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 'Fat Suppression' 
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Result : Searchterm 'Fat Suppression' found in 2 terms [] and 27 definitions []
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Fat SuppressionForum -
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Fat suppression is the process of utilizing specific MRI parameters to remove the deleterious effects of fat from the resulting images, e.g. with STIR, FAT SAT sequences, water selective (PROSET WATS - water only selection, also FATS - fat only selection possible) excitation techniques, or pulse sequences based on the Dixon method.
Spin magnetization can be modulated by using special RF pulses. CHESS or its variations like SPIR, SPAIR (Spectral Selection Attenuated Inversion Recovery) and FAT SAT use frequency selective excitation pulses, which produce fat saturation.
Fat suppression techniques are nearly used in all body parts and belong to every standard MRI protocol of joints like knee, shoulder, hips, etc.


Image Guidance
Imaging of, e.g. the foot can induce bad fat suppression with SPIR/FAT SAT due to the asymmetric volume of this body part. The volume of the foot alters the magnetic field to a different degree than the smaller volume of the lower leg affecting the protons there. There is only a small band of tissue where the fat protons are precessing at the frequency expected, resulting in frequency selective fat saturation working only in that area. This can be corrected by volume shimming or creating a more symmetrical volume being imaged with water bags.
Even with their longer scan time and motion sensitivity, STIR (short T1//tau inversion recovery) sequences are often the better choice to suppress fat. STIR images are also preferred because of the decreased sensitivity to field inhomogeneities, permitting larger fields of views when compared to fat suppressed images and the ability to image away from the isocenter.
See also Knee MRI.
Recently introduced Dixon turbo spin echo (fast spin echo) sequences can deliver a significant better fat suppression than conventional TSE//FSE imaging.

 
Images, Movies, Sliders:
 Shoulder Axial T2 FatSat FRFSE  Open this link in a new window
    

Courtesy of  Robert R. Edelman
 MRI Orbita T2 FatSat  Open this link in a new window
    
 Knee MRI Sagittal STIR 001  Open this link in a new window
 MRI - Anatomic Imaging of the Ankle 3  Open this link in a new window
    
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• Related Searches:
    • Water Fat Shift
    • Spectral Selection Attenuated Inversion Recovery
    • Image Contrast Characteristics
    • Fat Saturation
    • Out of Phase
 
Further Reading:
  Basics:
Techniques of Fat Suppression(.pdf)
   by cds.ismrm.org    
  News & More:
Enhanced Fast GRadient Echo 3-Dimensional (efgre3D) or THRIVE
   by www.mri.tju.edu    
Ultrashort echo time (UTE) MRI of the spine in thalassaemia
February 2004   by bjr.birjournals.org    
MRI Resources 
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Multi Slice Off Resonance Fat SuppressionInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
(MSOFT) See Off Resonance and Fat Suppression.
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MRI Resources 
Safety Training - Breast MRI - Health - Musculoskeletal and Joint MRI - Online Books - Pacemaker
 
DixonInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
The Dixon technique is a MRI method used for fat suppression and/or fat quantification. The difference in magnetic resonance frequencies between fat and water-bound protons allows the separation of water and fat images based on the chemical shift effect.
This imaging technique is named after Dixon, who published in 1984 the basic idea to use phase differences to calculate water and fat components in postprocessing. Dixon’s method relies on acquiring an image when fat and water are 'in phase', and another in 'opposed phase' (out of phase). These images are then added together to get water-only images, and subtracted to get fat-only images. Therefore, this sequence type can deliver up to 4 contrasts in one measurement: in phase, opposed phase, water and fat images. An additional benefit of Dixon imaging is that source images and fat images are also available to the diagnosing physician.
The original two point Dixon sequence (number of points means the number of images acquired at different TE) had limited possibilities to optimize the echo time, spatial resolution, slice thickness, and scan time; but Dixon based fat suppression can be very effective in areas of high magnetic susceptibility, where other techniques fail. This insensitivity to magnetic field inhomogeneity and the possibility of direct image-based water and fat quantification have currently generated high research interests and improvements to the basic method (three point Dixon).
The combination of Dixon with gradient echo sequences allows for example liver imaging with 4 image types in one breath hold. With Dixon TSE/FSE an excellent fat suppression with high resolution can be achieved, particularly useful in imaging of the extremities.
For low bandwidth imaging, chemical shift correction of fat images can be made before recombination with water images to produce images free of chemical shift displacement artifacts. The need to acquire more echoes lengthens the minimum scan time, but the lack of fat saturation pulses extends the maximum slice coverage resulting in comparable scan time.
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• View the DATABASE results for 'Dixon' (8).Open this link in a new window

 
Further Reading:
  Basics:
Separation of fat and water signal in magnetic resonanace imaging
2011   by www.diva-portal.org    
Direct Water and Fat Determination in Two-Point Dixon Imaging
April 2013   by scholarship.rice.edu    
Measurement of Fat/Water Ratios in Rat Liver Using 3DThree-Point Dixon MRI
2004   by www.civm.duhs.duke.edu    
  News & More:
Liver Imaging Today
February 2013   by www.healthcare.siemens.it    
mDIXON being developed to simplify and accelerate liver MRI
September 2010   by incenter.medical.philips.com    
Searchterm 'Fat Suppression' was also found in the following services: 
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Quadrupole ArtifactInfoSheet: - Artifacts - 
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etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview

Artifact Information
NAME Quadrupole artifact
DESCRIPTION Signal loss, intensity variations
REASON B1 disturbance
HELP STIR

Fat suppression (SPIR or FatSat) is very critical to the magnetic field homogeneity. Eddy currents in the patient results in B1 disturbance from left to right and from anterior to posterior. The artifact is seen as signal intensity variations with SPIR, like a signal intensity loss diagonal in the image. The short T1 inversion recovery (STIR) sequence is due to another type of fat suppression insensitive to this artifact.


Image Guidance
Take short T1 inversion recovery (STIR) instead spectral presaturation inversion recovery (SPIR) for fat suppression.
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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 
Pacemaker - Examinations - Non-English - Colonography - Claustrophobia - Blood Flow Imaging
 
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