| 摘要 |
<p>In order to control the magnetic field in a permanet magnet arrangement for magnetic resonance imaging comprising opposing permanent magnet assemblies, a temperature sensor (5) is provided in each of the permanent magnetic material which is connected to a respective electronic circuit (6) which provides current to a thermoelectric heat pumping device (7) connected to the permanent magnetic material. In this way the temperature of the permanent magnetic material is controlled and therefore the field of the magnet is controlled. Each of the permanent magnetic assemblies may be of disc shaped and each disc may have an inner ring (9) and outer ring (8). If the permanent magnetic material has a negative temperature coefficient then a higher temperature on the outer ring rather than the inner ring will result in a positive second order field shape. The present invention avoids the use of correction coils and/or shimming elements and also avoids the need for the use of high specification power supplies to control the magnetic field.</p> |
