Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Patent
1997-07-30
1999-01-26
Arana, Louis
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
324322, G01V 300
Patent
active
058642358
DESCRIPTION:
BRIEF SUMMARY
The present invention is directed to a nuclear magnetic tomography apparatus having a basic field magnet with an examination space in which at least one gradient coil and one radio-frequency antenna are integrated, with each gradient coil being composed of useful conductors and of connecting conductors as used herein, "useful conductor" means a conductor which is designed to essentially determine the gradient field which is employed in producing a tomographic image.
DESCRIPTION OF THE PRIOR ART
In a nuclear magnetic resonance tomography apparatus, as is known, a basic field magnet is required with which nuclear spins in an examination region are oriented in a specific direction. For the deflection of the nuclear spins in this direction, electromagnetic energy is beamed onto the examination subject with a radio-frequency antenna and--possibly with the same radio-frequency antenna--the arising nuclear magnetic resonance signal is received. U.S. Pat. No. 4,506,224 discloses a simple example of such a radio-frequency antenna. The radio-frequency antenna is thereby composed of individual rods that are connected to ground at one side via capacitors.
Further, magnetic gradient fields are required for the location coding of the arising nuclear magnetic resonance signals, these magnetic gradient fields being generated by a set of gradient coils for each spatial direction (for example, the x, y, z directions of a Cartesian coordinate system). U.S. Pat. No. 4,486,711 discloses a simple exemplary embodiment of such gradient coils. As schematically shown in FIG. 1, therein this basic structure includes a superconductive basic field magnet 1 having a cylindrical opening 1a. The cylindrical opening 1a, which is generally referred to as the "warm bore", is constricted in conventional systems by the gradient coils 2 and the radio-frequency antenna 3 to be introduced within the opening 1a. FIG. 1 also schematically shows a radio-frequency shield 5 that shields the radio-frequency antenna 3 toward the outside. The diameter of the warm bore 1 a is correspondingly larger in view of the elements integrated therein than the patient opening available for the examination. Since the diameter of the patient opening cannot be permitted to fall below a certain minimum dimension in view of the bearing comfort for the patient, the size of the warm bore 1a is determined by the defined patent opening and the thickness of the radio-frequency antenna, the gradient coil and further elements built thereinto. These further built-in elements such as, for example, shim elements for improving the uniformity of the basic magnetic field, are not shown in FIG. 1 for clarity. Compared to the gradient coil and to the radio-frequency antenna, however, these elements occupy far less space.
The outlay therefor becomes higher the warm bore of the magnet becomes larger, particularly due to the higher costs for superconductors.
The above applies analogously to pole shoe magnets wherein radio-frequency antenna and gradient coils are applied onto the pole shoes and the spacing between the pole shoes is essentially defined by the height of the patient opening and the height of radio-frequency antenna and of the gradient coil.
European Application 0 307 981 discloses an integrated arrangement of radio-frequency antenna and gradient coils. The space requirements for these elements should thus be reduced and the energy requirement for the gradient coils should also be reduced. In one embodiment, parts of the radio-frequency antenna thereby lie between turns of the gradient coils. In this arrangement, however, the coupling between the radio-frequency antenna and the gradient coils is problematical.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a nuclear magnet resonance tomography apparatus of the type described above wherein, given a prescribed size of the patient opening, the basic field magnet can be kept optimally small, with the radio-frequency antenna and gradient coils being largely decoupled.
The above object is achieve
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Moritz Michael
Pausch Guenther
Arana Louis
Siemens Aktiengesellschaft
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