Magnetic Resonance - Technology Information Portal Welcome to MRI Technology
Info
  Sheets

Out-
      side
 



 
 'Gradient' 
SEARCH FOR    
 
  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' found in 59 terms [] and 252 definitions []
previous     86 - 90 (of 311)     next
Result Pages : [1 2 3 4 5 6 7 8 9 10 11 12]  [13 14 15 16 17 18 19 20 ... ]
Searchterm 'Gradient' was also found in the following services: 
spacer
News  (6)  Resources  (7)  Forum  (35)  
 
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:
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 (-268.8Ā° 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 Medical-Ultrasound-Imaging.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.comradGamma Camera,  Linear Accelerator
spacer
Medical-Ultrasound-Imaging.comUltrasound Machine,  Real-Time Scanner
spacer
 
• Related Searches:
    • Computer
    • Fringe Field
    • Hardware
    • Class I, II, III Devices
    • Permanent Magnet
 
Further Reading:
  News & More:
small-steps-can-yield-big-energy-savings-and-cut-emissions-mris
Thursday, 27 April 2023   by www.itnonline.com    
Portable MRI can detect brain abnormalities at bedside
Tuesday, 8 September 2020   by news.yale.edu    
Point-of-Care MRI Secures FDA 510(k) Clearance
Thursday, 30 April 2020   by www.diagnosticimaging.com    
World's First Portable MRI Cleared by FDA
Monday, 17 February 2020   by www.medgadget.com    
Low Power MRI Helps Image Lungs, Brings Costs Down
Thursday, 10 October 2019   by www.medgadget.com    
Cheap, portable scanners could transform brain imaging. But how will scientists deliver the data?
Tuesday, 16 April 2019   by www.sciencemag.org    
The world's strongest MRI machines are pushing human imaging to new limits
Wednesday, 31 October 2018   by www.nature.com    
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    
Searchterm 'Gradient' was also found in the following services: 
spacer
Radiology  (1) Open this link in a new windowUltrasound  (3) Open this link in a new window
Dual Echo Steady StateInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
(DESS) This sequence was originally known as FADE. It combines both the gradient echoes acquired in FISP and PSIF sequences in separate acquisition periods during a single interpulse interval. Phase encoding gradients are balanced to maintain the transverse steady state signals. The frequency encoding gradient is left on for the period of both the echoes, and is incompletely balanced to avoid dark banding artifacts otherwise associated with long TR fully balanced steady state sequences. The contrast of DESS is quite unique, true T2 or T1 contrast weighting is not possible. There is a strong fluid signal but fat is bright and other soft tissues appear similar to the short TR FISP image.
Used for, e.g. the joints, cartilage and the prostate.

See Steady State Free Precession and Dual Echo Sequence.
spacer

• View the DATABASE results for 'Dual Echo Steady State' (2).Open this link in a new window

MRI Resources 
Blood Flow Imaging - Image Quality - Databases - DICOM - Pregnancy - Stimulator pool
 
ENCORE 0.5Tā„¢InfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.MRI Resource Directory:
 - Devices -
 
www.isoltech.co.kr/english/product/05t.htm 'MRI system is not an expensive equipment anymore. ENCORE developed by ISOL Technology is a low cost MRI system with the advantages like of the 1.0T MRI scanner. Developed specially for the overseas market, the ENCORE is gaining popularity in the domestic market by medium sized hospitals.
Due to the optimum RF and Gradient application technology. ENCORE enables to obtain high resolution imaging and 2D/3D Angio images which was only possible in high field MR systems.'
- Less consumption of the helium gas due to the ultra-lightweight magnet specially designed and manufactured for ISOL. - Cost efficiency MR system due to air cooling type (equivalent to permanent magnetic). - Patient processing speed of less than 20 minutes.'
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Short bore compact
Head, C-spine, L-spine, TMJ, Knee, Shoulder, General purpose, Phased Array System: 4 digital receiver channels (Up to 12 channels)
SYNCHRONIZATION
ECG/peripheral: Optional/yes, respiratory gating
SINGLE/MULTI SLICE
Image reconstruction time (2562 ) : 0.02 s
FOV
40 cm
BORE DIAMETER
or W x H
58 cm diameter
MAGNET WEIGHT
3200 kg
H*W*D
200 x 168 x 187 cm
COOLING SYSTEM TYPE
Air-cooled coil and amplifier
CRYOGEN USE
0.05 L/hr helium
STRENGTH
15 mT/m
5-GAUSS FRINGE FIELD
2.3 m / 3.1 m
Passive and active
spacer

• View the DATABASE results for 'ENCORE 0.5T™' (2).Open this link in a new window

Searchterm 'Gradient' was also found in the following services: 
spacer
News  (6)  Resources  (7)  Forum  (35)  
 
Eddy Current Compensation
 
Eliminate Gibb's artifact (Border ringing) for sharp images. Means of reducing the influence of eddy currents on pulsed gradient fields by employing an electrical preemphasis in the gradient amplifiers. Usually multiple time constants have to be used to correct for eddy current effects in various structures of the MR system such as the cryoshields and RF-shields.

See also Eddy Currents and Shielded Gradient Coils.
spacer

• View the DATABASE results for 'Eddy Current Compensation' (4).Open this link in a new window

 
Further Reading:
  Basics:
Generic Eddy Current Compensation for Rapid Magnetic Resonance Imaging(.pdf)
   by www.switt.ch    
Searchterm 'Gradient' was also found in the following services: 
spacer
Radiology  (1) Open this link in a new windowUltrasound  (3) Open this link in a new window
Eddy CurrentsForum -
related threadsInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.
 
Electric currents induced in a conductor by a changing magnetic field or by motion of the conductor through a magnetic field.
One of the sources of concern about a potential hazard to subjects in very high magnetic fields or rapidly varying gradient or main magnetic fields. Can be a practical problem in the cryostat of superconducting magnets. Eddy currents can cause artifacts in images and may seriously degrade overall magnet performance. Common means to reduce the influence of eddy currents on gradient fields are eddy current compensation and shielded gradient coils (active or passive).

See also Eddy Current Compensation.

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

• View the DATABASE results for 'Eddy Currents' (8).Open this link in a new window

 
Further Reading:
  Basics:
Electrical eddy currents in the human body: MRI scans and medical implants
   by www.phy.olemiss.edu    
MRI Resources 
Jobs pool - MRI Technician and Technologist Jobs - Directories - Developers - Nerve Stimulator - Shielding
 
previous      86 - 90 (of 311)     next
Result Pages : [1 2 3 4 5 6 7 8 9 10 11 12]  [13 14 15 16 17 18 19 20 ... ]
 Random Page
 
Share This Page
FacebookTwitterLinkedIn

MR-TIP    
Community   
User
Pass
Forgot your UserID/Password ?    



How AI will impact MRI :
only diagnostics 
saving time 
reducing cost 
makes planning obsolete 
reduce human knowledge 
not at all 

Look
      Ups





MR-TIP.com uses cookies! By browsing MR-TIP.com, you agree to our use of cookies.

Magnetic Resonance - Technology Information Portal
Member of SoftWays' Medical Imaging Group - MR-TIP • Radiology-TIP • Medical-Ultrasound-Imaging • 
Copyright © 2003 - 2024 SoftWays. All rights reserved. [ 28 March 2024]
Terms of Use | Privacy Policy | Advertising
 [last update: 2024-02-26 03:41:00]