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Result : Searchterm 'Element' found in 2 terms [] and 42 definitions []
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Element
 
An element consists of atoms having the same structure and the same chemically reaction.
See also Magnetic Resonance Spectroscopy, Isomer, Isotope, Helium, and Gadolinium.
Mathematically, an element or member of a set is any one of the separate objects that make up that set. Elements in arrays (parallel arrangement of many identical items) are used in MRI coils.
See also Array Coil, Array Processor, and Array Spatial Sensitivity Encoding Technique.
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Resolution Element
 
Size of smallest spatially resolved regions in an image. It may be anisotropic, e.g. with an asymmetric acquisition matrix or slice thickness, and may be larger than the pixel or voxel.
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Further Reading:
  News & More:
Micro-MRI Principles, Strengths, and Weaknesses
Tuesday, 10 January 2017   by www.news-medical.net    
MRI Resources 
MRI Accidents - NMR - Shoulder MRI - MRI Physics - Anatomy - Nerve Stimulator
 
Array Spatial Sensitivity Encoding TechniqueInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
(ASSETT) ASSET is a parallel imaging technique of the SENSE type (image domain reconstruction).
Each coil element is sensitivity encoded and the covered spatial zone is mapped. By reducing the field of view in the phase encoding gradient direction the scan time decreases, but this images of each coil element contain foldover artifacts. The sensitivity profiles of the elements are used to calculate unfolded images.
See also Sensitivity Encoding, Generalized Autocalibrating Partially Parallel Acquisition.
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Further Reading:
  Basics:
Scanning the Abdomen
   by www.mrprotocols.com    
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Magnetic Resonance SpectroscopyMRI Resource Directory:
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(MRS / MRSI - Magnetic Resonance Spectroscopic Imaging) A method using the NMR phenomenon to identify the chemical state of various elements without destroying the sample. MRS therefore provides information about the chemical composition of the tissues and the changes in chemical composition, which may occur with disease processes.
Although MRS is primarily employed as a research tool and has yet to achieve widespread acceptance in routine clinical practice, there is a growing realization that a noninvasive technique, which monitors disease biochemistry can provide important new information for the clinician.
The underlying principle of MRS is that atomic nuclei are surrounded by a cloud of electrons, which very slightly shield the nucleus from any external magnetic field. As the structure of the electron cloud is specific to an individual molecule or compound, then the magnitude of this screening effect is also a characteristic of the chemical environment of individual nuclei.
In view of the fact that the resonant frequency is proportional to the magnetic field that it experiences, it follows that the resonant frequency will be determined not only by the external applied field, but also by the small field shift generated by the electron cloud. This shift in frequency is called the chemical shift (see also Chemical Shift). It should be noted that chemical shift is a very small effect, usually expressed in ppm of the main frequency. In order to resolve the different chemical species, it is therefore necessary to achieve very high levels of homogeneity of the main magnetic field B0. Spectra from humans usually require shimming the magnet to approximately one part in 100. High resolution spectra of liquid samples demand a homogeneity of about one part in 1000.
In addition to the effects of factors such as relaxation times that can affect the NMR signal, as seen in magnetic resonance imaging, effects such as J-modulation or the transfer of magnetization after selective excitation of particular spectral lines can affect the relative strengths of spectral lines.
In the context of human MRS, two nuclei are of particular interest - H-1 and P-31. (PMRS - Proton Magnetic Resonance Spectroscopy) PMRS is mainly employed in studies of the brain where prominent peaks arise from NAA, choline containing compounds, creatine and creatine phosphate, myo-inositol and, if present, lactate; phosphorus 31 MR spectroscopy detects compounds involved in energy metabolism (creatine phosphate, adenosine triphosphate and inorganic phosphate) and certain compounds related to membrane synthesis and degradation. The frequencies of certain lines may also be affected by factors such as the local pH. It is also possible to determine intracellular pH because the inorganic phosphate peak position is pH sensitive.
If the field is uniform over the volume of the sample, "similar" nuclei will contribute a particular frequency component to the detected response signal irrespective of their individual positions in the sample. Since nuclei of different elements resonate at different frequencies, each element in the sample contributes a different frequency component. A chemical analysis can then be conducted by analyzing the MR response signal into its frequency components.
See also Spectroscopy.
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Contrast AgentsForum -
related threadsInfoSheet: - Contrast Agents - 
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Contrast agents are chemical substances introduced to the anatomical or functional region being imaged, to increase the differences between different tissues or between normal and abnormal tissue, by altering the relaxation times. MRI contrast agents are classified by the different changes in relaxation times after their injection.
Positive contrast agents cause a reduction in the T1 relaxation time (increased signal intensity on T1 weighted images). They (appearing bright on MRI) are typically small molecular weight compounds containing as their active element Gadolinium, Manganese, or Iron. All of these elements have unpaired electron spins in their outer shells and long relaxivities.
Some typical contrast agents as gadopentetate dimeglumine, gadoteridol, and gadoterate meglumine are utilized for the central nervous system and the complete body; mangafodipir trisodium is specially used for lesions of the liver and gadodiamide for the central nervous system.
Negative contrast agents (appearing predominantly dark on MRI) are small particulate aggregates often termed superparamagnetic iron oxide (SPIO). These agents produce predominantly spin spin relaxation effects (local field inhomogeneities), which results in shorter T1 and T2 relaxation times.
SPIO's and ultrasmall superparamagnetic iron oxides (USPIO) usually consist of a crystalline iron oxide core containing thousands of iron atoms and a shell of polymer, dextran, polyethyleneglycol, and produce very high T2 relaxivities. USPIOs smaller than 300 nm cause a substantial T1 relaxation. T2 weighted effects are predominant.
A special group of negative contrast agents (appearing dark on MRI) are perfluorocarbons (perfluorochemicals), because their presence excludes the hydrogen atoms responsible for the signal in MR imaging.
The design objectives for the next generation of MR contrast agents will likely focus on prolonging intravascular retention, improving tissue targeting, and accessing new contrast mechanisms. Macromolecular paramagnetic contrast agents are being tested worldwide. Preclinical data shows that these agents demonstrate great promise for improving the quality of MR angiography, and in quantificating capillary permeability and myocardial perfusion.
Ultrasmall superparamagnetic iron oxide (USPIO) particles have been evaluated in multicenter clinical trials for lymph node MR imaging and MR angiography, with the clinical impact under discussion. In addition, a wide variety of vector and carrier molecules, including antibodies, peptides, proteins, polysaccharides, liposomes, and cells have been developed to deliver magnetic labels to specific sites. Technical advances in MR imaging will further increase the efficacy and necessity of tissue-specific MRI contrast agents.
See also Adverse Reaction and Nephrogenic Systemic Fibrosis.

See also the related poll result: 'The development of contrast agents in MRI is'
 
Images, Movies, Sliders:
 Delayed Myocardial Contrast Enhancement from Infarct  Open this link in a new window
      

Courtesy of  Robert R. Edelman
 Left Circumflex Ischemia First-pass Contrast Enhancement  Open this link in a new window
 MR Colonography Gadolinium per Rectum  Open this link in a new window
      

Courtesy of  Robert R. Edelman
 CE MRA of the Aorta  Open this link in a new window
    
SlidersSliders Overview

 
Radiology-tip.comContrast Agents,  Safety of Contrast Agents
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Radiology-tip.comUltrasound Contrast Agents,  Ultrasound Contrast Agent Safety
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Further Reading:
  Basics:
New guidelines urge caution on use of contrast agents during MR scans
Tuesday, 8 August 2017   by www.dotmed.com    
Manganese-based MRI contrast agents: past, present and future
Friday, 4 November 2011   by www.ncbi.nlm.nih.gov    
A safer approach for diagnostic medical imaging
Monday, 29 September 2014   by www.eurekalert.org    
Drastic market changes with MRI contrast media and PET radiopharmaceuticals emerging as most promising segments
Thursday, 21 October 2004   by www.news-medical.net    
  News & More:
Sodium MRI May Show Biomarker for Migraine
Friday, 1 December 2017   by psychcentral.com    
Manganese-based MRI contrast agent may be safer alternative to gadolinium-based agents
Wednesday, 15 November 2017   by www.eurekalert.org    
3D 'bone maps' could spot early signs of osteoporosis
Monday, 27 February 2017   by www.gmanetwork.com    
New Study Sheds Light on Safety of Gadolinium-Based Contrast Agents
Wednesday, 29 November 2017   by www.empr.com    
Engineered atherosclerosis-specific zinc ferrite nanocomplex-based MRI contrast agents
Monday, 18 January 2016   by 7thspace.com    
A natural boost for MRI scans
Monday, 21 October 2013   by www.eurekalert.org    
For MRI, time is of the essence A new generation of contrast agents could make for faster and more accurate imaging
Tuesday, 28 June 2011   by scienceline.org    
MRI Resources 
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