Picker International, Inc.

Koninklijke Philips Corporation N.v.

John V M McGinley

Gordon D DeMeester

Ian R Young

Michael Andrew Morich

Ilmari V Kinanen

Gerardus B J Mulder

In a method for aligning a magnetic field-modifying structure ( ) in a magnet bore ( ) of a magnetic resonance imaging scanner ( ), a reference magnetic field map of the magnet bore ( ) is measured without the magnetic field-modifying structure ( ) inserted. The magnetic field-modifying structure ( ) is inserted into the magnet bore ( ). A second magnetic field map of the magnetic bore ( ) is measured with the magnetic field-modifying structure ( ) inserted. At least one odd harmonic component of the first and second magnetic field maps is extracted. The magnetic field-modifying structure ( ) is aligned in the magnet bore ( ) based on a comparison of the odd harmonic component of the first and second magnetic field maps.

Method and apparatus for aligning a magnetic field modifying structure in a magnetic resonance imaging scanner

A pair of annular magnets (,) generate a vertical magnetic flux field through an imaging volume (,). The flux is focused by a pair of Rose rings (,) of high cobalt steel. A high order shim set includes a plurality of permanently magnetized or magnetized iron rings (,) which cooperatively interact with the magnet assembly to optimize the homogeneity of the magnetic flux through the imaging volume. One of the permanent magnetic rings (,), is mounted with an opposite polarity relative to the others. The magnetized rings are mounted in a non-ferrous, electrically insulating support structure (,) such that gradient coils (,) can be positioned behind the permanent magnet rings. A flux return path (,) provides a low flux resistant path from adjacent the Rose ring at one side of the imaging volume remotely around the imaging volume to a position adjacent the Rose ring at the other side of the imaging volume.

MRI magnet with high homogeneity, patient access, and low forces on the driver coils

A region of interest of a subject (,) on a subject support (,) is positioned above a ferrous pedestal (,) that is supported on a ferrous floor yoke portion (,). A lower imaging coil assembly (,) including a lower gradient coil (,), a radio frequency coil (,), and a lower pole piece (,) are disposed between the pedestal and a region of interest of the subject. An upper imaging coil assembly (,) including an annular gradient coil (,) and an upper annular pole piece (,) is supported from a ceiling ferrous yoke member (,). The upper imaging coil assembly is supported by supports (,) which are moved by drives (,) to raise and lower the upper imaging coil assembly. A laser gauging system (,) gauges the position of the upper imaging coil assembly such that, with a control circuit (,), the upper imaging coil assembly is accurately repositioned at preselected imaging positions. A main magnetic field coil (,) is positioned adjacent one of the ceiling ferrous yoke member and the floor ferrous yoke member to provide an asymmetric source of magnetic flux. Pre-polarizing coils (,) are supported on the upper and lower imaging coil assemblies for boosting the magnetic field strength through the region of interest immediately preceding imaging sequences.

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London, United Kingdom

John V M McGinley