Low-inductance transverse litz foil coils
First Claim
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1. A litz coil formed on the surface of a substantially elliptical coilform for use in a main polarizing magnetic field BZ for magnetic resonance for the purpose of generating or detecting rf B1 transverse to the axis of said coilform in, for example, the y-direction inside an external rf shield, said litz coil comprising:
- a litz group comprising multiple, parallel, conductor foils having interwoven sub-routes from a first node to a second node and insulated crossovers such that at least two well-defined flux sub-windows are formed,a first litz semi-coil on the +y side of said coilform comprising at least one litz group and a series-parallel combination of conductors forming axial and azimuthal conductor elements around a central flux window centered on the +y axis,a second substantially equivalent litz semi-coil on the -y side of said coilform with electrical coupling means to said first litz semi-coil,said first litz semi-coil further characterized as having leads for connecting to a tuning capacitor,said sub-routes positioned such that when said litz coil is driven by rf current at a predetermined frequency the total rf magnetic flux through said central flux window is less than 50% of the total rf magnetic flux through the y=0 plane.
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Abstract
A family of NMR coils based on Litz foil conductor groups is disclosed. The simplest embodiment is a two-element Litz foil coil. The foils are joined at node (1) and node (2) and are electrically insulated at crossover (3). When the coil is positioned in a plane perpendicular to a uniform magnetic field, the areas (A) defining two flux sub-windows must be equal.
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Citations
37 Claims
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1. A litz coil formed on the surface of a substantially elliptical coilform for use in a main polarizing magnetic field BZ for magnetic resonance for the purpose of generating or detecting rf B1 transverse to the axis of said coilform in, for example, the y-direction inside an external rf shield, said litz coil comprising:
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a litz group comprising multiple, parallel, conductor foils having interwoven sub-routes from a first node to a second node and insulated crossovers such that at least two well-defined flux sub-windows are formed, a first litz semi-coil on the +y side of said coilform comprising at least one litz group and a series-parallel combination of conductors forming axial and azimuthal conductor elements around a central flux window centered on the +y axis, a second substantially equivalent litz semi-coil on the -y side of said coilform with electrical coupling means to said first litz semi-coil, said first litz semi-coil further characterized as having leads for connecting to a tuning capacitor, said sub-routes positioned such that when said litz coil is driven by rf current at a predetermined frequency the total rf magnetic flux through said central flux window is less than 50% of the total rf magnetic flux through the y=0 plane. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. A litz coil for use in an external polarizing magnetic field BZ for magnetic resonance for the purpose of generating or detecting rf B1 transverse to the axis of a sample in, for example, the y-direction, said litz coil comprising:
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a litz group comprising multiple, parallel, conductors having interwoven sub-routes from a first node to a second node and insulated crossovers such that at least two well-defined flux sub-windows are formed, a first litz semi-coil on the +y side of said sample comprising at least one litz group and a series-parallel combination of conductors forming axial and azimuthal conductor elements around a central flux window centered on the +y axis, a second litz semi-coil on the -y side of said sample with coupling means to said first litz semi-coil, said first litz semi-coil further characterized as having leads for connecting to a tuning capacitor, said sub-routes positioned such that when said litz coil is driven by rf current at a predetermined frequency the total rf magnetic flux through said central flux window is less than 80% of the total rf magnetic flux through the y=0 plane.
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32. A litz coil for magnetic resonance formed on the surface of a coilform of mean diameter dC inside an external rf shield of mean diameter sdC for the purpose of generating or detecting a transverse rf B1, said coil comprising:
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multiple, parallel, interwoven, axial and azimuthal conductor elements circumscribing central flux windows of axial length h1 on opposite sides of said coilform, low-inductance leads for connecting said coil to capacitive tuning means, current paths such that when rf current is applied to said leads at resonance the current in conductor elements adjacent to one of said central flux windows is less than 35% of the sum of the current in all axial elements in one quadrant of said coil and the net flux between adjacent said conductor elements is greater than the 70% of the flux through one of said central flux windows, effective parallel coil inductance L that satisfies the following over a wide range of frequencies;
##EQU5## where the coefficient has units of nH/mm.
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33. A half-turn-fixed-frequency (HTF) rf coil for NMR formed on the surface of an elliptical coilform, said rf coil comprising a first HTF semi-coil on, for example, the +y side of said coilform and a second substantially equivalent HTF semi-coil on the -y side of said coilform with electrical coupling means to said first HTF semi-coil, said first HTF semi-coil comprising,
a segmented outer saddle loop executing one turn around said +y axis, said outer loop subtending mean azimuthal angle greater than 125° - but less than 155°
,segmenting capacitors at opposite axial ends of said outer loop, an unsegmented inner loop executing one turn around a central flux window centered on said +y axis and subtending azimuthal angle greater than 50°
but less than 80°
, said inner loop connected in parallel with one of said segmenting capacitors.
- but less than 155°
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34. A quadrature litz coil approximately aligned with the main polarizing magnetic field BZ for magnetic resonance for the purpose of generating or detecting a rotating transverse rf B1 inside an external cylindrical rf shield, said quadrature litz coil comprising two concentric litz coils of slightly differing diameters rotated 90°
- with respect to the other, each said litz coil tuned to resonate at the same frequency and each comprising;
a litz group comprising multiple, parallel, conductors having interwoven sub-routes from a first node to a second node and insulated crossovers such that at least two well-defined litz flux sub-windows are formed, a first litz semi-coil on, for example, the +y side of said coilform comprising at least one litz group and a series-parallel combination of conductors forming axial and azimuthal conductor elements around a central flux window centered on the +y axis, a second substantially equivalent litz semi-coil on the -y side of said coilform with electrical coupling means to said first litz semi-coil, said first litz semi-coil further characterized as having leads for connecting to a tuning capacitor, said sub-routes positioned such that when said litz coil is driven by rf current at a predetermined frequency the total rf magnetic flux through said central flux window is less than 50% of the total rf magnetic flux through the y=0 plane.
- with respect to the other, each said litz coil tuned to resonate at the same frequency and each comprising;
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35. A quadrature litz birdcage coil approximately aligned with the main polarizing magnetic field BZ for magnetic resonance for the purpose of generating or detecting a rotating transverse rf B1 inside an external cylindrical rf shield, said quadrature litz birdcage coil comprising a conventional MRI birdcage coil in which a plurality of conductor elements have been replaced by litz groups, where a litz group comprises multiple, parallel, conductor foils having interwoven sub-routes from a first node to a second node and insulated crossovers such that at least two well-defined flux sub-windows are formed.
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36. A quadrature litz birdcage coil approximately aligned with the main polarizing magnetic field BZ for magnetic resonance for the purpose of generating or detecting a rotating transverse rf B1 inside an external cylindrical rf shield, said quadrature litz birdcage coil comprising a conventional MRI birdcage coil in which a plurality of conductor elements have been replaced with conventional litz wire.
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37. The quadrature litz birdcage coil of 36 wherein said litz wire is loosely woven and spread out to cover a greater portion of the surface area of said coil.
Specification