Diagnostic magnetic resonance apparatus having a radio frequency shield between the radio frequency antenna and the gradient coil system

• US 5,574,372 A
• Filed: 01/18/1995
• Issued: 11/12/1996
• Est. Priority Date: 01/19/1994
• Status: Expired due to Term

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Oppelt, Ralph, Moritz, Michael, Duerr, Wilhelm
• Primary Examiner(s): O'Shea, Sandra L.
• Assistant Examiner(s): MAH, RAYMOND
• Application Number:
  US08/374,028
• Time in Patent Office: 664 Days
• Field of Search: 324/318, 324/322, 324/300, 324/314, 335/298, 335/301, 128/653.5
• US Class Current: 324/318
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: G01R 33/422 of the radio frequency field

Abstract

In a diagnostic magnetic resonance apparatus having an examination space, a radio-frequency antenna and a gradient coil system, the radio-frequency antenna is arranged closer to the examination space than is the gradient coil system. A radio-frequency shield arranged between the radio-frequency antenna and the gradient coil system, and has a first electrically conductive layer arrangement and a second electrically conductive layer arrangement arranged lying opposite the first arrangement, these being separated from one another by a dielectric. The layer arrangements have interconnects arranged side-by-side that are separated from one another by electrically insulating slots. The slots of the first layer arrangement are arranged offset relative to the slots in the second layer arrangement. Neighboring interconnects in at least one layer arrangement are connected to one another via bridges that conduct high-frequency currents, the bridges being arranged such that currents induced in the layer arrangement by the radio-frequency antenna can essentially flow only between the neighboring interconnects via the bridges.

Claims

1. A diagnostic magnetic resonance apparatus comprising:

means for defining an examination space for accepting at least part of an examination subject;

means for generating a basic magnetic field in said examination space;

gradient coil means for generating a plurality of gradient magnetic fields in said examination space superimposed on said basic magnetic field;

radio frequency antenna means for transmitting excitation pulses into said examination subject in said examination space in the presence of said basic magnetic field and said gradient fields, and thereby causing said examination subject to produce magnetic resonance signals, and for receiving said magnetic resonance signals, said radio-frequency antenna means being disposed closer to said examination space than is said gradient coil means; and

a radio-frequency shield disposed between said radio-frequency antenna means and said gradient coils means, said radio-frequency shield comprising a first electrically conductive layer and a second electrical conducive layer disposed opposite said first electrical conductive layer, a dielectric disposed between said first and second electrically conductive layers, each of said first and second electrically conductive layers having a plurality of interconnects disposed side-by-side and separated from each other by electrically insulating slots, said slots in the respective first and second electrically conductive layers being disposed offset relative to each other, and adjacent interconnects in at least one of said first and second electrically conductive layers being connected to each other by respective bridges which conduct high-frequency currents, said bridges being disposed in an arrangement preventing inducement of ring currents, having a resonant frequency approximating an operating frequency of the magnetic resonance apparatus, over a plurality of said interconnects, said bridges being disposed on the as least one electrically conductive layer causing currents induced in said at least one electrically conductive layer by said radio-frequency means to flow between said adjacent interconnects substantially only via said bridges.

2. A magnetic resonance diagnostic apparatus as claimed in claim 1, wherein at least some of said bridges comprise pieces of metal foil.

3. A magnetic resonance diagnostic apparatus as claimed in claim 1 wherein at least some of said bridges are formed by capacitors.

4. A magnetic resonance diagnostic apparatus as claimed in claim 1 wherein at least some of said bridges are connected to said interconnects by soldered connections.

5. A magnetic resonance diagnostic apparatus as claimed in claim 1 wherein said first and second electrically conductive layers and said dielectric comprise at least one printed circuit board, and wherein at least some of said bridges are unitarily constructed with said interconnects.

6. A magnetic resonance diagnostic apparatus as claimed in claim 1 wherein said interconnects are disposed parallel to each other.

7. A magnetic resonance diagnostic apparatus as claimed in claim 1 wherein only said one of said electrically conductive layers has said bridges, and wherein said only one electrically conductive layer faces toward said radio-frequency antenna means.