Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
1999-04-29
2001-03-06
Williams, Hezron (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S300000, C324S307000, C335S306000, C335S297000
Reexamination Certificate
active
06198286
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a magnet structure, particularly for Nuclear Magnetic Resonance imaging machines and of the type comprising a bearing structure for generating magnetic fields inside a volume, a cavity or similar space, defined by the structure.
The invention particularly relates, but is not limited, to magnet structures for Nuclear Magnetic Resonance imaging machines of the type known as dedicated machines, i.e., designed for Nuclear Magnetic Resonance imaging of individual parts of the body, and in which the volume or cavity are such that they generally do not house therein the whole patient, or a considerable part thereof, but only the part limited to one of a few limbs or body regions.
One aspect of the invention relates to magnet structures for permanent magnets.
2. Description of Related Art
Prior art magnet structures have a bearing structure generally made of a ferromagnetic or high-permeability material, with layers of magnetized material, eventually associated with further layers of a more or less permeable material, being fixed thereto in a predetermined position. Although, in dedicated machines, the magnet structure is dimensionally reduced, it is still considerably large.
The fabrication of magnets also requires a high accuracy in dimensioning and mutually positioning the parts forming the structure. This requirement is urged by the fact that, inside the relevant volume wherein the body or the part thereof under examination has to be received, the magnetic field must have high homogeneity characteristics.
The manufacture of the parts forming the magnet structure with the required high accuracy in shape and dimensions and the considerable size of said parts are contrasting needs, which may be integrated only with a considerable cost increase.
OBJECT AND SUMMARY
An object of the invention is to provide a magnet structure having such a construction as to ensure a high accuracy in the fabrication of the individual parts forming it and a considerable reduction of fabrication costs.
The invention achieves the above objects by providing a magnet structure of the type described hereinbefore, in which at least the bearing structure and/or at least a part of the other construction elements are modular.
The bearing structure may comprise, for example, one or more plates, depending on geometry, which may be mutually fastened by fastening means provided in a predetermined position and adjustable by centering means.
The plates may be joined together in such a way as to obtain several configurations.
Generally, a closed annular structure may be obtained, in which the plates are connected in such a way as to form a rectangular or polygonal section, or an inverted U-shaped or C-shaped open structure. Here, at least one or two, or even three of the plates of which the closed annular structure is made may be used.
The bearing structure may advantageously form the yoke for enclosing the magnetic flux, whereas the magnetic flux itself may be generated by magnetic means of any type, attached to the inner and/or outer faces of the plates.
In accordance with a further characteristic, the means for generating the magnetic field may also have a modular structure. Especially, this modular structure has a limited number of basic pieces which, when combined together, form the means for generating the magnetic field, said basic pieces being advantageously dimensioned as preferably rational submultiples of the dimensions of the areas whereat they are attached to the plates which form the bearing structure.
A further improvement provides that the basic pieces of the means for generating the magnetic field may be further fastened to support bases, the support being as large as a rational submultiple which is greater than that of the basic elements, so as to form intermediate modular elements, i.e., comprising a certain predetermined number of basic pieces and designed to form the field generating element, in combination with other modular intermediate elements.
Particularly in permanent magnets, the field generating means have at least one pole, which is composed of one or more layers of basic pieces made of a permanently magnetized or magnetizable material, having the shape of parallelepipeds, with a very small number of different sizes, i.e., with a single standard size for most required basic pieces and with a very small number of special basic pieces.
In combination with said basic pieces, there are provided bases for supporting them, all of the same size, which size corresponds to a rational submultiple of the area whereat they are attached to the bearing structure, each of them being meant to bear a predetermined number of identical basic pieces and possibly a predetermined number of special basic pieces.
The material forming the basic pieces, of standard or special size, may be permanently magnetized prior to assembly or may be magnetized after the assembly of the bearing structure.
According to a further characteristic, the bearing structure and the field generating means or the modular elements composing them, or the bases for the intermediate modules may have means for preventive restrained joint attachment, providing at least one and/or, limited to predetermined tolerances, even two or three degrees of freedom. Said means may consist of undercut complementary guides, provided on the bearing structure and on the field generating means, or vice versa, or even restrained joints between adjacent modular elements which form the magnetic field generating elements.
A further characteristic of the invention consists in that the means for fastening the individual elements together may be positioned so as to allow direct access thereto from the outer peripheral sides of the bearing structure, in such a way that an easy and quick fastening action is allowed.
In combination with the above provisions, it is also possible to provide means for inserting parts of the magnet structure, which parts may be modularly assembled outside said structure, and attached thereto while being substantially joined together.
Thanks to the arrangements according to the invention, several different magnet structures may be provided with a very small number of construction parts, which may be used, at least partially, for the different possible configurations of the structure. All the modular elements may be easily fabricated in the form of bars or plates having multiple dimensions with respect to those of the individual pieces, which are obtained by being subsequently cut therefrom. This is particularly advantageous for basic elements made of permanently magnetized or magnetizable material, which is very expensive and whose processing is also expensive. By providing that most of the field generating elements is composed of said basic elements, a considerably greater number of pieces is provided for one or only a few sizes, thus involving a reduction of the fabrication cost per piece and a considerable reduction of the unused materials in stock, which form an unused or anyway tied up capital.
The provision of the different configurations will substantially depend on the need to provide, besides the standard basic pieces shared by the different configurations, also a few special dedicated elements for integrating the standard basic pieces or other standard modular parts of the structure.
As for the quality of the magnetic field obtained therefrom, the modular construction involves no problem, since the possible tolerances, even as regards positioning, may destroy each other, or may be counted among the aberrations and errors found anyway in any type of structure with any type of construction.
Moreover, for example, with reference to the basic pieces made of a permanently magnetized or magnetizable material, even the possible dimensional tolerances causing the formation of interstices between said basic pieces have been observed to be without particular consequences for the field, especially when the support bases for the intermediate modules, if there are any
Coscia Gianluca
Sanfilippo Carlo
Trequattrini Alessandro
Burns Doane Swecker & Mathis L.L.P.
Esaote S.p.A.
Shrivastav Brij B.
Williams Hezron
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