MR apparatus and gradient saturation method for suppressing MR signals from peripheral regions situated outside an isocenter
AssigneeKoninklijke Philips Electronics N.V.
InventorsBernd Aldefeld, Johannes Adrianus Overweg
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Abstract
The invention relates to an MR method wherein disturbing MR signals from peripheral regions outside the isocenter are suppressed in that a location-dependent, brief, steady magnetic field is produced simultaneously with an RF pulse. When the field strength of the magnetic field in the peripheral regions is either larger or smaller than that at the isocenter, it can be achieved that exclusively the nuclear magnetization in the peripheral regions is excited, which magnetization can subsequently be dephased. The subsequent MR sequence then influences only the region around the isocenter.
Claims6
An MR method for suppressing MR signals from peripheral regions situated outside a specified FOV region proximate an isocenter of a main field magnet, said method comprising:
- a) generating a location-dependent magnetic field (Bsat) pulse with use of a saturation coil system, the saturation coil system being separate and distinct from the main field magnet, the location-dependent magnetic field (Bsat) pulse having a field strength in the peripheral regions situated outside the FOV region proximate the isocenter of the main field magnet either larger or smaller than the location-dependent magnet field pulse's field strength at the isocenter of the main field magnet, wherein the saturation coil system includes three coaxial coil sections which are offset in space and that, in an operating condition, the direction of the current in a central coil section of the saturation coil system opposes that of the currents in two outer coil sections of the saturation coil system;
- b) generating at least one RF pulse (RF1) with the use of an RF coil during an application of the magnetic field pulse generated by the saturation coil system, wherein the RF pulse excites a nuclear magnetization in the peripheral regions situated outside the FOV region proximate the isocenter of the main field magnet but not in the FOV region around the isocenter;
- and
- c) dephasing the excited nuclear magnetization utilizing one of magnetic field gradients Gx, Gy, and Gz of a gradient coil system, wherein the gradient coil system is separate and distinct from the main field magnet and the saturation coil system.
An MR apparatus including a main field magnet for generating a uniform, steady magnetic field, said apparatus further comprising:
- a saturation coil system in addition to said main field magnet, said saturation coil system for generating a location-dependent magnetic field of a limited duration which can be superimposed on the uniform magnetic field of the main field magnet, and whose field strength in the peripheral regions situated outside a FOV region proximate an isocenter of the main field magnet is either larger or smaller than its field strength at the isocenter of the main field magnet, wherein said saturation coil system includes three coaxial coil sections which are offset in space and that, in an operating condition, the direction of the current in a central coil section of said saturation coil system opposes that of the currents in two outer coil sections of said saturation coil system;
- means for generating at least one RF pulse (RF1) during the application of the location-dependent magnetic field generated by said saturation coil system, wherein the RF pulse excites the nuclear magnetization in the peripheral regions situated outside the FOV region proximate the isocenter of the main field magnet but not at the FOV region;
- and
- means for dephasing the excited nuclear spins utilizing one of magnetic field gradients Gx, Gy, and Gz of a gradient coil system, wherein the gradient coil system is separate and distinct from the saturation coil system and the main field magnet.
Dependencies are inferred from the claim text.