Magnetic Resonance - Technology Information Portal Welcome to MRI Technology••
Info
  Sheets


Out-
      side
 



 
 'Presaturation' 
SEARCH FOR    
 
  2 3 5 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Result : Searchterm 'Presaturation' found in 2 terms [] and 14 definitions []
1 - 5 (of 16)     next
Result Pages : [1]  [2 3 4]
Searchterm 'Presaturation' was also found in the following service: 
spacer
Forum  (1)  
 
PresaturationInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
(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.
spacer
 
• Share the entry 'Presaturation':  Facebook  Twitter  LinkedIn  
 
• Related Searches:
    • Fat Suppression
    • Quadrupole Artifact
    • Ghosting Artifact
    • Black Blood MRA
    • Saturation
 
Further Reading:
  Basics:
Techniques of Fat Suppression(.pdf)
   by cds.ismrm.org    
MRI Resources 
Implant and Prosthesis pool - Homepages - Most Wanted - Jobs - Anatomy - Quality Advice
 
Spectral Presaturation Inversion Recovery
 
(SPIR) 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.
 
Images, Movies, Sliders:
 MRI Orbita T2 FatSat  Open this link in a new window
    
 
spacer

• View the DATABASE results for 'Spectral Presaturation Inversion Recovery' (2).Open this link in a new window

 
Further Reading:
  Basics:
Sequence for Philips(.pdf)
   by www.droid.cuhk.edu.hk    
Optimizing SPIR and SPAIR fat suppression
Tuesday, 30 November 2004   by clinical.netforum.healthcare.philips.com    
Techniques of Fat Suppression(.pdf)
   by cds.ismrm.org    
MRI Resources 
Absorption and Emission - Patient Information - Crystallography - Mobile MRI - Liver Imaging - MRI Reimbursement
 
Black Blood MRAForum -
related threadsInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.MRI Resource Directory:
 - Cardiovascular Imaging -
 
With this magnetic resonance angiography technique flowing blood appears dark.
MR black blood techniques have been developed for cardiovascular imaging to improve segmentation of myocardium from the blood pool. Black blood MRA techniques decrease the signal from blood with reference to the myocardium and make it easier to perform cardiac chamber segmentation.
ECG gated spin echo sequences with presaturation pulses for magnetization preparation will show strong intravascular signal loss due to flow effects when appropriate imaging conditions including spatial presaturation are used. The sequence use the flow void effect as blood passes rapidly through the selected slice.
For dark blood preparation, a pair of nonselective and selective 180° inversion pulses are used, followed by a long inversion time to null signal from inflowing blood. A second selective inversion pulse can also be applied with short inversion time to null the fat signal. These in cardiac imaging used black blood techniques are referred to as double inversion recovery T1 measurement turbo spin echo or fast spin echo, and double-inversion recovery STIR.
 
Images, Movies, Sliders:
 Normal Dual Inversion Fast Spin-echo  Open this link in a new window
      

Courtesy of  Robert R. Edelman

 
spacer

• View the DATABASE results for 'Black Blood MRA' (6).Open this link in a new window

Searchterm 'Presaturation' was also found in the following service: 
spacer
Forum  (1)  
 
Phase Encoded Motion 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 Phase encoded motion, motion, phase effect
DESCRIPTION Blurring and ghosting
REASON Movement of the imaged object
HELP Compensation techniques, more averages, anti spasmodic, presaturation

This artifact is caused by movements of the patient or organic processes taking place in the body of the patient. The artifact appears as bright noise, repeating densities or ghosting in the phase encoding direction.


Image Guidance
There are different solutions for reduction of phase encoded motion artifacts.
Cardiac and respiratory gating, breath holding, sedation of the patient, presaturation pulses for flow artifacts (e.g. arterial pulsation, breathing), fast imaging sequences, etc.
See also Motion Artifact, Ghosting Artifact, Motion Compensation Pulse Sequences and Artifact Reduction - Motion.
spacer

• View the DATABASE results for 'Phase Encoded Motion Artifact' (5).Open this link in a new window

 
Further Reading:
  Basics:
Artifacts in MRI
Saturday, 1 October 2011   by www.huc.min-saude.pt    
MRI Resources 
Bioinformatics - MRCP - Process Analysis - MR Myelography - Spine MRI - MRI Accidents
 
Aliasing ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Please note that there are different common names for this MRI artifact.

Artifact Information
NAME Aliasing, backfolding, foldover, phase wrapping, wrap around
DESCRIPTION Image wrap around
REASON Undersampling in k-space
HELP Larger FOV, oversampling, foldover suppression

Aliasing is an artifact that occurs in MR images when the scanned body part is larger than field of view (FOV). As a consequence of the acquired k-space frequencies not being sampled densely enough, whereby portions of the object outside of the desired FOV get mapped to an incorrect location inside the FOV. The cyclical property of the Fourier transform fills the missing data of the right side with data from behind the FOV of the left side and vice versa. This is caused by a too small number of samples acquired in, e.g. the frequency encoding direction, therefore the spectrums will overlap, resulting in a replication of the object in the x direction.
Aliasing in the frequency direction can be eliminated by twice as fast sampling of the signal or by applying frequency specific filters to the received signal.
A similar problem occurs in the phase encoding direction, where the phases of signal-bearing tissues outside of the FOV in the y-direction are a replication of the phases that are encoded within the FOV. Phase encoding gradients are scaled for the field of view only, therefore tissues outside the FOV do not get properly phase encoded relative to their actual position and 'wraps' into the opposite side of the image.


Image Guidance
Use a larger FOV, RFOV or 3D Volume, apply presaturation pulses to the undesired tissue, adjust the position of the FOV, or select a small coil which will only receive signal from objects inside or near the coil. The number of phase encoding steps must be increased in phase direction, unfortunately resulting in longer scan times.
When this is not possible it can be corrected by oversampling the data. Aliasing is eliminated by Oversampling in frequency direction. No Phase Wrap (Foldover Suppression) options typically correct the phase encoding by doubling the field of view, doubling the number of phase encodes (to keep resolution constant) and halving the number of averages (to keep scan time constant) then discarding the additional data and processing the image within the desired field of view (but this is more time consuming).
Tissue outside this doubled area can be folded nevertheless into the image as phase wrap. In this case combine more than 2 number of excitations / number of signal averages with foldover suppression.
See also Aliasing, Foldover Suppression, Oversampling, and Artifact Reduction - Aliasing.

spacer

• View the DATABASE results for 'Aliasing Artifact' (11).Open this link in a new window

MRI Resources 
Chemistry - Sequences - Spectroscopy pool - Services and Supplies - MRA - MRCP
 
     1 - 5 (of 16)     next
Result Pages : [1]  [2 3 4]
 Random Page
 
Share This Page
FacebookTwitterLinkedIn

MR-TIP    
Community   
User
Pass
Forgot your UserID/Password ?  



In 2020 your scanner will probably work with a field strength of :
lower 
1T 
1.5T 
2T 
3T 
7T 
higher 

Look
      Ups





MR-TIP.com uses cookies! By browsing MR-TIP.com, you agree to our use of cookies.

Magnetic Resonance - Technology Information Portal
Member of SoftWays' Medical Imaging Group - MR-TIP • Radiology-TIP • US-TIP • The-Medical-Market
Copyright © 2003 - 2016 SoftWays. All rights reserved. [ 28 April 2017]
Terms of Use | Privacy Policy | Advertising
 [last update: 2017-04-24 06:47:00]