[go: up one dir, main page]

WO1992017799A1 - Bobine en sellette hf destinee a etre utilisee avec des champs magnetiques pulses - Google Patents

Bobine en sellette hf destinee a etre utilisee avec des champs magnetiques pulses Download PDF

Info

Publication number
WO1992017799A1
WO1992017799A1 PCT/US1992/002738 US9202738W WO9217799A1 WO 1992017799 A1 WO1992017799 A1 WO 1992017799A1 US 9202738 W US9202738 W US 9202738W WO 9217799 A1 WO9217799 A1 WO 9217799A1
Authority
WO
WIPO (PCT)
Prior art keywords
ring
par
conductor
disposed
axial
Prior art date
Application number
PCT/US1992/002738
Other languages
English (en)
Inventor
Xuan Z. Ni
Howard Hill
Original Assignee
Varian Associates, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Varian Associates, Inc. filed Critical Varian Associates, Inc.
Publication of WO1992017799A1 publication Critical patent/WO1992017799A1/fr

Links

Classifications

    • 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
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
    • 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
    • G01R33/343—Constructional details, e.g. resonators, specially adapted to MR of slotted-tube or loop-gap type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/06—Electromagnets; Actuators including electromagnets
    • H01F7/20—Electromagnets; Actuators including electromagnets without armatures

Definitions

  • the present invention relates generally to instrumentation based upon magnetic resonance phenomena and particularly relates to reduction of transient magnetic field perturbations occasioned by eddy currents.
  • the sample volume is ordinarily limited by the bore of a superconducting magnet housed in a cryostat of complex construction.
  • the pulsed gradient coils occupy a peripheral region of the bore and the RF coil occupies another (inner) region within the bounds of the gradient coil(s).
  • eddy currents may be induced on the inner structural members of the cryostat and also on the RF coil conductor disposed within the gradient coil(s).
  • the eddy currents decay exponentially and there results an exponentially time dependent contribution to the magnetic field experienced by the sample.
  • the present work is directed to reduction of eddy currents induced on the RF coil. In the present invention the reduction is achieved by distinct structural features.
  • a known single turn RF saddle coil structure shown in FIG.
  • the 2(a)) comprises two parallel conductors 40 and 42 both of which terminate on an upper ring-shaped conductor 46.
  • a lower ring shaped conductor 48 is disposed in contact with one of the par-axial conductors 40 and that one, or the ring 48 itself, provides one terminal or feed to the coil.
  • the second par-axial conductor 42 is disposed so as not to contact the lower ring 48, and it forms the return for the RF current.
  • the structure was intended to provide for a constant axial distribution of coil conductor material in the sensitive region of an NMR instrument. This structure is described in U.S. 4,563,648, commonly assigned herewith.
  • a single turn saddle coil is disposed about a cylindrical locus forming two current loops on opposite (azimuthal) sides of a cylindrical locus.
  • the loops are formed by conductive portions parallel to the axis and by cylindrical (ring) portions joining the par-axial portions.
  • one of the par-axial members includes a slot along the entire axial length thereof which also interrupts the end ring portions.
  • the slot effectively interrupts an eddy current which would appear around (continuous) ring portions and separates one of the par-axial portions into two sub-portions. These sub-portions support parallel current flow originating from one terminal of the coil.
  • Another embodiment combines the above structure with a slotted coaxial cylinder disposed within one of the ring portions.
  • the outer ring comprises additional slots situated on either side of the full length slot to provide for RF terminals geometrically antisymmetrical with respect to the full length slot.
  • FIG. 1 shows the general context of the system embodying this invention.
  • FIG. 2 shows a prior art coil.
  • FIG. 2(b) shows the coil of FIG. 2(a) unrolled onto a plane.
  • FIG 3(a) shows another known RF coil.
  • FIG. 3(b) shows the RF coil of FIG. 3(a) unrolled onto a plane.
  • FIG. 4(a) shows an embodiment of the present invention.
  • FIG. 4(b) shows the RF coil of FIG. 4(a) unrolled onto a plane.
  • FIG. 5 shows a pulse diagram for examining eddy current effects.
  • FIG. 6 is another embodiment of the invention.
  • FIG. 7 compares the Q of a prior art coil of FIG. 2b with the coil of FIG. 6.
  • FIG. 8 shows another embodiment of the invention.
  • FIG. 1 Portions of a typical NMR data acquisition instrument are schematically illustrated on FIG. 1.
  • An acquisition/control processor 10 communicates with an RF transmitter 12, modulator 14 and receiver 16, including analog-to-digital convertor 18 and a further digital processor 20.
  • the modulated RF power irradiates an object
  • a magnetic field 21 through a probe assembly 22 and response of the object is intercepted by probe 22 communicating with receiver 16.
  • the response typically takes the form of a transient time domain waveform or free induction decay.
  • This transient waveform is sampled at regular intervals and samples are digitized in adc 18.
  • the digitized time domain wave form is then subject to further processing in processor 20.
  • the nature of such processing may include averaging the time domain waveform over a number of similar of such waveforms and transformation of the average time domain wave form to the frequency domain yields a spectral distribution function directed to output device 24. Alternatively this procedure may thus be repeated with variation of some other parameter and the transformation(s) from the data set may take on any of a number of identities for display or further analysis.
  • the magnetic field 21 which polarizes the sample and defines the Larmor frequency thereof, is established by an appropriate means, not shown.
  • Coil(s) 19 are employed for imposing a desired spacial and time dependence of magnetic field.
  • FIG. 2(a) is one prior art single loop saddle coil which includes in its construction a gap 50 and ring portion 48.
  • This gap 50 would (fortuitously) serve to reduce circulating eddy current induced from a pulsed magnetic field in proximity thereto and having an axial component.
  • the upper ring 46 would support such induced eddy currents, in contrast to the lower ring.
  • the RF current supported in the lower ring depends upon the capacitance between ring 48 and conductor 42 across gap 50.
  • FIG. 2(b) is a variant of FIG. 2(a) and does not include the gap 50.
  • This form of coil serves conveniently as a standard by which to reference performance for the present invention.
  • FIG. 3(a) is another prior RF coil, discussed above, which includes slots 56 and 58 and chip capacitors 60 and 62 respectively bridging gaps 64 and 66 in a lower ring portion 68.
  • This structure is mapped onto a plane in FIG. 3(b) with the eddy current distribution qualitatively shown. (The edges BB and B'B' coincide to form the structure of FIG. 3(a).
  • This prior art is similar to that of
  • FIG. 2a where the circulating current is interrupted in one ring only to the extent of the capacitance between corresponding members.
  • FIG. 4(a) there is shown one embodiment of the present invention.
  • the structure resembles that of FIG. 2(b), with the addition of slot 70 which removes the possibility of circulating eddy currents around both ring members 46 and 48.
  • FIG. 4(b) the coil structure of FIG. 4(a) is mapped onto a plane and a qualitative current distribution is indicated. (The edges AA and A ⁇ ' coincide to form the structure of FIG. 4(a).)
  • the single slot 70 is placed in such a position as to leave unaffected the RF current paths compared to prior art but to introduce substantially different conditions for circulating eddy currents introduced by pulsed magnetic fields.
  • FIG. 6 is a variation of the prior art structure of FIG. 2b where the terminal extension of conductor 42 of that prior art is extended azimuthally to form lower ring 49 (FIG. 6) in known manner.
  • the variation employed here adds two slots 82 and 84 to the outer ring 49.
  • This structure is driven from a balanced feed derived from an RF source, not shown, instead of employing inner ring 48 (of FIG. 2b) for one such terminal.
  • This structure does not inhibit circulating eddy currents in either the upper ring or the lower, inner ring.
  • the balanced RF feed provides that the floating inner ring 84 and the common ring 85 behave as virtual grounds.
  • the performance of a structure following FIG. 6 has been compared with a prior art coil (FIG. 2b including outer ring 49).
  • the Q of each of these coils was compared by measurement as a function of distance along the axis for insertion of a capillary tube (from the top direction in the drawings) containing a sample substance.
  • the Q value is derived from measurement of the RF pulse duration (for constant amplitude) required to obtain a 180° nutation of sample spins.
  • the Q of the coil is proportional to the inverse square of the 180° pulse duration.
  • FIG. 7 Q as a function of displacement along the axis of the coil was found to decrease as expected with the capillary insertion and also found to continue to decrease as the insertion of the capillary tip continued beyond the operative edge 69 into the lower ring structure 49 of the prior art coil.
  • the measured Q became independent of insertion length beyond the corresponding aperture edge 69' as shown by the dotted line as the capillary tip entered the region surrounded by the ring structure 49.
  • FIG. 8 there is shown another embodiment. The construction here follows that of FIG. 4a with the addition of slots 64 and 66 in the lower ring 68 to provide for a balanced feed from an RF source not shown.
  • An electrically floating inner coaxial lower ring 72 is provided to furnish desired capacitance coupling between portions of the (segmented) lower ring.
  • This inner coaxial ring is also slotted to substantially eliminate support for circulating eddy currents.
  • the slot in the inner coaxial ring 72 is properly aligned with slot 70 or aligned in 180° relationship with slot 70. That is, the slot coincides with a locus of vanishing RF current distribution.
  • the conductor 60a and that portion of the lower ring between gaps 70 and 66 are inductively coupled to the symmetrically corresponding portions of the coil with the result that the interior value of the coil is uniformly irradiated by an RF field of TM-like symmetry.
  • the balanced RF feed may be applied to terminals 92 and 94 or terminals 90 and 94. Both of these alternatives are rich in RF resonant response requiring values for the several capacitances and inductances even for quantitative analysis.
  • the simplest excitation via terminals 92 and 94 yields an RF field distribution of
  • slot 70 need not be continued through lower ring 68 in the embodiment of FIG. 8 because slots 66 and 68 serve the purpose of impeding a circulating eddy current.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Abstract

Structure simple de bobine en sellette HF comprenant au moins deux éléments (42, 40) parallèles à un axe z et se terminant par deux éléments annulaires (46, 48). L'introduction d'au moins une fente (70) à travers un élément parallèle (40) et les éléments annulaires associés (46, 48) élimine les courants de Foucault circulant dans les éléments annulaires lorsqu'on applique un champ magnétique pulsé dans la direction z.
PCT/US1992/002738 1991-04-05 1992-04-03 Bobine en sellette hf destinee a etre utilisee avec des champs magnetiques pulses WO1992017799A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US68121891A 1991-04-05 1991-04-05
US681,218 1991-04-05

Publications (1)

Publication Number Publication Date
WO1992017799A1 true WO1992017799A1 (fr) 1992-10-15

Family

ID=24734313

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1992/002738 WO1992017799A1 (fr) 1991-04-05 1992-04-03 Bobine en sellette hf destinee a etre utilisee avec des champs magnetiques pulses

Country Status (1)

Country Link
WO (1) WO1992017799A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1120664A3 (fr) * 2000-01-25 2002-05-29 Varian, Inc. Insertion distribuée de capacitances dans des têtes de RMN
US6812703B2 (en) 2002-12-17 2004-11-02 Varian, Inc. Radio frequency NMR resonator with split axial shields

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4737715A (en) * 1985-02-14 1988-04-12 Jeol Ltd. Coil system for nuclear magnetic resonance spectrometer probe
US4875013A (en) * 1987-03-13 1989-10-17 Hitachi, Ltd. High-frequency coil for nuclear magnetic imaging

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4737715A (en) * 1985-02-14 1988-04-12 Jeol Ltd. Coil system for nuclear magnetic resonance spectrometer probe
US4875013A (en) * 1987-03-13 1989-10-17 Hitachi, Ltd. High-frequency coil for nuclear magnetic imaging

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1120664A3 (fr) * 2000-01-25 2002-05-29 Varian, Inc. Insertion distribuée de capacitances dans des têtes de RMN
US6498487B1 (en) 2000-01-25 2002-12-24 Varian, Inc. Distributed capacitance inserts for NMR probes
EP1703295A3 (fr) * 2000-01-25 2007-04-18 Ronald L. Haner Ajout de capacité électrostatique distribuée aux sondes NMR
US6812703B2 (en) 2002-12-17 2004-11-02 Varian, Inc. Radio frequency NMR resonator with split axial shields

Similar Documents

Publication Publication Date Title
US6696838B2 (en) Nuclear magnetic resonance analysis of multiple samples
Hoult et al. Critical factors in the design of sensitive high resolution nuclear magnetic resonance spectrometers
US8106657B2 (en) Apparatus for high-resolution NMR spectroscopy and/or imaging with an improved filling factor and RF field amplitude
US7081753B2 (en) Multiple tuned scroll coil
EP0968437B1 (fr) Agencement coplanaire d'enroulements de sonde haute frequence et a supraconduction haute temperature (hts) pour excitation rmn multifrequence
US5212450A (en) Radio frequency volume resonator for nuclear magnetic resonance
Jensen et al. Reduction of pulsed gradient settling time in the superconducting magnet of a magnetic resonance instrument
US6573720B1 (en) Resonant structure for spatial and spectral-spatial imaging of free radical spin probes using radiofrequency time domain electron paramagnetic resonance spectroscopy
US4573015A (en) Method of measuring internal information from a target by using nuclear magnetic resonance
JP2004526547A (ja) Ｍｒ装置用の送信及び受信コイル
CA2008555C (fr) Methode et appareil de reduction des variations du champ magnetique de base dans un dispositif a resonnance magnetique par les gradients de champs pulses
US4866387A (en) NMR detector network
US4626784A (en) NMR imaging device
US5382903A (en) Magnetic resonance apparatus
US6812703B2 (en) Radio frequency NMR resonator with split axial shields
Rinard et al. A wire‐crossed‐loop resonator for rapid scan EPR
WO1992017799A1 (fr) Bobine en sellette hf destinee a etre utilisee avec des champs magnetiques pulses
EP0856744B1 (fr) Sonde de RMN incorporant un blindage HF de l'échantillon
JPH1090385A (ja) Ｒｆコイルアセンブリ
US5019778A (en) Magnetic resonance apparatus with an optimized detection field
EP0845108B1 (fr) Imagerie par resonance magnetique
WO2012174249A2 (fr) Procédé et appareil de production de signal de résonateur et mesure de celui-ci
Murphy et al. A comparison of three radiofrequency coils for NMR studies of conductive samples
EP1247114B1 (fr) Reseaux supraconducteurs servant a optimiser des bobines de rmn accord es de facon multiple
JP2001041913A (ja) Ｎｍｒプローブ

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): DE GB JP

REG Reference to national code

Ref country code: DE

Ref legal event code: 8642