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DeviceForum -
related threadsInfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.
 
Magnetic resonance imaging (MRI) is based on the magnetic resonance phenomenon, and is used for medical diagnostic imaging since ca. 1977 (see also MRI History).
The first developed MRI devices were constructed as long narrow tunnels. In the meantime the magnets became shorter and wider. In addition to this short bore magnet design, open MRI machines were created. MRI machines with open design have commonly either horizontal or vertical opposite installed magnets and obtain more space and air around the patient during the MRI test.
The basic hardware components of all MRI systems are the magnet, producing a stable and very intense magnetic field, the gradient coils, creating a variable field and radio frequency (RF) coils which are used to transmit energy and to encode spatial positioning. A computer controls the MRI scanning operation and processes the information.
The range of used field strengths for medical imaging is from 0.15 to 3 T. The open MRI magnets have usually field strength in the range 0.2 Tesla to 0.35 Tesla. The higher field MRI devices are commonly solenoid with short bore superconducting magnets, which provide homogeneous fields of high stability.
There are this different types of magnets:
Resistive Magnet
Permanent Magnet
Superconducting Magnet
The majority of superconductive magnets are based on niobium-titanium (NbTi) alloys, which are very reliable and require extremely uniform fields and extreme stability over time, but require a liquid helium cryogenic system to keep the conductors at approximately 4.2 Kelvin (-268.8 Celsius). To maintain this temperature the magnet is enclosed and cooled by a cryogen containing liquid helium (sometimes also nitrogen).
The gradient coils are required to produce a linear variation in field along one direction, and to have high efficiency, low inductance and low resistance, in order to minimize the current requirements and heat deposition. A Maxwell coil usually produces linear variation in field along the z-axis; in the other two axes it is best done using a saddle coil, such as the Golay coil.
The radio frequency coils used to excite the nuclei fall into two main categories; surface coils and volume coils. The essential element for spatial encoding, the gradient coil sub-system of the MRI scanner is responsible for the encoding of specialized contrast such as flow information, diffusion information, and modulation of magnetization for spatial tagging.
An analog to digital converter turns the nuclear magnetic resonance signal to a digital signal. The digital signal is then sent to an image processor for Fourier transformation and the image of the MRI scan is displayed on a monitor.

For Ultrasound Imaging (USI) see Ultrasound Machine at US-TIP.com.

See also the related poll results: 'In 2010 your scanner will probably work with a field strength of' and 'Most outages of your scanning system are caused by failure of'
Radiology-tip.comGamma Camera,  Linear Accelerator
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Radiology-tip.comUltrasound Machine,  Real-Time Scanner
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• Share the entry 'Device':  Facebook  Twitter  LinkedIn  
 
• Related Searches:
    • Daily Quality Assurance
    • Class I, II, III Devices
    • Active Device
    • Fringe Field
    • Permanent Magnet
 
Further Reading:
  News & More:
Kyoto University and Canon reduce cost of MRI scanner to one tenth
Monday, 11 January 2016   by www.electronicsweekly.com    
A transportable MRI machine to speed up the diagnosis and treatment of stroke patients
Wednesday, 22 April 2015   by medicalxpress.com    
Portable 'battlefield MRI' comes out of the lab
Thursday, 30 April 2015   by physicsworld.com    
Chemists develop MRI technique for peeking inside battery-like devices
Friday, 1 August 2014   by www.eurekalert.org    
New devices doubles down to detect and map brain signals
Monday, 23 July 2012   by scienceblog.com    
MRI Resources 
Used and Refurbished MRI Equipment - Breast MRI - General - Jobs pool - Pacemaker - MRI Centers
 
Active Device
 
The term 'active' refers to any medical device that can only serve its intended use with the supply of power by any means including, but not limited to line, battery, or gas power. Examples of active devices include ventilators, pacemakers, and patient monitoring devices.
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• View the DATABASE results for 'Active Device' (4).Open this link in a new window

 
Further Reading:
  News & More:
Modern Implantable Heart Devices Safe For Use In MRI Scans
Wednesday, 16 March 2005   by www.sciencedaily.com    
Newer Heart Devices Safe During MRI
Monday, 23 August 2004   by www.hospimedica.com    
MRI Resources 
Spectroscopy pool - Shoulder MRI - Societies - Quality Advice - Safety Training - Corporations
 
Passive Device
 
The term "passive" refers to any medical device that serves its function without the supply of power. Examples of passive devices include but are not limited to aneurysm clips, shunts, scalpels, IV poles, and oxygen bottles.
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• View the DATABASE results for 'Passive Device' (2).Open this link in a new window

 
Further Reading:
  Basics:
Physics of MRI Safety
   by www.aapm.org    
  News & More:
FDA Releases New Guidance On Establishing Safety, Compatibility Of Passive Implants In MR Environments
Tuesday, 16 December 2014   by www.meddeviceonline.com    
MRI Resources 
Contrast Agents - Movies - Colonography - Education pool - Absorption and Emission - Implant and Prosthesis
 
Class I, II, III Devices
 
Classification by the Food and Drug Administration of medical devices according to potential MRI risks or hazards.

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Further Reading:
  Basics:
A Primer on Medical Device Interactions with Magnetic Resonance Imaging Systems
   by govpulse.us    
MRI Resources 
Most Wanted - Mobile MRI - MRI Accidents - Brain MRI - Manufacturers - Pediatric and Fetal MRI
 
MR Compatibility
 

MRI Safety Guidance
If a device is to be labeled MR Safe, the following information should be provided:
Data demonstrating that when the device is introduced or used in the MRI environment (i.e. the MRI scan room) it does not pose an increased safety risk to the patient or other personnel,
a scientifically-based rationale for why data are not necessary to prove the safety of the device in the MR environment (for example, a passive device made entirely of a polymer known to be nonreactive in strong magnetic fields).
If a device is to be labeled MR Compatible, the following information should be provided:
Data demonstrating that when the device is introduced or used in the MRI environment, it is MR safe that it performs its intended function without performance degradation, and that it does not adversely affect the function of the MRI scanner (e.g. no significant image artifacts or noise). Any image artifact or noise due to the medical device should be quantified (e.g., % volume affected, signal to noise ratio),
a scientifically-based rationale for why data are not necessary to prove the compatibility of the device in the MRI environment.
Test Conditions:
The static magnetic field strength (Gauss (G) or Tesla (T)) to which the device was tested and demonstrated to be MRI 'safe', 'compatible', or 'intended for use in' should be related to typical machine ratings (e.g. 0.5 T, 1.5 T, 2.0 T, and shielded or unshielded magnet, etc).
The same conditions should be used for the spatial gradient (field strength per unit distance (i.e., G/cm)) in which the device was tested and demonstrated to be 'safe', 'compatible', or 'intended for use in'.
Also the RF transmitter power used during testing of the device, should be related to this typical machine ratings.
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• View the DATABASE results for 'MR Compatibility' (4).Open this link in a new window


• View the NEWS results for 'MR Compatibility' (2).Open this link in a new window.
 
Further Reading:
  Basics:
Newer Heart Devices Safe During MRI
Monday, 23 August 2004   by www.hospimedica.com    
  News & More:
Boston Scientific and Biophan in MRI Collaboration
Friday, 21 November 2003   by www.medimaging.net    
MRI safety targeted as new group offers credentialing test
Monday, 12 January 2015   by www.modernhealthcare.com    
FDA Releases New Guidance On Establishing Safety, Compatibility Of Passive Implants In MR Environments
Tuesday, 16 December 2014   by www.meddeviceonline.com    
MRI Resources 
MRI Centers - MRI Accidents - Corporations - Implant and Prosthesis pool - Image Quality - Directories
 
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