CA2244847C - Center-fed paralleled coils for mri - Google Patents
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- CA2244847C CA2244847C CA002244847A CA2244847A CA2244847C CA 2244847 C CA2244847 C CA 2244847C CA 002244847 A CA002244847 A CA 002244847A CA 2244847 A CA2244847 A CA 2244847A CA 2244847 C CA2244847 C CA 2244847C
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
- G01R33/34046—Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils
- G01R33/34069—Saddle coils
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Abstract
The two halves (10, 20) of a conventional RF saddle coil, such as spirals or other related structures, for use in high resolution NMR or MRI, are dispose d on opposite sides of a cylindrical coilform, and rotated from the convention al orientation 90~ about the B1 axis so that the leads (31, 32) are paralleled near the axial center of the RF coil.
Description
CENTER-FED PARALLELED COILS FOR MRI
Technical Field S
The field of this invention is the measurement of nuclear magnetic resonance (NMR and MRI) for the purpose of determining molecular or microscopic structure, and, more particularly, an improvement in rf sample coils for double-resonance multinuclear applications.
Background Art This invention pertains to improving the tunability of NMR and MRI coils, particularly in double-resonance multinuclear experiments on large samples at high fields, by means of novel paralleling and rf feed arrangement on saddle coils and the like for use on cylindrical surfaces aligned with Bo. Related NMR coils are described by Zens in U.S. Pat no. 4,398,149, Hill and Zens in U.S: Pat no. 4,5I7,5I6, and Doty in U.S. Pat.
no. 4, 641, 098.
Center-fed Alderman-Grant resonators (J. Magn. Reson. 36, 1979) are disclosed by Nishihara and Yoda in U.S. Pat. no.
4,837,515. Hayes uses center feeding in his low-pass birdcage in U.S. Pat. no. 4,699,255. Unsegmented saddle coils (saddle coils of at least one full turn without a segmenting capacitor) have always been fed from one end for the simple reason that this reduces lead inductance and lead resistance.
Also, notwithstanding U.S. Pat. no. 5,192,9II by Hill and Cummings, for at least the past twelve years, it has been standard practice to fully shield the leads and tuning elements from the sample with internal rf shields.
The Zens US. pat. no. 4,398,149 illustrates the traditional WO 97!33185 PCT/US97/03429 methods of connecting spiral windings (referred to as sem~.-coils) on opposite sides of a cylinder inseries. More recently, as magnet technology has- progressed to higi~.or fields, it has become common to connect 2-turn semicoils in parallel, thereby achieving the higher B1 homogeneity that is possible with the conventional 4-turn saddle coil but at the lower inductance of the 2-turn saddle coil.
Prior art inter-connections of semi-coils, whether series or parallel, have always been made beyond the axial end of the high-B1 sample region. There are a number of convincing reasons for this tradition: ( 1 ) it reduces di.sturbance~s- in ~o homogeneity within the sample region caused by the unavoidable use of slightly magnetic materials (such as copper, silver, and dielectrics~; (2) it reduces disturbances in B1 homogeneity within the sample regiorf from both induced and driven currents in the jumpers and leads; (3) it permits reduced parasitic lead capacitance, inductance, and resistance. However, there are a number of applications where it is desirable to sacri~f-ic-e all of the above advantages fcr~a single compelling reason: to be able to provide double-resonance multi-nuclear capability in large samples at high fields with minimal tuning complications and loss in efficiency from spurious resonarzcws.
The NMR spectroscopist often finds it necessary to observe a wide variety of nuclides, especially. 13C, 1H, 19F, 2'A1, 29Si, 2sNa, ZH, and 15N in the study of commercially and scientifically important chemicals, and considerable interest is developing in multi-nuclear localized MR spectroscopy.
Often it is important to simultaneously decouple dipolar effects of1H; and inverse experiments, in which the effects of decoupling a low-gamma nuclide are observed,in the 3H spectra, t have become extremely powerful and popular.- Multi-nuclear double-tuning is readily achieved in prior art designs with sample diameters up to 12 mm at fields up to 9.4 T witYm~cltz-turn saddle coils having inductance typically in the range of 30 to 70 nH. Multi-nuclear triple-resonance is available far 5-mm samples at fields up to 17.6 T (750 MHZ). A copending application discloses coil geametries suitable for drf~le-resonance multinuclear tuning for large samples at high fields with improved B1 homogeneity.
T~Te have discovered that paralleled semi-coils are susceptible to twin-line (parallel transmis'sio'n wires) resonancw modes, in which each entire semi-coil on each side behaves as if it were a solid planar conductor (rather than a spiral or parallel spirals, for example) at frequencies that may cause serious tuning difficulties. That is, at sufficiently high frequencies, the currents in all axially aligned portions of the spiral are in phase with respect to the z axis rather than with respect to the low-frequency (LF) spiral path (curl of transverse B1). As a result o-f the relatively large capacitance to the internal floating rt cylindrical shield and perhaps to another orthogonal coil and closely spaced external shield, the lowest frequency twin-line semi-coil mode is generally the differential mode. For the conventional configuration with the leads from each semi-coil oriented toward one end of the coil form, the if-voltages in this mode on ea Of each the leads is zero somewhere near the point where they are paralleled, the voltage at- the remote end of one semi-coil is a maximum with phase ~ and the voltage at the remote end of the opposite semi-coil is a maximum with phase c~+n. The B1 from the differential twin-line mode is generally orthogonal to the z axis and to the LF B1 axis_ The twin-line modes of paralleled semi-coils are not known to f cause problems in single-tuned multinuclear applications, as one is normally limited in these cases to operation at frequencies below the fundamental self-resonance of ~tl~e complete coil, which is normally much lower thaw the lowest twin-line mode. However, when two orthogonal saddle coils are used in double-tuned multinuclear situations such as 1H=X1 the differential twin-line mode of the multi-X (low-gamma)coil could easily be very near the 1H frequency. It is usually npt difficult to shift this twin-line mode downward a substantial amount by adding capacitance between the remote ends of the problematic saddle coil, but since the B1 from the twin-line mode is approximately collinear with the Bi from~the normally behaving orthogonal 1H (proton) coil, these two modes are strongly coupled and the proton Q is severely degraded unless this spurious resonance is well above the proton frequency.
The instant invention provides a simple method of approximately doubling the frequency of the differential twin-line mode of paralleled semi-coils. This nearly doubles the limiting frequency-diameter product for which efficient multinuclear double resonance is practi.ca~..
Disclosure of Invention The two halves (semi-coils) of a conventz:o al rf saddle coil, such as spirals or other related structures, for use in high resolution NMR or MRI, on opposite sides of a cylindrical coilform, are rotated from the conventional orientation 90°
about the B~ axis so that the leads from the two semi-coils meet and are paralleled near the axial center of the rf coil, thereby greatly increasing the differential twin-line mode of the resonant structure.
Brief Description of Drawings Figure 1 illustrates a center-feed method of paralleling two 2-turn semi-coils.
Technical Field S
The field of this invention is the measurement of nuclear magnetic resonance (NMR and MRI) for the purpose of determining molecular or microscopic structure, and, more particularly, an improvement in rf sample coils for double-resonance multinuclear applications.
Background Art This invention pertains to improving the tunability of NMR and MRI coils, particularly in double-resonance multinuclear experiments on large samples at high fields, by means of novel paralleling and rf feed arrangement on saddle coils and the like for use on cylindrical surfaces aligned with Bo. Related NMR coils are described by Zens in U.S. Pat no. 4,398,149, Hill and Zens in U.S: Pat no. 4,5I7,5I6, and Doty in U.S. Pat.
no. 4, 641, 098.
Center-fed Alderman-Grant resonators (J. Magn. Reson. 36, 1979) are disclosed by Nishihara and Yoda in U.S. Pat. no.
4,837,515. Hayes uses center feeding in his low-pass birdcage in U.S. Pat. no. 4,699,255. Unsegmented saddle coils (saddle coils of at least one full turn without a segmenting capacitor) have always been fed from one end for the simple reason that this reduces lead inductance and lead resistance.
Also, notwithstanding U.S. Pat. no. 5,192,9II by Hill and Cummings, for at least the past twelve years, it has been standard practice to fully shield the leads and tuning elements from the sample with internal rf shields.
The Zens US. pat. no. 4,398,149 illustrates the traditional WO 97!33185 PCT/US97/03429 methods of connecting spiral windings (referred to as sem~.-coils) on opposite sides of a cylinder inseries. More recently, as magnet technology has- progressed to higi~.or fields, it has become common to connect 2-turn semicoils in parallel, thereby achieving the higher B1 homogeneity that is possible with the conventional 4-turn saddle coil but at the lower inductance of the 2-turn saddle coil.
Prior art inter-connections of semi-coils, whether series or parallel, have always been made beyond the axial end of the high-B1 sample region. There are a number of convincing reasons for this tradition: ( 1 ) it reduces di.sturbance~s- in ~o homogeneity within the sample region caused by the unavoidable use of slightly magnetic materials (such as copper, silver, and dielectrics~; (2) it reduces disturbances in B1 homogeneity within the sample regiorf from both induced and driven currents in the jumpers and leads; (3) it permits reduced parasitic lead capacitance, inductance, and resistance. However, there are a number of applications where it is desirable to sacri~f-ic-e all of the above advantages fcr~a single compelling reason: to be able to provide double-resonance multi-nuclear capability in large samples at high fields with minimal tuning complications and loss in efficiency from spurious resonarzcws.
The NMR spectroscopist often finds it necessary to observe a wide variety of nuclides, especially. 13C, 1H, 19F, 2'A1, 29Si, 2sNa, ZH, and 15N in the study of commercially and scientifically important chemicals, and considerable interest is developing in multi-nuclear localized MR spectroscopy.
Often it is important to simultaneously decouple dipolar effects of1H; and inverse experiments, in which the effects of decoupling a low-gamma nuclide are observed,in the 3H spectra, t have become extremely powerful and popular.- Multi-nuclear double-tuning is readily achieved in prior art designs with sample diameters up to 12 mm at fields up to 9.4 T witYm~cltz-turn saddle coils having inductance typically in the range of 30 to 70 nH. Multi-nuclear triple-resonance is available far 5-mm samples at fields up to 17.6 T (750 MHZ). A copending application discloses coil geametries suitable for drf~le-resonance multinuclear tuning for large samples at high fields with improved B1 homogeneity.
T~Te have discovered that paralleled semi-coils are susceptible to twin-line (parallel transmis'sio'n wires) resonancw modes, in which each entire semi-coil on each side behaves as if it were a solid planar conductor (rather than a spiral or parallel spirals, for example) at frequencies that may cause serious tuning difficulties. That is, at sufficiently high frequencies, the currents in all axially aligned portions of the spiral are in phase with respect to the z axis rather than with respect to the low-frequency (LF) spiral path (curl of transverse B1). As a result o-f the relatively large capacitance to the internal floating rt cylindrical shield and perhaps to another orthogonal coil and closely spaced external shield, the lowest frequency twin-line semi-coil mode is generally the differential mode. For the conventional configuration with the leads from each semi-coil oriented toward one end of the coil form, the if-voltages in this mode on ea Of each the leads is zero somewhere near the point where they are paralleled, the voltage at- the remote end of one semi-coil is a maximum with phase ~ and the voltage at the remote end of the opposite semi-coil is a maximum with phase c~+n. The B1 from the differential twin-line mode is generally orthogonal to the z axis and to the LF B1 axis_ The twin-line modes of paralleled semi-coils are not known to f cause problems in single-tuned multinuclear applications, as one is normally limited in these cases to operation at frequencies below the fundamental self-resonance of ~tl~e complete coil, which is normally much lower thaw the lowest twin-line mode. However, when two orthogonal saddle coils are used in double-tuned multinuclear situations such as 1H=X1 the differential twin-line mode of the multi-X (low-gamma)coil could easily be very near the 1H frequency. It is usually npt difficult to shift this twin-line mode downward a substantial amount by adding capacitance between the remote ends of the problematic saddle coil, but since the B1 from the twin-line mode is approximately collinear with the Bi from~the normally behaving orthogonal 1H (proton) coil, these two modes are strongly coupled and the proton Q is severely degraded unless this spurious resonance is well above the proton frequency.
The instant invention provides a simple method of approximately doubling the frequency of the differential twin-line mode of paralleled semi-coils. This nearly doubles the limiting frequency-diameter product for which efficient multinuclear double resonance is practi.ca~..
Disclosure of Invention The two halves (semi-coils) of a conventz:o al rf saddle coil, such as spirals or other related structures, for use in high resolution NMR or MRI, on opposite sides of a cylindrical coilform, are rotated from the conventional orientation 90°
about the B~ axis so that the leads from the two semi-coils meet and are paralleled near the axial center of the rf coil, thereby greatly increasing the differential twin-line mode of the resonant structure.
Brief Description of Drawings Figure 1 illustrates a center-feed method of paralleling two 2-turn semi-coils.
WO 97!33185 PCTlUS97103429 I?figure 2 illustrates a center-feed method of paralle-ling two 1-turn semi-coils.
Modes for Carrying Out Invention d Figure 1 illustrates the center-feed method of essmntially eliminating the differential twin-line mode in, for example, a typical two-turn paralleled saddle coil intended to be used as i~he low-frequency (LF) multinuclear coil in combination with a second orthogonal coil fo-r~ the high frcquwcy (HF7 . The two semi-coils 10, 20 in this case are substantially rectangular spirals that may be made by any of the conventional processes:
(a) laser cutting of magnetically compensated metal foil laminate, (b) chemical etching of copper=clad dielectric laminate, (c) mechanical forming of aluminum-filled copper tubing, etc. The two semi-coils of Figure 1 are symmetrically related and similar to those by Golay, Hoult, Hill, Zens, and others, with the notable difference that the leads !l, 12, 21, 22 are brought out and paralleled by arcs 13, 23 between the two semi-coils near the center rather than at one end. The pattern is similar to a 90° rotation of a conventional semi-coil with respect to the Bl axis.
The paralleling arcs 13, 23 generate a short-range field orthogonal to the major B1 field from the coil, but their effect on B1 homogeneity may easily be made negligible by a a small internal floating shield patch under the arcs- if necessary.
It should be noted that only recently has it become common practice to use parallel rather than series connections between the two semi-coils. Paralleling permits more turns in each semicoil for the desired inductance, and hence much better B1 homogeneity may be achieved. The WO 97/331.85 PCT/US97/03429 paralleling direction is such that the two fields add.
That is, the parallel saddle coil inductance is greater than half of the inductance of the individual semi-coils.
The instant invention is specifically directed toward mufti-nuclear double-tuned applications, in which a lower inductance orthogonal HF resonator is used in combination with a center-fed LF mufti-nuclear saddle coil. The LF' rf center-feed is accomplished by a balanced, half-shielded l0 transmission stripline 30 formed from copper-clad 3~.minate with the ground side toward the sample, as RF magnetic field from this transmission line is negligible compared to the central B1 and the leads 31, 32 must have low inductance for minimal loss in filling factor. Bringing the LF feed line into the center of the coil allows the LF
feed line to be at any impedance at the HF with respect to ground and still have negligible effect on the typical orthogonal HF coil (for example, an Aldermian-Grant resonator, etc.), which is normally near zero Impedance with respect to ground near its center. Moreover, the arcs at the two axial ends 14, 15, 24, 25 of each semi-coil now float freely, and the leads 31, 32 do notform part of a large loop around substantial net flux emanating from an orthogonal HF coil -- as opposed to the prior art where the paralleling leads subtend roughly a mean arc of 180° at the base of the coil. Hence, there is no major magnetic coupling from an orthogonal HF to drive a differential twin-line mode -- that is, the mode in which, the current in conductors 16, 17, 18, 19 flows in the positive z-direction while the current in conductors 26, 27, 28, 29 flows in the negative z direction. It should be emphasized that this mode may exist even when the semi-coil circumference is much less than the HF wavelength because the large external capacitance between arcs 14, 15, 24, 25 and the internal rf shield effectively produces ' a periodic delay line.
Clearly, this coil and center-feed arrangement lack the symmetry desired for best Bo homogeneity -- with the major perturbation coming from the center-feed stripline dielectric. By extending the dielectric spacer 33. axially l0 well beyond the ends of the coil, the adverse affect on Bo homogeneity of a large truncated object is eliminated.
The preferred dielectric material is usually foamed FTFE
(teflon) because of its low dielectric constant and low 1H
content (after a bakeout). Copper-clad FTFE foam may nQt be commercially available, but it may be approximated by separating two single-clad thin laminates by PTFE~ fcfa~n.
l~Tumerous other types of transmission feed lines may be selected. In some cases, it.may not be preferable to balance the LF coil, in which case an unbalanced stripline, with the grounded lead toward the sample and the high voltage lead away from the sample, would be preferred for the center-feed line. Figure 2 illustrates a one-turn saddle coil with an unbalanced, truncated, center-feed line. Many other semi-moil patterns are possible, and a number of numerically optimized patterns offering higher B1 homogeneity are the subject of a copending application.
a 30 Inverse (low-gamma) decoupling techniques are becoming more popular than conventional proton decoupling techniques. Thus, the center-fed LF saddle coil will usually be positioned on the outside witv the HF res'or~ator on the inside. Even with closely spaced coils, the high order (unshimable) magnetic disturbances from the outer coil are typically about an order of magnitude less than from the inner coil. Hence, it is not g-articularly difficult to achieve the Bo homogeneity required for critical high-resolution~NMR when the center-fed coil is the outer coil. When the center-fed coil is the inner coil, it may be necessary to plate the copper cladding on the stripline first with a paramagnetic metal (such as aluminum or iridium) and then apply another copper plate.
to achieve the desired reduction in magnetism while maintaining high surface conductivity. Obviously, the semicoils too would need to be precisely compensated for minimum magnetism, according to the prior art. Moreover, the width of the center-feed line would have to be reduced to minimize degradation of B1 homogeneity of the outer coil.
Although this invention has been described herein.with . reference to specific embodiments, it will be recognized that changes and modifications may be made without-departing from the spirit of the present invention. All such modifications and changes are intended to be included within the scope of the following claims.
Modes for Carrying Out Invention d Figure 1 illustrates the center-feed method of essmntially eliminating the differential twin-line mode in, for example, a typical two-turn paralleled saddle coil intended to be used as i~he low-frequency (LF) multinuclear coil in combination with a second orthogonal coil fo-r~ the high frcquwcy (HF7 . The two semi-coils 10, 20 in this case are substantially rectangular spirals that may be made by any of the conventional processes:
(a) laser cutting of magnetically compensated metal foil laminate, (b) chemical etching of copper=clad dielectric laminate, (c) mechanical forming of aluminum-filled copper tubing, etc. The two semi-coils of Figure 1 are symmetrically related and similar to those by Golay, Hoult, Hill, Zens, and others, with the notable difference that the leads !l, 12, 21, 22 are brought out and paralleled by arcs 13, 23 between the two semi-coils near the center rather than at one end. The pattern is similar to a 90° rotation of a conventional semi-coil with respect to the Bl axis.
The paralleling arcs 13, 23 generate a short-range field orthogonal to the major B1 field from the coil, but their effect on B1 homogeneity may easily be made negligible by a a small internal floating shield patch under the arcs- if necessary.
It should be noted that only recently has it become common practice to use parallel rather than series connections between the two semi-coils. Paralleling permits more turns in each semicoil for the desired inductance, and hence much better B1 homogeneity may be achieved. The WO 97/331.85 PCT/US97/03429 paralleling direction is such that the two fields add.
That is, the parallel saddle coil inductance is greater than half of the inductance of the individual semi-coils.
The instant invention is specifically directed toward mufti-nuclear double-tuned applications, in which a lower inductance orthogonal HF resonator is used in combination with a center-fed LF mufti-nuclear saddle coil. The LF' rf center-feed is accomplished by a balanced, half-shielded l0 transmission stripline 30 formed from copper-clad 3~.minate with the ground side toward the sample, as RF magnetic field from this transmission line is negligible compared to the central B1 and the leads 31, 32 must have low inductance for minimal loss in filling factor. Bringing the LF feed line into the center of the coil allows the LF
feed line to be at any impedance at the HF with respect to ground and still have negligible effect on the typical orthogonal HF coil (for example, an Aldermian-Grant resonator, etc.), which is normally near zero Impedance with respect to ground near its center. Moreover, the arcs at the two axial ends 14, 15, 24, 25 of each semi-coil now float freely, and the leads 31, 32 do notform part of a large loop around substantial net flux emanating from an orthogonal HF coil -- as opposed to the prior art where the paralleling leads subtend roughly a mean arc of 180° at the base of the coil. Hence, there is no major magnetic coupling from an orthogonal HF to drive a differential twin-line mode -- that is, the mode in which, the current in conductors 16, 17, 18, 19 flows in the positive z-direction while the current in conductors 26, 27, 28, 29 flows in the negative z direction. It should be emphasized that this mode may exist even when the semi-coil circumference is much less than the HF wavelength because the large external capacitance between arcs 14, 15, 24, 25 and the internal rf shield effectively produces ' a periodic delay line.
Clearly, this coil and center-feed arrangement lack the symmetry desired for best Bo homogeneity -- with the major perturbation coming from the center-feed stripline dielectric. By extending the dielectric spacer 33. axially l0 well beyond the ends of the coil, the adverse affect on Bo homogeneity of a large truncated object is eliminated.
The preferred dielectric material is usually foamed FTFE
(teflon) because of its low dielectric constant and low 1H
content (after a bakeout). Copper-clad FTFE foam may nQt be commercially available, but it may be approximated by separating two single-clad thin laminates by PTFE~ fcfa~n.
l~Tumerous other types of transmission feed lines may be selected. In some cases, it.may not be preferable to balance the LF coil, in which case an unbalanced stripline, with the grounded lead toward the sample and the high voltage lead away from the sample, would be preferred for the center-feed line. Figure 2 illustrates a one-turn saddle coil with an unbalanced, truncated, center-feed line. Many other semi-moil patterns are possible, and a number of numerically optimized patterns offering higher B1 homogeneity are the subject of a copending application.
a 30 Inverse (low-gamma) decoupling techniques are becoming more popular than conventional proton decoupling techniques. Thus, the center-fed LF saddle coil will usually be positioned on the outside witv the HF res'or~ator on the inside. Even with closely spaced coils, the high order (unshimable) magnetic disturbances from the outer coil are typically about an order of magnitude less than from the inner coil. Hence, it is not g-articularly difficult to achieve the Bo homogeneity required for critical high-resolution~NMR when the center-fed coil is the outer coil. When the center-fed coil is the inner coil, it may be necessary to plate the copper cladding on the stripline first with a paramagnetic metal (such as aluminum or iridium) and then apply another copper plate.
to achieve the desired reduction in magnetism while maintaining high surface conductivity. Obviously, the semicoils too would need to be precisely compensated for minimum magnetism, according to the prior art. Moreover, the width of the center-feed line would have to be reduced to minimize degradation of B1 homogeneity of the outer coil.
Although this invention has been described herein.with . reference to specific embodiments, it will be recognized that changes and modifications may be made without-departing from the spirit of the present invention. All such modifications and changes are intended to be included within the scope of the following claims.
Claims (9)
1. An rf LP saddle coil for use in nuclear magnetic resonance and characterized with respect to a Cartesian coordinate system having z and y axes, the coil comprising:
a first semi-coil on the surface of a cylindrical coilform aligned with the z axis, said first semi-coil comprising a conductor pattern executing at least one loop around the positive y axis and having inductance L1, a second semi-coil on the opposite surface of said cylindrical coilform, said second semi-coil comprising a conductor pattern executing at least one loop around the negative y axis and having inductance approximately equal to L1, two conductive paralleling strips near the central transverse plane of said coilform providing parallel inter-connection between terminations of said first and second semi-coils such that the parallel inductance L p is greater than L1/2, and a center-feed rf line connected to said paralleling strips.
a first semi-coil on the surface of a cylindrical coilform aligned with the z axis, said first semi-coil comprising a conductor pattern executing at least one loop around the positive y axis and having inductance L1, a second semi-coil on the opposite surface of said cylindrical coilform, said second semi-coil comprising a conductor pattern executing at least one loop around the negative y axis and having inductance approximately equal to L1, two conductive paralleling strips near the central transverse plane of said coilform providing parallel inter-connection between terminations of said first and second semi-coils such that the parallel inductance L p is greater than L1/2, and a center-feed rf line connected to said paralleling strips.
2. The coil of claim 1 wherein said second semi-coil is further characterized as being symmetrically related to said first semi-coil.
3. The coil of claim 1 wherein said center-feed line is further characterized as being a longitudinally oriented transmission stripline of inductance less than L p.
4. The coil of claim 3 wherein said first semi-coil has an axial extent, and wherein said stripline is further characterized as comprising a dielectic strip of uniform cross-section between at least two parallel conductor strips, said dielectric strip extending axially in both directions beyond the axial extent of said first semi-coil.
5. The coil of claim 4 wherein said conductor strips comprise platings of diamagnetic and paramagnetic metals.
6. The coil of claim 4 wherein said dielectric strip is substantially foamed PTFE.
7. The coil of claim 1 wherein said LF coil has a fundamental self-resonance, said coil in combination with a second, concentric, orthogonal HF coil tuned to a higher frequency than the fundamental self resonance of said LF coil.
8. The coil of claim 1 defining a sample region inside said coilform, wherein said semi-coils have been numerically designated to generate homogeneous B1 throughout the sample region inside said coilform.
9
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US1284996P | 1996-03-05 | 1996-03-05 | |
| US60/012,849 | 1996-03-05 | ||
| PCT/US1997/003429 WO1997033185A1 (en) | 1996-03-05 | 1997-03-05 | Center-fed paralleled coils for mri |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2244847A1 CA2244847A1 (en) | 1997-09-12 |
| CA2244847C true CA2244847C (en) | 2003-06-10 |
Family
ID=21757023
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002244847A Expired - Fee Related CA2244847C (en) | 1996-03-05 | 1997-03-05 | Center-fed paralleled coils for mri |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU2067797A (en) |
| CA (1) | CA2244847C (en) |
| WO (1) | WO1997033185A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT407463B (en) * | 1998-06-04 | 2001-03-26 | Siemens Ag Oesterreich | REEL FOR STANDAL MOUNTING ON CIRCUIT BOARDS |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5329233A (en) * | 1992-12-10 | 1994-07-12 | General Electric Company | Cylindrical local coil for nuclear magnetic resonance imaging |
| US5517120A (en) * | 1993-11-24 | 1996-05-14 | Medrad, Inc. | Quadrature coil for neurovascular imaging and spectroscopy of the human anatomy |
| DE4434948C2 (en) * | 1994-09-29 | 1998-05-20 | Siemens Ag | Mammography antenna arrangement for magnetic resonance examinations of a female breast |
-
1997
- 1997-03-05 CA CA002244847A patent/CA2244847C/en not_active Expired - Fee Related
- 1997-03-05 AU AU20677/97A patent/AU2067797A/en not_active Abandoned
- 1997-03-05 WO PCT/US1997/003429 patent/WO1997033185A1/en active Application Filing
Also Published As
| Publication number | Publication date |
|---|---|
| WO1997033185A1 (en) | 1997-09-12 |
| AU2067797A (en) | 1997-09-22 |
| CA2244847A1 (en) | 1997-09-12 |
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| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |