Magnetic resonance imaging with integrated poleface features

A magnetic resonance imaging scanner comprising:

• a pair of opposing pole pieces disposed symmetrically about an imaging volume facing one another, said pair of opposing pole pieces including:
• a first ferrous pole piece having a front side facing the imaging volume and a back side;
• and,
• a second ferrous pole piece having a front side facing the imaging volume and a back side;
• a source of magnetic flux which generates a magnetic flux through the imaging volume, and the pair of opposing pole pieces;
• a number of annular hoops of permanently magnetized material integrated with the pair of opposing pole pieces for homogenizing the magnetic flux through the imaging volume.

A magnetic resonance imaging scanner comprising:

• a pair of opposing pole pieces disposed symmetrically about an imaging volume facing one another, said pair of opposing pole pieces including;
• a first ferrous pole piece having a front side facing the imaging volume and a back side;
• second ferrous pole piece having a front side facing the imaging volume and a back side;
• a number of annular hoops integrated with the pair of opposing pole pieces for homogenizing the magnetic flux through the imaging volume, said annular hoops being made of a material different from a remainder of the pole pieces and selected from a group consisting of neodymium boron iron, and samarium cobalt
• a source of magnetic flux which generates a magnetic flux through the imaging volume and the pair of opposing pole pieces.

A pole piece assembly for homogenizing a main magnetic field produced in an examination region of a magnetic resonance imaging apparatus;

• said magnetic resonance imaging apparatus having at least one magnet for generating said main magnetic field through said examination region;
• a couch which supports a subject to be examined within said examination region;
• a gradient coil assembly which generates substantially linear magnetic gradients across said main magnetic field in said examination region;
• a radio frequency coil disposed adjacent said examination region for transmitting radio frequency signals into said examination region and selectively exciting dipoles disposed therein;
• a radio frequency transmitter for driving said radio frequency coil;
• a receiver which receives magnetic resonance signals from resonating dipoles within said examination region;
• and, an image processor which reconstructs an image representation from received magnetic resonance signals for display on a human-readable display;
• said pole piece assembly comprising:
• a first ferrous pole piece positioned on a first side of said examination region, said first pole piece having a front side facing said examination region and a back side;
• and,
• an array of annular hoops arranged on or near said first pole piece, said annular hoops being made from a material having a different magnetic susceptibility from that of said first pole piece such that the hoops have a different magnetization from the first pole piece in the presence of the magnetic field.

A pole piece assembly for homogenizing a main magnetic field produced in an examination region of a magnetic resonance imaging apparatus;

• said magnetic resonance imaging apparatus having at least one for generating said main magnetic field through said examination region;
• a support which supports an object to be examined within said examination region;
• a radio frequency coil disposed adjacent said examination region for transmitting radio frequency signals into said examination region and selectively exciting dipoles disposed therein;
• a radio frequency transmitter for driving said radio frequency coil;
• a receiver which receives magnetic resonance signals from resonating dipoles within said examination region;
• said pole piece assembly comprising:
• a first ferrous pole piece positioned on a first side of said examination region, said first pole piece having a front side facing said examination region and a back side;
• and,
• an array of annular hoops arranged on or near said first pole piece, said annular hoops being made from a material having at least one magnetic property different from that of said first pole piece and at least one of said array of annular hoops being made out of a permanent magnet material.

A method of homogenizing a magnetic field in an imaging volume of a magnetic resonance imaging scanner comprising:

• (a) defining a pair of parallel circularly symmetrical circular-shaped regions arranged symmetrically with respect to one another on opposite sides of the imaging volume;
• (b) defining spaced arrays of concentric annular hoops in the circular-shaped region, the annular hoops having a higher magnetic susceptibility than other material occupying the circular-shaped regions;
• and,
• (c) generating a magnetic field in the imaging volume and improving a homogeneity of the magnetic field in the imaging volume with differential magnetic effects from the high susceptibility annular hoops.

A method of homogenizing a magnetic flux in an examination volume of a magnetic resonance scanner comprising:

• (a) cutting annular grooves in a pair of circular-shaped ferrous pole elements;
• (b) at least partially filling the annular grooves with at least one material that has a magnetic property different from the ferrous pole elements, to vary at least one magnetic property at the annular grooves relative to a remainder of the pole elements;
• (c) positioning the pair of circular-shaped ferrous pole elements symmetrically with respect to one another on opposite sides of the examination volume;
• (d) generating the magnetic field in the examination volume between the pole elements.