|
Magnetic
Resonance -
Technology
Information
Portal |
Friday, 10 September 2010 •• |
|
|
 | Info
Sheets |
| | | | | | | | | | | | | | | | | | | | | | |
 | Out-
side |
| | | | |
|
| | | | |
Result : Searchterm 'Celsius' found in 1 term [ ] and 4 definitions [ ]
| | 1 - 5 (of 5) Result Pages : [1] | | | | |
 |
MRI Resources |
|
| | | | | | | |  |
| |
|
The lowest possible temperature that can be obtained, at which all molecular motion discontinues. The unit is written as 0 K or 0 Kelvin, named after William Thomson, who developed the scale and became Lord Kelvin in 1892.
The analogous temperature in other units is:
| |
|
| | | | | |
| |
|
MRI Resources |
|
| | | | | |
|
| |
| Device |   |
| |
|
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 US-TIP.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' |
| | | | | | | | |
 Further Reading: |
Basics:
|
|
News & More:
| | | | | •• There are 29 news about 'Device'. | |
| | |
| |
|
This unit of temperature is still used customarily in the United States.
Definition: 0° is the coldest temperature achieved by using an ice and salt mixture, and 100° is set at the temperature of the human body. On this scale, the freezing point of water turned out to be about 32 °F and the boiling point about 212 °F.
1°F equals 5/9 °C. To convert a temperature in °F to the Celsius scale, first subtract 32° and then multiply by 5/9. In the other direction, to convert a temperature in °C to the Fahrenheit scale, multiply by 9/5 and then add 32°. The unit was defined by the German physicist Fahrenheit.
|
| | | |
| Further Reading: |
News & More:
|
| | |
| |
|
| |
| |
|
(K) The SI unit of temperature.
Definition: One Kelvin is 1/273.16 of the difference between the triple point of water (at exactly 273.16 K) and absolute zero.
The triple point of water is the temperature at which water can exist simultaneously in the gaseous, liquid, and solid states. Absolute zero is the temperature at which all molecular motion discontinues.
0 K is according to -273,15° Celsius and -459° Fahrenheit. |
| | | | | |
| |
|
|
MRI Resources |
|
| | | | | | | 1 - 5 (of 5) Result Pages : [1] |
| |
|
| |
 | Look
Ups |
| |
|
| | [last update: 2010-09-06 01:57:00] |
|
|
bottom
Random Page
top