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FlowForum -
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Flow phenomena are intrinsic processes in the human body. Organs like the heart, the brain or the kidneys need large amounts of blood and the blood flow varies depending on their degree of activity. Magnetic resonance imaging has a high sensitivity to flow and offers accurate, reproducible, and noninvasive methods for the quantification of flow. MRI flow measurements yield information of blood supply of of various vessels and tissues as well as cerebro spinal fluid movement.
Flow can be measured and visualized with different pulse sequences (e.g. phase contrast sequence, cine sequence, time of flight angiography) or contrast enhanced MRI methods (e.g. perfusion imaging, arterial spin labeling).
The blood volume per time (flow) is measured in: cm3/s or ml/min. The blood flow-velocity decreases gradually dependent on the vessel diameter, from approximately 50 cm per second in arteries with a diameter of around 6 mm like the carotids, to 0.3 cm per second in the small arterioles.

Different flow types in human body:
Behaves like stationary tissue, the signal intensity depends on T1, T2 and PD = Stagnant flow
Flow with consistent velocities across a vessel = Laminar flow
Laminar flow passes through a stricture or stenosis (in the center fast flow, near the walls the flow spirals) = Vortex flow
Flow at different velocities that fluctuates = Turbulent flow

See also Flow Effects, Flow Artifact, Flow Quantification, Flow Related Enhancement, Flow Encoding, Flow Void, Cerebro Spinal Fluid Pulsation Artifact, Cardiovascular Imaging and Cardiac MRI.
 
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• Related Searches:
    • Signal Intensity
    • Inflow Magnetic Resonance Angiography
    • Velocity
    • Flow Related Enhancement
    • Flow Quantification
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Flow VoidForum -
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The occurrence of a low signal in regions of flow. For a spin echo sequence, this is caused in part by a lack of refocusing of blood, which is excited by the 90° pulse but not by the 180° pulse. For a gradient echo sequence, this is caused by the dephasing of blood signal.
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• View the DATABASE results for 'Flow Void' (5).Open this link in a new window

 
Further Reading:
  Basics:
MRI Artifacts, Flow void and Signal void
   by www.neuroradiologycases.com    
Flow comp off: An easy technique to confirm CSF flow within syrinx and aqueduct
Wednesday, 2 January 2013   by medind.nic.in    
DRIVE: shorter scan time, brighter fluid
   by clinical.netforum.healthcare.philips.com    
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Vortex Flow
 
Area within a blood vessel where the blood is suddenly accelerated, then rapidly decelerated. This would be commonly seen in blood passing through a vascular stenosis (narrowing), and becomes a factor in MRA.
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• View the DATABASE results for 'Vortex Flow' (2).Open this link in a new window

 
Further Reading:
  Basics:
MRI measure of blood flow over atherosclerotic plaque may detect dangerous plaque
Friday, 5 April 2013   by www.sciencecodex.com    
Magnetic resonance imaging zooms in on microscopic flow
Thursday, 7 October 2010   by www.nanowerk.com    
Searchterm 'Flow' was also found in the following services: 
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Flow Effects
 
Motion of material being imaged, particularly flowing blood, can result in many possible effects in the images.
Fast moving blood produces flow voids, blood flowing in to the outer slices of an imaging volume produces high signals (flow related enhancement, entry slice phenomenon), pulsatile flow creates ghost images of the vessel extending across the image in the phase encoding direction (image misregistration).
Flow-related dephasing occurring when spin isochromats are moving with different velocities in an external gradient field G so that they acquire different phases. When these phases vary by more then 180° within a voxel, substantial spin dephasing results leading to considerable intravascular signal loss.
These effects can be understood as caused by time of flight effects (washout or washin due to motion of nuclei between two consecutive spatially selective RF excitations, repeated in times on the order of, or shorter than the relaxation times of blood) or phase shifts (delay between phase encoding and frequency encoding) that can be acquired by excited spins moving along magnetic field gradients.
The inconsistency of the signal resulting from pulsatile flow can lead to artifacts in the image. The flow effects can also be exploited for MR angiography or flow measurements.
See also Flow Artifact.
 
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• View the DATABASE results for 'Flow Effects' (16).Open this link in a new window

 
Further Reading:
  News & More:
Magnetic resonance flow velocity and temperature mapping of a shape memory polymer foam device
Thursday, 31 December 2009   by 7thspace.com    
MRI measure of blood flow over atherosclerotic plaque may detect dangerous plaque
Friday, 5 April 2013   by www.sciencecodex.com    
Searchterm 'Flow' was also found in the following services: 
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Radiology  (25) Open this link in a new windowUltrasound  (120) Open this link in a new windowMarket  (2) Open this link in a new window
Flow 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 Spin phase effect, flow
DESCRIPTION Vascular ghosts (ghosting artifact), anomalous intensities in images
REASON Movement of body fluids
HELP Flow compensation, presaturation, triggering

Flow effects in MRI produce a range of artifacts, e.g. intravascular signal void by time of flight effects; turbulent dephasing and first echo dephasing, caused by flowing blood.
Through movement of the hydrogen nuclei (e.g. blood flow), there is a location change between the time these nuclei experience a radio frequency pulse and the time the emitted signal is received (because the repetition time is asynchronous with the pulsatile flow).
The blood flow occasionally produces intravascular high signal intensities due to flow related enhancement, even echo rephasing and diastolic pseudogating. The pulsatile laminar flow within vessels often produces a complex multilayered band that usually propagates outside the head in the phase encoded direction. Blood flow artifacts should be considered as a special subgroup of motion artifacts.


Image Guidance
Artifacts can be reduced by reduction of phase shifts with flow compensation (gradient moment nulling), suppression of the blood signal with saturation pulses parallel to the slices, synchronization of the imaging sequence with the heart cycle (cardiac triggering) or can be flipped 90° by swapping the phase//frequency encoding directions.
See also Flow Related Enhancement and Flow Effects.
 
Images, Movies, Sliders:
 Knee MRI Sagittal T1 003  Open this link in a new window
 
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• View the DATABASE results for 'Flow Artifact' (6).Open this link in a new window

 
Further Reading:
  News & More:
MRI measure of blood flow over atherosclerotic plaque may detect dangerous plaque
Friday, 5 April 2013   by www.sciencecodex.com    
Advanced Visualization Techniques Could Change the Paradigm for Diagnosis and Treatment of Heart Disease
Thursday, 31 May 2012   by www.sciencedaily.com    
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