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

Out-
      side
 



 
 'Magnetic Field' 
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 'Magnetic Field' found in 5 terms [] and 219 definitions []
previous     11 - 15 (of 224)     next
Result Pages : [1]  [2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 ... ]
Searchterm 'Magnetic Field' was also found in the following services: 
spacer
News  (76)  Resources  (16)  Forum  (18)  
 
Cardiac PacemakerMRI Resource Directory:
 - Safety -
 
A pacemaker is a device for internal or external battery-operated cardiac pacing to overcome cardiac arrhythmias or heart block. All implanted electronic devices are susceptible to the electromagnetic fields used in magnetic resonance imaging. Therefore, the main magnetic field, the gradient field, and the radio frequency (RF) field are potential hazards for cardiac pacemaker patients.
The pacemaker's susceptibility to static field and its critical role in life support have warranted special consideration. The static magnetic field applies force to magnetic materials. This force and torque effects rise linearly with the field strength of the MRI machines. Both, RF fields and pulsed gradients can induce voltages in circuits or on the pacing lead, which will heat up the tissue around e.g. the lead tip, with a potential risk of thermal injury.
Regulations for pacemakers provide that they have to switch to the magnet mode in static magnetic fields above 1.0 mT. In MR imaging, the gradient and RF fields may mimic signals from the heart with inhibition or fast pacing of the heart. In the magnet mode, most of the current pacemakers will pace with a fix pulse rate because they do not accept the heartsignals. However, the state of an implanted pacemaker will be unpredictable inside a strong magnetic field. Transcutaneous controller adjustment of pacing rate is a feature of many units. Some achieve this control using switches activated by the external application of a magnet to open/close the switch. Others use rotation of an external magnet to turn internal controls. The fringe field around the MRI magnet can activate such switches or controls. Such activations are a safety risk.
Areas with fields higher than 0.5 mT (5 Gauss Limit) commonly have restricted access and/or are posted as a safety risk to persons with pacemakers.
mri safety guidance
MRI Safety Guidance
A Cardiac pacemaker is because the risks, under normal circumstances an absolute contraindication for MRI procedures.
Nevertheless, with special precaution the risks can be lowered. Reprogramming the pacemaker to an asynchronous mode with fix pacing rate or turning off will reduce the risk of fast pacing or inhibition. Reducing the SAR value reduces the potential MRI risks of heating. For MRI scans of the head and the lower extremities, tissue heating also seems to be a smaller problem. If a transmit receive coil is used to scan the head or the feet, the cardiac pacemaker is outside the sending coil and possible heating is very limited.
spacer
• For this and other aspects of MRI safety see our InfoSheet about MRI Safety.
• Patient-related information is collected in our MRI Patient Information.

 
• Related Searches:
    • Magnetic Forces
    • MRI Scan
    • Specific Absorption Rate
    • MRI Safety
    • Cardiovascular Imaging
 
Further Reading:
  Basics:
MRI in Patients with Implanted Devices: Current Controversies
Monday, 1 August 2016   by www.acc.org    
Magnetic resonance imaging in patients with cardiac pacemakers: era of MR Conditional designs
Thursday, 27 October 2011   by 7thspace.com    
  News & More:
Newer Heart Devices Safe During MRI
Monday, 23 August 2004   by www.hospimedica.com    
BIOTRONIK debuts pacemaker with continuous MRI sensor
Wednesday, 30 August 2023   by www.medicaldevice-network.com    
Patients with standard pacemakers, ICDs may safely undergo MRIs
Friday, 24 February 2017   by www.cardiovascularbusiness.com    
ITOCHU Named the Exclusive Distributor for ViewRay's MRI-Guided Radiation Therapy System in Japan
Thursday, 22 January 2015   by www.prnewswire.com    
Modern Implantable Heart Devices Safe For Use In MRI Scans
Wednesday, 16 March 2005   by www.sciencedaily.com    
Searchterm 'Magnetic Field' was also found in the following services: 
spacer
Radiology  (9) Open this link in a new windowUltrasound  (2) Open this link in a new window
Diamagnetism
 
Diamagnetism is a form of magnetism that is only exhibited by a substance in the presence of an externally applied magnetic field. It is the result of changes in the orbital motion of electrons due to the application of an externally applied magnetic field. Applying a magnetic field causes a momentary electromotive force (a consequence of Faraday's law), which modifies the electronic orbitals of atoms/molecules in a substance in such a way, that the orbitals produce an induced magnetic field, which opposes the applied field (a consequence of Lenz's law). However, the induced magnetic moment is very small in most everyday materials.
Diamagnets are repelled by magnetic fields. However, since diamagnetism is such a weak property its effects are not observable in every-day life.
However, in Magnetic Resonance Imaging for example barium sulfate suspensions lead with its weak negative magnetic susceptibility to a decrease in signal.

See also magnetism, ferromagnetism, paramagnetism, and superparamagnetism.
spacer

• View the DATABASE results for 'Diamagnetism' (7).Open this link in a new window

 
Further Reading:
  Basics:
Magnet basics
   by my.execpc.com    
Diamagnetism
   by en.wikipedia.org    
MRI Safety Resources 
Nerve Stimulator - Stimulator pool - Claustrophobia - Guidance - Implant and Prosthesis pool
 
Gradient CoilForum -
related threadsInfoSheet: - Coils - 
Intro, 
Overview, 
etc.MRI Resource Directory:
 - Coils -
 
Current carrying coils designed to produce a desired magnetic field gradient (so that the magnetic field will be stronger in some locations than others).
Proper design of the size and configuration of the coils is necessary to produce a controlled and uniform gradient. Three paired orthogonal current-carrying coils located within the magnet that are designed to produce desired gradient magnetic fields, which collectively and sequentially are superimposed on the main magnetic field (B0) so that selective spatial excitation of the imaging volume can occur.
Gradients are also used to apply reversal pulses in some fast imaging techniques. Gradient coils in general vary the main magnetic field, so that each signal can be related to an exact location. The gradient coil configuration for the z-axis consists of e.g., Helmholtz pair coils, and of paired saddle coils for the x- and y-axis.

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

• View the DATABASE results for 'Gradient Coil' (19).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    
HEAD AND NECK MRI GRADIENT COIL DESIGN
Thursday, 26 August 1999   by www.imaging.robarts.ca    
Searchterm 'Magnetic Field' was also found in the following services: 
spacer
News  (76)  Resources  (16)  Forum  (18)  
 
MRI SafetyMRI Resource Directory:
 - Safety -
 
There are different types of contraindications that would prevent a person from being examined with an MRI scanner. MRI systems use strong magnetic fields that attract any ferromagnetic objects with enormous force. Caused by the potential risk of heating, produced from the radio frequency pulses during the MRI procedure, metallic objects like wires, foreign bodies and other implants needs to be checked for compatibility. High field MRI requires particular safety precautions. In addition, any device or MRI equipment that enters the magnet room has to be MR compatible. MRI examinations are safe and harmless, if these MRI risks are observed and regulations are followed.

Safety concerns in magnetic resonance imaging include:
•
the magnetic field strength;
•
possible 'missile effects' caused by magnetic forces;
•
the potential for heating of body tissue due to the application of the radio frequency energy;
•
the effects on implanted active devices such as cardiac pacemakers or insulin pumps;
•
magnetic torque effects on indwelling metal (clips, etc.);
•
the audible acoustic noise;
•
danger due to cryogenic liquids;
•
the application of contrast medium;
mri safety guidance
MRI Safety Guidance
It is important to remember when working around a superconducting magnet that the magnetic field is always on. Under usual working conditions the field is never turned off. Attention must be paid to keep all ferromagnetic items at an adequate distance from the magnet. Ferromagnetic objects which came accidentally under the influence of these strong magnets can injure or kill individuals in or nearby the magnet, or can seriously damage every hardware, the magnet itself, the cooling system, etc.. See MRI resources Accidents.
The doors leading to a magnet room should be closed at all times except when entering or exiting the room. Every person working in or entering the magnet room or adjacent rooms with a magnetic field has to be instructed about the dangers. This should include the patient, intensive-care staff, and maintenance-, service- and cleaning personnel, etc..
The 5 Gauss limit defines the 'safe' level of static magnetic field exposure. The value of the absorbed dose is fixed by the authorities to avoid heating of the patient's tissue and is defined by the specific absorption rate. Leads or wires that are used in the magnet bore during imaging procedures, should not form large-radius wire loops. Leg-to-leg and leg-to-arm skin contact should be prevented in order to avoid the risk of burning due to the generation of high current loops if the legs or arms are allowed to touch. The patient's skin should not be in contact with the inner bore of the magnet.
The outflow from cryogens like liquid helium is improbable during normal operation and not a real danger for patients.
The safety of MRI contrast agents is tested in drug trials and they have a high compatibility with very few side effects. The variations of the side effects and possible contraindications are similar to X-ray contrast medium, but very rare. In general, an adverse reaction increases with the quantity of the MRI contrast medium and also with the osmolarity of the compound.

See also 5 Gauss Fringe Field, 5 Gauss Line, Cardiac Risks, Cardiac Stent, dB/dt, Legal Requirements, Low Field MRI, Magnetohydrodynamic Effect, MR Compatibility, MR Guided Interventions, Claustrophobia, MRI Risks and Shielding.
Radiology-tip.comradRadiation Safety,  Ionizing Radiation
spacer
Medical-Ultrasound-Imaging.comUltrasound Safety,  Absorbed Dose
spacer

• View the DATABASE results for 'MRI Safety' (42).Open this link in a new window


• View the NEWS results for 'MRI Safety' (13).Open this link in a new window.
 
Further Reading:
  Basics:
MRI Safety
2001   by www.fda.gov    
What MRI Sequences Produce the Highest Specific Absorption Rate (SAR), and Is There Something We Should Be Doing to Reduce the SAR During Standard Examinations?
Thursday, 16 April 2015   by www.ajronline.org    
Contrast Agents: Safety Profile
   by www.clinical-mri.com    
  News & More:
How safe is 7T MRI for patients with neurosurgical implants?
Thursday, 17 November 2022   by healthimaging.com    
Newer Heart Devices Safe During MRI
Monday, 23 August 2004   by www.hospimedica.com    
Study: Face Masks Unsafe in MRI Machines
Wednesday, 13 July 2022   by www.laboratoryequipment.com    
COVID-19: Attention shifts to MRI infection control
Thursday, 9 July 2020   by https://www.auntminnieeurope.com/index.aspx?sec=ser§sub=def§pag=dis§ItemID=619012    
FDA Releases New Guidance On Establishing Safety, Compatibility Of Passive Implants In MR Environments
Tuesday, 16 December 2014   by www.meddeviceonline.com    
Modern Implantable Heart Devices Safe For Use In MRI Scans
Wednesday, 16 March 2005   by www.sciencedaily.com    
Searchterm 'Magnetic Field' was also found in the following services: 
spacer
Radiology  (9) Open this link in a new windowUltrasound  (2) Open this link in a new window
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 3600 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.
spacer

• View the DATABASE results for 'Nerve Conductivity' (2).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    
  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 
Case Studies - Veterinary MRI - Non-English - MRCP - Coils - Cardiovascular Imaging
 
previous      11 - 15 (of 224)     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 ?    



MRI is trending to low field magnets :
reduced costs will lead to this change 
AI will close the gap to high field 
only in remote areas 
is only temporary 
never 

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. [ 18 December 2024]
Terms of Use | Privacy Policy | Advertising
 [last update: 2024-02-26 03:41:00]