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Contrast Agents
A contrast agent (or contrast medium) is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiopharmaceuticals, which emit radiation themselves. In x-rays, contrast agents enhance the radiodensity in a target tissue or structure. In MRIs, contrast agents shorten (or in some instances increase) the relaxation times of nuclei within body tissues in order to alter the contrast in the image. Contrast agents are commonly used to improve the visibility of blood vessels and the gastrointestinal tract. Several types of contrast agent are in use in medical imaging and they can roughly be classified based on the imaging modalities where they are used. Most common contrast agents work based on X-ray attenuation and magnetic resonance signal enhancement. Radiocontrast media For radiography, which is based on X-rays, iodine and barium are the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Substance
A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be simple substances (substances consisting of a single chemical element), chemical compounds, or alloys. Chemical substances are often called 'pure' to set them apart from mixtures. A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory. Other chemical substances commonly encountered in pure form are diamond (carbon), gold, table salt (sodium chloride) and refined sugar (sucrose). However, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical. Chemical substances exist as solids, liquids, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimer (chemistry)
A dimer () ('' di-'', "two" + ''-mer'', "parts") is an oligomer consisting of two monomers joined by bonds that can be either strong or weak, covalent or intermolecular. Dimers also have significant implications in polymer chemistry, inorganic chemistry, and biochemistry. The term ''homodimer'' is used when the two molecules are identical (e.g. A–A) and ''heterodimer'' when they are not (e.g. A–B). The reverse of dimerization is often called dissociation. When two oppositely charged ions associate into dimers, they are referred to as ''Bjerrum pairs'', after Niels Bjerrum. Noncovalent dimers Anhydrous carboxylic acids form dimers by hydrogen bonding of the acidic hydrogen and the carbonyl oxygen. For example, acetic acid forms a dimer in the gas phase, where the monomer units are held together by hydrogen bonds. Under special conditions, most OH-containing molecules form dimers, e.g. the water dimer. Excimers and exciplexes are excited structures with a short lifetime. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perfluorocarbon
Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often has distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Fluorocarbons and their derivatives are commercial polymers, refrigerants, drugs, and anesthetics. Nomenclature Perfluorocarbons or PFCs, are organofluorine compounds with the formula CxFy, i.e., they contain only carbon and fluorine. The terminology is not strictly followed and many fluorine-containing organic compounds are called fluorocarbons. Compounds with the prefix perfluoro- are hydrocarbons, including those with heteroatoms, wherein all C-H bonds have been replaced by C-F bonds. Fluorocarbons includes perfluoroalkanes, fluoroalkenes, fluoroalkynes, and perfluoroaromatic compounds. Perfluoroalkanes Chemical properties Perfluoroalkanes are very stable because of the strength of the carbon–fluorine bond, one of the strongest in organic chemistry. Its strength is a re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bond to form N2, a colorless and odorless diatomic gas. N2 forms about 78% of Earth's atmosphere, making it the most abundant uncombined element. Nitrogen occurs in all organisms, primarily in amino acids (and thus proteins), in the nucleic acids ( DNA and RNA) and in the energy transfer molecule adenosine triphosphate. The human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes the movement of the element from the air, into the biosphere and organic compounds, then back into the atmosphere. Many indus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Right-to-left Shunt
A right-to-left shunt is a cardiac shunt which allows blood to flow from the right heart to the left heart. This terminology is used both for the abnormal state in humans and for normal physiological shunts in reptiles. Clinical Significance A right-to-left shunt occurs when: #there is an opening or passage between the atria, ventricles, and/or great vessels; ''and'', #right heart pressure is higher than left heart pressure and/or the shunt has a one-way valvular opening. Small physiological, or "normal", shunts are seen due to the return of bronchial artery blood and coronary blood through the Thebesian veins, which are deoxygenated, to the left side of the heart. Causes Congenital defects can lead to right-to-left shunting immediately after birth: *Persistent truncus arteriosus (minimal cyanosis) * Transposition of great vessels *Tricuspid atresia *Tetralogy of Fallot * Total anomalous pulmonary venous return A mnemonic to remember the conditions associated with right-to-l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Saline (medicine)
Saline (also known as saline solution) is a mixture of sodium chloride (salt) and water. It has a number of uses in medicine including cleaning wounds, removal and storage of contact lenses, and help with dry eyes. By injection into a vein it is used to treat dehydration such as that from gastroenteritis and diabetic ketoacidosis. Large amounts may result in fluid overload, swelling, acidosis, and high blood sodium. In those with long-standing low blood sodium, excessive use may result in osmotic demyelination syndrome. Saline is in the crystalloid family of medications. It is most commonly used as a sterile 9 g of salt per litre (0.9%) solution, known as normal saline. Higher and lower concentrations may also occasionally be used. Saline is acidic, with a pH of 5.5 (due mainly to dissolved carbon dioxide). The medical use of saline began around 1831. It is on the World Health Organization's List of Essential Medicines. In 2020, sodium was the 274th most commonly p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cardiac Shunt
A cardiac shunt is a pattern of blood flow in the heart that deviates from the normal circuit of the circulatory system. It may be described as right-left, left-right or bidirectional, or as systemic-to-pulmonary or pulmonary-to-systemic. The direction may be controlled by left and/or right heart pressure, a biological or artificial heart valve or both. The presence of a shunt may also affect left and/or right heart pressure either beneficially or detrimentally. Terminology The left and right sides of the heart are named from a dorsal view, i.e., looking at the heart from the back or from the perspective of the person whose heart it is. There are four chambers in a heart: an atrium (upper) and a ventricle (lower) on both the left and right sides. In mammals and birds, blood from the body goes to the right side of the heart first. Blood enters the upper right atrium, is pumped down to the right ventricle and from there to the lungs via the pulmonary artery. Blood going to the lungs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Echocardiography
An echocardiography, echocardiogram, cardiac echo or simply an echo, is an ultrasound of the heart. It is a type of medical imaging of the heart, using standard ultrasound or Doppler ultrasound. Echocardiography has become routinely used in the diagnosis, management, and follow-up of patients with any suspected or known heart diseases. It is one of the most widely used diagnostic imaging modalities in cardiology. It can provide a wealth of helpful information, including the size and shape of the heart (internal chamber size quantification), pumping capacity, location and extent of any tissue damage, and assessment of valves. An echocardiogram can also give physicians other estimates of heart function, such as a calculation of the cardiac output, ejection fraction, and diastolic function (how well the heart relaxes). Echocardiography is an important tool in assessing wall motion abnormality in patients with suspected cardiac disease. It is a tool which helps in reaching an ear ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Medical Ultrasonography
Medical ultrasound includes diagnostic techniques (mainly medical imaging, imaging techniques) using ultrasound, as well as therapeutic ultrasound, therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal body structures such as tendons, muscles, joints, blood vessels, and internal organs, to measure some characteristics (e.g. distances and velocities) or to generate an informative audible sound. Its aim is usually to find a source of disease or to exclude pathology. The usage of ultrasound to produce visual images for medicine is called medical ultrasonography or simply sonography. The practice of examining pregnant women using ultrasound is called obstetric ultrasonography, and was an early development of clinical ultrasonography. Ultrasound is composed of sound waves with frequency, frequencies which are significantly higher than the range of human hearing (>20,000 Hz). Ultrasonic images, also known as sonograms, are created by se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microbubbles
Microbubbles (MBs) are bubbles smaller than one hundredth of a millimetre in diameter, but larger than one micrometre. They have widespread application in industry, life science, and medicine. The composition of the bubble shell and filling material determine important design features such as buoyancy, crush strength, thermal conductivity, and acoustic properties. They are used in medical diagnostics as a contrast agent for ultrasound imaging. The gas-filled microbubbles, typically air or perfluorocarbon, oscillate, and vibrate if a sonic energy field is applied and may reflect ultrasound waves. This distinguishes the microbubbles from surrounding tissues. Because gas bubbles in liquid lack stability and would therefore quickly dissolve, microbubbles are typically encapsulated by shells. The shell is made from elastic, viscoelastic, or viscous material. Common shell materials are lipid, albumin, and protein. Materials having a hydrophilic outer layer to interact with the bloodstrea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MRI Contrast Agent
MRI contrast agents are contrast agents used to improve the visibility of internal body structures in magnetic resonance imaging (MRI). The most commonly used compounds for contrast enhancement are gadolinium-based. Such MRI contrast agents shorten the relaxation times of nuclei within body tissues following oral or intravenous administration. In MRI scanners, sections of the body are exposed to a strong magnetic field causing primarily the hydrogen nuclei ("spins") of water in tissues to be polarized in the direction of the magnetic field. An intense radiofrequency pulse is applied that tips the magnetization generated by the hydrogen nuclei in the direction of the receiver coil where the spin polarization can be detected. Random molecular rotational oscillations matching the resonance frequency of the nuclear spins provide the "relaxation" mechanisms that bring the net magnetization back to its equilibrium position in alignment with the applied magnetic field. The magnitude of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body. MRI does not involve X-rays or the use of ionizing radiation, which distinguishes it from CT and PET scans. MRI is a medical application of nuclear magnetic resonance (NMR) which can also be used for imaging in other NMR applications, such as NMR spectroscopy. MRI is widely used in hospitals and clinics for medical diagnosis, staging and follow-up of disease. Compared to CT, MRI provides better contrast in images of soft-tissues, e.g. in the brain or abdomen. However, it may be perceived as less comfortable by patients, due to the usually longer and louder measurements with the subject in a long, confining tube, though "Open" MRI designs mostly relieve this. Additionally, implants and oth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
