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| Perfluorocarbon |
PerfluorocarbonPerfluorocarbons (or PFCs) are compounds derived from hydrocarbons by replacement of hydrogen atoms by fluorine atoms. PFC is 6000 times more effective than carbon-dioxide at trapping heat in the atmosphere, entirely toxin-free, and made up of atoms of carbon, fluorine, and/or sulfur.
Medicine
Perfluorocarbons are commonly used in eye surgery as temporary replacements of the vitreous gel in retinal detachment surgery. The length of the perfluorated carbon chain determines the physical properties of a particular perfluorocarbon. Small chain chain perfluorocarbons, such as perfluoro-propane, are gases that rise inside the eye and seal retinal holes. Larger chain perfluorocarbons, such as perfluoro-octane, are liquids heavier than water and are used in surgery to movilize an infolded retina.
Perfluorocarbons are also used in contrast enhanced ultrasound to improve ultrasound signal backscatter. The perfluorocarbons used in the microbubbles of some ultrasound contrast media are liquids at room temperature, but gases at body temperature. The gas-filled microbubbles oscillate and vibrate when a sonic energy field is applied and characteristically reflect ultrasound waves. This distinguishes the microbubbles from surrounding tissues.
Their stability, inertness, low diffusion rate and solubility increase the duration of contrast enhancement as compared to microbubbles containing air. PFC is also being used in artificial blood and liquid breathing.
Industry and the environment
PFC is being used in refrigerating units and "clean" fire extinguishers. However PFCs are hugely potent greenhouse gases and they are a long-term problem with a lifetime up to 50,000 years. Several governments concerned about the properties of PFCs have already tried to implement international agreements to limit their usage before it becomes a future global warming issue. PFC is one of the gases regulated in the Kyoto Protocol.
See also
- Fluoropolymer
External link
- [http://classes.kumc.edu/cahe/respcared/liquidventilation/wikeper.html Perfluorocarbons as a transport for Oxygen to the lungs], e.g. partial liquid ventilation.
Category:Organic chemistry
HydrocarbonIn chemistry, a hydrocarbon is any chemical compound that consists only of the elements carbon (C) and hydrogen (H). They all contain a carbon backbone, called a carbon skeleton, and have hydrogen atoms attached to that backbone. (Often the term is used as a shortened form of the term aliphatic hydrocarbon.)
Examples
aliphaticFor example, methane (swamp/marsh gas) is a hydrocarbon with one carbon atom and four hydrogen atoms: CH4. Ethane is a hydrocarbon (more specifically, an alkane) consisting of two carbon atoms held together with a single bond, each with three hydrogen atoms bonded: C2H6. Propane has three C atoms (C3H8) and so on (CnH2n+2).
Three types of hydrocarbons
PropaneThere are essentially three types of hydrocarbons:
#aromatic hydrocarbons, which have at least one aromatic ring
#saturated hydrocarbons, also known as alkanes, which don't have double, triple or aromatic bonds
#unsaturated hydrocarbons, which have one or more double or triple bonds between carbon atoms, are divided into:
#
- alkenes
#
- alkynes
#
- dienes
diene
The number of hydrogen atoms
The number of hydrogen atoms in hydrocarbons can be determined, if the number of carbon atoms is known, by using these following equations:
- Alkanes: CnH2n+2
- Alkenes: CnH2n (assuming only one double bond)
- Alkynes: CnH2n-2 (assuming only one triple bond)
Each of these hydrocarbons must follow the 4-hydrogen rule which states that all carbon atoms must have the maximum number of hydrogen atoms that it can hold (the limit is four). Note, an extra bond removes 2 hydrogen atoms and only saturated hydrocarbons can attain the full four. This is because of the unique positions of the carbon's four electrons.
Molecular graph
Usually carbon backbone is represented as molecular graph in which only carbon atoms are represented as vertices and bonds as edges. Molecular graphs contain the structure of the hydrocarbon in which missing hydrogen atoms can be added in a unique way. Hydrocarbons are extensively studied in mathematical chemistry.
Petroleum
Liquid geologically-extracted hydrocarbons are referred to as petroleum (literally "rock oil") or mineral oil, while gaseous geologic hydrocarbons are referred to as natural gas. All are significant sources of fuel and raw materials as a feedstock for the production of organic chemicals and are commonly found in the Earth´s subsurface using the tools of petroleum geology.
Oil reserves in sedimentary rocks are the principal source of hydrocarbons for the energy, transport and chemicals industries. The production of liquid hydrocarbon fuel from a number of sedimentary basins has been integral to modern energy development.
Hydrocarbons are of prime economic importance because they encompass the constituents of the major fossil fuels (coal, petroleum, natural gas, etc.) and biofuels, as well as plastics, waxes, solvents and oils. In urban pollution, these components--along with NOx and sunlight--all contribute to the formation of tropospheric ozone.
Burning Hydrocarbons
Hydrocarbons are currently the main source of the world’s electric energy and heat sources (such as home heating) because of the energy produced when burnt. Hydrocarbons are all substances with low entropy (meaning they hold a lot of energy potential), which can be released and harnessed by burning them. Often this energy is used directly as heat such as in home heaters, which use either oil or natural gas. The hydrocarbon is burnt and the heat is used to heat water, which is then circulated in pipes around the building heating every room. A similar principle is used to create electric energy in power plants. Hydrocarbons (usually coal) are burnt and the energy released in this way is used to turn water in to steam, which is used to turn a turbine that generates energy much like a windmill does. In an ideal reaction the byproducts would be only water and carbon dioxide but because the coal is not pure or cleaned there are often many toxic byproducts such as mercury and arsenic. Also, incomplete combustion causes the production of carbon-monoxide which is toxic because it will bind with hemoglobin more readily than oxygen, so if it is breathed in oxygen can not be absorbed, causing suffocation. Clean coal technology is currently under development.
External links
- [http://www.gasresources.net/DisposalBioClaims.htm Dismissal of the Claims of a Biological Connection for Natural Petroleum.]
- [http://www.gasresources.net/Introduction.htm An introduction to the modern petroleum science, and to the Russian-Ukrainian theory of deep, abiotic petroleum origins.]
- [http://www.aapg.org/explorer/2002/11nov/abiogenic.cfm Abiogenic Gas Debate 11:2002 (EXPLORER)]
See also
- Abiogenic petroleum origin
- Energy storage
- Petroleum geology
- Oil well
Category:Hydrocarbons
Category:Fossil fuels
ms:Hidrokarbon
ja:炭化水素
Fluorine
Fluorine (from L. fluere, meaning "to flow"), is the chemical element in the periodic table that has the symbol F and atomic number 9. It is a poisonous pale yellow-green, univalent gaseous halogen that is the most chemically reactive and electronegative of all the elements. In its pure form, it is highly dangerous, causing severe chemical burns on contact with skin.
Notable characteristics
Pure fluorine is a corrosive pale yellow gas that is a powerful oxidizing agent. It is the most reactive and electronegative of all the elements, and readily forms compounds with most other elements. Fluorine even combines with the noble gases krypton, xenon, and radon. Even in dark, cool conditions, fluorine reacts explosively with hydrogen. It is so reactive that, glass, metals, and even water, as well as other substances, burn with a bright flame in a jet of fluorine gas. It is far too reactive to be found in elemental form and has such an affinity for most elements, including silicon, that it can neither be prepared nor should be kept in glass vessels. In moist air it reacts with water to form the equally dangerous hydrofluoric acid.
In aqueous solution, fluorine commonly occurs as the fluoride ion F-.
Other forms are fluoro-complexes (such as [FeF4]-) or H2F+.
Fluorides are compounds that combine fluoride with some positively charged counterpart. They often consist of ions. Fluorine compounds with metals are among the most stable of salts.
Applications
Atomic fluorine and molecular fluorine are used for plasma etching in semiconductor manufacturing, flat panel display production and MEMs fabrication.
Other uses:
- Hydrofluoric acid (chemical formula HF) is used to etch glass in light bulbs and other products.
- Fluorine is indirectly used in the production of low friction plastics such as Teflon, and in halons such as Freon
- Along with some of its compounds, fluorine is used in the production of uranium (from the hexafluoride) and in the synthesis of numerous commercial fluorochemicals, including vitally important pharmaceuticals, agrochemical compounds, lubricants, textiles, etc.
- Fluorochlorohydrocarbons are used extensively in air conditioning and in refrigeration. Chlorofluorocarbons have been banned for these applications because they contribute to the ozone hole.
- Sulfur hexafluoride is an extremely inert and nontoxic gas. These classes of compounds are potent greenhouse gases
- Many important agents for general anaesthesia are fluorohydrocarbon derivatives, e.g. sevoflurane, desflurane, and isoflurane.
- Potassium hexafluoroaluminate, the so-called cryolite, is used in electrolysis of aluminium.
- Sodium fluoride has been used as an insecticide, especially against cockroaches.
- Some other fluorides are often added to toothpaste and, somewhat controversially, to municipal water supplies to prevent dental cavities.
- It has been used in the past to help molten metal flow, hence the name.
- Fluorine-18, a radioactive isotope that emits positrons, is often used in positron emission tomography because of its half-life of 110 minutes.
Some researchers - including US space scientists in the early 1960s have studied elemental fluorine gas as a possible rocket propellant due to its exceptionally high specific impulse. Experiments failed since fluorine was so hard to handle.
History
Fluorine in the form of fluorspar (calcium fluoride) was described in 1529 by Georgius Agricola for its use as a flux, which is a substance that is used to promote the fusion of metals or minerals. In 1670 Schwandhard found that glass was etched when it was exposed to fluorspar that was treated with acid. Karl Scheele and many later researchers, including Humphry Davy, Gay-Lussac, Antoine Lavoisier, and Louis Thenard all would experiment with hydrofluoric acid, easily obtained by treating calcium fluoride (fluorspar) with concentrated sulfuric acid.
It was eventually realized that hydrofluoric acid contained a previously unknown element. This element was not isolated for many years after this due to its extreme reactivity - it is separated from its compounds only with difficulty and then it immediately attacks the remaining materials of the compound. Finally in 1886 fluorine was isolated by Henri Moissan after almost 74 years of continuous effort. It was an effort which cost several researchers their health or even their lives, and for Moissan, it earned him the 1906 Nobel Prize in chemistry.
The first large scale production of fluorine was needed for the atomic bomb Manhattan project in World War II where the compound uranium hexafluoride (UF6) was used to separate the U-235 and U-238 isotopes of uranium. Today both the gaseous diffusion process and the gas centrifuge process use gaseous (UF6) to produce enriched uranium for nuclear power applications.
The derevation of elemental flourine from hydroflouric acid is exceptionally dangerous, killing or blinding several scientists who attempted early experiments on this halogen. These men came to be referred to as "Flourine Martyrs".
Precautions
Both fluorine and HF must be handled with great care and any contact with skin and eyes should be strictly avoided. All equipment must be passivated before exposure to fluorine.
Both elemental fluorine and fluoride ions are highly toxic. When it is a free element, fluorine has a characteristic pungent odor that is detectable in concentrations as low as 20 nL/L. It is recommended that the maximum allowable concentration for a daily 8-hour time-weighted exposure is 1 µL/L (part per million by volume) (lower than, for example, hydrogen cyanide).
Fluorine is a powerful oxidizer which can cause organic material, combustibles, or other flammable materials to ignite. However, safe handling procedures enable the transport of liquid fluorine by the ton.
Preparation
Elemental fluorine is prepared industrially by Moissan's original process: electrolysis of anhydrous HF in which KHF2 has been dissolved to provide enough ions for conduction to take place.
In 1986, preparing for a conference to celebrate the 100th aniversary of the discovery of fluorine, Karl Christe discovered a purely-chemical preparation by reacting together at 150C solutions in anhydrous HF of K2MnF6 and of SbF5. This is not a practical synthesis, but demonstrates that electrolysis is not essential.
Compounds
Fluorine can often be substituted for hydrogen when it occurs in organic compounds. Through this mechanism, fluorine can have a very large number of compounds. Fluorine compounds involving noble gases were first synthesised by Neil Bartlett in 1962 - xenon hexafluoroplatinate, XePtF6, being the first. Fluorides of krypton and radon have also been prepared. Also Argon Fluorohydride has been prepared, althought it is only stable at cryogenic temperatures.
This element is recovered from fluorite, cryolite, and fluorapatite.
See also: Fluorocarbon
- Ammonium fluoride (NH4F)
- Antimony pentafluoride (SbF5)
- Boron trifluoride (BF3)
- Bromine pentafluoride (BrF5)
- Bromine trifluoride (BrF3)
- Caesium fluoride (CsF)
- Calcium fluoride (CaF2)
- Chlorine pentafluoride (ClF5)
- Fluorosulfuric acid (FSO3(H)
- Hydrofluoric Acid (HF)
- Iodine pentafluoride (IF5)
- Iodine heptafluoride (IF7)
- Lithium fluoride (LiF)
- Nitrogen trifluoride (NF3)
- Nitrosyl fluoride (NOF)
- Nitryl fluoride (NO2F)
- Phosphorus trifluoride (PF3)
- Phosphorus pentafluoride (PF5)
- Potassium fluoride (KF)
- Radon difluoride (RnF2)
- Silver(I) fluoride (AgF)
- Sulfur hexafluoride (SF6)
- Thionyl fluoride (SOF2)
- Tungsten(VI) fluoride (WF6)
- Uranium hexafluoride (UF6)
- Xenon hexafluoroplatinate (XePtF6)
- Xenon tetrafluoride (XeF4)
References
- [http://periodic.lanl.gov/elements/9.html Los Alamos National Laboratory – Fluorine]
External links
- [http://www.webelements.com/webelements/elements/text/F/index.html WebElements.com – Fluorine]
- [http://education.jlab.org/itselemental/ele009.html It's Elemental – Fluorine]
- [http://www.chemie-master.de/pse/pse.php?modul=F Picture of liquid fluorine – chemie-master.de]
- [http://www.chemsoc.org/viselements/pages/fluorine.html Chemsoc.org]
- [http://nautilus.fis.uc.pt/st2.5/index-en.html Periodic Table of Elements]
Category:Chemical elements
Category:Halogens
ko:플루오르
ja:フッ素
th:ฟลูออรีน
Contrast enhanced ultrasoundContrast enhanced ultrasound (CEU) is the application of ultrasound contrast agents to traditional medical sonography. Ultrasound contrast agents are gas-filled microbubbles that are administered intravenously to the systemic circulation. Microbubbles have a high degree of echogenicity, which is the ability of an object to reflect the ultrasound waves. The echogenicity difference between the gas in the microbubbles and the soft tissue surroundings of the body is immense. Thus, ultrasonic imaging using microbubble contrast agents enhances the ultrasound backscatter, or reflection of the ultrasound waves, to produce a unique sonogram with increased contrast due to the high echogenicity difference. Contrast enhanced ultrasound can be used to image blood perfusion in organs, measure blood flow rate in the heart and other organs, and has other applications as well.
Targeting ligands that bind to receptors characteristic of intravascular diseases can be conjugated to microbubbles, enabling the microbubble complex to accumulate selectively in areas of interest, such as diseased or abnormal tissues. This form of molecular imaging, known as targeted contrast enhanced ultrasound, will only generate a strong ultrasound signal if targeted microbubbles bind in the area of interest. Targeted contrast enhanced ultrasound can potentially have many applications in both medical diagnostics and medical therapeutics. However, the targeted technique has not yet been approved for clinical use; it is currently under preclinical research and development.
Microbubble Contrast Agents
General Features
There are a variety of microbubbles contrast agents. Microbubbles differ in their shell makeup, gas core makeup, and whether or not they are targeted.
- Microbubble Shell: selection of shell material determines how easily the microbubble is taken up by the immune system. A more hydrophilic material tends to be taken up more easily, which reduces the microbubble residence time in the circulation. This reduces the time available for contrast imaging. The shell material also affects microbubble mechanical elasticity. The more elastic the material, the more acoustic energy it can withstand before bursting (McCulloch et al., 2000). Currently, microbubble shells are composed of albumin, galactose, lipid, or polymers (Lindner, 2004).
- Microbubble Gas Core: The gas core is the most important part of the ultrasound contrast microbubble because it determines the echogenicity. When gas bubbles are caught in an ultrasonic frequency field, they compress, oscillate, and reflect a characteristic echo- this generates the strong and unique sonogram in contrast enhanced ultrasound. Gas cores can be composed of air, or heavy gases like perfluorocarbon, octafluoropropane, or nitrogen (Lindner, 2004). Heavy gases are less water-soluble so they are less likely to leak out from the microbubble to impair echogenicity (McCulloch et al., 2000). Therefore, microbubbles with heavy gas cores are likely to last longer in circulation.
Optison, a FDA-approved microbubble made by GE Healthcare, has an albumin shell and octafluoropropane gas core. The second FDA-approved microbubble, Levovist, made by Schering, has a lipid/galactose shell and an air core. (Lindner, 2004)
Regardless of the shell or gas core composition, microbubble size is fairly uniform. They lie within in a range of 1-4 micrometres in diameter. That makes them smaller than red blood cells, which allows them to flow easily through the circulation as well as the microcirculation.
Targeted Microbubbles
Targeted microbubbles are under preclinical development. They retain the same general features as untargeted microbubbles, but they are outfitted with ligands that bind specific receptors expressed by cell types of interest, such as inflamed cells or cancer cells. Current microbubbles in development are composed of a lipid monolayer shell with a perflurocarbon gas core. The lipid shell is also covered with a polyethylene glycol (PEG) layer. PEG prevents microbubble aggregation and makes the microbubble more non-reactive. It temporarily “hides” the microbubble from the immune system uptake, increasing the amount of circulation time, and hence, imaging time (Klibanov, 2005). In addition to the PEG layer, the shell is modified with molecules that allow for the attachment of ligands that bind certain receptors. These ligands are attached to the microbubbles using carbodiimide, maleimide, or biotin-streptavidin coupling (Klibanov, 2005). Biotin-streptavidin is the most popular coupling strategy because biotin’s affinity for streptavidin is very strong and it is easy to label the ligands with biotin. Currently, these ligands are monoclonal antibodies produced from animal cell cultures that bind specifically to receptors and molecules expressed by the target cell type. Since the antibodies are not humanized, they will elicit an immune response when used in human therapy. Humanizing antibodies is an expensive and time-intensive process, so it would be ideal to find an alternative source of ligands, such as synthetically manufactured targeting peptides that perform the same function, but without the immune issues.
How Contrast Enhanced Ultrasound Works
There are two forms of contrast enhanced ultrasound, untargeted (used in the clinic today) and targeted (under preclinical development). The two methods slightly differ from each other.
Untargeted CEU
Untargeted microbubbles, such as the aforementioned Optison or Levovist, are injected intravenously into the systemic circulation in a small bolus. The microbubbles will remain in the systemic circulation for a certain period of time. During that time, ultrasound waves are directed on the area of interest. When microbubbles in the blood flow past the imaging window, the microbubbles’ compressible gas cores oscillate in response to the high frequency sonic energy field, as described in the ultrasound article. The microbubbles reflect a unique echo that stands in stark contrast to the surrounding tissue due to the orders of magnitude mismatch between microbubble and tissue echogenicity. The ultrasound system converts the strong echogenicity into a contrast-enhanced image of the area of interest. In this way, the bloodstream’s echo is enhanced, thus allowing the clinician to distinguish blood from surrounding tissues.
Targeted CEU
Targeted contrast enhanced ultrasound works in a similar fashion, with a few alterations. Microbubbles targeted with ligands that bind certain molecular markers that are expressed by the area of imaging interest are still injected systemically in a small bolus. Microbubbles theoretically travel through the circulatory system, eventually finding their respective targets and binding specifically. Ultrasound waves can then be directed on the area of interest. If a sufficient number of microbubbles have bound in the area, their compressible gas cores oscillate in response to the high frequency sonic energy field, as described in the ultrasound article. The targeted microbubbles also reflect a unique echo that stands in stark contrast to the surrounding tissue due to the orders of magnitude mismatch between microbubble and tissue echogenicity. The ultrasound system converts the strong echogenicity into a contrast-enhanced image of the area of interest, revealing the location of the bound microbubbles (Klibanov, 1999). Detection of bound microbubbles may then show that the area of interest is expressing that particular molecular, which can be indicative of a certain disease state, or identify particular cells in the area of interest.
Applications of Contrast Enhanced Ultrasound
Untargeted contrast enhanced ultrasound is currently applied in echocardiography. Targeted contrast enhanced ultrasound is being developed for a variety of medical applications.
Untargeted CEU
Untargeted microbubbles like Optison and Levovist are currently used in echocardiography.
- Organ Edge Delineation: microbubbles can enhance the contrast at the interface between the tissue and blood. A clearer picture of this interface gives the clinician a better picture of the structure of an organ. Tissue structure is crucial in echocardiograms, where a thinning, thickening, or irregularity in the heart wall indicates a serious heart condition that requires either monitoring or treatment.
- Blood Volume and Perfusion: contrast enhanced ultrasound holds the promise for (1) evaluating the degree of blood perfusion in an organ or area of interest and (2) evaluating the blood volume in an organ or area of interest. When used in conjunction with Doppler Ultrasound, microbubbles can measure myocardial flow rate to diagnose valve problems. And the relative intensity of the microbubble echoes can also provide a quantitative estimate on blood volume.
Targeted CEU
- Inflammation: in inflammatory diseases such as Crohn’s disease, atherosclerosis, and even heart attacks, the inflamed blood vessels specifically express certain receptors like VCAM-1, ICAM-1, E-selectin. If microbubbles are targeted with ligands that bind these molecules, they can be used in contrast echocardiography to detect the onset of inflammation. Early detection allows the design of better treatments.
- Cancer: cancer cells also express a specific set of receptors, mainly receptors that encourage angiogenesis, or the growth of new blood vessels. If microbubbles are targeted with ligands that bind receptors like VEGF, they can non-invasively and specifically identify areas of cancers.
- Gene Delivery: Vector DNA can be conjugated to the microbubbles. Microbubbles can be targeted with ligands that bind to receptors expressed by the cell type of interest. When the targeted microbubble accumulates at the cell surface with its DNA payload, ultrasound can be used to burst the microbubble. The force associated with the bursting may temporarily permeablize surrounding tissues and allow the DNA to more easily enter the cells.
- Drug Delivery: drugs can be incorporated into the microbubble’s lipid shell. The microbubble’s large size relative to other drug delivery vehicles like liposomes may allow a greater amount of drug to be delivered per vehicle. By targeted the drug-loaded microbubble with ligands that bind to a specific cell type, microbubble will not only deliver the drug specifically, but can also provide verification that the drug is delivered if the area is imaged using ultrasound.
Recent Microbubble Targeting History
Microbubbles can be used in various contrast enhanced ultrasound applications, as shown above. The area of greatest area of promise and growth lies in targeted contrast enhanced ultrasound. Current microbubble targeting strategies produce low adhesion efficiencies at high vessel shear stresses of physiological relevance. This means that only a small fraction of microbubbles injected into the test subject actually binds to the molecular markers of interest (Takalkar et al., 2004). This is one of the main issues preventing targeted contrast enhanced ultrasound’s jump from bench to bedside.
There has been an increasing interest in the biomedical research community to enhance the adhesion efficiency of microbubble contrast agents in order to realize targeted contrast enhanced ultrasound’s immense diagnostic and therapeutic potentials. Scientists have outfitted microbubbles with monoclonal antibodies that bind endothelial markers of inflammation, specifically the cell adhesion molecules P-selectin, ICAM-1, and VCAM-1. They showed that these complexes enable targeted ultrasound imaging of inflammation (Lindner, 2004). But, the aforementioned efficiency of microbubble adhesion to the molecular target was poor and a large fraction of microbubbles that bound to the target rapidly detached, especially at high shear stresses of physiological relevance (Takalkar et al., 2004). Effective contrast-enhanced ultrasound requires efficient microbubble binding at the area of imaging interest (Klibanov, 1999).
Leukocytes possess high adhesion efficiencies, partly due to a dual-ligand selectin-integrin cell arrest system (Eniola et al., 2003). One ligand:receptor pair (PSGL-1:selectin) has a fast bond on-rate to slow the leukocyte and allows the second pair (integrin:immunoglobulin superfamily), which has a slower on-rate but slow off-rate to arrest the leukocyte, kinetically enhancing adhesion.
Several research groups have taken advantage of this concept. Eniola and Hammer at the University of Pennsylvania applied dual-ligand targeting of distinct receptors to polymer microspheres for drug delivery and reported an increase in microsphere binding (Eniola and Hammer, 2005). Similarly, Weller and colleagues at the University of Pittsburgh used microbubbles targeted to bind two distinct receptors and showed increased microbubble adhesion strength (Weller et al., 2005). Biomimcry of the leukocyte’s selectin-integrin cell arrest system has also been investigated in the context of improving microbubble adhesion efficiency at the University of Virginia (Rychak et al., 2005). All three research groups showed that dual-targeted microbubbles showed enhanced adhesion compared to single-targeted microbubbles. Though this strategy markedly improves upon prior adhesion, it is still less than ideal. The adhesion efficiency must be higher to allow clinical use of targeted contrast enhanced ultrasound.
Advantages of Contrast Enhanced Ultrasound
On top of the strengths mentioned in the medical sonography entry, contrast enhanced ultrasound adds these additional advantages:
- The body is 90% water, and therefore, acoustically homogeneous. Blood and surrounding tissues have similar echogenicities, so it is also difficult to clearly discern the degree of blood flow, perfusion, or the interface between the tissue and blood using traditional ultrasound (Lindner, 2004).
- Ultrasound imaging allows real-time evaluation of blood flow (Lindner et al., 2002).
- Ultrasonic molecular imaging is safer than molecular imaging modalities such as radionuclide imaging because it does not involve radiation (Lindner et al., 2002).
- Alternative molecular imaging modalities, such as MRI, PET, and SPECT are very costly. Ultrasound, on the other hand, is very cost-efficient and widely available (Klibanov, 1999).
- Since microbubbles can generate such strong signals, a lower intravenous dosage is needed, micrograms of microbubbles are needed compared to milligrams for other molecular imaging modalities such as MRI contrast agents (Klibanov, 1999).
- Targeting strategies for microbubbles are versatile and modular. Targeting a new area only entails conjugating a new ligand.
Disadvantages of Contrast Enhanced Ultrasound
In addition to the weaknesses mentioned in the medical sonography entry, contrast enhanced ultrasound suffers from the following disadvantages:
- Microbubbles don’t last very long in circulation. They have low circulation residence times because they either get taken up by immune system cells or get taken up by the liver or spleen even when they are coated with PEG (Klibanov, 1999).
- Ultrasound produces more heat as the frequency increases, so the ultrasonic frequency must be carefully monitored.
- Microbubbles burst at low ultrasound frequencies and at high mechanical indices (MI), which is the measure of the acoustic power output of the ultrasound imaging system. Increasing MI increases image quality, but there are tradeoffs with microbubble destruction. Microbubble destruction could cause local microvasculature ruptures and hemolysis (Klibanov, 2005).
- Targeting ligands can be immunogenic, since current targeting ligands used in preclinical experiments are derived from animal culture (Klibanov, 2005).
- Low targeted microbubble adhesion efficiency, which means a small fraction of injected microbubbles bind to the area of interest (Takalkar et al., 2004). This is one of the main reasons that targeted contrast enhanced ultrasound remains in the preclinical development stages.
See Also
- ultrasound
- sonography
- medical imaging
- medical ultrasonography
- echocardiography
- Doppler effect
References
#Eniola, A.O., and D.A. Hammer. 2005. In vitro characterization of leukocyte mimetic for targeting therapeutics to the endothelium using two receptors. Biomaterials. 26: 7136-44.
#Eniola, A.O., P.J. Willcox, and D.A. Hammer. 2003. Interplay between rolling and firm adhesion elucidated with a cell-free system engineered with two distinct receptor-ligand pairs. Biophys. J. 85: 2720-31.
#Klibanov, A.L. 2005. Ligand-carrying gas-filled microbubbles: ultrasound contrast agents for targeted molecular imaging. Bioconjug Chem. 16: 9-17.
#Klibanov, A.L. 1999. Targeted delivery of gas-filled microspheres, contrast agents for ultrasound imaging. Adv Drug Deliv Rev. 37: 139-157.
#Lindner, J.R. 2004. Microbubbles in medical imaging: current applications and future directions. Nat Rev Drug Discov. 3: 527-32.
#Lindner, J.R., A.L. Klibanov, and K. Ley. Targeting inflammation, In: Biomedical aspects of drug targeting. (Muzykantov, V.R., Torchilin, V.P., eds.) Kluwer, Boston, 2002; pp. 149-172.
#McCulloch, M., C. Gresser, S. Moos, J. Odabashian, S. Jasper, J. Bednarz, P. Burgess, D. Carney, V. Moore, E. Sisk, A. Waggoner, S. Witt, and D. Adams. Ultrasound contrast physics: A series on contrast echocardiography, article 3. J Am Soc Echocardiogr. 13: 959-67.
#Rychak J.J., A.L. Klibanov, W. Yang, B. Li, S. Acton, A. Leppanen, R.D. Cummings, and K. Ley. "Enhanced Microbubble Adhesion to P-selectin with a Physiologically-tuned Targeting Ligand," 10th Ultrasound Contrast Research Symposium in Radiology, San Diego, CA, March 2005.
#Takalkar, A.M., A.L. Klibanov, J.J. Rychak, J.R. Lindner, and K. Ley. 2004. Binding and detachment dynamics of microbubbles targeted to P-selectin under controlled shear flow. J. Contr. Release. 96: 473-482.
#Weller, G.E., F.S. Villanueva, E.M. Tom, and W.R. Wagner. 2005. Targeted ultrasound contrast agents: In vitro assessment of endothelial dysfunction and multi-targeting to ICAM-1 and sialyl Lewis(x). Biotechnol. Bioeng. 92: 780-8.
External Links
- [http://www.amershamhealth-us.com/optison Optison Information from GE Healthcare]
- [http://www.medsafe.govt.nz/Profs/Datasheet/l/Levovistinj.htm Levovist Data Sheet from New Zealand Medicines and Medical Devices Safety Authority]
- [http://www.schering-diagnostics.de/scripts/index.php Schering Diagnostics Webpage]
- [http://www.amershamhealth.com/medcyclopaedia/medical/Volume%20I/ULTRASOUND%20CONTRAST%20MEDIUM.asp GE Healthcare on Ultrasound Contrast Media]
- [http://www.asecho.org The American Society of Echocardiography]
- [http://www.contrastzone.com/ The Contrast Zone at the American Society of Echocardiography]
Category: Bioengineering
Category: Cardiology
Category: Cardiovascular medicine
Category: Medical equipment
Category: Medical imaging
Category: Medical research
Ultrasound
Ultrasound is sound with a frequency greater than the upper limit of human hearing, approximately 20 kilohertz. Some animals, such as dogs, dolphins, bats, and mice have an upper limit that is greater than that of the human ear and thus can hear ultrasound.
Ultrasound has industrial and medical applications. Medical Sonography (also called ultrasonography) can visualise muscle and soft tissue, making them useful for scanning the organs, and obstetric sonography is commonly used during pregnancy. The use of microbubble contrast media in medical sonography to improve ultrasound signal backscatter is known as contrast enhanced ultrasound. This technique is currently used in echocardiography, and may have future applications in molecular imaging and drug delivery.
Typical diagnostic sonography scanners operate in the frequency range of 2 to 13 megahertz. More powerful ultrasound sources may be used to generate local heating in biological tissue, with applications in physical therapy and cancer treatment. Focused ultrasound sources may be used to break up kidney stones or for cataract treatment by phacoemulsification.
Diagnostic Sonography is often incorrectly referred to as "ultrasound"; however, ultrasound is a term of physics meaning acoustic energy with a frequency above human hearing. To call a sonogram an “ultrasound” is analogous to calling a photograph a "light". There are other uses of ultrasound in medicine that are not imaging or sonography. These include heating tissue in physical therapy, cleaning teeth in dental hygiene. Ultrasound is also used by iron workers for nondestructive testing of metals and welds, and jewelers use ultrasound to clean rings and watches. These other uses are not included in the definition of Diagnostic Sonography.
Ultrasonic cleaners, sometimes mistakenly called supersonic cleaners, are used at frequencies from 20-40 kHz for jewellery, lenses and other optical parts, watches, dental instruments, surgical instruments and industrial parts. The main mechanism for cleaning action in an ultrasonic cleaner is actually the energy released from the collapse of millions of microscopic cavitation events occurring in the liquid of the cleaner. Home cleaners are available and costs range from approximately US $100.
Ultrasound when applied in specific configurations can produce exotic phenomena such as sonoluminescence. These phenomena are being investigated partly because of the possibility of bubble fusion.
Ultrasound generator/speaker systems are sold with claims that they frighten away rodents and insects, but there is no scientific evidence that the devices work; controlled tests have shown that rodents quickly learn that the speakers are harmless.
Dangers of Ultrasound
There have been disputes whether ultrasound is safe. But since ultrasound is energy, there are questions such as, "What are the energy waves doing to my tissue?" There are some reports of low birth weight babies being born to mothers who had more than the recommended ultrasound examination.
There may be side-effects of the following:
- Heat development: Local tissue absorb the ultrasound energy and increases the temperature of those tissues
- Bubble formation: Gasses, that are dissolved, come out of the solution due to local heat increases
However, there are no substantiated side-effects documented in studies.
From sound to image
The creation of an image from sound is done in three steps - producing a soundwave, receiving echos, and interpreting those echos.
Producing a sound wave
In medical ultrasonography, a soundwave is produced by creating short, strong pulses of sound from a phased array of piezoelectric transducers (usually a type of ceramic). The electrical wiring and transducers are encased in a probe. The electrical pulses vibrate the ceramic to create a series of sound pulses from each. The frequencies present in this sound wave can be anywhere between 2 and 10 MHz; well above the capabilities of the human ear. Any frequency above the capabilities of the human ear is referred to as 'ultrasound'. The goal is to produce a single focused arc-shaped soundwave from the sum of all the individual pulses emitted by the transducer.
To make sure the sound is transmitted efficiently into the body (a form of impedance matching), the transducer is coated with rubber and a special gel.
The soundwave, which is able to penetrate bodily fluids, but not solids, bounces off the solid object and returns to the Transducer, this return is an echo.
Receiving the echos
The return of the soundwave to the Transducer results in the same process that it took to send the soundwave, just in reverse. The return soundwave vibrates the Transducer and turns that vibration into an electrical pulse that is sent through the probe and into sonographer's computer where it can be interpreted and transformed into a digital image.
Interpreting the echo
The computer must determine three things from each electrical impulse received: 1.) Which wire did the impulse come from (There are multiple receiving wires on a transducer). 2.) How strong was the impulse. 3.) How long did it take the impulse to be received from when it was sent. Once the computer determines these three things, it can locate which portion of the monitor to light up and what color. Transforming the electrical signal into a digital image can be best explained by using a blank Microsoft Excel Worksheet as an analogy. The wire receiving the impulse determines the 'Column' in our Excel Worksheet (A,B,C,etc.). The time that it took to receive the impulse determines the 'Row' (1,2,3,etc.), and the strength of the impulse determines the color that the cell should change too (white for a strong pulse, black for a weak pulse, and varying shades of grey for everything in between.)
See also
- Dog whistle
- Infrasound (sound at extremely low frequencies)
- Light
- Pelvic ultrasound
- Physics
- Ultrasound weapons
- Gravis Ultrasound
- SoundTechNarrative2
- From Sound to Image
- Ultrasound flow meter
- Medical ultrasonography
- Contrast enhanced ultrasound
External links
- [http://www.xraylinks.com Radiology Web Site Directory]
- [http://www.radiologyworkers.com Ultrasound Job Outlooks]
- [http://www.rtstudents.com Radiology Resources for Students and Professionals]
- [http://clinical.medicalengineer.co.uk/Measurement+of+Blood+Flow.php Medical Engineer - Clinical Ultrasound for Blood Flow]
Category:Hearing
Category:Acoustics
ja:超音波
Artificial blood: Blood substitutes
Liquid breathingLiquid breathing is a form of respiration in which a normally air-breathing organism breathes an oxygen rich liquid (usually from the perfluorocarbon family), rather than breathing air. It is used for medical treatment and could someday find use in deep diving and space travel. Liquid breathing is sometimes called "fluid breathing", but this is misleading as both liquids and gases are classed by scientists as fluids.
The early experiments
In the mid 1960's Dr. J. Kylstra, a physiologist at the State University of New York at Buffalo, realized that salt solutions could be saturated with oxygen at high pressures. In a US Navy recompression chamber, Kylstra experimented to see if mice could move the saline solution in and out of their lungs, while extracting enough oxygen from the fluid to survive. The mice and rats could breathe the liquid (he could keep the animals alive for up to 18 hours), but carbon dioxide was not removed fast enough from the system, and quickly built up to near-toxic levels. This had to be fixed before liquid breathing could be used in humans.
In 1966 Dr. Leland Clark and Dr. Golan experimented on liquid breathing in mice. Oxygen and carbon dioxide are very soluble in fluorocarbon liquids such as freon. Leland Clark realized that, if the alveoli of the lungs can draw oxygen out of the liquid and unload carbon dioxide into the liquid, these fluorocarbons should support respiration of animals. Testing first on anesthetized mice, he temporarily paralyzed each animal and put a tube down its trachea, inflating a cuff inside the airway to provide a seal and ensure that no air entered the lungs, and no solution leaked out.
After bubbling oxygen through the fluorocarbon, the oxygenated fluid was pumped into the animals' lungs, and recirculated at about 6 cycles of inhalation and exhalation per minute. Most of the animals who were kept in the fluid for up to an hour survived for several weeks after their removal, before eventually succumbing to pulmonary damage. Autopsies uniformly revealed that the lungs appeared congested when collapsed but normal when inflated.
As in Kylstra's studies, Clark had problems due to the size of the animals' airways. The tiny size limited the amount of fluid that could get into the lungs. For that and other reasons, carbon dioxide tended to build up in the system and could not be removed fast enough. Dr. Clark discovered that the length of time the mice could survive in the fluid was directly related to the fluorocarbon's temperature: the colder the fluid, the lower the respiration rate, which prevented carbon dioxide buildup. The only way was to induce hypothermia in the animals. This technique seemed to give him the most success, as one animal survived over 20 hours breathing fluid at 18 ºC.
All animals in the earliest studies suffered lung damage, but whether that was due to toxic impurities in the fluorocarbon, chemical interaction of the fluorocarbon with the lung, or some unknown effect, was undetermined. This mystery of the lung damage, and the problem of carbon dioxide elimination, and the body tissues tending to retain the fluorocarbon, would have to be solved before the process could be attempted on human subjects. Also, perfluorocarbon is denser and more viscous than air. This increases resistance and thus the effort needed to breathe.
Later developments
During later years, the techniques of fluid breathing were constantly refined and improved. The survival rate of all the tested animals in recent years has been very high, thanks mainly to improvements in carbon dioxide elimination. Current fluids used can dissolve over 65 ml of oxygen and 228 ml of carbon dioxide per 100 ml perfluorocarbon. By the early 1990s this procedure developed:
#The animal was anesthetized with intravenous sodium thiopental.
#The animal was put on its back. A tube was placed down its airway, ready for the liquid breathing medium.
#A blood sample was taken. The temperature of the fluid was adjusted correspondingly. It was no longer necessary to make the animals hypothermic.
#The perfluorocarbon was instilled into the animal's lungs through the tube.
#A floor-mounted 3-litre reservoir was filled with the perfluorocarbon. The liquid was driven by a pump through a series of machines which warmed and oxygenated the liquid and took the carbon dioxide out of it. The liquid flowed through a tube into a 3-way pneumatic valve which directed flow to the animal. A computer controlled the inspiration (18 ml of fluid per second), pumping the liquid into the animal's lungs, then back out again to the reservoir, at a rate of about 6 complete respirations per minute.
#At the end of the test, the animal was tilted for about 15 seconds and the perfluorocarbon was allowed to drain from the lungs. This can be seen in the film The Abyss where Ensign Monk drained the fluid out of the rat's lungs: in the filming, the rat genuinely breathed liquid.
These tests of the early 90s were successful: dogs could be kept alive in the perfluorcarbon medium for about 2 hours; after removal the dogs were usually slightly hypoxic, but returned to normal after a few days. When the animals were autopsied, the typical findings were mild oedema and some hemorrhaging, clearly an improvement over the lung damage of earlier tests.
Use in diving
Breathing liquid instead of air seems odd, but if the technique could be perfected it would revolutionize diving.
In diving, the pressure inside the lungs must equal the pressure outside the body, otherwise the lungs collapse. Thus, if the diver is f feet or m meters deep, and the air pressure at the water surface is p bars (usually p = 1, but it is less at high-altitude lakes such as Lake Titicaca), he must breathe fluid at a pressure of f/33+p = m/10+p bars. This pressure quickly gets high with depth: around 13 bars at 400 feet (120m), and around 500 bars on the oceans' abyssal plains. These high pressures cause harmful effects on the body: air emboli and other diving disorders, like nitrogen narcosis and decompression sickness. One solution is a rigid articulated diving suit, but these are bulky and clumsy. A more moderate option is to breathe heliox or trimix, in which some or all of the nitrogen is replaced by helium.
With liquid in the lungs, the pressure in our body could accommodate changes in the pressure of the surrounding water without the huge density changes typical of gases. That would eliminate the need for decompression and its above inherent problems.
If the technique could be perfected, it would be extremely useful for submarine escape and undersea oxygen support facilities, and for underwater work, as portrayed in the 1989 science-fiction film The Abyss.
Medical uses
The immediate use of liquid breathing is likely to be in treating premature babies, and adults with severe lung damage from causes such as fires.
Liquid breathing began to be used by the medical community after the development by Alliance Pharmaceuticals of the fluorochemical perfluorooctyl bromide, or perflubron for short. Useful as a blood substitute and for liquid ventilation, perflubron (under Alliance Pharmaceutical's brand name LiquiVent) is instilled directly into the lungs of patients with acute respiratory failure (caused by infection, severe burns, inhalation of toxic substances, and premature birth), whose air sacs have collapsed. Once inside the lungs, perflubron enables collapsed alveoli (air sacs) to open and permits a more efficient transport of oxygen and carbon dioxide. Current tests are focussing on premature babies, but trials with adults are ongoing.
All blood that flows out from the heart to the rest of the body first must go through the lungs, where it picks up oxygen and gets rid of carbon dioxide. If the lungs do not function properly, as is common in premature infants with respiratory distress syndrome, the lungs become stiff and collapse, and the infants must be put on ventilators. A study, led by Dr. Corrinne Leach of the State University of New York at Buffalo, tested 13 infants on ventilators who were born prematurely with respiratory distress syndrome. The infants were at risk of dying because they could not produce a natural surfactant that stops the lungs from collapsing from surface tension. They were at risk of severe and permanent lung damage from the force of the ventilators that were inflating their lungs. Their lungs were filled with perflubron which would let the air sacs of the lungs open and permit breathing. The perflubron let the lungs inflate with less pressure and let oxygen pass through the lungs and into the blood stream and carbon dioxide out more efficiently and with less stress. This was successful.
The 13 premature infants received partial liquid ventilation for 24 to 76 hours; they were weaned back to gas ventilation without difficulties or adverse side effects, and 11 of the 13 showed significant improvement in lung functioning. Six of the infants eventually died, but of causes apparently unrelated to the liquid ventilation.
Clinical trials with premature infants, children and adults are ongoing. Since the safety of the procedure and the effectiveness of the gas exchange have improved so much, the US Food and Drug Administration (FDA) has given the product "fast track" status (meaning a speeded-up review of the product, designed to get it to the public as quickly as is safely possible) due to its life-saving potential.
Mode of application
Despite recent advances in liquid ventilation, a standard mode of application of perfluorocarbon (PFC) has not been established yet.
TLV
Although total liquid ventilation (TLV) with completely liquid filled lungs is beneficial, the necessity for a liquid filled tube system that contains pumps, heater and membrane oxygenator to deliver and remove tidal volume aliquots of conditioned perfluorocarbon to the lungs is of great disadvantage.
PLV
In contrast, partial liquid ventilation (PLV) can be applied using standard ventilators connected with gas filled standard respirator systems, delivering tidal volumes of oxygen-air mixture to perfluorocarbon filled lungs.
The influence of PLV on oxygenation, carbon dioxide removal and lung mechanics has been investigated in several animal studies using different models of lung injury. Clinical applications of PLV have been reported in patients with acute respiratory distress syndrome (ARDS), meconium aspiration syndrome, congenital diaphragmatic hernia and respiratory distress syndrome (RDS) of neonates. PLV requires extreme respiratory care, because the ventilatory setting is determined by the perfluorocarbon filled lung. Profound expertise is mandatory to perform and maintain filling of the lung with perfluorocarbon to functional residual capacity (FRC). Disruption of PLV immediately deteriorates gas exchange. Incomplete filling of the lung has been shown to be less effective than filling the lung to functional residual capacity volume. Severe adverse events affecting gas exchange and pulmonary circulation limit the use of PLV.
New application modes for PFC have been developed.
PFC vapor
Vaporization of perfluorohexane with two anesthetic vaporizers calibrated for perfluorohexane has been shown to improve gas exchange in oleic acid induced lung injury in sheep . Predominantly PFCs with high vapor pressure are suitable for vaporization.
Aerosol-PFC
With aerosolized perfluorooctane, significant improvement of oxygenation and pulmonary
mechanics was shown in adult sheep with oleic acid-induced lung injury.
In surfactant-depleted piglets, persistent improvement of gas exchange and lung mechanics was demonstrated with Aerosol-PFC .
The aerosol device is of decisive importance for the efficacy of PFC aerosolization, as aerosolization of PF5080 (a less purified FC77) has been shown to be ineffective using a different aerosol device in surfactant-depleted rabbits (Kelly). Partial liquid ventilation and Aerosol-PFC reduced pulmonary inflammatory response .
Space Travel
Around 1970, liquid breathing found its way into fiction, in alien spacesuits in the Gerry Anderson UFO series, which enabled a spaceman to withstand extreme acceleration forces.
Forces applied to fluids (such as gravitational forces on Earth) are distributed as omnidirectional pressures. This fact is fundamental to all hydraulics. In the ocean, this distribution of force allows organisms such as whales to grow to sizes that would be unsupportable on dry land.
Because liquids are incompressible fluids, they do not change density under high acceleration such as performed in aerial maneuvers or space travel. Individuals immersed in such liquids would feel inertial forces distributed around their body, rather than applied at a single point such as a seat. High accelerations would feel like the high pressures experienced in deep sea diving. For the same reason that liquid breathing would be useful in diving, breathable liquids would be useful in space travel.
Acknowledgement
Taken, with permission from: [http://www.scienceweb.org/movies/abyss.html Fluid Breathing], and afterwards edited.
References
# Science (24 June 1966).
#
#
#
#
See also
- Mechanical ventilation
- Breathing gas
External links
- [http://www.allp.com/ Alliance Pharmaceutical Corp]
Category:Respiration
Category:Diving
FluoropolymerA fluoropolymer is a polymer that contains atoms of fluorine. They are characterized by an unusual resistance to solvents, acids, and bases.
Fluoropolymers were discovered serendipitously in 1938 by Dr. Roy J. Plunkett. He was working on freon (for the DuPont corporation) and accidentally polymerized tetrafluoroethylene. The result was PTFE (polytetrafluoroethylene), more commonly known as Teflon. It turned out to be the most slippery material known to man and inert to virtually all chemicals.
Examples of fluoropolymers:
- PTFE (Teflon)
- PFA
- FEP
- ETFE (Tefzel), (Fluon)
- PVDF (Kynar)
- TFE
- FPM
- CTFE
- FFKM (Kalrez)
- FKM (Viton)
Fluoropolymers may be either thermosets or thermoplastics.
See also
- Perfluorocarbon (PFC)
Category:Organic polymers
Category:Organic chemistryOrganic chemistry is the study of organic, or carbon based, molecules. Carbon is the only element that can make bonds with itself so that chains are produced, silicon has similar properties, but Carbon is a main element in everyday life, and thus, is lucky enough to have a whole subject in chemistry dedicated to it.
Category:Chemistry
ko:분류:유기화학
Coroebus:Coroebus of Elis [http://www.geometry.net/detail/basic_o/olympics_ancient_page_no_5.html] was an ancient Olympic victor and a chef. There is also a place called Koroivos.
In Greek mythology, Coroebus (Greek: Κόροιβος) was the son of King Mygdon of Phrygia. He came to the aid of Troy during the Trojan War out of love for Princess Cassandra. During the Sack of Troy, Coroebus convinced some of his fellow soldiers to dress in enemy armor to disguise themselves. When he tried to defend Cassandra from rape by Ajax the Lesser, he was killed, either by Penelaus, Diomedes or Neoptolemus.
External links
- [http://classics.mit.edu/Virgil/aeneid.2.ii.html Book II, Aeneid]
Category:People who fought in the Trojan War
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