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Result : Searchterm 'Diffusion' found in 8 terms [] and 36 definitions []
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B-Value
 
The b-value is a factor of diffusion weighted sequences. The b factor summarizes the influence of the gradients on the diffusion weighted images. The higher the value b, the stronger the diffusion weighting.

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• Related Searches:
    • Diffusion Weighted Imaging
    • Apparent Diffusion Coefficient
    • Eigenvalues
    • Diffusion Weighted Whole Body Imaging
    • Liver Imaging
 
Further Reading:
  Basics:
Diffusion-Weighted MRI in the Body: Applications and Challenges in Oncology
Friday, 1 June 2007   by www.ajronline.org    
Implementation of Dual-Source RF Excitation in 3 T MR-Scanners Allows for Nearly Identical ADC Values Compared to 1.5 T MR Scanners in the Abdomen
Wednesday, 29 February 2012   by www.plosone.org    
High-b-value Diffusion-weighted MR Imaging of Suspected Brain Infarction
2000   by www.ajnr.org    
  News & More:
EORTC study aims to qualify ADC as predictive imaging biomarker in preoperative regimens
Monday, 4 January 2016   by www.eurekalert.org    
Searchterm 'Diffusion' was also found in the following services: 
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Intravoxel Incoherent Motion
 
(IVIM) Spins moving in fluids with different velocities and possibly in different directions. This is being found to a small degree in all tissues as a result of capillary perfusion or diffusion. Important velocity changes occur as one moves from the vessel wall towards the center of the vessel. Hence, spins (to a variable degree) have different velocities within a single imaging voxel.
This effect can be measured using special pulse sequences such as in diffusion imaging or diffusion weighed imaging. When the velocity differences are marked, as occurs in larger blood vessels, effects due to IVIM are visible in standard MR images and give rise to flow related dephasing. The effects are more visible when longer echo times are used.
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Further Reading:
  Basics:
Diffusion Imaging: From Basic Physics to Practical Imaging
1999   by ej.rsna.org    
  News & More:
EVALUATION OF HUMAN STROKE BY MR IMAGING
2000
Technical Assessment of Artifact Production from Neuro Endovascular Coil At 3 Tesla MRI: An In Vitro Study
2012   by www.tmps.or.th    
MRI Resources 
Veterinary MRI - Open Directory Project - MRI Technician and Technologist Jobs - Education pool - Journals - Stent
 
Perfusion ImagingForum -
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(PWI - Perfusion Weighted Imaging) Perfusion MRI techniques (e.g. PRESTO - Principles of Echo Shifting using a Train of Observations) are sensitive to microscopic levels of blood flow. Contrast enhanced relative cerebral blood volume (rCBV) is the most used perfusion imaging. Both, the ready availability and the T2* susceptibility effects of gadolinium, rather than the T1 shortening effects make gadolinium a suitable agent for use in perfusion imaging. Susceptibility here refers to the loss of MR signal, most marked on T2* (gradient echo)-weighted and T2 (spin echo)-weighted sequences, caused by the magnetic field-distorting effects of paramagnetic substances.
T2* perfusion uses dynamic sequences based on multi or single shot techniques. The T2* (T2) MRI signal drop within or across a brain region is caused by spin dephasing during the rapid passage of contrast agent through the capillary bed. The signal decrease is used to compute the relative perfusion to that region. The bolus through the tissue is only a few seconds, high temporal resolution imaging is required to obtain sequential images during the wash in and wash out of the contrast material and therefore, resolve the first pass of the tracer. Due to the high temporal resolution, processing and calculation of hemodynamic maps are available (including mean transit time (MTT), time to peak (TTP), time of arrival (T0), negative integral (N1) and index.
An important neuroradiological indication for MRI is the evaluation of incipient or acute stroke via perfusion and diffusion imaging. Diffusion imaging can demonstrate the central effect of a stroke on the brain, whereas perfusion imaging visualizes the larger 'second ring' delineating blood flow and blood volume. Qualitative and in some instances quantitative (e.g. quantitative imaging of perfusion using a single subtraction) maps of regional organ perfusion can thus be obtained.
Echo planar and potentially echo volume techniques together with appropriate computing power offer real time images of dynamic variations in water characteristics reflecting perfusion, diffusion, oxygenation (see also Oxygen Mapping) and flow.
Another type of perfusion MR imaging allows the evaluation of myocardial ischemia during pharmacologic stress. After e.g., adenosine infusion, multiple short axis views (see cardiac axes) of the heart are obtained during the administration of gadolinium contrast. Ischemic areas show up as areas of delayed and diminished enhancement. The MRI stress perfusion has been shown to be more accurate than nuclear SPECT exams. Myocardial late enhancement and stress perfusion imaging can also be performed during the same cardiac MRI examination.
 
Images, Movies, Sliders:
 Normal Lung Gd Perfusion MRI  Open this link in a new window
      

Courtesy of  Robert R. Edelman

 Left Circumflex Ischemia First-pass Contrast Enhancement  Open this link in a new window
 
Radiology-tip.comPerfusion Scintigraphy
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Radiology-tip.comBolus Injection
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• View the DATABASE results for 'Perfusion Imaging' (16).Open this link in a new window


• View the NEWS results for 'Perfusion Imaging' (3).Open this link in a new window.
 
Further Reading:
  Basics:
CHAPTER 55: Ischemia
2003
EVALUATION OF HUMAN STROKE BY MR IMAGING
2000
  News & More:
Motion-compensation of Cardiac Perfusion MRI using a Statistical Texture Ensemble(.pdf)
June 2003   by www.imm.dtu.dk    
Implementation of Dual-Source RF Excitation in 3 T MR-Scanners Allows for Nearly Identical ADC Values Compared to 1.5 T MR Scanners in the Abdomen
Wednesday, 29 February 2012   by www.plosone.org    
Turbo-FLASH Based Arterial Spin Labeled Perfusion MRI at 7 T
Thursday, 20 June 2013   by www.plosone.org    
Measuring Cerebral Blood Flow Using Magnetic Resonance Imaging Techniques
1999   by www.stanford.edu    
Vascular Filters of Functional MRI: Spatial Localization Using BOLD and CBV Contrast
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EigenvaluesForum -
related threads
 
Mathematically, the eigenvalue is the factor by which a linear transformation multiplies one of its eigenvectors. In an appropriate spatial reference frame, the diffusion tensor is diagonal (contains only three nonzero elements). These elements in diffusion tensor imaging are called the eigenvalues. The vectors characterizing the reference frame are the eigenvectors.
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Nerve Conductivity
 
Rapid echo planar imaging and high-performance MRI gradient systems create fast-switching magnetic fields that can stimulate muscle and nerve tissues produced by either changing the electrical resistance or the potential of the excitation. There are apparently no effects on the conduction of impulses in the nerve fiber up to field strength of 0.1 T. A preliminary study has indicated neurological effects by exposition to a whole body imager at 4.0 T. Theoretical examinations argue that field strengths of 24 T are required to produce a 10% reduction of nerve impulse conduction velocity.
Nerve stimulations during MRI scans can be induced by very rapid changes of the magnetic field. This stimulation may occur for example during diffusion weighted sequences or diffusion tensor imaging and can result in muscle contractions caused by effecting motor nerves. The so-called magnetic phosphenes are attributed to magnetic field variations and may occur in a threshold field change of between 2 and 5 T/s. Phosphenes are stimulations of the optic nerve or the retina, producing a flashing light sensation in the eyes. They seem not to cause any damage in the eye or the nerve.
Varying magnetic fields are also used to stimulate bone-healing in non-unions and pseudarthroses. The reasons why pulsed magnetic fields support bone-healing are not completely understood. The mean threshold levels for various stimulations are 3 600 T/s for the heart, 900 T/s for the respiratory system, and 60 T/s for the peripheral nerves.
Guidelines in the United States limit switching rates at a factor of three below the mean threshold for peripheral nerve stimulation. In the event that changes in nerve conductivity happens, the MRI scan parameters should be adjusted to reduce dB/dt for nerve stimulation.
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Further Reading:
  Basics:
Electrical eddy currents in the human body: MRI scans and medical implants
   by www.phy.olemiss.edu    
  News & More:
NERVE STIMULATORS
Tuesday, 18 January 2005   by www.health.adelaide.edu.au    
Conductivity tensor mapping of the human brain using diffusion tensor MRI
   by www.pnas.org    
MRI Resources 
Mobile MRI Rental - MRCP - Most Wanted - Sequences - Functional MRI - Manufacturers
 
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