Positron emission computed tomography (PET) is an advanced imaging technique for clinical examination in the field of nuclear medicine. The general method is to use short-lived radionuclides (such as F 18, C 1 1 etc.) to label some substances that are generally necessary for biological life metabolism, such as glucose, protein, nucleic acids, fatty acids, etc. ), and then injected into the human body, through the accumulation of the substance in metabolism to reflect the metabolic activities of life, so as to achieve the purpose of diagnosis. Recently, the main substance used in hospitals is fluorodeoxyglucose, or FDG for short. The mechanism is that the metabolic state of different tissues in human body is different, and the glucose metabolism of high metabolic malignant tumor tissues is vigorous and accumulates more, which can be reflected by images, so as to diagnose and analyze the lesions.

Principle of 1 PET detector

Some short-lived substances release a positron in the process of decay, which will be annihilated when it meets an electron after traveling 1 to 3 cm, thus producing a pair of energy of 5 1 1KeV with basically opposite directions. This information is captured by a highly sensitive camera, and after the scattered and random information is corrected by a computer, we can get a three-dimensional image of the aggregates in the organism.

Two advantages of PET detection

PET is the only new imaging technology that can show the metabolism of biomolecules, the activity of receptors and neurotransmitters in vivo, and has been widely used in the diagnosis and differential diagnosis of various diseases, disease judgment, curative effect evaluation, organ function research and new drug development. (1) has high sensitivity. PET is an imaging that reflects molecular metabolism. When the disease is in the early stage of molecular level change, and the morphological structure of the lesion area is not abnormal, and MRI and CT examination can not make a clear diagnosis, PET examination can find the lesion, obtain three-dimensional images, and make quantitative analysis to realize early diagnosis, which is incomparable to other imaging examinations at present. (2) High specificity. It is difficult to judge whether an organ has a tumor by MRI and CT, but PET can make a diagnosis according to the characteristics of high metabolism of malignant tumor. (3) Whole body imaging. PET disposable whole body imaging examination can obtain images of all regions of the whole body. (4) Good safety. The nuclides needed for PET examination are radioactive, but the amount of nuclides used is very small, and the half-life is very short (short about 12 minutes, long about 120 minutes). After physical attenuation and biological metabolism, they stay in the subject for a short time. The radiation dose of PET whole body examination is far less than that of conventional CT examination, which is safe and reliable.

3 Which patients are suitable for PET examination?

(1) Cancer patients. At present, 85% of PET examination is used for tumor examination, because most 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 distinguish malignant tumors from benign tumors and normal tissues, and can also distinguish recurrent tumors from surrounding necrosis and scar tissues. Now it is mostly used for lung cancer, breast cancer, colorectal cancer, ovarian cancer, lymphoma, melanoma, etc., and the diagnostic accuracy rate is 90%. This kind of examination can see at a glance whether the malignant tumor has metastasized and where it has metastasized, which plays an important guiding role in the staging of tumor diagnosis and whether surgery and surgical resection are needed. According to foreign data, nearly one-third of tumor patients need to change their original surgical plan after preoperative PET examination. In the early stage of tumor chemotherapy and radiotherapy, PET examination can find out whether the tumor treatment has taken effect, which is helpful to determine 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) Patients with nervous system diseases and mental diseases. It can be used for the localization of epileptic focus, the early diagnosis and differentiation of Alzheimer's disease, the evaluation of Parkinson's disease and the judgment of tissue damage and survival after cerebral infarction. PET examination shows unique advantages in pathological diagnosis and curative effect evaluation of mental illness, and it is expected to make breakthrough progress in the near future. It plays an important guiding role in the development of new drugs for the treatment of AIDS encephalopathy and drug rehabilitation. (3) Patients with cardiovascular diseases. It can detect the location and range of myocardial ischemia in coronary heart disease, accurately evaluate myocardial vitality and determine whether thrombolytic therapy, coronary stent implantation or coronary artery bypass surgery is needed. Through the analysis of myocardial blood flow, combined with drug load, we can measure the coronary reserve capacity and evaluate the therapeutic effect of coronary heart disease.

4.PET/CT and MR/PET

Due to the characteristics of nuclear medicine technology, PET has certain limitations in accuracy and location. Therefore, we consider combining the results of this equipment with the results of radiology. However, if the scanning time is different and the low-density tissue state is unstable, the results of image fusion between the two devices are often inaccurate. Since 2000, the industry has solved the problem of integration and synchronous scanning of PET and CT equipment. PET/CT can not only solve the problem of synchronous scanning, but also obtain the density map through CT scanning for scattering correction, which can greatly improve the accuracy and diagnostic accuracy. At present, the most advanced equipment can realize the integration of 52-ring PET and 64-slice CT (such as Biograph64 of Siemens). Synchronization of concentric electrograms (called gating) and manual ECG editing and reconstruction considering arrhythmia can be used to accurately locate cardiac function and malignant lesions. At present, some companies are testing the integrated equipment of MR and PET, which is called MR/PET. The device can fully integrate the ability of Mr to detect soft tissue density and the ability of PET to detect molecular level, which will have a very important performance in the diagnosis of brain and nervous system diseases and is worth looking forward to. Although PET has many advantages, it still has the following disadvantages: (1) still has some limitations in the diagnosis of tumor pathological properties, such as poor specificity for inflammation. (2) Examiners need to have rich experience, especially for patients with different body types and different diagnostic needs, such as what examination posture to use and how many nuclides to inject. In addition, movie readers sometimes have to have knowledge of both radiology and nuclear medicine. (3) Exams are expensive. At present, it costs about 10 thousand yuan to do a full-body pet examination, which is not popular.

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Thermoplastic elastomer (TPE) has the physical and mechanical properties of vulcanized rubber and the processability of thermoplastic. Because there is no need for thermal vulcanization, the production of products can be completed by using general plastic processing equipment. This feature shortens the production process of rubber industry by 1/4, saves energy consumption by 25%~40%, and improves efficiency by 10 ~20 times, which is called another material and technology revolution in rubber industry. In recent years, with the increasing communication between China and the world, some domestic TPE\TPR manufacturers began to develop in the direction of halogen-free flame retardant, which had a far-reaching impact on China and even the world.

Advantages of TPE

1. can be processed by general thermoplastic molding machine without special processing equipment. 2. The production efficiency is greatly improved. It can be vulcanized directly by rubber injection molding machine, and the time is shortened from about 20min minutes to less than 1 minute; Because the required vulcanization time is very short, it can be vulcanized directly by extruder, and the production efficiency is greatly improved. 3. It is easy to recycle and reduce the cost. Wastes (burrs, rubber extrusion) and final wastes generated in the production process can be directly returned for reuse; Used TPE products can be recycled after simple regeneration, which reduces environmental pollution and expands the source of renewable resources. 4. Save energy. Most thermoplastic elastomers do not need vulcanization or the vulcanization time is very short, which can effectively save energy. Take the energy consumption of high-pressure hose production as an example: rubber is 188MJ/kg, and TPE is 144MJ/kg, which can save energy by more than 25%. 5. The application field is wider. Because TPE has the advantages of both rubber and plastic, it has opened up a new application field for rubber industry. 6. It can be used to strengthen and toughen plastics. The self-reinforcing property is great, the formula is simplified, the influence of the compounding agent on the polymer is less, and the quality and performance are easier to master. However, the heat resistance of TPE is not as good as that of rubber. With the increase of temperature, the physical properties are greatly reduced, and the application scope is limited. At the same time, the compression deformation, elastic recovery and durability are worse than those of the same rubber, and the price is often higher than that of similar rubber. Nevertheless, the advantages of TPE are still outstanding, and various new TPE products are continuously developed. As a new rubber raw material with energy saving and environmental protection, its development prospect is very promising. Application scope of transparent series: ordinary transparent toys, sports equipment, etc. Product performance: good transparency, flexibility and low price, with broad design space. Application scope of transparent series: high-grade transparent toys, adult products, sucker materials, sports equipment and sealing rings. Product performance: hardness ranges from ultra-soft to 90A. Excellent transparency, luster and comfortable feel, widely used in adult products. It has good ultraviolet resistance, weather resistance and high temperature resistance, and is used outdoors for a long time.

Scope of application: product performance such as household appliance shell, handle, grip, etc.: excellent hand feeling, and firmly bonded with hard rubber ABS, PC, PC/ABS, PA6, PA66, etc. Anti-skid and labor-saving, easy to color and process, with a wide range of design space oiling series applications: all kinds of oiled toys, daily necessities and so on. , widely replacing PVC. Product performance: low price, the first choice to replace PVC, healthy, safe, environmentally friendly and easy to produce oil. General application: stationery, sports equipment, sealing rings, handles and other products: excellent hand feeling, good ultraviolet resistance and chemical resistance, easy coloring processing and wide design space. Scope of application: sealing rings, auto parts, handles, gears, etc. Product performance: It has good shock absorption, pressure resistance, electrical insulation and rigidity. (2) China-US Trans-Pacific Direct International Optical Cable (TPE) The construction of China-US Trans-Pacific Direct International Optical Cable (TPE) has started recently. According to the Associated Press, this submarine cable will be named "Trans-Pacific Express", which is1.65,438+0,000 miles long and can handle the data equivalent to 62 million calls at the same time. The maximum data transmission speed of individual users will reach 10Gb per second. The optical cable will be completed and put into use in July 2008. The TPE optical cable with a total investment of 500 million US dollars and a length of about 26,000 kilometers was jointly built by China Netcom, China Telecom, China Unicom, Chunghwa Telecom, Korea Telecom and Verizon USA. It is the submarine optical cable system with the largest capacity, the longest span and the most advanced technology in China. As the second submarine cable between China and the United States, TPE is also the first submarine high-speed direct cable in the world. After the completion of the optical cable, the trans-Pacific transmission bandwidth will be significantly increased to meet the growing demand for broadband communication services from Asia to the United States.

At present, thermoplastic elastomers are mainly divided into the following categories:

1. Styrene TPE Styrene TPE, also known as TPS, is a block polymer of butadiene or isoprene and styrene, and its performance is closest to SBR rubber. At present, the world TPS production has reached more than 700,000 t, accounting for about half of all TPE. The representative variety is styrene-butadiene-styrene block copolymer (SBS), which is widely used in footwear industry and has largely replaced rubber. At the same time, its application in industrial rubber products such as adhesive tape and rubber sheet is also expanding. SBS is also widely used as an impact modifier for PS plastics, and it is also an excellent modifier for wear resistance, crack resistance, softness resistance and skid resistance of asphalt pavement. PS plastics modified by SBS can not only greatly improve the impact resistance like rubber, but also have very good transparency. Compared with SBR and WRP rubber powder, SBS modified asphalt pavement is easier to dissolve in asphalt. So although the price is more expensive, it is still widely used. Now the waterproofing membrane is further extended to the waterproofing and moistureproof of building roofs, subways, tunnels and ditches. Sponges made of SBS, S-SBR and NP rubber are richer in rubber touch than the original PVC and EVA plastic sponges, lighter than vulcanized rubber, with bright colors and clear patterns. Therefore, it is not only suitable for making sponges in rubber overshoes, but also an ideal material for disposable soles such as travel shoes, sports shoes and fashion shoes. In recent years, isoprene-substituted butadiene block styrene polymer (S-type S) has developed rapidly, accounting for about 1/3 of TPS, of which about 90% is used as adhesive. The hot melt adhesive made of SIS not only has superior viscosity, but also has good heat resistance. Now it has become the main material of hot melt adhesive in the United States, Europe and Japan. The biggest problem of SBS and SIS is that they are not heat-resistant, and the service temperature generally cannot exceed 80℃. At the same time, its tensile strength, weather resistance, oil resistance and wear resistance are incomparable to rubber. Therefore, in recent years, the United States and Europe and other countries have made a series of performance improvements, and SEBS and SEPS with saturated hydrogenation of SBS and SIS have appeared successively. SEBS (with BR hydrogenation as soft segment) and SEPS (with IR hydrogenation as soft segment) can greatly improve impact strength, weather resistance and thermal aging resistance. 1984 Mitsubishi chemical of Japan made a mixture with better performance on the basis of SEBS and SEPS, and named this saturated TPS "Rubberron" for listing. Therefore, SEBS and SEPS are not only universal, but also mixed materials of engineering plastics to improve weather resistance, wear resistance and thermal aging resistance, so they have rapidly developed into compatibilizers for engineering plastics such as nylon (PA) and polycarbonate (PC). In addition, many new varieties have been developed, such as highly transparent thermoplastics for epoxy resin and bio-nontoxic thermoplastics for medical care. IPN TPS can also be formed when SBS or SEBS is melted and mixed with PP plastic. The so-called IPN is actually a polymer with two interpenetrating networks, so it is also called interpenetrating network compound. Although most of them belong to thermosetting resins, there are also many thermoplastic elastomers like TPE in the form of cross continuous phases. TPS formed by IPN——SBS or SES and other engineering plastics can be directly coated without pretreatment. The coating is not easy to scratch and has certain oil resistance, and the elastic coefficient does not change in a wide temperature range at low temperature; The cold resistance and heat resistance of engineering plastics are greatly improved. Styrene compound grafted rubber can also become thermoplastic TPE, and EPDM// styrene, BR/ styrene, CI-IIR// styrene, NP/ styrene and so on have been developed. 2. olefin TPE olefin TPE is a mixture of PP as a hard segment and EPDM as a soft segment, abbreviated as TPO. Because its specific gravity is lighter than other TPEs (only O.88), its heat resistance is as high as 100℃, and its weather resistance and ozone resistance are good, it has become another fast-growing variety of TPE. 1972 Since UniroyaI Company was first listed in the United States under the trade name of TPR, it has been growing by double digits for many years. In 2000, the output reached 350,000 tons, and it is expected to reach 400,000 tons in 2002. Now, TPO has become the main rubber and plastic material in the fields of automobiles and household appliances in the United States, Japan and Europe. Especially in cars, it has accounted for 3/4 of the total, and the car bumper made of it has basically replaced the original metal and PU. In 1973, a dynamic partially vulcanized TPO appeared. Especially, after Mansanto Company of the United States successfully developed a fully dynamic vulcanized TPO named Santoprere in 198 1, its performance was greatly improved, and the highest temperature could reach 120℃. This dynamic vulcanization TPO is called TPV for short. When the mixture of PP and EPDM is melted and mixed by TPO, the crosslinking agent which can vulcanize it is added, and the fully vulcanized fine EPDM crosslinked rubber particles are fully dispersed in the PP matrix by using the high shear force of internal mixer, screw machine and other machinery. Through the "particle effect" of this cross-linked rubber, the compression deformation resistance, thermal aging resistance and oil resistance of TPO are obviously improved, even reaching the level of CR rubber, so people call it thermoplastic vulcanizate. 3. Diene TPE Diene TPE is mainly an isomer of natural rubber, so it is also called thermoplastic trans natural rubber (1-NR). As early as 400 years ago, people discovered that this material is natural rubber, but it is called Gupta rubber and balata rubber because it is produced in wild trees such as Gupta and balata, which is different from the three-leaf rubber tree. Although this T-NR has been used as the skin of submarine cables and golf balls for more than 65,438+000 years, its application has not been expanded for a long time due to its thermoplastic state, strong crystallinity and limited supply. T-NR- trans polyisoprene rubber synthesized with organometallic catalyst is called TPI. Its microstructure is just opposite to that of isoprene rubber (IR), with 99% trans-bonding, 40% crystallinity and melting point of 67℃, which is very similar to natural Gutap and balata rubber. Therefore, natural products are gradually replaced and further developed into plastic surgery instruments, gypsum substitutes and sports protective equipment. In recent years, TPI has been successfully developed as a shape memory rubber material because of its excellent crystallinity and temperature sensitivity, which is favored by people. Structurally, TPI is a thermoplastic rubber with high crystallinity, which is composed of trans structure as hard segment and then combined with other arbitrary soft segments in elastic phase. Compared with other TPE, it has the advantages of good mechanical strength, damage resistance and vulcanization, but the disadvantage is that the softening temperature is very low, generally only 40-70℃, and its use is limited. BR Isomer of rubber (cis-1, 4 polybutadiene)-syndiotactic 1, 2 polybutadiene, abbreviated as TPB. It is syndiotactic polybutadiene rubber with more than 90% 1, and its trade name is RB. The microstructure is a block polymer composed of crystalline parts with the same structure between any soft segment and hard segment. Although its heat resistance and mechanical strength are not as good as rubber, it is widely used in industrial rubber products such as shoes, sponges and optical films because of its good transparency, weather resistance, electrical insulation and photodegradation. The biggest difference between TPB and TPI is that it can be vulcanized. It solves the problem that general TPE cannot be vulcanized by sulfur and peroxide, but must be vulcanized by special devices such as electric wave and radiation. It can improve the quality and modification, thus improving the shortcomings of TPE such as poor heat resistance, oil resistance and durability. TPB can be processed at will in the melting point range of 75- 1 10℃, and can be used to produce unvulcanized injection-molded slippers and casual shoes, as well as to vulcanize and foam the midsole of sports shoes and travel shoes. Compared with EVA sponge midsole, it is not easy to collapse and deform, and it is comfortable to wear, which is beneficial to improve the effect of sports competition. The film made of TPB has good air permeability, water resistance and transparency, is easily decomposed by light, is very safe, and is especially suitable for fresh-keeping packaging of families, vegetables and fruits. 4. TPE of vinyl chloride is divided into thermoplastic PVC and thermoplastic CPE, the former is called TPVC and the latter is called TCPE. TPVC is mainly the elastic modification of PVC, which is divided into two forms: chemical polymerization and mechanical blending. Mechanical blending is mainly a mixture (PVC/NBR) formed by mixing partially crosslinked NBR into PVC. In fact, TPVC is just an extension of soft PVC resin, only because the compression deformation is greatly improved, thus forming a rubber-like PVC. This TPVC can be regarded as a modified product of PVC and a substitute of rubber, which is mainly used to manufacture rubber hoses, rubber sheets, adhesive tapes and some rubber parts. At present, more than 70% are consumed in the automotive field, such as steering wheel, wiper blade and so on. For other purposes, wires account for about 75%, and building waterproof membrane accounts for about 10%. In recent years, it has been extended to household appliances, gardening, industry and daily raincoats. 5. Polyurethane TPE Polyurethane TPE is a thermoplastic polyurethane rubber, which consists of a polyurethane hard segment that reacts with isocyanate and a polyester or polyether soft segment. It is called TPU for short. TPU has excellent mechanical strength, wear resistance, oil resistance and flexibility, especially wear resistance. Disadvantages are poor heat resistance, hot water resistance and pressure resistance, easy yellowing of appearance and easy mold sticking during processing. At present, it is mainly used to manufacture sports goods such as ski boots and hiking shoes in Europe and America, and a large number of sports shoes and travel shoes are produced, which consumes a lot. TPU can also be used to produce automobile, machinery, clocks and other parts by injection molding and extrusion, and is widely used in high-pressure hoses (outer rubber), pure hoses, sheets, transmission belts, conveyor belts, wires and cables, adhesive tapes and other products. Injection molding accounts for more than 40%, and extrusion molding accounts for about 35%. In recent years, in order to improve the processability of TPU, many new easy-to-process varieties have appeared. If it is suitable for two-color molding, it can increase transparency, high fluidity and high recovery, and improve processing and production efficiency. TPU with no plastic, low hardness and easy processing is used to manufacture transparent rubber hose. It can be used as a special TPU for large parts such as automobile bumper, reinforced with glass fiber, which can improve rigidity and impact resistance. Especially when reactive components are added to TPU, after thermoplastic molding, incomplete IPN (IPN formed by crosslinked polymer and non-crosslinked polymer) develops rapidly. This IPN TPU further improves the physical and mechanical properties of TPU. In addition, TPU/PC * * * mixed alloy TPU further improves the safety performance of automobile bumper. In addition, there are high moisture permeability TPU, conductive TPU, TPU and so on, which are specially used for living bodies, tapes, safety glasses and so on.

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