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Result : Searchterm 'Image Guidance' found in 0 term [] and 54 definitions []
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News  (2)  
 
Staircase ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
NAME
Staircase
DESCRIPTION
Staircase like nuance
REASON
Slices too thick, no overlapping
HELP
Overlapping slices
Staircase artifacts might be seen in projection of the slice thickness in case of MIP or MPR reconstructions.
mri safety guidance
Image Guidance
Use overlapping slices to reduce this artifact by changing the slice gap to a negative value. In most cases, a negative value of 20-30% is sufficient.
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MRI Resources 
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Stimulated Echo
 
A form of a spin echo produced by three pulse RF sequences, consisting of two RF pulses following an initial exciting RF pulse. The stimulated echo appears at a time delay after the third pulse equal to the interval between the first two pulses. Although classically produced with 90° pulses, any RF pulses other than an ideal 180° can produce a stimulated echo. The intensity of the echo depends in part on the T1 relaxation time because the excitation is 'stored' as longitudinal magnetization between the second and third RF pulses. For example, use of stimulated echoes with spatially selective excitation with orthogonal magnetic field gradients permits volume-selective excitation for spectroscopic localization.
mri safety guidance
Image Guidance
Artifacts may appear as a series of fine lines. A narrow bandwidth causes a wide read window, which allows the stimulated echo to be incorporated into the image data. This can be supported by increasing the received bandwidth, which would narrow the read window, thus not incorporating the extraneous echo. Another help would be to change the first echo time, which may change the spacing of the stimulated echoes to outside that of the read window for the second echo.
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• View the DATABASE results for 'Stimulated Echo' (8).Open this link in a new window

 
Further Reading:
  Basics:
Magnetic resonance imaging
   by www.scholarpedia.org    
Clinical evaluation of a speed optimized T2 weighted fast spin echo sequence at 3.0 T using variable flip angle refocusing, half-Fourier acquisition and parallel imaging
Wednesday, 25 October 2006
MRI Resources 
Research Labs - Service and Support - Libraries - Open Directory Project - Functional MRI - Stent
 
Stuck ADC Bit ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
NAME
Stuck ADC bit
DESCRIPTION
Ghosting
REASON
Hardware problem
HELP
Data correction
This artifact is uncommon with modern MRI equipment, but possible. It can occur if there are bad memory locations or bad connectors in the parallel data bus of the computer.
mri safety guidance
Image Guidance
This artifact is the result of a hardware failure and must be addressed by a service representative.
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Further Reading:
  News & More:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
Searchterm 'Image Guidance' was also found in the following service: 
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News  (2)  
 
Susceptibility ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
DESCRIPTION
Signal dropout, bright spots, spatial distortion
REASON
HELP
Remove the metal, do not take a gradient echo sequence, take a short echo time
Materials with magnetic susceptibility cause this artifact. There are in general three kinds of materials with magnetic susceptibility: ferromagnetic materials (iron, nickel etc.) with a strong influence and paramagnetic/diamagnetic (aluminium, platinum etc./gold, water, most organic compounds etc.) materials with a minimal/non influence on magnetic fields. In MRI, susceptibility artifacts are caused for example by medical devices in or near the magnetic field or by implants of the patient. These materials with magnetic susceptibility distort the linear magnetic field gradients, which results in bright areas (misregistered signals) and dark areas (no signal) nearby the magnetic material.
mri safety guidance
Image Guidance
Use a spin echo or a fast spin echo sequence, because gradient echo sequences are more sensitve to susceptibility artifacts. A high bandwidth (small water fat shift) and a short echo time help also to reduce this artifact.
In some cases it is even beneficial to use a gradient echo sequence, e.g. a cavernom contains some iron-rich haemosiderin, which also causes a signal void on gradient echo sequences and for this purpose increases the diagnostic image quality.
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• View the DATABASE results for 'Susceptibility Artifact' (8).Open this link in a new window

 
Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
Susceptibility Artifacts
   by www.mritutor.org    
  News & More:
Metal Artefact Reduction
Thursday, 9 June 2011   by www.revisemri.com    
Ultrashort echo time (UTE) MRI of the spine in thalassaemia
February 2004   by bjr.birjournals.org    
MRI Resources 
Case Studies - Process Analysis - Examinations - MRI Training Courses - Breast Implant - Movies
 
Truncation 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
DESCRIPTION
Edge ringing, syrinx-like stripe
REASON
Sharp changes in intensity (incomplete digitization of the echo)
HELP
Take more samples
A data truncation artifact may occur when the interface between high and low signal intensities is encountered in one imaging plane. The 2D-FT techniques transform the MR signal to spatial intensity image data with frequency and phase information encoding each axis in the plane of the scan. This artifact is found in both frequency and phase axes. Artifactual ripples adjacent to edges in an image or sharp features in a spectrum, caused by omission of higher frequency terms in Fourier transformation, particularly with the use of zero filling to replace unsampled higher frequencies.
Complex shapes are specified by series of sine and cosine waves of various frequencies, phase and amplitude. Some shapes are more difficult to encode than others. The most difficult shapes to represent with Fourier series of terms are waveforms with instantaneous transitions, tissue discontinuities or edges. The low-frequency components of the series describe the overall shape of the step function. Higher frequency components are needed to describe the corners if the step function more accurately. If not enough samples are taken, these areas cannot be accurately represented. The truncation of the infinite data series results in a ringing artifact because of the inability to accurately approximate this tissue discontinuity with a shorter truncated data set. Therefore, the ringing that occurs at all tissue boundaries on MR is called truncation artifact.
mri safety guidance
Image Guidance
This problem can be easily resolved by taking more samples - a higher acquisition matrix and/or a smaller FOV. See Gibbs Artifact and Gibbs Phenomenon.
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• View the DATABASE results for 'Truncation Artifact' (2).Open this link in a new window

 
Further Reading:
  News & More:
Magnetic Resonance Imaging (MRI)
2003   by www.hull.ac.uk    
MRI Resources 
MRI Technician and Technologist Career - Spectroscopy - Patient Information - Pathology - Safety pool - Shielding
 
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