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Back Projection Imaging
 
This imaging technique is probably the earliest, but rarely used today. Most of today's imaging techniques are based on the Fourier transform, and fill the Cartesian grid of points in k-space line by line by a sequence of applied gradients. Back projection imaging performs a radial filling of the k-space by a one dimensional field gradient, applied at different angles. Back projection imaging is still in use in laser polarized noble gas imaging (see ventilation agents and lung imaging).
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• View the DATABASE results for 'Back Projection Imaging' (3).Open this link in a new window

 
Further Reading:
  Basics:
Primer on Magentic Resonance Imaging Tomography
   by research.physics.lsa.umich.edu    
The Basics of MRI
   by www.cis.rit.edu    
Backfolding 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
Backfolding, foldover, phase wrapping, wrap around
DESCRIPTION
Image wrap around
Backfolding always occurs due to wrong phase encoding caused by objects outside the planned FOV. Phase encoding gradients are scaled for the field of view only. Tissues outside the FOV do not get properly phase encoded relative to their actual position and 'wraps' into the opposite side of the image. The Backfolding artifact projects image contents which fall outside the imaging FOV back into the image; the back folded information thus reappearing on the other side of the image. In fact, information along the phase encoding direction can be viewed as projected onto a cylindrical screen with a circumference corresponding to the linear field of view dimension in the phase encoding direction.

See also Aliasing Artifact.
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• View the DATABASE results for 'Backfolding Artifact' (2).Open this link in a new window

 
Further Reading:
  Basics:
Aliasing or wrap around artifacts
Thursday, 31 March 2011   by de.slideshare.net    
MRI Resources 
Online Books - Mass Spectrometry - Crystallography - Societies - Contrast Agents - Claustrophobia
 
Balanced Fast Field EchoInfoSheet: - Sequences -
Intro, Overview, 
Types of, 
etc.MRI Resource Directory:
 - Sequences -
 
(bFFE) A FFE sequence using a balanced gradient waveform. A balanced sequence starts out with a RF pulse of 90° or less and the spins in the steady state. Before the next TR in the slice phase and frequency encoding, gradients are balanced so their net value is zero. Now the spins are prepared to accept the next RF pulse, and their corresponding signal can become part of the new transverse magnetization. Since the balanced gradients maintain the transverse and longitudinal magnetization, the result is, that both T1 and T2 contrast are represented in the image. This pulse sequence produces images with increased signal from fluid, along with retaining T1 weighted tissue contrast. Because this form of sequence is extremely dependent on field homogeneity, it is essential to run a shimming prior the acquisition. A fully balanced (refocused) sequence would yield higher signal, especially for tissues with long T2 relaxation times.

See Steady State Free Precession and Gradient Echo Sequence.
 
Images, Movies, Sliders:
 Cardiac Infarct Short Axis Cine bFFE 1  Open this link in a new window
    
 
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• View the DATABASE results for 'Balanced Fast Field Echo' (3).Open this link in a new window

 
Further Reading:
  News & More:
T1rho-prepared balanced gradient echo for rapid 3D T1rho MRI
Monday, 1 September 2008   by www.ncbi.nlm.nih.gov    
Utility of the FIESTA Pulse Sequence in Body Oncologic Imaging: Review
June 2009   by www.ajronline.org    
Balanced Gradient
 
A gradient waveform, which will act on any stationary spin on resonance between two consecutive RF pulses and return it to the same phase it had before the gradients were applied.
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• View the DATABASE results for 'Balanced Gradient' (7).Open this link in a new window

 
Further Reading:
  Basics:
T1rho-prepared balanced gradient echo for rapid 3D T1rho MRI
Monday, 1 September 2008   by www.ncbi.nlm.nih.gov    
Steady-state free precession imaging
   by en.wikipedia.org    
Balanced SARGEInfoSheet: - Sequences -
Intro, Overview, 
Types of, 
etc.MRI Resource Directory:
 - Sequences -
 
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• View the DATABASE results for 'Balanced SARGE' (3).Open this link in a new window

MRI Resources 
Case Studies - Knee MRI - MRI Technician and Technologist Schools - Stimulator pool - MRI Physics - Hospitals
 
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