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Result : Searchterm 'Pulse Sequence' found in 5 terms [] and 166 definitions []
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Flip Angle
 
(FA) The flip angle a is used to define the angle of excitation for a field echo pulse sequence. It is the angle to which the net magnetization is rotated or tipped relative to the main magnetic field direction via the application of a RF excitation pulse at the Larmor frequency. It is also referred to as the tip angle, nutation angle or angle of nutation.
The radio frequency power (which is proportional to the square of the amplitude) of the pulse is proportional to a through which the spins are tilted under its influence. Flip angles between 0° and 90° are typically used in gradient echo sequences, 90° and a series of 180° pulses in spin echo sequences and an initial 180° pulse followed by a 90° and a 180° pulse in inversion recovery sequences.
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• Related Searches:
    • Net Magnetization Vector
    • Magnetic Resonance
    • Pulse, 90°
    • Abdominal Imaging
    • Echo
 
Further Reading:
  Basics:
Mapping of low flip angles in magnetic resonance(.pdf)
Saturday, 1 January 2011   by www.hal.inserm.fr    
  News & More:
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
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FlowForum -
related threads
 
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.
 
Images, Movies, Sliders:
 MVP Parasternal  Open this link in a new window
    

Courtesy of  Robert R. Edelman
 TOF-MRA Circle of Willis Inverted MIP  Open this link in a new window
    

 Circle of Willis, Time of Flight, MIP  Open this link in a new window
    
SlidersSliders Overview

 
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• View the DATABASE results for 'Flow' (113).Open this link in a new window


• View the NEWS results for 'Flow' (7).Open this link in a new window.
MRI Resources 
Spectroscopy - Crystallography - Services and Supplies - Case Studies - PACS - Journals
 
Fluid Attenuation Inversion RecoveryInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
(FLAIR) Fluid attenuation inversion recovery is a special inversion recovery sequence with long TI to remove the effects of fluid from the resulting images. The TI time of the FLAIR pulse sequence is adjusted to the relaxation time of the component that should be suppressed. For fluid suppression the inversion time (long TI) is set to the zero crossing point of fluid, resulting in the signal being 'erased'.
Lesions that are normally covered by bright fluid signals using conventional T2 contrast are made visible by the dark fluid technique FLAIR is an important technique for the differentiation of brain and spine lesions.
See also Inversion Recovery.
 
Images, Movies, Sliders:
 Brain MRI Coronal FLAIR 001  Open this link in a new window
    
 
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• View the DATABASE results for 'Fluid Attenuation Inversion Recovery' (5).Open this link in a new window

 
Further Reading:
  Basics:
Newer Sequences for Spinal MR Imaging: Smorgasbord or Succotash of Acronyms?
   by www.ajnr.org    
  News & More:
Early Identification of Ischemic Stroke With DWI-FLAIR Mismatch
Wednesday, 5 January 2011   by www.doctorslounge.com    
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G-SCANInfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.MRI Resource Directory:
 - Devices -
 
www.esaote.de/04_kernspin/gscan/gscan.htm From Esaote S.p.A.; Esaote introduced the new G-SCAN at the RSNA in Dec. 2004. The G-SCAN covers almost all musculoskeletal applications including the spine. The tilting gantry is designed for scanning in weight-bearing positions. This unique MRI scanner is developed in line with the Esaote philosophy of creating high quality MRI systems that are easy to install and that have a low breakeven point.

Device Information and Specification (Under Development)
CLINICAL APPLICATION Musculoskeletal, extremity
CONFIGURATION Open MRI
SURFACE COILS Spine, extremity, shoulder, flex coil, knee dual phased array, ankle//foot dual phased array, hand//wrist dual phased array
PULSE SEQUENCES SE, GE, IR, STIR, TSE, 3D CE, GE-STIR, 3D GE, ME, TME, HSE
IMAGING MODES Single, multislice, volume study, fast scan, multi slab, cine
FOV 100 up to 350 mm, 25 mm displayed
DISPLAY MATRIX 512 x 512
MEASURING MATRIX 256 x 256 maximum
MAGNET TYPE Permanent
BORE DIAMETER
or W x H
33 cm H, open
POWER REQUIREMENTS 100/110/200/220/230/240
FIELD STRENGTH 0.25 T
STRENGTH 25 mT/m
5-GAUSS FRINGE FIELD, radial/axial 180 cm
SHIMMING Passive
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Ghosting ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview

Artifact Information
NAME Ghosting, ghost
DESCRIPTION Displaced reduplications of image in phase encoding direction
REASON Motion, heartbeat, respiration
HELP Triggering, breath hold, pharmaceuticals to reduce bowel motion

Ghosting artifacts are in the most cases caused by movements (e.g., respiratory motion, bowel motion, arterial pulsations, swallowing, and heartbeat) and appear in the phase encoding direction.


Image Guidance
Ghosting artifacts can be reduced by respiratory and cardiac triggering, the use of breath holding pulse sequences, flow compensation or presaturation pulses, depending on their origin. To reduce bowel motion also pharmaceuticals, such as glucagon or scopolamine are useful. This will decrease artifacts from both peristalsis and breathing.
See also Motion Artifact, Phase Encoded Motion Artifact, Cardiac Motion Artifact, and Artifact Reduction - Motion.
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• View the DATABASE results for 'Ghosting Artifact' (5).Open this link in a new window

 
Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
MRI Resources 
Abdominal Imaging - Pediatric and Fetal MRI - Breast Implant - Bioinformatics - Artifacts - Open Directory Project
 
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