EP0216404A1
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Magnetic resonance imaging apparatus including-homogenizing magnetic elements
Assignee: Koninklijke Philips NV
•
Filing: 1986-08-04
•
Granted: —
•
Expires: 2006-08-04
Abstract
Abstract In a magnetic resonance imaging apparatus having a comparatively large measurement region, such as used for medical diagnosis, high-order contributions to the magnetic field are compensated for by the addition of pairs of rings made of a soft-magnetic material, so that the homogeneity of the magnetic field is locally increased to a high degree. By taking this possibility into account in designing the magnet, a substantially shorter coil is obtained whilst the field homogeneity in the measurement zone is still improved.
Inventors
- 👤 Ewoud Vreugdenhil
- 👤 Franciscus Ferdinand Van Der Vlugt
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 11:24
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/28; G01R33/38; G01R33/387; G01R33/3873
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
58 words
A magnetic resonance imaging apparatus which includes a magnet system for generating a steady magnetic field in a measurement space situated within the magnet system and having an increased spatial field homogeneity, characterized in that within the magnetic system there is provided a magnetic material which increases the spatial field homogeneity also for errors beyond the fourth order.
Claim 2
Dependent Claim
58 words
A magnetic resonance imaging apparatus which includes a magnet system for generating a steady magnetic field in a measurement space situated within the magnet system and having an increased spatial field homogeneity, characterized in that within the magnetic system there is provided a magnetic material which increases the spatial field homogeneity also for errors beyond the fourth order.
Claim 3
Dependent Claim
32 words
A magnetic resonance imaging apparatus as claimed in Claim 1, characterized in that the magnetic material is provided on an inner side of a carrier for coils of an electromagnetic magnet system.
Claim 4
Dependent Claim
34 words
A magnetic resonance imaging apparatus as claimed in Claim 1, characterized in that the magnetic material is provided in a carrier of a further electromagnetic coil included in the magnet system of the apparatus.
Claim 5
Dependent Claim
31 words
A magnetic resonance imaging apparatus as claimed in Claim 2, characterized in that the magnetic material is provided in recesses formed in an inner side of a cylindrical gradient coil carrier.
Claim 6
Dependent Claim
32 words
A magnetic resonance imaging apparatus as claimed in Claim 2, 3 or 4, characterized in that the magnetic material is provided in the magnet system in the form of coaxial, ring-shaped elements.
Claim 7
Dependent Claim
30 words
A magnetic resonance imaging apparatus as claimed in Claim 5, characterized in that the ring-shaped elements of magnetic material are sub-divided into a plurality of sector arcs by azimuthal interruptions.
Claim 8
Dependent Claim
27 words
A magnetic resonance imaging apparatus as claimed in any one of the preceding Claims, characterized in that the magnetic material is formed by stacks or wire-shaped material.
Claim 9
Dependent Claim
31 words
A magnetic resonance apparatus as claimed in any one of the Claims 1 to 6, characterized in that the magnetic material is arranged substantially in the form of coaxially oriented strips.
Claim 10
Dependent Claim
37 words
A magnetic resonance imaging apparatus as claimed in any one of the preceding Claims, characterized in that the magnetic material comprises at least three pairs of ring-shaped elements which are adjacently situated, viewed in the axial direction.
Claim 11
Dependent Claim
35 words
A magnetic resonance imaging apparatus as claimed in any one of the Claims 5 to 9, characterized in that coaxially arranged ring-shaped elements of magnetic material are situated at different axial distances from one another.
Claim 12
Dependent Claim
35 words
A magnetic resonance imaging apparatus as claimed in any one of the Claims 5 to 9, characterized in that coaxially situated ring-shaped elements of magnetic material are situated at different radial distances from one another.
Claim 13
Dependent Claim
25 words
A magnetic resonance imaging apparatus as claimed in any one of the preceding Claims, characterized in that the magnetic material consists mainly of ferromagnetic material.
Claim 14
Dependent Claim
30 words
A magnetic resonance imaging apparatus as claimed in any one of the Claims 1 to 11, characterized in that the homogenizing magnetic material consists at least partly of premagnetized material.
Claim 15
Dependent Claim
55 words
A magnetic resonance imaging apparatus as claimed in any one of the preceding Claims, characterized in that within a magnet system having an axial dimension of less than 150 cm there can be generated a spherical measurement region having a diameter of at least 50 cm and a field homogeneity of less than 25 ppm.
Claim 16
Dependent Claim
88 words
A method of improvind the spatial homogeneity of a steady magnetic field in a measurement space within a magnet system of a magnetic resonance imaging apparatus as claimed in Claim 1, characterized in that a measurement space within the magnet system there are performed magnetic field intensity, coefficients of different order of a field intensity polynomial which describes the steady magnetic field, being determined therefrom in order to determine the position and the quantity of ferromagnetic material to be provided within the magnet system and in the magnet.
Claim 17
Dependent Claim
23 words
A method as claimed in Claim 13, characterized in that the magnetic field measurements are performed on a surface of a measurement space.
Claim 18
Dependent Claim
41 words
A method as claimed in Claim 13 or 14, characterized in that there is selected a number of field measurement points which is adapted to the order of magnitude of the terms of the field polynomial whereto the field is homogenized.
Claim 19
Independent Claim
31 words
A method as claimed in any one of the Claims 13 to 15, characterized in that the field measurements are at-least also used for reducing field inhomcgeneities by mutual compensation thereof.
Claim 20
Independent Claim
50 words
A method as claimed in any one of the Claims 13 to 16, characterized in that a non-homogenizing magnet is first optimized as regards further requirements while permitting spatial field inhomogeneities, after which the field homogeneity occuring is reduced by means of ferromagnetic material-to be introduced into the magnet system.
Claim 21
Dependent Claim
31 words
A method as claimed in Claim 19, characterized in that optimizing is aimed at an internal diameter and length of the magnet system which are optimally adapted to the intended use.
Claim 22
Independent Claim
48 words
A method as claimed in any one of the Claims 15 to 20, characterized in that in order to compensate for zonal disturbances, substantially ring-shaped correction elements which are to be coaxially oriented about an axis of the magnet system are determined and introduced into the magnet system.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.