Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
1998-11-24
2001-07-10
Oda, Christine (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C029S609000
Reexamination Certificate
active
06259252
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a laminate tile pole piece for an MRI system, a method manufacturing the pole piece and a mold used for bonding a pole piece tiles.
BACKGROUND OF THE INVENTION
In recent years, a so-called laminate tile pole piece has been developed for an MRI. In view of such development, a plan view of the laminate tile pole piece is shown in
FIG. 1A and a
side view is shown in FIG.
1
B. The pole piece
10
comprises a soft iron circular base plate
11
, a soft iron ring
12
around the circumference of the base
11
for directing the magnetic flux into the gap between magnets, soft ferrite laminate tiles
13
and
14
and a soft iron core
15
for mounting a gradient magnetic coil. The laminate tiles
13
,
14
and the core
15
comprise the pole piece face. The laminate tiles
14
in the center of the base plate
11
have a greater thickness than laminate tiles
13
at the periphery of the base plate
11
to form a convex protrusion
16
. The convex protrusion
16
improves the uniformity of the magnetic field.
However, the prior art laminate tile pole piece has several disadvantages. First, most laminate tiles
13
,
14
have a square or rectangular shape. However, the base
11
and the ring
12
have a circular shape. Therefore, in order to fit square or rectangular tiles into a circular opening, edge filler tiles
13
A are required. As shown in
FIG. 1A
, each edge filler tile
13
A has a unique, odd shape to allow the peripheral tiles
13
to completely fill the circular base
11
and ring
12
. Each edge filler tile
13
A must be formed separately from other tiles
13
to create its unique shape. This increases process costs and complexity.
Second, the protrusion
16
also has a circular shape, as shown in FIG.
1
A. Therefore, in order to arrange the square or rectangular central tiles
14
in a circle, edge filler tiles
14
A are required, as shown in
FIGS. 1A and 1B
. The edge filler tiles
14
A also have a unique, odd shape to allow central tiles
14
to form a circular protrusion
16
. Furthermore, in order to allow central tiles
14
to fit with the peripheral tiles
13
without leaving gaps, edge filler tiles
14
A also must have two different thicknesses, as shown in FIG.
1
B. Each uniquely shaped edge filler tile
14
A must also be formed separately from other central tiles
14
. This further increases process costs.
Third, the prior art methods of attaching individual laminate tiles
13
,
14
to the base
11
involve placing the individual tiles onto the base and then poring epoxy over the tiles. However, the epoxy may flow out of the base and coat portions of the pole piece not intended to be coated by epoxy. Some tiles may also be insufficiently coated with the epoxy because the epoxy is not supplied under pressure. These tiles may become delaminated during MRI use. Furthermore, it becomes very difficult to achieve the optimum height for the protrusion
16
by manually stacking tiles
14
onto a base
11
because of human error. Therefore, different pole pieces manufactured by the prior art method suffer from poor reproducibility and have different performance characteristics due to a variance in the height of the protrusion.
SUMMARY OF THE INVENTION
In view of the foregoing, it would be desirable to decrease the manufacturing process cost and complexity by forming a laminated tile pole piece that does not contain oddly shaped edge filler tiles. The present invention provides a pole piece for a magnetic resonance imaging (MRI) system. The pole piece comprises a plurality of trapezoid or annular sector shaped tiles arranged in a plurality of concentric annular arrays.
It would also be desirable to obtain a reproducible and accurate laminate tile pole piece manufacturing process. The present invention provides a method of making a pole piece. The method comprises placing a plurality of tiles into a mold cavity, filling the mold cavity with an adhesive substance to bind the plurality of tiles into a unitary body, removing the unitary body from the mold cavity and attaching a second surface of the unitary body to a pole piece base to form a first pole.
The present invention also provides a mold containing an non-uniform cavity surface for forming a laminate tile pole piece for an MRI system. The mold is made by performing a simulation of magnetic flux density between a first magnet of the MRI system and a second magnet of the MRI system, determining an optimum contour of a first surface of the pole piece based on an optimum value of the magnetic flux density between the first magnet and the second magnet and forming the mold cavity surface contour as a substantial inverse of the optimum contour of the first surface of the pole piece.
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Aksel Bulent
Barber William D.
Laskaris Evangelos T.
Ogle Michele D.
Thompson Paul S.
Fetzner Tiffany A.
Foley & Lardner
General Electric Company
Oda Christine
LandOfFree
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