摘要 |
The invention relates to a radio-frequent (RF) coil system ( 17, 17' ) for use in a magnetic resonance imaging (MRI) system. The RF coil system comprises at least one main coil ( 35 ) for transmitting an RF magnetic field (B<SUB>1</SUB>) into and/or receiving an RF magnetic field (B<SUB>1</SUB>') from an examination volume ( 3 ) of the MRI system. The main coil has a main coil axis ( 37 ), which is or is to be oriented parallel to a main magnetic field (B<SUB>0</SUB>) in the examination volume, and at least one electrical conductor ( 39, 41 ) which extends mainly parallel to the main coil axis. According to the invention, the RF coil system comprises at least two electrical auxiliary coils ( 51, 53, 55, 57 ) which are assigned to said conductor of the main coil. The auxiliary coils are arranged on opposite sides of said conductor of the main coil. Each auxiliary coil has a coil axis ( 59, 61, 63, 65 ) which extends substantially parallel to the main coil axis at a distance from the conductor of the main coil to which the respective auxiliary coil is assigned, said distance being small relative to a main dimension (L) of the main coil. The auxiliary coils constitute passive electrical coils in which electrical currents are generated under the influence of an RF magnetic field (B<SUB>11</SUB>, B<SUB>11</SUB>') present at the location of the auxiliary coils. The RF magnetic field (B<SUB>12</SUB>, B<SUB>34</SUB>) generated by the auxiliary coils as a result of said currents in the auxiliary coils suppresses said RF magnetic field present at the location of the auxiliary coils. Thus, the auxiliary coils provide a sensitivity reducing effect of the RF coil system in local regions ( 47, 49 ) which are at relatively small distances from the conductor of the main coil. For regions at a distance from the conductor of the main coil comparable to the main dimension of the main coil, said sensitivity reducing effect is negligible.
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