home appliances, gardening, industry and daily work raincoat and so on. 5. polyurethane TPE polyurethane TPE polyurethane TPE by the reaction with isocyanate ammonia ester hard chain segment and polyester or polyether soft chain segment mutual block combination of thermoplastic polyurethane rubber, referred to as TPU, TPU has excellent mechanical strength, abrasion resistance, oil resistance and resistance to flexing, especially abrasion resistance is most prominent. The disadvantage is heat resistance, hot water resistance, compression resistance is poor, the appearance of easy to turn yellow, easy to stick to the mold in processing. Currently in Europe and the United States and other countries are mainly used in the manufacture of ski boots, mountaineering boots and other sporting goods, and a large number of sports shoes, travel shoes, consumption is very high.TPU can also be injection molding and extrusion molding production of automobiles, machinery, and clocks and other parts, and a large number of high-pressure rubber hose (rubber), pure rubber hose, sheet, drive belts, conveyor belts, wires and cables, rubber cloth and other products. Among them, injection molding accounted for more than 40%, extrusion molding is about 35% or so. In recent years, in order to improve the process of TPU plus 7 work performance, there are also many new easy-to-process varieties. Such as for two-color molding, can increase transparency and high flow, high recycling can improve the processing efficiency of TPU shoes, for the manufacture of transparent hoses without plastic, low hardness of the easy-to-process TPU for large parts such as automotive bumpers, for the exclusive use of glass fiber reinforced to improve the rigidity and impact of the reinforced TPU and so on. In particular, the addition of reactive components to TPU has led to the rapid development of the formation of incomplete IPN (IPN formed by crosslinked polymers and non-crosslinked polymers) by aging after thermoplastic molding. This IPN TPU further improves the physical and mechanical properties of TPU. In addition, TPU / PC **** blended alloy TPU, more to improve the safety performance of automobile bumpers. In addition, there are high moisture permeability TPU, conductive TPU, and the emergence of TPU dedicated to the body, magnetic tape, safety glass, etc.
Source:/view/478478.htm