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MRI Resources 
Sequences - IR - Cardiovascular Imaging - Pregnancy - Process Analysis - Hospitals
 
Jet Effect
 
Spin dephasing for complex flow patterns like turbulence. This effect must be taken into account when evaluating the extent of vascular stenosis. The degree of the signal loss depends on the flow model and pulse sequence used.
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Devices - Databases - General - MRCP - Pacemaker - Pediatric and Fetal MRI
 
Motion Compensation Pulse SequencesInfoSheet: - Sequences - 
Intro, 
Overview, 
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Pulse sequences, designed to be insensitive to flow, e.g. at every even echo, a spin echo sequence is not flow sensitive. Velocity compensation is achieved by using gradients, which are either symmetrical around a 180° pulse and switched on twice as is the case for motion compensated spin echo pulse sequences, or two antisymmetrical gradient lobes without 180° pulse, which is the way to produce a velocity compensated gradient echo pulse sequence.
The signal of the second echo (and all other even echoes) is independent of the velocity of the object. Thus, velocity-based motion effects stemming from the entire voxel or from spins within a voxel (intravoxel incoherent motion) are suppressed with such pulse sequences.
If higher order motion is relevant, as it may be in turbulent jets across valves, acceleration and jerk effects can also be compensated for by the use of appropriate combinations of gradient- and radio frequency pulses.
With the increasingly stronger gradients, echo times in MR systems can be shortened to the point at which effects other than velocity effects hardly ever become relevant.
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Further Reading:
  Basics:
Motion Compensation in MR Imaging
   by ccn.ucla.edu    
  News & More:
Patient movement during MRI: Additional points to ponder
Tuesday, 5 January 2016   by www.healthimaging.com    
Motion-compensation of Cardiac Perfusion MRI using a Statistical Texture Ensemble(.pdf)
June 2003   by www.imm.dtu.dk    
MRI Resources 
Services and Supplies - Image Quality - Shoulder MRI - MRI Physics - MR Myelography - Hospitals
 
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