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Result : Searchterm 'Frequency Encoding Gradient' found in 1 term [] and 11 definitions [], (+ 10 Boolean[] results
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Quadrature Detector
 
The quadrature detector is a part of the receiver that converts the high-frequency MRI signal to a lower frequency. This phase sensitive detector or demodulator detects the components of the signal in phase with a reference signal and 90° out of phase with the reference signal. The modulated signal contains i.e. the frequency range across the field of view encoded by the frequency encoding gradient. This may be performed by either analog or digital means.
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Readout Gradient
 
Magnetic field gradient applied during the period when the receiver components are on. The application of this gradient, which is active during the period when the echo is being formed, results in the frequency encoding of the object being imaged.
Also called frequency encoding gradient.
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• View the DATABASE results for 'Readout Gradient' (9).Open this link in a new window

 
Further Reading:
  News & More:
Evaluation of Absorbed Dose by MRI Read-Out
Saturday, 18 November 2017   by www.jstage.jst.go.jp    
MRI Resources 
Breast Implant - Abdominal Imaging - Manufacturers - MR Guided Interventions - Spectroscopy - Pacemaker
 
MRI History
 
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Sir Joseph Larmor (1857-1942) developed the equation that the angular frequency of precession of the nuclear spins being proportional to the strength of the magnetic field. [Larmor relationship]
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In the 1930's, Isidor Isaac Rabi (Columbia University) succeeded in detecting and measuring single states of rotation of atoms and molecules, and in determining the mechanical and magnetic moments of the nuclei.
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Felix Bloch (Stanford University) and Edward Purcell (Harvard University) developed instruments, which could measure the magnetic resonance in bulk material such as liquids and solids. (Both honored with the Nobel Prize for Physics in 1952.) [The birth of the NMR spectroscopy]
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In the early 70's, Raymond Damadian (State University of New York) demonstrated with his NMR device, that there are different T1 relaxation times between normal and abnormal tissues of the same type, as well as between different types of normal tissues.
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In 1973, Paul Lauterbur (State University of New York) described a new imaging technique that he termed Zeugmatography. By utilizing gradients in the magnetic field, this technique was able to produce a two-dimensional image (back-projection). (Through analysis of the characteristics of the emitted radio waves, their origin could be determined.) Peter Mansfield further developed the utilization of gradients in the magnetic field and the mathematically analysis of these signals for a more useful imaging technique. (Paul C Lauterbur and Peter Mansfield were awarded with the 2003 Nobel Prize in Medicine.)
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In 1975, Richard Ernst introduced 2D NMR using phase and frequency encoding, and the Fourier Transform. Instead of Paul Lauterbur's back-projection, he timely switched magnetic field gradients ('NMR Fourier Zeugmatography'). [This basic reconstruction method is the basis of current MRI techniques.]
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1977/78: First images could be presented. A cross section through a finger by Peter Mansfield and Andrew A. Maudsley. Peter Mansfield also could present the first image through the abdomen.
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In 1977, Raymond Damadian completed (after 7 years) the first MR scanner (Indomitable). In 1978, he founded the FONAR Corporation, which manufactured the first commercial MRI scanner in 1980. Fonar went public in 1981.
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1981: Schering submitted a patent application for Gd-DTPA dimeglumine.
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1982: The first 'magnetization-transfer' imaging by Robert N. Muller.
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In 1983, Toshiba obtained approval from the Ministry of Health and Welfare in Japan for the first commercial MRI system.
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In 1984, FONAR Corporation receives FDA approval for its first MRI scanner.
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1986: Jürgen Hennig, A. Nauerth, and Hartmut Friedburg (University of Freiburg) introduced RARE (rapid acquisition with relaxation enhancement) imaging. Axel Haase, Jens Frahm, Dieter Matthaei, Wolfgang Haenicke, and Dietmar K. Merboldt (Max-Planck-Institute, Göttingen) developed the FLASH (fast low angle shot) sequence.
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1988: Schering's MAGNEVIST gets its first approval by the FDA.
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In 1991, fMRI was developed independently by the University of Minnesota's Center for Magnetic Resonance Research (CMRR) and Massachusetts General Hospital's (MGH) MR Center.
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From 1992 to 1997 Fonar was paid for the infringement of it's patents from 'nearly every one of its competitors in the MRI industry including giant multi-nationals as Toshiba, Siemens, Shimadzu, Philips and GE'.
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Images, Movies, Sliders:
 Cardiac Infarct Short Axis Cine Overview  Open this link in a new window
    

Courtesy of  Robert R. Edelman
 
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• View the DATABASE results for 'MRI History' (6).Open this link in a new window


• View the NEWS results for 'MRI History' (1).Open this link in a new window.
 
Further Reading:
  Basics:
Magnetic Resonance Imaging, History & Introduction
2000   by www.cis.rit.edu    
A Short History of the Magnetic Resonance Imaging (MRI)
   by www.teslasociety.com    
Fonar Our History
   by www.fonar.com    
  News & More:
Scientists win Nobels for work on MRI
Tuesday, 10 June 2003   by usatoday30.usatoday.com    
2001 Lemelson-MIT Lifetime Achievement Award Winner
   by web.mit.edu    
MRI's inside story
Thursday, 4 December 2003   by www.economist.com    
MRI Resources 
PACS - Crystallography - MRI Training Courses - Cochlear Implant - Jobs - Sequences
 
Chemical Shift ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Please note that there are different common names for this artifact.
Artifact Information
NAME
Chemical shift, black boundary, spatial misregistration, relief
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.
mri safety guidance
Image Guidance
For artifact reduction helps a smaller water fat shift (higher bandwidth), a higher matrix, an in phase TE or a spin echo technique. Since the misregistration offset is present in the read out axis the patient may be rescanned with this axis parallel to the fat-water interface. Steeper gradient may be employed to reduce the chemical shift offset in mm. Another strategy is to employ specialized pulse sequences such as fat saturation or inversion recovery imaging. Fat suppression techniques eliminate chemical shift artifacts caused by the lack of fat signal.

See also Black Boundary Artifact and Magnetic Resonance Spectroscopy.
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• View the DATABASE results for 'Chemical Shift Artifact' (7).Open this link in a new window

 
Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
  News & More:
What is chemical shift artefact? Why does it occur? How many Hz at 1.5 T?
   by www.revisemri.com    
Abdominal MRI at 3.0 T: The Basics Revisited
Wednesday, 20 July 2005   by www.ajronline.org    
MRI Resources 
Universities - Spectroscopy - Movies - Breast MRI - Blood Flow Imaging - Education
 
Balanced Fast Field EchoInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.MRI Resource Directory:
 - Sequences -
 
(bFFE) A FFE sequence using a balanced gradient waveform. A balanced sequence starts out with a RF pulse of 90° or less and the spins in the steady state. Before the next TR in the slice phase and frequency encoding, gradients are balanced so their net value is zero. Now the spins are prepared to accept the next RF pulse, and their corresponding signal can become part of the new transverse magnetization. Since the balanced gradients maintain the transverse and longitudinal magnetization, the result is, that both T1 and T2 contrast are represented in the image. This pulse sequence produces images with increased signal from fluid, along with retaining T1 weighted tissue contrast. Because this form of sequence is extremely dependent on field homogeneity, it is essential to run a shimming prior the acquisition. A fully balanced (refocused) sequence would yield higher signal, especially for tissues with long T2 relaxation times.

See Steady State Free Precession and Gradient Echo Sequence.
 
Images, Movies, Sliders:
 Cardiac Infarct Short Axis Cine bFFE 1  Open this link in a new window
    
 
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• View the DATABASE results for 'Balanced Fast Field Echo' (3).Open this link in a new window

 
Further Reading:
  News & More:
T1rho-prepared balanced gradient echo for rapid 3D T1rho MRI
Monday, 1 September 2008   by www.ncbi.nlm.nih.gov    
Utility of the FIESTA Pulse Sequence in Body Oncologic Imaging: Review
June 2009   by www.ajronline.org    
MRI Resources 
Pregnancy - Used and Refurbished MRI Equipment - Artifacts - MRI Centers - MRI Accidents - Abdominal Imaging
 
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