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MRI is trending to low field magnets :
reduced costs will lead to this change 
AI will close the gap to high field 
only in remote areas 
is only temporary 
never 




 
MRI Artifacts
  
Ultrasound Imaging Artifacts Open this link in a new window
Artifact Reduction
- Disturbing Signal
Fat Saturation 
(FAT SAT) A specialized technique that selectively saturates fat protons prior to acquiring data as in standard sequences, so that they produce a negligible signal. The presaturation pulse is applied prior to each slice selection. This technique requires a very homogeneous magnetic field and very precise frequency calibration.
Fat saturation does not work well on inhomogeneous volumes of tissue due to a change in the precessional frequencies as the difference in volume affects the magnetic field homogeneity. The addition of a water bag simulates a more homogeneous volume of tissue, thus improving the fat saturation. Since the protons in the water bag are in motion due to recent motion of the bag, phase ghosts can be visualized.
Fat saturation can also be difficult in a region of metallic prosthesis. This is caused by an alteration in the local magnetic field resulting in a change to the precessional frequencies, rendering the chemical saturation pulses ineffective.

See also Fat Suppression, and Dixon.

• View the DATABASE results for 'Fat Saturation' (9).Open this link in a new window

 
Further Reading:
  Basics:
Techniques of Fat Suppression(.pdf)
   by cds.ismrm.org    
  News & More:
New Imaging Technique Reveals Fatty Hearts In Pre-diabetics
Wednesday, 5 September 2007   by www.sciencedaily.com:80    
Fat Suppression 
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.
mri safety guidance
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.
Sequences based on Dixon turbo spin echo (fast spin echo) can deliver a significant better fat suppression than conventional TSE/FSE imaging.

• View the DATABASE results for 'Fat Suppression' (28).Open this link in a new window

 
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    
Presaturation 
(REST - regional saturation technique / SAT - saturation/ Pre-Sat / spatial Pre-Sat) A specialized technique employing repeated RF excitation of structures adjacent to the ROI for the purpose of reducing or eliminating their phase effect artifacts. This presaturation can be performed on both sides parallel or perpendicular to the slice. Vascular ghosting is eliminated by saturation areas parallel (outside) to the slice plane, because flowing blood produces almost no signal. The possibility of moving presaturation (moving REST / traveling SAT) makes sequence planning and scanning comfortable.

• View the DATABASE results for 'Presaturation' (17).Open this link in a new window

 
Further Reading:
  Basics:
Techniques of Fat Suppression(.pdf)
   by cds.ismrm.org    
Signal Suppression 
The elimination or reduction of a particular signal by, for example, the application of a narrow band frequency-selective preparation pulse centered at the resonant frequency of the signal. This can also be accomplished using an inversion recovery technique to null the signal as it recovers its longitudinal magnetization.

• View the DATABASE results for 'Signal Suppression' (2).Open this link in a new window

Water Suppression 
The elimination or reduction of water signal from the image by application of a narrow-band frequency-selective pulse centered around the resonant frequency of the tissue. Also called water saturation.

• View the DATABASE results for 'Water Suppression' (4).Open this link in a new window

 
Further Reading:
  News & More:
Proton MR Spectroscopic Imaging without Water Suppression1
2000   by radiology.rsnajnls.org    
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