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Coherence
 
The act of maintaining a constant phase relationship between oscillating waves or rotating objects.
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• View the DATABASE results for 'Coherence' (19).Open this link in a new window

 
Further Reading:
  Basics:
Measuring T1 and T2 Relaxation - Introductory NMR & MRI from Magritek
   by www.azom.com    
Coherent
 
A state of a spin sample in which all spins in a voxel are in phase.
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• View the DATABASE results for 'Coherent' (16).Open this link in a new window

 
Further Reading:
  News & More:
New Study Brings MRI on Nanoscale and Quantum Computer One Step Closer to Reality
Monday, 27 February 2012   by www.azonano.com    
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Coherent Gradient EchoInfoSheet: - Sequences -
Intro, Overview, 
Types of, 
etc.MRI Resource Directory:
 - Sequences -
 
Coherent gradient echo sequences can measure the free induction decay (FID), generated just after each excitation pulse or the echo formed prior to the next pulse. Coherent gradient echo sequences are very sensitive to magnetic field inhomogeneity. An alternative to spoiling is to incorporate residual transverse magnetization directly into the longitudinal steady state. These GRE sequences use a refocusing gradient in the phase encoding direction during the end module to maximize remaining transverse (xy) magnetization at the time when the next excitation is due, while the other two gradients are, in any case, balanced.
When the next excitation pulse is sent into the system with an opposed phase, it tilts the magnetization in the -a direction. As a result the z-magnetization is again partly tilted into the xy-plane, while the remaining xy-magnetization is tilted partly into the z-direction.
A fully refocused sequence with a properly selected and uniform f would yield higher signal, especially for tissues with long T2 relaxation times (high water content) so it is used in angiographic, myelographic or arthrographic examinations and is used for T2* weighting. The repetition time for this sequence has to be short. With short TR, coherent GE is also useable for breath hold and 3D technique. If the repetition time is about 200 msec there's no difference between spoiled or unspoiled GE. T1 weighting is better with spoiled techniques.
The common types include GRASS, FISP, FAST, and FFE.
The T2* component decreases with long TR and short TE. The T1 time is controlled by flip angle. The common TR is less than 50 ms and the common TE less than 15 ms
Other types have stronger T2 dependence but lower SNR. They include SSFP, CE-FAST, PSIF, and CE-FFE-T2.
Examples of fully refocused FID sequences are TrueFISP, bFFE and bTFE.
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• View the DATABASE results for 'Coherent Gradient Echo' (6).Open this link in a new window

CoilForum -
there are related threadsInfoSheet: - Coils -
Intro, 
Overview, 
etc.MRI Resource Directory:
 - Coils -
 
A coil consists of one or more loops of conductive wire, looped around the core of the coil. Coils are part of the hardware of MRI machines and are used to create a magnetic field or to detect a changing magnetic field by voltage induced in the wire. A coil is usually a physically small antenna.
The perfect coil produces a uniform magnetic field without significant radiation.
Different types of MRI coils are used in MR systems:
Gradient coils are used to produce controlled variations in the main magnetic field (B0) to provide spatial localization of the signals and to apply reversal pulses in some imaging techniques.
MR imaging radio frequency coils to receive and/or transmit the RF signal.
Shim coils provide auxiliary magnetic fields in order to compensate for inhomogeneities in the main magnetic field of the MRI machine.

See also Gradient Coil, Radio Frequency Coil, Hardware and Coil Loading.

See also the related POLL result: '3rd party coils are better than the original manufacturer coils'
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• View the NEWS results for 'Coil' (11).Open this link in a new window.

• View the DATABASE results for 'Coil' (193).Open this link in a new window

 
Further Reading:
  News & More:
3T MRI-Compatible Small Body Array Gets FDA Nod
Monday, 15 January 2024   by www.diagnosticimaging.com    
High-field MRI Coils – that work, superbly, even at 750 MHz
   by www.dotynmr.com    
New superconducting coil improves MRI performance
Wednesday, 20 July 2016   by www.eurekalert.org    
First European fully superconductive coil reaching a magnetic field of 25 Tesla produced
Wednesday, 8 June 2016   by www.news-medical.net    
ScanMed Introduces a Groundbreaking New Orbit and Mandible Array to the MRI Market
Wednesday, 26 March 2014   by www.digitaljournal.com    
MRI coil optimized for imaging of infants gets FDA clearance
Tuesday, 17 April 2012   by www.medcitynews.com    
Low-profile MRI coil company inching toward commercialization
Wednesday, 21 December 2011   by www.medcitynews.com    
High-Resolution Uniform MR Imaging of Finger Joints Using a Dedicated RF Coil at 3 Tesla
Sunday, 31 January 2010   by www.ncbi.nlm.nih.gov    
DOTmed Industry Sector Report: MRI Coil Sales & Service Companies
Thursday, 13 December 2007   by www.dotmed.com    
Coil DiameterInfoSheet: - Coils -
Intro, 
Overview, 
etc.
 
MRI coils with a small diameter obtain a higher signal to noise ratio (SNR) than coils with a large diameter. A surface coil with a small diameter can be used to improve the resolution because the area of interest is around the optimal signal depth. The field of view of a (superficial) surface coil is half the diameter of the coil. A disadvantage is a lower sensitive volume of the coil. By combining several coils with small diameters (phased array coil) to record the signal simultaneously and independently, the SNR level improves considerably.
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• View the DATABASE results for 'Coil Diameter' (3).Open this link in a new window

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