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Dynamic Contrast Enhanced MRI
Perfusion MRI or perfusion-weighted imaging (PWI) is perfusion scanning by the use of a particular MRI sequence. The acquired data are then post-processed to obtain perfusion maps with different parameters, such as BV (blood volume), BF (blood flow), MTT (mean transit time) and TTP (time to peak). Clinical use In cerebral infarction, the penumbra has decreased perfusion. Another MRI sequence, diffusion weighted MRI, estimates the amount of tissue that is already necrotic, and the combination of those sequences can therefore be used to estimate the amount of brain tissue that is salvageable by thrombolysis and/or thrombectomy. Sequences There are 3 main techniques for perfusion MRI: * Dynamic susceptibility contrast (DSC): Gadolinium contrast is injected, and rapid repeated imaging (generally gradient-echo echo-planar T2 weighted) quantifies susceptibility-induced signal loss. * Dynamic contrast enhanced (DCE): Measuring shortening of the spin–lattice relaxation (T1) induced b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Penumbra (medicine)
In pathology and anatomy the penumbra is the area surrounding an ischemic event such as thrombotic or embolic stroke. Immediately following the event, blood flow and therefore oxygen transport is reduced locally, leading to hypoxia of the cells near the location of the original insult. This can lead to hypoxic cell death (infarction) and amplify the original damage from the ischemia; however, the penumbra area may remain viable for several hours after an ischemic event due to the collateral arteries that supply the penumbral zone. As time elapses after the onset of stroke, the extent of the penumbra tends to decrease; therefore, in the emergency department a major concern is to protect the penumbra by increasing oxygen transport and delivery to cells in the danger zone, thereby limiting cell death. The existence of a penumbra implies that salvage of the cells is possible. There is a high correlation between the extent of spontaneous neurological recovery and the volume of penum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spin–lattice Relaxation
During nuclear magnetic resonance observations, spin–lattice relaxation is the mechanism by which the longitudinal component of the total nuclear magnetic moment vector (parallel to the constant magnetic field) exponentially relaxes from a higher energy, non-equilibrium state to thermodynamic equilibrium with its surroundings (the "lattice"). It is characterized by the spin–lattice relaxation time, a time constant known as ''T1''. There is a different parameter, ''T2'', the spin-spin relaxation time, which concerns the exponential relaxation of the transverse component of the nuclear magnetization vector ( to the external magnetic field). Measuring the variation of ''T1'' and ''T2'' in different materials is the basis for some magnetic resonance imaging techniques. Nuclear physics ''T1'' relaxation or longitudinal relaxation curve ''T1'' characterizes the rate at which the longitudinal ''Mz'' component of the magnetization vector recovers exponentially towards its thermodynam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PET Imaging
Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, regional chemical composition, and absorption. Different tracers are used for various imaging purposes, depending on the target process within the body. For example, -FDG is commonly used to detect cancer, NaF is widely used for detecting bone formation, and oxygen-15 is sometimes used to measure blood flow. PET is a common imaging technique, a medical scintillography technique used in nuclear medicine. A radiopharmaceutical — a radioisotope attached to a drug — is injected into the body as a tracer. When the radiopharmaceutical undergoes beta plus decay, a positron is emitted, and when the positron collides with an ordinary electron, the two particles annihilate and gamma rays are emitted. These gamma rays are detecte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gadolinium
Gadolinium is a chemical element with the symbol Gd and atomic number 64. Gadolinium is a silvery-white metal when oxidation is removed. It is only slightly malleable and is a ductile rare-earth element. Gadolinium reacts with atmospheric oxygen or moisture slowly to form a black coating. Gadolinium below its Curie point of is ferromagnetic, with an attraction to a magnetic field higher than that of nickel. Above this temperature it is the most paramagnetic element. It is found in nature only in an oxidized form. When separated, it usually has impurities of the other rare-earths because of their similar chemical properties. Gadolinium was discovered in 1880 by Jean Charles de Marignac, who detected its oxide by using spectroscopy. It is named after the mineral gadolinite, one of the minerals in which gadolinium is found, itself named for the Finnish chemist Johan Gadolin. Pure gadolinium was first isolated by the chemist Paul-Émile Lecoq de Boisbaudran around 1886. Gadoliniu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cells (biology)
The cell is the basic structural and functional unit of life forms. Every cell consists of a cytoplasm enclosed within a membrane, and contains many biomolecules such as proteins, DNA and RNA, as well as many small molecules of nutrients and metabolites.Cell Movements and the Shaping of the Vertebrate Body in Chapter 21 of Molecular Biology of the Cell '' fourth edition, edited by Bruce Alberts (2002) published by Garland Science. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos. It is also common to describe small molecules such as < ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extracellular Matrix
In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide structural and biochemical support to surrounding cells. Because multicellularity evolved independently in different multicellular lineages, the composition of ECM varies between multicellular structures; however, cell adhesion, cell-to-cell communication and differentiation are common functions of the ECM. The animal extracellular matrix includes the interstitial matrix and the basement membrane. Interstitial matrix is present between various animal cells (i.e., in the intercellular spaces). Gels of polysaccharides and fibrous proteins fill the Interstitial fluid, interstitial space and act as a compression buffer against the stress placed on the ECM. Basement membranes are sheet-like depositions of ECM on which various epithelial cells rest ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
T2*-weighted
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 othe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intravoxel Incoherent Motion
Intravoxel incoherent motion (IVIM) imaging is a concept and a method initially introduced and developed by Le Bihan et al. to quantitatively assess all the microscopic translational motions that could contribute to the signal acquired with diffusion MRI. In this model, biological tissue contains two distinct environments: molecular diffusion of water in the tissue (sometimes referred to as 'true diffusion'), and microcirculation of blood in the capillary network (perfusion). The concept introduced by D. Le Bihan is that water flowing in capillaries (at the voxel level) mimics a random walk (“pseudo-diffusion” ) (Fig.1), as long as the assumption that all directions are represented in the capillaries (i.e. there is no net coherent flow in any direction) is satisfied. It is responsible for a signal attenuation in diffusion MRI, which depends on the velocity of the flowing blood and the vascular architecture. Similarly to molecular diffusion, the effect of pseudodiffusion on the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arterial Spin Labelling
Arterial spin labeling (ASL), also known as arterial spin tagging, is a magnetic resonance imaging technique used to quantify cerebral blood perfusion by labelling blood water as it flows throughout the brain. ASL specifically refers to magnetic labeling of arterial blood below or in the imaging slab, without the need of gadolinium contrast. A number of ASL schemes are possible, the simplest being flow alternating inversion recovery (FAIR) which requires two acquisitions of identical parameters with the exception of the out-of-slice saturation; the difference in the two images is theoretically only from inflowing spins, and may be considered a 'perfusion map'. The ASL technique was developed by Alan P. Koretsky, Donald S. Williams, John A. Detre and John S. Leigh, Jr in 1992. Physics Arterial spin labeling utilizes the water molecules circulating with the brain, and using a radiofrequency pulse, tracks the blood water as it circulates throughout the brain. After a period of time in m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gadolinium Contrast
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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiopaedia
Radiopaedia is a wiki-based international collaborative educational web resource containing a radiology encyclopedia and imaging case repository. It is currently the largest freely available radiology related resource in the world with more than 50,000 patient cases and over 16,000 reference articles on radiology-related topics. The open edit nature of articles allows radiologists, radiology trainees, radiographers, sonographers, and other healthcare professionals interested in medical imaging to refine most content through time. An editorial board peer reviews all contributions. Background Radiopaedia was started as a past-time project to store radiology notes and cases online by the Australian neuroradiologist Associate Professor Frank Gaillard in December 2005, while he was a radiology resident. He later became passionate in building the website and decided to release it on the web, advocating free dissemination of knowledge. The domain name for radiopaedia.org was registered ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Middle Cerebral Artery
The middle cerebral artery (MCA) is one of the three major paired cerebral artery, cerebral arteries that supply blood to the cerebrum. The MCA arises from the internal carotid artery and continues into the lateral sulcus where it then branches and projects to many parts of the lateral cerebral cortex. It also supplies blood to the anterior temporal lobes and the insular cortex, insular cortices. The left and right MCAs rise from trifurcations of the internal carotid artery, internal carotid arteries and thus are connected to the anterior cerebral artery, anterior cerebral arteries and the posterior communicating artery, posterior communicating arteries, which connect to the posterior cerebral artery, posterior cerebral arteries. The MCAs are not considered a part of the Circle of Willis. Structure The middle cerebral artery divides into four segments, named by the region they supply as opposed to order of branching as the latter can be somewhat variable: *M1: The ''sphenoidal' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
