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Result : Searchterm 'Chemical Shift' found in 6 terms [] and 30 definitions []
| 1 - 5 (of 36) nextResult Pages : [1 2] [3 4 5 6 7 8] | | | | Searchterm 'Chemical Shift' was also found in the following services: | | | | |
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| | | | | • Share the entry 'Chemical Shift': | | | | | | | | Further Reading: | Basics:
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(CSI) Chemical shift imaging is an extension of MR spectroscopy, allowing metabolite information to be measured in an extended region and to add the chemical analysis of body tissues to the potential clinical utility of Magnetic Resonance. The spatial location is phase encoded and a spectrum is recorded at each phase encoding step to allow the spectra acquisition in a number of volumes covering the whole sample. CSI provides mapping of chemical shifts, analog to individual spectral lines or groups of lines.
Spatial resolution can be in one, two or three dimensions, but with long acquisition times od full 3D CSI. Commonly a slice-selected 2D acquisition is used. The chemical composition of each voxel is represented by spectra, or as an image in which the signal intensity depends on the concentration of an individual metabolite. Alternatively frequency-selective pulses excite only a single spectral component.
There are several methods of performing chemical shift imaging, e.g. the inversion recovery method, chemical shift selective imaging sequence, chemical shift insensitive slice selective RF pulse, the saturation method, spatial and chemical shift encoded excitation and quantitative chemical shift imaging.
See also Magnetic Resonance Spectroscopy. | | | | • View the DATABASE results for 'Chemical Shift Imaging' (6).
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Quick Overview Please note that there are different common names for this artifact.
DESCRIPTION
Black or bright band
During frequency encoding, fat protons precess slower than water protons in the same slice because of their magnetic shielding. Through the difference in resonance frequency between water and fat, protons at the same location are misregistrated (dislocated) by the Fourier transformation, when converting MRI signals from frequency to spatial domain. This chemical shift misregistration cause accentuation of any fat-water interfaces along the frequency axis and may be mistaken for pathology. Where fat and water are in the same location, this artifact can be seen as a bright or dark band at the edge of the anatomy.
Protons in fat and water molecules are separated by a chemical shift of about 3.5 ppm. The actual shift in Hertz (Hz) depends on the magnetic field strength of the magnet being used. Higher field strength increases the misregistration, while in contrast a higher gradient strength has a positive effect. For a 0.3 T system operating at 12.8 MHz the shift will be 44.8 Hz compared with a 223.6 Hz shift for a 1.5 T system operating at 63.9 MHz.
Image Guidance
| | | | • View the DATABASE results for 'Chemical Shift Artifact' (7).
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A compound with respect to whose frequency the chemical shifts of other compounds can be compared. The standard can be either internal or external to the sample. Because of the need for possible corrections due to differential magnetic susceptibility between an external standard and the sample being measured, the use of an internal standard is generally preferred. | | | | | |
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