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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
- Techniques
Apodization 
The multiplication of acquired MR data by a function smoothly tapering off at higher spatial frequencies so as to reduce ringing artifacts near edges in the corresponding image or spectrum due to truncation and Gibbs phenomenon. It is a form of filtering.

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

Eddy Current Compensation 
Eliminate Gibb's artifact (Border ringing) for sharp images. Means of reducing the influence of eddy currents on pulsed gradient fields by employing an electrical preemphasis in the gradient amplifiers. Usually multiple time constants have to be used to correct for eddy current effects in various structures of the MR system such as the cryoshields and RF-shields.

See also Eddy Currents and Shielded Gradient Coils.

• View the DATABASE results for 'Eddy Current Compensation' (4).Open this link in a new window

Fast Spin Echo Optimization 
FSE optimization runs a preliminary TR period at the central slice and compares the phase of each echo in the echo train. If the phases do not compliment each other the RF is recalibrated and then the entire sequence is run. If there is an error in calibrating the phases of each of the echoes artifacts will appear.
Filling Factor 
A measure of the geometrical relationship of the RF coil and the object being studied. It affects the efficiency of exciting the object and detecting MR signals, thereby affecting the signal to noise ratio and image quality. Achieving a high filling factor requires fitting the coil closely to the object, thus potentially decreasing patient comfort.
Filtering 
Filtering deletes components of the signal, high or low frequencies, band-pass, analog or digital. Whatever pattern or algorithms can be defined for data decimation.
Low pass filtering attenuates high frequency data and passes low frequency data. The reconstructed image will look a little blurrier, but nearly similar to the original image. The blurring is caused by the fact that the high spatial frequencies are lost, which contain information about edges in the image.
High pass filtering attenuates low frequencies and passes high frequencies. Most of the objects and contrast of the original image are lost in the reconstructed image, but the edges are clearly visible because high frequency data has been preserved.

• View the DATABASE results for 'Filtering' (8).Open this link in a new window

Phase Cycling 
Techniques of signal excitation in which the phases of the exciting or refocusing RF pulses are systematically varied and the resulting signals are then suitably combined in order to reduce or eliminate certain artifacts.
Ringing Artifact Reduction 
Multiplication of acquired MR data by a function smoothly tapering off at higher spatial frequencies so as to reduce ringing artifacts near edges in the corresponding image or spectrum due to truncation and Gibbs phenomenon. It is a form of filtering.

• View the DATABASE results for 'Ringing Artifact Reduction' (2).Open this link in a new window

Tilt Optimized Nonsaturated Excitation 
(TONE) Used to decrease the saturation effect of inflowing blood in 3D MRA scans, the flip angle varies linearly over the excited chunk. In multi chunk scans TONE decreases the Venetian blind artifact or allows thicker chunks to cover a larger anatomical region.

See also Variable Flip Angle.

• View the DATABASE results for 'Tilt Optimized Nonsaturated Excitation' (2).Open this link in a new window

  Artifacts - Reduction Index - Aliasing top

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