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 'Opposed Phase Image' 
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Result : Searchterm 'Opposed Phase Image' found in 1 term [] and 4 definitions [], (+ 1 Boolean[] results
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Opposed Phase ImageInfoSheet: - Sequences - 
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etc.
 
An image in which the signal from two spectral components (such as fat and water) is 180° out of phase and leads to destructive interference in a voxel.
Since fat precesses slower than water, based on their chemical shift, their signals will decay and precess in the transverse plane at different frequencies. When the phase of the TE becomes opposed (180°), their combined signal intensities subtract with each other in the same voxel, producing a signal void or dark band at the fat/water interface of the tissues being examined.
Opposed phase gradient echo imaging for the abdomen is a lipid-type tissue sensitive sequence particularly for the liver and adrenal glands, which puts a signal intensity around abnormal water-based tissues or lesions that are fatty. Due to the increased sensitivity of opposed phase, the tissue visualization increases the lesion-to-liver contrast and exhibits more signal intensity loss in tissues containing small amounts of lipids compared to a spin echo T1 with fat suppression. Using an opposed phase gradient echo also provides the ability to differentiate various pathologies in the brain, including lipids, methaemoglobin, protein, calcifications and melanin.
See also Out of Phase, and Dixon.
 
Images, Movies, Sliders:
 MRI Liver Out Of Phase  Open this link in a new window
    
 
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• Related Searches:
    • Field Echo with Echo Time set for Water and Fat Signals in Opposition
    • Chemical Shift
    • In Phase
    • Chemical Shift Artifact
    • Out of Phase
 
Further Reading:
  Basics:
Scanning the Abdomen
   by www.mrprotocols.com    
  News & More:
Adrenal Myelolipoma
Tuesday, 19 June 2001   by www.emedicine.com    
Iron overload: accuracy of in-phase and out-of-phase MRI as a quick method to evaluate liver iron load in haematological malignancies and chronic liver disease
Friday, 1 June 2012   by www.ncbi.nlm.nih.gov    
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Black Boundary ArtifactInfoSheet: - Artifacts - 
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 - Artifacts -
 
Quick Overview
Please note that there are different common names for this artifact.

Artifact Information
NAME Black boundary, dark boundary, contour, chemical shift, relief
DESCRIPTION Black contours at boundaries
REASON Chemical shift, opposed phase image, motion shear (flow effects), inversion recovery null point
HELP Smaller water fat shift (high bandwidth), in phase image, SE sequences

Black boundary artifacts are black lines following voxels where both water and fat protons are present in the same voxel. This artifact arise along the boundary of organs or tissues perpendicular to the frequency encoding direction, and occurs preferentially in gradient echo sequences with out of phase echo times.


Image Guidance
Fat suppression techniques eliminate this artifact. For artifact reducing helps a smaller water fat shift (high bandwidth), a higher matrix or/and an in phase TE.
See also Chemical Shift Artifact.

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• View the DATABASE results for 'Black Boundary Artifact' (4).Open this link in a new window

 
Further Reading:
  Basics:
Artifacts in MRI
Saturday, 1 October 2011   by www.huc.min-saude.pt    
What is chemical shift artefact? Why does it occur? How many Hz at 1.5 T?
   by www.revisemri.com    
MRI Resources 
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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
REASON Chemical shift, opposed phase image
HELP Fat suppression, smaller water fat shift (high bandwidth), in phase image, SE sequences

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
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 
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Field Echo with Echo Time set for Water and Fat Signals in OppositionInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
(FEDIF) See Out of Phase and Opposed Phase Image.
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Out of Phase
 
Water and fat signals being in or out of phase result from the FFE method and the slight difference in resonance frequencies of the protons. It can cause black "outlining" of tissues and decrease in signal from voxel containing both water and fat. At 1.5 T, the water and fat signal are in phase when TE is an even multiple, and out of phase when TE is an odd multiple of 2.3 ms.
1.5T: OUT of PHASE = 2.3, 6.9, 11.5, 16.1, 20.7 ms
1.0T: OUT of PHASE = 3.5, 10.4, 17.3, 24.2 ms
0.5T: OUT of PHASE = 6.9, 20.7 ms
See also Opposed Phase Image, and Dixon.
 
Images, Movies, Sliders:
 MRI Liver Out Of Phase  Open this link in a new window
    
 
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• View the DATABASE results for 'Out of Phase' (17).Open this link in a new window

 
Further Reading:
  Basics:
Artifacts in MRI
Saturday, 1 October 2011   by www.huc.min-saude.pt    
  News & More:
Adrenal Myelolipoma
Tuesday, 19 June 2001   by www.emedicine.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    
MRI Resources 
Musculoskeletal and Joint MRI - Non-English - Pathology - MRI Technician and Technologist Schools - Breast Implant - Pediatric and Fetal MRI
 
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