ACTIVE-PASSIVE ELECTROMAGNETIC SHIELDING TO REDUCE MRI ACOUSTIC NOISE
First Claim
1. A method for reducing acoustic noise in a magnetic resonance imaging device, the method comprising the steps of:
- providing an electrically conductive passive shielding element adjacent an actively shielded gradient coil winding of the device contained within an annular support structure; and
ensuring the actively shielded gradient coil winding is insulated from the passive shielding element,wherein a first portion of the passive shielding element is located adjacent an outer surface of the actively shielded gradient winding and a second portion is located adjacent an end of the actively shielded gradient winding.
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Accused Products
Abstract
The present invention provides an apparatus for reducing acoustic noise in a magnetic resonance imaging device including passive shielding located outside the actively shielded gradient winding elements in order to reduce the magnitude of fields that spread outside the gradient coil assembly in unwanted directions and interact with the magnet cryostat or other metallic magnet parts, inducing eddy currents that cause consequent acoustic noise. The passive shielding elements are conducting layers located on the outer radius of the cylindrical gradient coil assembly in a cylindrical magnet system, conducting layers located at the ends of the gradient coil assembly in a cylindrical magnet system, and conducting layers located inside the actively shielded gradient winding inner elements in a cylindrical magnet system. The passive shielding could also be located on separate structures that are vibrationally isolated from the magnet cryostat. The actively shielded gradient winding can also be extended to portions at the ends of the actively shielded gradient winding and further to portions inside the inner radius of the inner portion of the actively shielded gradient winding. The actively shielded gradient windings and passive shielding should be designed concurrently in order to substantially optimize the gradient linearity and reduce the eddy currents generated in metallic parts of the magnetic resonance imaging system.
30 Citations
19 Claims
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1. A method for reducing acoustic noise in a magnetic resonance imaging device, the method comprising the steps of:
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providing an electrically conductive passive shielding element adjacent an actively shielded gradient coil winding of the device contained within an annular support structure; and ensuring the actively shielded gradient coil winding is insulated from the passive shielding element, wherein a first portion of the passive shielding element is located adjacent an outer surface of the actively shielded gradient winding and a second portion is located adjacent an end of the actively shielded gradient winding. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus for reducing acoustic noise in a magnetic resonance imaging device, the apparatus comprising:
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an actively shielded gradient coil winding; an annular cylindrical support structure substantially enclosing the actively shielded gradient coil winding; and an electrically conductive passive shielding element adjacent the actively shielded gradient coil winding, wherein a first portion of the passive shielding element is located adjacent an outer surface of the actively shielded gradient coil and a second portion is located adjacent an end of the actively shielded gradient coil and positioned to form a non-perpendicular angle with the first portion of the passive shielding element. - View Dependent Claims (9, 10, 11, 12, 13)
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14. An apparatus for reducing acoustic noise in a magnetic resonance imaging device, the apparatus comprising:
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an actively shielded gradient coil winding; an annular cylindrical support structure substantially enclosing the actively shielded gradient coil winding; and an electrically conductive passive shielding element adjacent the actively shielded gradient coil winding, wherein a first portion of the passive shielding element is located adjacent an outer surface of the actively shielded gradient coil and a second curvilinearly shaped portion is located adjacent an end of the actively shielded gradient coil. - View Dependent Claims (15, 16, 17, 18, 19)
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Specification