Magnetic Resonance - Technology Information Portal Welcome to MRI Technology••


 'Gradient Coils' 
  2 3 5 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Result : Searchterm 'Gradient Coils' found in 1 term [] and 15 definitions [], (+ 12 Boolean[] results
1 - 5 (of 28)     next
Result Pages : [1]  [2 3 4]  [5 6]
Shielded Gradient CoilsInfoSheet: - Coils - 
etc.MRI Resource Directory:
 - Coils -
Current-carrying gradient coils with reduced gradient fringe field inside of the magnet cryostat structures like cryoshields and He-vessel. The shielding can be accomplished by secondary actively driven coils or by passive screens, which are inductively coupled to the gradient coils. In both cases eddy currents outside of the gradient system will be reduced.
See also Eddy Currents.
• Share the entry 'Shielded Gradient Coils':  Facebook  Twitter  LinkedIn  
Further Reading:
Faraday's Law
MRI Resources 
Absorption and Emission - Contrast Enhanced MRI - Portals - Anatomy - Nerve Stimulator - MRI Reimbursement
DeviceForum -
related threadsInfoSheet: - Devices -
Types of Magnets, 
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

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
Radiology-tip.comUltrasound Machine,  Real-Time Scanner

• View the DATABASE results for 'Device' (141).Open this link in a new window

• View the NEWS results for 'Device' (29).Open this link in a new window.
Further Reading:
  News & More:
Kyoto University and Canon reduce cost of MRI scanner to one tenth
Monday, 11 January 2016   by    
A transportable MRI machine to speed up the diagnosis and treatment of stroke patients
Wednesday, 22 April 2015   by    
Portable 'battlefield MRI' comes out of the lab
Thursday, 30 April 2015   by    
Chemists develop MRI technique for peeking inside battery-like devices
Friday, 1 August 2014   by    
New devices doubles down to detect and map brain signals
Monday, 23 July 2012   by    
MRI Resources 
Stimulator pool - Distributors - Open Directory Project - General - MRCP - Pacemaker
Gradient Amplifier
In MRI systems, the gradient amplifier increases the energy of the signal before it reaches the gradient coils, in a way, that the field strength is intense enough to produce the variations in the main magnetic field for localization of the later received signal. Three gradient coils normally require three gradient amplifiers. As all amplifiers, gradient amplifiers produce heat, which requires cooling.

See also the related poll result: 'Most outages of your scanning system are caused by failure of'

• View the DATABASE results for 'Gradient Amplifier' (2).Open this link in a new window

Helmholtz Pair CoilInfoSheet: - Coils - 
etc.MRI Resource Directory:
 - Coils -
A Helmholtz pair consists of two identical circular magnetic coils that are placed symmetrically one on each side of the experimental area along a common axis, and separated by a distance equal to the radius of the coil. Actually, a slightly larger separation improves the field uniformity. Each coil carries an equal electrical current flowing in the same direction. A cylindrical region extending between the centers of the two coils and approximately 1/5 of their diameter will have a nearly spatially uniform magnetic field.
In MRI, the Helmholtz pair coils are used as z-gradient coils to produce linear variations in the main magnetic field along the z-axis. Also in use as z-gradient coils are the Maxwell coils (three coils in a slightly more complicated geometry than the Helmholtz configuration). These coils are only occasionally used as RF coils for imaging.

• View the DATABASE results for 'Helmholtz Pair Coil' (2).Open this link in a new window

Further Reading:
How strong are magnets?
Helmholtz coil
Imaging Hardware
  News & More:
Design & Development of Helmholtz Coil for Hyperpolarized MRI
2010   by    
MRI Resources 
MRI Physics - Hospitals - Sequences - Developers - Libraries - Databases
Hardware components from MRI systems. The radio frequency (RF) amplifier increases the power (measured in Watt) of the pulses from mW to kW and the gradient amplifier increases the power of the gradient pulses for the gradient coils.
See also Hardware.

• View the DATABASE results for 'Amplifier' (15).Open this link in a new window

• View the NEWS results for 'Amplifier' (2).Open this link in a new window.
Further Reading:
Tech Spotlight: How to calibrate an MRI RF amplifier
Saturday, 1 December 2012   by    
MRI Resources 
Directories - Breast Implant - Pediatric and Fetal MRI - RIS - MRI Technician and Technologist Career - Sequences
     1 - 5 (of 28)     next
Result Pages : [1]  [2 3 4]  [5 6]
 Random Page
Share This Page

Forgot your UserID/Password ?  

In 2075 (after about 100 years of ...) the MRI scan will be :
done with handheld probe 
done at home (app, ...) 
a 3 second walk through 
daily done 
replaced by something much ... 

      Ups uses cookies! By browsing, you agree to our use of cookies.

Magnetic Resonance - Technology Information Portal
Member of SoftWays' Medical Imaging Group - MR-TIP • Radiology-TIP • US-TIP • 
Copyright © 2003 - 2018 SoftWays. All rights reserved. [ 21 January 2019]
Terms of Use | Privacy Policy | Advertising
 [last update: 2018-03-08 05:11:00]