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 'Frequency Encoding Gradient' 
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Result : Searchterm 'Frequency Encoding Gradient' found in 1 term [] and 11 definitions [], (+ 11 Boolean[] results
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Frequency Encoding Gradient
 
(Gf) A frequency encoding gradient produces a magnetic gradient field present during MR signal acquisition to encode signals into different frequencies, depending on their position toward the gradient.
Also called readout gradient.
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Magnetic resonance imaging
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BIOPAC Systems, Inc. Announces MRI Gradient Artifact Removal Tools for ECG and EMG Data
Tuesday, 10 February 2009   by www.biospace.com    
Improved shim method based on the minimization of the maximum off-resonance frequency for balanced SSFP
Monday, 1 June 2009   by www.ncbi.nlm.nih.gov    
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Gradient Recalled Echo SequenceInfoSheet: - Sequences - 
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The gradient recalled echo MRI sequence generates gradient echoes as a consequence of echo refocusing. The initial slice selective RF pulse applied to the tissue is less than 90° (typically rotation angles are between 10° and 90°). Immediately after this RF pulse, the spins begin to dephase.
Instead of a refocusing 180° RF pulse, reversing the gradient polarity produces a gradient echo. A negative phase encoding gradient and a dephasing frequency encoding gradient are used simultaneous. The switch on of the frequency encoding gradient produces an echo caused by refocusing of the dephasing, which is caused by the dephasing gradient.
TR and flip angle together control the T1, and TE control T2* weighting.
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Chemical Shift Spatial OffsetInfoSheet: - Artifacts - 
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Image artifact of apparent spatial offset of regions with different chemical shifts along the direction of the frequency encoding gradient;; a similar effect may be found in the slice selection direction.
See Chemical Shift Artifact.
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1H MR Spectroscopy and Chemical Shift Imaging of the In Vivo Brain at 7 Tesla
Sunday, 26 November 2006   by tobias-lib.uni-tuebingen.de    
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Dual Echo Steady StateInfoSheet: - Sequences - 
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(DESS) This sequence was originally known as FADE. It combines both the gradient echoes acquired in FISP and PSIF sequences in separate acquisition periods during a single interpulse interval. Phase encoding gradients are balanced to maintain the transverse steady state signals. The frequency encoding gradient is left on for the period of both the echoes, and is incompletely balanced to avoid dark banding artifacts otherwise associated with long TR fully balanced steady state sequences. The contrast of DESS is quite unique, true T2 or T1 contrast weighting is not possible. There is a strong fluid signal but fat is bright and other soft tissues appear similar to the short TR FISP image.
Used for, e.g. the joints, cartilage and the prostate. See Steady State Free Precession and Dual Echo Sequence.
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Echo Planar ImagingInfoSheet: - Sequences - 
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Echo Planar Imaging Timing Diagram

(EPI) Echo planar imaging is one of the early magnetic resonance imaging sequences (also known as Intascan), used in applications like diffusion, perfusion, and functional magnetic resonance imaging. Other sequences acquire one k-space line at each phase encoding step. When the echo planar imaging acquisition strategy is used, the complete image is formed from a single data sample (all k-space lines are measured in one repetition time) of a gradient echo or spin echo sequence (see single shot technique) with an acquisition time of about 20 to 100 ms. The pulse sequence timing diagram illustrates an echo planar imaging sequence from spin echo type with eight echo train pulses. (See also Pulse Sequence Timing Diagram, for a description of the components.)
In case of a gradient echo based EPI sequence the initial part is very similar to a standard gradient echo sequence. By periodically fast reversing the readout or frequency encoding gradient, a train of echoes is generated.
EPI requires higher performance from the MRI scanner like much larger gradient amplitudes. The scan time is dependent on the spatial resolution required, the strength of the applied gradient fields and the time the machine needs to ramp the gradients.
In EPI, there is water fat shift in the phase encoding direction due to phase accumulations. To minimize water fat shift (WFS) in the phase direction fat suppression and a wide bandwidth (BW) are selected. On a typical EPI sequence, there is virtually no time at all for the flat top of the gradient waveform. The problem is solved by "ramp sampling" through most of the rise and fall time to improve image resolution.
The benefits of the fast imaging time are not without cost. EPI is relatively demanding on the scanner hardware, in particular on gradient strengths, gradient switching times, and receiver bandwidth. In addition, EPI is extremely sensitive to image artifacts and distortions.

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Further Reading:
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New Imaging Method Makes Brain Scans 7 Times Faster
Sunday, 9 January 2011   by www.dailytech.com    
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