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 'Permanent Magnet' 
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Permanent Magnet
A magnet whose magnetic field originates from permanently ferromagnetic materials (permanent magnets) to generate a magnetic field between the two poles of the magnet. There is no requirement for additional electrical power or cooling, and the iron-core structure of the magnet leads to a limited fringe field and no missile effect. Due to weight considerations, permanent magnets are usually limited to maximum field strengths of 0.4 T. The main disadvantages of a permanent magnet are the cost of the magnet itself and supporting structures and the varying changes in the magnetic field. Field homogeneity can be an on-going problem in permanent magnets.
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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 neighbourhoods 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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Magnet Stability
Temporal stability of the magnetic field. Factors to be considered are field decay of superconducting magnets in persistent mode, aging of permanent magnet material, temperature dependence of permanent magnet material, and temporal stability of magnet power supplies.
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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'
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ENCORE 0.5T™InfoSheet: - Devices -
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From ISOL Technology
'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
CONFIGURATION Short bore compact
SURFACE COILS 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
PULSE SEQUENCES Spin Echo, Gradient Echo, Fast Spin Echo, Inversion Recovery (STIR, FLAIR), FLASH, FISP, PSIF, Turbo Flash ( MPRAGE ),TOF MR Angiography
IMAGING MODES 2D/3D, Travelling Sat, Multi-Slab 3D, MTC and TONE Pulse Sequence, Fat/Water Suppression, Presaturation (up to 6 bands), Flow Compensation using GMR pulse, Multi-Slice, Multi-Group Imaging
SINGLE/MULTI SLICE Image reconstruction time (2562 ) : 0.02 s
FOV 40 cm
MAGNET TYPE Superconducting
or W x H
58 cm diameter
H*W*D 200 x 168 x 187 cm
COOLING SYSTEM TYPE Air-cooled coil and amplifier
CRYOGEN USE 0.05 L/hr helium
5-GAUSS FRINGE FIELD 2.3 m / 3.1 m
SHIMMING Passive and active


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In 2075 (after about 100 years of ...) the MRI scan will be :
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