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Electromagnet
 
A type of magnet that utilizes coils of wire, typically wound on an iron core, so that as current flows through the coil it becomes magnetized. The direction of the magnetic field is parallel to the long axis of the coil. Whole body electromagnets, used in medical imaging (also called resistive) are limited to their field strength, because the weight becomes prohibitively large at high field MRI. The magnetic field shuts down, if the current is switched of. Because this type of magnet generates heat, a good cooling system is essential.
For a stronger magnetic field, the wires must be manufactured of superconducting materials to reduce the power needed to produce the field.

See also Resistive Magnet, Superconducting Magnet and Upright™ MRI
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Further Reading:
  Basics:
What types of magnets are there?
   by my.execpc.com    
  News & More:
'Electromagnetic Wormhole' Possible with Invisibility Technology
Monday, 15 October 2007   by www.brightsurf.com    
Superconductors Face the Future
Wednesday, 15 September 2010   by www.nanotech-now.com    
Searchterm 'Electromagnet' was also found in the following services: 
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Radiology  (22) Open this link in a new windowUltrasound  (3) Open this link in a new window
Electromagnetic Spectrum
 
Continuum of electromagnetic energy.
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MRI Resources 
Diffusion Weighted Imaging - Collections - Crystallography - Case Studies - Open Directory Project - Sequences
 
MagnetForum -
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A magnet is by definition an object with magnetic properties (magnetism) that attracts iron and produces a magnetic field. It can be a permanent magnet or an electromagnet.
Permanent magnets do not rely upon outside influences to generate their field. In permanent magnets are the atoms and molecules ordered in long range. The specific electron configuration and the distance of the atoms is what lead to this long range ordering. The electrons exist in a lower energy state if they all have the same orientation. Magnetic domains can be likened to microscopic neighborhoods in which there is a strong reinforcing interaction between particles, resulting in a high degree of order. The greater the degree of ordering within and between domains, the greater the resulting field will be. Long range ordering is one of the hallmarks of a ferromagnetic material.
A current carrying conductor for example a piece of wire, produces a magnetic field that encircles the wire. An electromagnet, in its simplest form, is a wire that has been coiled into one or more loops. This coil is known as a solenoid. The more loops of wire and the greater the current, the stronger the field will be.
Superconducting magnets are a special type of electromagnets, often used in MRI machines with high field strength.
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Further Reading:
  Basics:
Magnetic Field
   by hyperphysics.phy-astr.gsu.edu    
  News & More:
Philips Signs Research Agreement to Explore New Magnet Technologies
Monday, 5 December 2022   by www.itnonline.com    
Impact of Magnetic Field Inhomogeneity on the Quality of Magnetic Resonance Images and Compensation Techniques: A Review
Saturday, 1 October 2022   by www.dovepress.com    
Magnetic seeds used to heat and kill cancer
Tuesday, 1 February 2022   by www.sciencedaily.com    
Harvard Scientists Create Nanoscale MRI
Monday, 28 April 2014   by www.meddeviceonline.com    
How Academic Research Solved the Puzzle of MRI and CAT Scanning
Monday, 21 April 2014   by www.engineering.com    
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Resistive Magnet
 
A type of magnet that utilizes the principles of electromagnetism to generate the magnetic field. Typically large current values and significant cooling of the magnet coils is required. The resistive magnet does not require cryogens, but needs a constant power supply to maintain a homogenous magnetic field, and can be quite expensive to maintain.
Resistive magnets fall into two general categories - iron-core and air-core.
Iron-core electromagnets provide the advantages of a vertically oriented magnetic field, and a limited fringe field with little, if any, missile effects due to the closed iron-flux return path.
Air-core electromagnets exhibit horizontally oriented fields, which have large fringe fields (unless magnetically shielded) and are prone to missile effects. Resistive magnets are typically limited to maximum field strengths of approximately 0.6T.
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MRI RisksMRI Resource Directory:
 - Safety -
 
The subacute risks and side effects of magnetic and RF fields (for patients and staff) have been intensively examined for a long time, but there have been no long-term studies following persons who have been exposed to the static magnetic fields used in MRI. However, no permanent hazardous effects of a static magnetic field exposure upon human beings have yet been demonstrated.
Temporary possible side effects of high magnetic and RF fields:
Varying magnetic fields can induce so-called magnetic phosphenes that occur when an individual is subject to rapid changes of 2-5 T/s, which can produce a flashing sensation in the eyes. This temporary side effect does not seem to damage the eyes. Static field strengths used for clinical MRI examinations vary between 0.2 and 3.0 tesla;; field changes during the MRI scan vary in the dimension of mT/s. Experimental imaging units can use higher field strengths of up to 14.0 T, which are not approved for human use.
The Radio frequency pulses mainly produce heat, which is absorbed by the body tissue. If the power of the RF radiation is very high, the patient may be heated too much. To avoid this heating, the limit of RF exposure in MRI is up to the maximum specific absorption rate (SAR) of 4 W/kg whole body weight (can be different from country to country). For MRI safety reasons, the MRI machine starts no sequence, if the SAR limit is exceeded.
Very high static magnetic fields are needed to reduce the conductivity of nerves perceptibly. Augmentation of T waves is observed at fields used in standard imaging but this side effect in MRI is completely reversible upon removal from the magnet. Cardiac arrhythmia threshold is typically set to 7-10 tesla. The magnetohydrodynamic effect, which results from a voltage occurring across a vessel in a magnetic field and percolated by a saline solution such as blood, is irrelevant at the field strengths used.

The results of some animal and cellular studies suggest the possibility that electromagnetic fields may act as co-carcinogens or tumor promoters, but the data are inconclusive. Up to 45 tesla, no important effects on enzyme systems have been observed. Neither changes in enzyme kinetics, nor orientation changes in macromolecules have been conclusively demonstrated.
There are some publications associating an increase in the incidence of leukemia with the location of buildings close to high-current power lines with extremely low-frequency (ELF) electromagnetic radiation of 50-60 Hz, and industrial exposure to electric and magnetic fields but a transposition of such effects to MRI or MRS seems unlikely.
Under consideration of the MRI safety guidelines, real dangers or risks of an exposure with common MRI field strengths up to 3 tesla as well as the RF exposure during the MRI scan, are not to be expected.

For more MRI safety information see also Nerve Conductivity, Contraindications, Pregnancy and Specific Absorption Rate.

See also the related poll result: 'In 2010 your scanner will probably work with a field strength of'
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Further Reading:
  Basics:
MRI in Patients with Implanted Devices: Current Controversies
Monday, 1 August 2016   by www.acc.org    
Working with MRI machines may cause vertigo: Study
Wednesday, 25 June 2014   by www.cos-mag.com    
Physics of MRI Safety
   by www.aapm.org    
When Your Kid Needs an MRI: Optimizing the Experience
Tuesday, 29 March 2016   by health.usnews.com    
  News & More:
How safe is 7T MRI for patients with neurosurgical implants?
Thursday, 17 November 2022   by healthimaging.com    
CT contrast reaction raises MRI contrast risk
Tuesday, 22 February 2022   by www.sciencedaily.com    
CSU study explores MRI distress and patient experience
Thursday, 7 May 2020   by www.portnews.com.au    
Noise from Magnetic Resonance Imaging Can Have Short-Term Impact on Hearing
Thursday, 22 February 2018   by www.diagnosticimaging.com    
Women with permanent make-up tattoos suffer horrific facial burns after going in for MRI scans - which create an electric current in the ink
Monday, 4 July 2016   by www.dailymail.co.uk    
FDA Dials in on MRI Safety of Passive Implantable Medical Devices
Wednesday, 24 June 2015   by www.raps.org    
MRI Resources 
MR Myelography - Chemistry - Guidance - Cochlear Implant - IR - Manufacturers
 
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