EP0132338A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Apparatus and method for reducing spurious currents in NMR imaging apparatus induced by pulsed gradient fields
Assignee: University of California Berkeley
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Filing: 1984-07-06
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Granted: —
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Expires: 2004-07-06
Abstract
Abstract NMR imaging apparatus having at least one pulsed magnetic field gradient coil generated pulsed magnetic gradients fields and having at least one other coil structure (L1, L2) magnetically linked thereto (and therefore subject to induced pulsed currents which create opposing magnetic fields if permitted to flow) includes apparatus connected in circuit with the other coil structure for suppressing such induced currents. The suppression is effected by causing the other coil structure to have increased electrical impedance with respect to such induced currents. Where the other coil structure is a radio frequency transmit/receive coil having plural parallel connected turns, the suppression apparatus includes at least one capacitor (C1, C2) in series with at least some of the turns so as to present a substantially open circuit condition at the relatively lower frequencies of the unwanted induced currents. Where the other coil is a static field profiling or "shimming" coil, it is driven with a wide-band current source so as to counteract the unwanted induced currents.
Inventors
- 👤 Lawrence E. Crooks
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-27 12:23
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/28; G01R33/32; G01R33/36; G01R33/3642; G01R33/3628; G01R33/38; G01R33/385; G01R33/387; G01R33/3875; G01R33/42; G01R33/422
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
92 words
NMR imaging apparatus comprising: at least one pulsed magnetic field gradient coil for controllably generating pulsed magnetic gradient fields; at least one other coil structure having plural parallel-connected coil portions magnetically linked to said gradient coil and therefore subject to induced currents caused by said pulsed gradient fields which induced currents, if permitted to flow, generate magnetic fields opposing the pulsed gradient fields, and suppression means connected in series with at least one of said other coil portions for causing it to have increased electrical impedance with respect to said induced currents.
Claim 2
Dependent Claim
92 words
NMR imaging apparatus comprising: at least one pulsed magnetic field gradient coil for controllably generating pulsed magnetic gradient fields; at least one other coil structure having plural parallel-connected coil portions magnetically linked to said gradient coil and therefore subject to induced currents caused by said pulsed gradient fields which induced currents, if permitted to flow, generate magnetic fields opposing the pulsed gradient fields, and suppression means connected in series with at least one of said other coil portions for causing it to have increased electrical impedance with respect to said induced currents.
Claim 3
Dependent Claim
28 words
NMR imaging apparatus as in claim 1 wherein said suppression means comprises at least one capacitor electrically connected in series with a portion of said other coil structure.
Claim 4
Dependent Claim
25 words
NMR imaging apparatus as in claim 2 wherein said other coil is a radio frequency signal coil including at least two portions connected in parallel.
Claim 5
Dependent Claim
39 words
NMR imaging apparatus as in claim 3 wherein said suppression means comprises at least two capacitors, each connected in series with one of the coil portions so as to maintain a balanced r.f. feed to/from said radio frequency coil.
Claim 6
Dependent Claim
89 words
NMR imaging apparatus comprising: at least one pulsed magnetic field gradient coil for controllably generating pulsed magnetic gradient fields; at least one other coil structure magnetically linked to said gradient coil and therefore subject to induced currents caused by said pulsed gradient fields which induced currents, if permitted to flow, generate magnetic fields opposing the pulsed gradient fields; and a substantially constant current source electrically connected to supply driving current to said other coil structure for causing it to have increased electrical impedance with respect to said induced currents.
Claim 7
Dependent Claim
89 words
NMR imaging apparatus comprising: at least one pulsed magnetic field gradient coil for controllably generating pulsed magnetic gradient fields; at least one other coil structure magnetically linked to said gradient coil and therefore subject to induced currents caused by said pulsed gradient fields which induced currents, if permitted to flow, generate magnetic fields opposing the pulsed gradient fields; and a substantially constant current source electrically connected to supply driving current to said other coil structure for causing it to have increased electrical impedance with respect to said induced currents.
Claim 8
Dependent Claim
28 words
NMR imaging apparatus as in claim 5 wherein said other coil is a field shimming coil used for improving the homogeneity of static magnetic fields within said apparatus.
Claim 9
Dependent Claim
26 words
NMR imaging apparatus as in claim 6 further comprising a power dissipating resistor connected in series with the constant current source and said field shimming coil.
Claim 10
Dependent Claim
56 words
An improved NMR imaging apparatus of the type that includes at least one pulsed field gradient coil magnetically linked to an r.f. coil including plural sets of turns connected in parallel, said improvement comprising: a capacitor connected in series with at least each but one of said sets of turns and a common r.f. feed point.
Claim 11
Dependent Claim
56 words
An improved NMR imaging apparatus of the type that includes at least one pulsed field gradient coil magnetically linked to an r.f. coil including plural sets of turns connected in parallel, said improvement comprising: a capacitor connected in series with at least each but one of said sets of turns and a common r.f. feed point.
Claim 12
Dependent Claim
47 words
An improved NMR imaging apparatus as in claim 8 wherein said improvement comprises at a capacitor connected in series with each of the sets of turns of said r.f. coil and a common r.f. feed point providing a balanced r.f. feed connection to the sets of turns.
Claim 13
Dependent Claim
45 words
An improved NMR imaging apparatus of the type that includes at least one pulsed field gradient coil magnetically linked to a static field shimming coil, said improvement comprising: a constant current source connected to drive a desired constant current through said static field shimming coil.
Claim 14
Dependent Claim
45 words
An improved NMR imaging apparatus of the type that includes at least one pulsed field gradient coil magnetically linked to a static field shimming coil, said improvement comprising: a constant current source connected to drive a desired constant current through said static field shimming coil.
Claim 15
Dependent Claim
28 words
An improved NMR imaging apparatus as in claim 10 further including a power dissipating resistor connected in series with the constant current source and with said shimming coil.
Claim 16
Dependent Claim
86 words
In an NMR imaging method using pulsed magnetic gradient fields and having at least one other coil structure magnetically linked to said pulsed gradient fields, the improvement comprising the step of suppressing the currents induced in said other coil by said pulsed gradient fields, said suppressing step causing the other coil to have an increased electrical impedance with respect to said induced currents, wherein said suppressing step comprises use of at least one capacitor electrically connected in series with a portion of said other coil structure.
Claim 17
Dependent Claim
86 words
In an NMR imaging method using pulsed magnetic gradient fields and having at least one other coil structure magnetically linked to said pulsed gradient fields, the improvement comprising the step of suppressing the currents induced in said other coil by said pulsed gradient fields, said suppressing step causing the other coil to have an increased electrical impedance with respect to said induced currents, wherein said suppressing step comprises use of at least one capacitor electrically connected in series with a portion of said other coil structure.
Claim 18
Dependent Claim
85 words
In an NMR imaging method using pulsed magnetic gradient fields and having at least one other coil structure magnetically-linked to said pulsed gradient fields, the improvement comprising the step of suppressing the currents induced in said other coil by said pulsed gradient fields, said suppressing step causing the other coil to have an increased electrical impedance with respect to said induced currents, wherein said suppressing step comprises use of a substantially constant current source electrically connected to supply driving current to said other coil structure.
Claim 19
Dependent Claim
85 words
In an NMR imaging method using pulsed magnetic gradient fields and having at least one other coil structure magnetically-linked to said pulsed gradient fields, the improvement comprising the step of suppressing the currents induced in said other coil by said pulsed gradient fields, said suppressing step causing the other coil to have an increased electrical impedance with respect to said induced currents, wherein said suppressing step comprises use of a substantially constant current source electrically connected to supply driving current to said other coil structure.
References Cited (Backward Citations)
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