Magnetic resonance imaging (MRI) system having a synchronized cryocooler
Publication Date: 2003-Apr-07
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Magnetic resonance imaging (MRI) system having a synchronized cryocooler � � � � � �
We describe a magnetic resonance imaging (MRI) system comprising a superconducting main magnet system for generating a uniform main magnetic field in an examination volume of the system. An essential part of the main magnet system is the cryocooler, which is used to cool the radiation shields of the main magnet system and to recondense the helium present in the main magnet system.
The cryocooler has moving internal parts, which constitute a source of distortions of the magnetic field in the examination volume. The reason is that the moving parts have conducting and/or magnetic materials, and field distortions arise as a result of the eddy currents induced in the conducting materials and as a result of the moving magnetic field of the magnetic materials. Furthermore, the moving parts lead to vibrations which are transmitted to other portions of the MRI system, and field distortions arise as a result of the eddy currents induced in these other portions when they vibrate in the magnetic field.
As said distortions are synchronous with the movement of the moving internal parts of the cryocooler, the distortions can be reduced or even prevented by synchronizing the moving internal parts of the cryocooler and the scanning process of the MRI system. This can be achieved in several ways.
In a first example of an embodiment, a trigger signal is derived from the cryocooler and is supplied to the contro...