Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2002-09-27
2004-01-06
Arana, Louis (Department: 2859)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S319000
Reexamination Certificate
active
06674284
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a magnetic resonance apparatus of the type having an “open” imaging volume.
2. Description of the Prior Art
The technique of magnetic resonance is a known technique for obtaining images of a body interior of an object under examination. Rapidly switched gradient fields that are produced by a gradient coil system are superimposed in a magnetic resonance apparatus on a static basic magnetic field that is produced by a basic field magnet. The magnetic resonance apparatus also has a radio-frequency system that emits radio-frequency signals into the object under examination in order to trigger magnetic resonance signals, and picks up the triggered magnetic resonance signals on the basis of which magnetic resonance images are created.
A gradient coil of the gradient coil system produces, for a specific direction in space a gradient field that has, in the ideal case, at least inside an imaging volume of the magnetic resonance apparatus, one field component which is collinear with the basic magnetic field. The field component has in this case a prescribable gradient that is approximately of the same magnitude at any desired instant, at least inside the imaging volume, in a fashion dependent on location. Since the gradient field is a temporally variable magnetic field, although the above is true for any instant, the strength of the gradient is variable from one instant to another instant. The direction of the gradient is generally permanently prescribed by the design of the gradient coil. Appropriate currents are created in the gradient coil in order to produce the gradient field. The amplitudes of the required currents are several 100 A. The rates of current rise and fall are several 100 kA/s. The gradient coils are connected to gradient amplifiers for the purpose of power supply.
A magnetic resonance machine with a C-shaped basic field magnet for producing a vertically directed basic magnetic field is known, for example, from German OS 40 37 894. The basic field magnet has two pole shoes between which an imaging volume of the magnetic resonance machine is arranged. In this case, access to the imaging volume in the horizontal direction is limited only by a yoke of the basic field magnet, and so the imaging volume is freely accessible in an angular range of approximately 270° with reference to a midpoint of the imaging volume. As a result of which the magnetic resonance machine is particularly suitable, owing to its open design, both for interoperative and intraoperative use and for examining patients with claustrophobia. In this arrangement, gradient coils designed as flat coils are laid in recesses in the pole plates in order to produce gradient fields.
Also known, for example from U.S. Pat. No. 4,829,252, is a magnetic resonance apparatus having a horizontally preceding basic magnetic field, with a basic field magnet essentially formed by two pole plates that extend in the vertical direction and that are spaced apart in the horizontal direction, and which are interconnected by four horizontally proceeding columns. An imaging volume situated at the center of the basic field magnet is accessible in the horizontal direction only from the two sides that are not blocked by the pole plates. The gradient coils are designed, in turn, as flat coils and are fastened on the sides of the pole plates, which face the imaging volume.
Also known from the above-named U.S. Pat. No. 4,829,252 is a magnetic resonance apparatus in which an imaging volume is arranged in a tunnel-like examination space such that the imaging volume is accessible only from the two tunnel openings. Here, the tunnel-like examination space is formed substantially by a hollow cylindrical, generally superconducting basic field magnet having a cavity in which a likewise hollow cylindrical gradient coil system is arranged. The basic field magnet produces a horizontally directed basic magnetic field in the examination space.
SUMMARY OF THE INVENTION
An object of the present invention is to create a highly efficient gradient coil system for a so-called open magnetic resonance apparatus having a basic magnetic field in the horizontal direction.
The object is achieved according to the invention in a magnetic resonance apparatus having a magnet arrangement which generates a basic magnetic field in a horizontal direction, an imaging volume with central region that is freely accessible in at least one horizontal direction substantially orthogonal to the basic magnetic field, upper and lower elements that are spaced apart in a vertical direction and between which the imaging volume is disposed, a connector element that connects the upper and the lower elements, and at least one gradient coil, which extends at least in sub-regions of the upper element, the lower element and the connector element.
Owing to the higher efficiency of the gradient coil composed to a comparable gradient coil of the type known in the prior art in which, in particular, the connector element is not used, advantages result with respect to the inductance of the gradient coil, the required installation volume, behavior in terms of waste heat and noise, and behavior of the gradient coil as an eddy current generator.
REFERENCES:
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patent: 5963117 (1999-10-01), Ohashi et al.
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Arana Louis
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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