Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterized by the complete absence of electrical resistance and the damping of the interior magnetic field. A ideal superconductor can carry an electrical current without experiencing energy losses (resistance, heat). The resistance of superconducting wire is nearly equal to zero at temperature near to absolute zero (-273.15° C or 0 K). This temperature is usually established by using liquid helium.

See also Superconducting Magnet, and Cryogen.

[B₀] A conventional symbol for the main magnetic field strength (magnetic flux density or induction) in a MRI system. Although historically used, H0 (units of magnetic field strength, ampere//meter) should be distinguished from the more appropriate B0 [units of magnetic induction, tesla].
In current MR systems it has a constant value over time varying from 0.02 to 4 T. Field strengths of 0.5 T and above are generated with superconductive magnets. High field strengths have a better signal to noise ratio (SNR). The optimal imaging field strength for clinical imaging is between 0.5 and 2.0 T.

See also the related poll result: 'In 2010 your scanner will probably work with a field strength of'

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 (-268.8° 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 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'

The company is a leading manufacturer and developer of magnetic resonance imaging (MRI) scanners. The Patient Friendly MRI Company, formed in 1978, is engaged in the business of inventing, manufacturing, selling and servicing magnetic resonance imaging (MRI) scanners. FONAR is the oldest MRI company in the world. After receiving hundreds of millions in a windfall from protecting their MRI patents, they made a MRI scanner that no other MRI manufacturer has. One that the patient stands in and they call Indomitable, the Stand-Up MRI. Patients like it because it is the least claustrophobic, most comfortable MRI on the market. Doctors like it because of its superior image quality and for the first time, the patient can be scanned in the weight-bearing position, or the position of pain or symptom. In October of 2004, the company changed the product name of the Stand-Up MRI to the Upright MRI. Fonar introduced the first "open" MRI scanner in 1980 and is the originator of the iron-core nonsuperconductive and permanent magnet technology.

MRI Scanners:

- 0.6T:

From Siemens Medical Systems;
the MAGNETOM Rhapsody™. This open MRI system offers the proven image quality of 1.0 Tesla. In addition to the resulting broad range of applications, the open magnet of the high field system MAGNETOM Rhapsodyâ„¢ facilitates examination of claustrophobic and pediatric patients. And the system allows for expanded interventional applications.