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Array Spatial Sensitivity Encoding TechniqueInfoSheet: - Sequences -
Intro, Overview, 
Types of, 
etc.
 
(ASSET) ASSET is a parallel imaging technique of the SENSE type (image domain reconstruction).
Each coil element is sensitivity encoded and the covered spatial zone is mapped. By reducing the field of view in the phase encoding gradient direction the scan time decreases, but this images of each coil element contain foldover artifacts. The sensitivity profiles of the elements are used to calculate unfolded images.

See also Sensitivity Encoding, Generalized Autocalibrating Partially Parallel Acquisition.
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• View the DATABASE results for 'Array Spatial Sensitivity Encoding Technique' (4).Open this link in a new window

Arrhythmia Rejection
 
With this method irregular RR intervals in cardiac gating during cardiovascular imaging are rejected and then repeated to improve the image quality, whereby the cardiac frequency is used as a basis of the normal heart rate.
The RR interval window determines the percentage variation of the heart rate. Variations of the acquired data outside the window are rejected and not used in the image reconstruction. Also one interval after the arrhytmic beat will be rejected.
Arrhythmia rejection may be inappropriate for patients with certain pathologies, because if the RR interval is constant long, short, long, - all intervals would be rejected. Also a disadvantage is the time consume, but in some cases this function is mandatory, e.g. for diverse retrospective triggered sequences.
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Further Reading:
  Basics:
A Guide To Cardiac Imaging
   by www.simplyphysics.com    
  News & More:
Irregular heartbeat may lead to silent strokes
Wednesday, 5 November 2014   by www.techtimes.com    
MRI Resources 
Contrast Agents - Stent - Implant and Prosthesis pool - Quality Advice - MR Guided Interventions - Pacemaker
 
Artefact
 
See Artifact
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• View the DATABASE results for 'Artefact' (2).Open this link in a new window

 
Further Reading:
  Basics:
ARTEFACT VERSUS ARTIFACT
Saturday, 26 January 2002   by www.worldwidewords.org    
Arterial Spin LabelingInfoSheet: - Sequences -
Intro, Overview, 
Types of, 
etc.MRI Resource Directory:
 - Sequences -
 
(ASL) A MR image can be sensitized to the effect of inflowing blood spins if those spins are in a different magnetic state to that of the static tissue. Techniques known as ASL techniques uses this idea by magnetically labeling blood flowing into the slices of interest. Contrast agents are not required for these techniques. This perfusion measurement is completely noninvasive.
Blood flowing into the imaging slice exchanges with tissue water, altering the tissue magnetization. A perfusion-weighted image can be generated by the subtraction of an image in which inflowing spins have been labeled from an image in which spin labeling has not been performed. Quantitative perfusion maps can be calculated if other parameters (such as tissue T1 and the efficiency of spin labeling) also are measured.
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• View the NEWS results for 'Arterial Spin Labeling' (3).Open this link in a new window.

• View the DATABASE results for 'Arterial Spin Labeling' (5).Open this link in a new window

 
Further Reading:
  News & More:
FDG-PET displays its prowess in dementia detection
Monday, 2 March 2020   by physicsworld.com    
Ischemic Stroke: Collateral Blood Vessels Detected by Arterial Spin Labeling MRI Correlates With Good Neurological Outcome
Thursday, 30 March 2017   by medicalresearch.com    
Turbo-FLASH Based Arterial Spin Labeled Perfusion MRI at 7 T
Thursday, 20 June 2013   by www.plosone.org    
Non-invasive MRI technique distinguishes between Alzheimer's and frontotemporal dementia
Saturday, 18 June 2005   by www.eurekalert.org    
ArtifactForum -
there are related threadsInfoSheet: - Artifacts -
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
An image artifact is a structure not normally present but visible as a result of a limitation or malfunction in the hardware or software of the MRI device, or in other cases a consequence of environmental influences as heat or humidity or it can be caused by the human body (blood flow, implants etc.). The knowledge of MRI artifacts (brit. artefacts) and noise producing factors is important for continuing maintenance of high image quality. Artifacts may be very noticeable or just a few pixels out of balance but can give confusing artifactual appearances with pathology that may be misdiagnosed.
Changes in patient position, different pulse sequences, metallic artifacts, or other imaging variables can cause image distortions, which can be reduced by the operator; artifacts due to the MR system may require a service engineer.
Many types of artifacts may occur in magnetic resonance imaging. Artifacts in magnetic resonance imaging are typically classified as to their basic principles, e.g.:
Physiologic (motion, flow)
Hardware (electromagnetic spikes, ringing)
Inherent physics (chemical shift, susceptibility, metal)

Several techniques are developed to reduce these artifacts (e.g. respiratory compensation, cardiac gating, eddy current compensation) but sometimes these effects can also be exploited, e.g. for flow measurements.

See also the related poll result: 'Most outages of your scanning system are caused by failure of'
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• View the DATABASE results for 'Artifact' (166).Open this link in a new window

 
Further Reading:
  Basics:
ARTEFACT VERSUS ARTIFACT
Saturday, 26 January 2002   by www.worldwidewords.org    
  News & More:
MRI results affected by movement? MIT researchers have an AI-powered solution
Friday, 25 August 2023   by healthimaging.com    
Magnetic eyelashes: A new source of MRI artifacts
Wednesday, 24 July 2019   by medicalxpress.com    
On the Horizon - Next Generation MRI
Wednesday, 23 October 2013   by thefutureofthings.com    
MRI Resources 
Cochlear Implant - Stimulator pool - Absorption and Emission - Mass Spectrometry - MRI Reimbursement - IR
 
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