CA1210061A - Nuclear magnetic resonance apparatus having semitoroidal rf coil for use in topical nmr and nmr imaging - Google Patents
Nuclear magnetic resonance apparatus having semitoroidal rf coil for use in topical nmr and nmr imagingInfo
- Publication number
- CA1210061A CA1210061A CA000449961A CA449961A CA1210061A CA 1210061 A CA1210061 A CA 1210061A CA 000449961 A CA000449961 A CA 000449961A CA 449961 A CA449961 A CA 449961A CA 1210061 A CA1210061 A CA 1210061A
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- Canada
- Prior art keywords
- coil
- semitoroidal
- nmr
- improvement defined
- magnetic field
- Prior art date
- Legal status (The legal status 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 status listed.)
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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
- G01R33/32—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
- G01R33/34053—Solenoid coils; Toroidal 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
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/483—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy
- G01R33/4831—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy using B1 gradients, e.g. rotating frame techniques, use of surface coils
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S505/00—Superconductor technology: apparatus, material, process
- Y10S505/825—Apparatus per se, device per se, or process of making or operating same
- Y10S505/842—Measuring and testing
- Y10S505/843—Electrical
- Y10S505/844—Nuclear magnetic resonance, NMR, system or device
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- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- High Energy & Nuclear Physics (AREA)
- Magnetic Resonance Imaging Apparatus (AREA)
Abstract
NUCLEAR MAGNETIC RESONANCE APPARATUS HAVING
SEMITOROIDAL RF COIL FOR USE IN TOPICAL NMR
AND NMR IMAGING
ABSTRACT OF THE DISCLOSURE
An improved nuclear magnetic resonance (NMR) apparatus for use in topical magnetic resonance (TMR) spectroscopy and other remote sensing NMR applications includes a semi-toroidal radio frequency (rf) coil. The semitoroidal rf coil produces an effective alternating magnetic field at a distance from the poles of the coil, so as to enable NMR
measurements to be taken from selected regions inside an object, particularly including human and other living sub-jects. The semitoroidal rf coil is relatively insensitive to magnetic interference from metallic objects located behind the coil, thereby rendering the coil particularly suited for use in both conventional and superconducting NMR magnets. The semitoroidal NMR coil can be constructed so that it emits little or no excess rf electric field associated with the rf magnetic field, thus avoiding adverse effects due to dielectric heating of the sample or to any other interaction of the electric field with the sample.
SEMITOROIDAL RF COIL FOR USE IN TOPICAL NMR
AND NMR IMAGING
ABSTRACT OF THE DISCLOSURE
An improved nuclear magnetic resonance (NMR) apparatus for use in topical magnetic resonance (TMR) spectroscopy and other remote sensing NMR applications includes a semi-toroidal radio frequency (rf) coil. The semitoroidal rf coil produces an effective alternating magnetic field at a distance from the poles of the coil, so as to enable NMR
measurements to be taken from selected regions inside an object, particularly including human and other living sub-jects. The semitoroidal rf coil is relatively insensitive to magnetic interference from metallic objects located behind the coil, thereby rendering the coil particularly suited for use in both conventional and superconducting NMR magnets. The semitoroidal NMR coil can be constructed so that it emits little or no excess rf electric field associated with the rf magnetic field, thus avoiding adverse effects due to dielectric heating of the sample or to any other interaction of the electric field with the sample.
Description
Q6~
NUCLEAR MAGNETIC RESONANCE APPARATUS HAVING
SEMITOROIDAL RF COIL ~OR USE IN TOPICAL NMR
AND NMR IMAGING
~he invention disclosed herein is generally related to the analytical and diagnostic applications of nuclear mag-netic resonanCe (NMR). More specifically, this invention is related to topical magnetic resonance (TMR) spectros-copy~ NMR imaging, and other NM~ applications.
Topical magne~ic resonance ~TM~ spectroscopy and NMR
imaging are variations of NMR spectroscopy in which an N~R
signal is obtained from material located inside an objeck. In recent years ~he development o~ TMR spectros-copy and of closely related NMR imaging have greatl~
lncreased the appli~ations of NMR in the fields of biology and medicineO 5pecifically, TMR has been shown to be use-~Ul as a non-invasive method of obtaining biochemical and physiological in~ormation ~rom localized regions inside living animals, particularly in~luding human sub jects. In actual demonstrations of the method, ~pecific metaboli~es have been identified, and from such information diseases and me~a~olic disorders have b~en diagnosed.
NMR ~pectroscopy has also been employed in a three-dimensional ~canning mode to provide NMR imaging. Such imaging has been shown to be comparable with x-ray com-puter tomoyraphy ~CT) imaging with respect to ~he quality of picture resolution tha~ can be ob~ained. ~nlike CT
imaging, however, NMR ~maging can distinguish regions hav-ing the same probe nucleu~ den~ity but having different ~l2~6~
local molecular environments. ~he major advantage of both NMR and CT imaging is that the internal tissues of a live animal can be studied without resorting to surgery or otherwise disturbing the metabolism of the animal. NMR
imaging offers an addltional advantage over CT imaging techniques in that no ioni~ing x-ray radiation is employed.
In all NMR instruments, the sample or article to be analyzed is positioned in the static magnetic field of a large magnet. A radio-frequency (rf) coil irradia~es the sample with an alterna~ing magnetic field, which ls absorbed at certain resonant frequencies that are charac-teristic of the chemical structure and composition of the sample. The absorbed energy is re-radiated by the sample and detected with a suitable receiving coil. In most mod-ern instruments, this ~ignal is detected by ~he rf irradi-ation coil, which serves in such ins~ruments in a duplex mode as bo~th transmitter and receiver.
In ty~ical NMR instruments th2 rf coil is a cylindri cal solenoidal coil which surrounds a small sample. ~n TMR applications, however, the object to be analyzed is ordinarily large and the rf coil must necessarily be located outside the object. ~ccordingly, remote sensing rf coils have been sought which can be placed against the 2S exterior surface of a sample object and selectively pro-ject an alternating magnetic field into the interior of the object, and which can ~urther operate to detect the induced rf signal~ all wi~hin ~he spatial confines imposed by the ~hape of the external electromagnet. Remote sens-ing studies to date have employed what is known as a sur-fac~ coil~ or pancake coil, which is a planar multi-turn coil that is placed flat against the surfa~e o~ an object.
There are sevaral disadvantages associated with ~uch a planar surface coil. First, the surfare coil gener~tes a large amount of undesirable rf electric field in addition 6 ~
to the rf magnetic field. The electric field is undesir-able because it induces dielectric as well as ohmic heat-ing of the ~ample, whioh must be avoided, particularly in hum~n and other living subjects. Further, a large rf 5 ~lectric field can present an electrical .shock hazard.
Addi~ionally, ~he surface coil is not very efficient in producing a deeply penetrating rf magnetic field because the rf field is shaped such that its strength diminishes rapidly with distance from the coil, resulting in proportionately stronger signals from regions near the coil an~ weaker signals from regions deeper in the sam-ple. Ano~her disadvantage is that the rf field from a planar surface coil projects in both directions from the plane of the coil, so that ~he stzength and shape of the field projected into the sample i5 affected by any metal components located behind ~he surface coil, such as the magnet polepieces, the magnet dewars in a liquid-helium-cooled superconducting magnet, or other components of the NMR spectrometer. Also, nearby metal objects may cause noise in the signal received by the rf coil.
SUMMARY OF THE INVENTION
Accordingly, it is an object and purpose of the pres-ent invention to provide an improved NMR apparatus for use in topical magnetic resonance spectroscopy and NMR imag-ing, ~herein the improvemen~ comprises an rf coil that iscapable of projec~ing an alternating magnetic field into an article from a location ou~side the article. It is also an object to provide su~h an rf coil which produces a minimum of r~ electric field, thereby minimizing adverse dielectric heating effects on the sample object.
I~ is also an object of he present invention to pro-vide, for use in an NMR spectrometer, an improved rf coil that projects an rf magnetic field at a distance from ~he coil, the intensity and shape of which are largely free of adverse effects from nearby metallic components~
Additional objects, advantages and novel features of the invention wlll be set forth in part in the de.scription which follows, and in part will beco~e apparent to those skilled in the art upon examination of the following or may be learned by practice of th~ invention~ The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combina-tions particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as embodied and broadly described herein, the present inven-tion provides an improved ~MR apparatus in which the improvement comprises an rf coil having a shape that is topologically equivalent to that of a truncated toroid, or semitoroid, and including open ends from which an alter-nating magnetic field may be projected. In application, the truncated ends of the semitoroidal coil are placed adjacent t-o or 1ush against the surface of an object to be studied. The semitoroidal rf coil produces an rf mag-netic field that is projected into the interior of theobject to a depth which is on the order of the diameter of the semitoroidal coil.
The semitoroidal rf coil is relatively insensitive to metallic objects located behind the coil, since the compo-nent of the rf magnetic field located behind the plane ofthe open coil ends is contained substantially within the confines of the semitoroid, where it is effectively shielded from effects of any nearby metallic objects.
The semitoroidal rf coil can be made relatively insen-sitive to NMR ~ignals from those regions of ~he sampleclosest to the coil~ i.e. t close ~o the surface o~ the object, by orienting the coil so that the axis of the ~tatic magnetic field extends parallel to ~he ~wo~fold rotation 3ymmetry axis of the coil. Since ~he nuclear magnetic resonance effect is proportional to ~he intensity of the component of the rf magnetic field extending pe~-pendicular to the axis of the static magnetic field/ NMR
signals produced in the sample object near ~he end~ of the semitoroid, where ~he rf magnetic field is approximately parallel to the static magnetic field, are attenuated.
The effective region ~rom which an NMR signal is obtained with such an arrangement is ~ volume centered about the aforementioned t~!o-fold symmetry axis and extending some dlstance away from the open ends of the coil~ This effec-tive region is more distinctly defined than the effectiveregion of siqnal generation for the previously known planar surface coils or, for that matter, ~or the semi-toroid with the magnetic fields arranged in ~ny other way.
In accordance with another aspect of the invention, a small semitoroidal shim coil can be nested concentrically inside the semitoroidal rf coil~ The shim coil is wound in the direction opposite to that of the rf coil (or, alternatively, the coil is wound in the same directlon and the current flow is in the opposite direction) so as to produce an rf magnetic shim field which ~ounteracts and partially cancels the primary rf field at short dis-tances. At greater distances ~he primary rf field is relatively unaffected by ~he field from the shim coil.
With such an arrangement the effective volume of signal generation within the sample is even more naxrowly define~
and is located at a distance from the coil~ The useful rf ~ignal is thus concentrated at a dis~ance from the nested pair of coils so that there can be obtained an NMR signal ~rom an isolated region at some distance ~rom the surface wlthin a living ~nimal.
In accordance with ano~her aspect of the invention~
the semitoroidal rf coil is employed as a deooupling coil in an NMR spectrometer. Decoupling coils are used to sup-press the NMR ~pec~rum of one class of nuclei ln a sample ~21~6~
so as ~o simplify and enhance the NMR spectrum of anotherclass of nuclei in the same sample. This is done by irra~
diating the sample at the resonant frequency of the nuclei which are to be suppressed. For exampley the carbon-13 NMR spectrum from a biological sample ~an be significantly simplified and enhanced by irradiating the sample with a magne~ic field alternating at the resonance frequency of hydrogen, thereby suppressing the hydrogen NMR spectrum that would otherwise obscure the mu~h weaker carbon-13 spectrum.
Previously known decoupling coils have suffered from the disadvantaqe of producing substantial stray electric rf fields and thereby causing dielectric heating of the sample. A semitoroidal r~ coil, and in particular a split semitoroidal rf coil coupled to a yrounded conductive plate, as described further below, can be used as a decou-pling coil with substantially redueed dielectric heating.
These and other aspects of the present invention will be apparent to one of ordinary skill in the art upon con-sideration of khe more detailed description of the inven-tion set forth below.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, whi~h are incorporated in and form a part of the specification~ illustrate several embodiments of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:
FIGURE 1 is an isometric view of a ~emitoroidal rf coil ~onstructed in accordance with the present invention ~0 FIG~RE 2 is a plan view of the coil shown in Figure 1, with field llnes to illustrate the shape o ~he magnetic ~ield produced by the coil;
~ IGURE 3 is ~chematic view of a ~emitoroi~al coil as in Figures 1 and 2, oriented with its two-fold symmetry ~xis parallel to an external ~tatic magnetic ield, and illustrating regions of different ~ensitivities;
6~
FIGURE 4 a pictorial isometric view illustrating how a semitoroidal rf coil such as that shown in Fi~ures 1 and 2 may be employed in the bore of a solenoidal superconduct-lng magnet to obtain an NMR signal from tissue inside the arm of a human subject, with a portion of the electromag-net removed for purposes of illustration;
FIGURE 5 i5 another isometric view of the semitoroidal rf coil and superconducting NMR e~ectromagnet shown in Figure 4;
FIGURE 6 is a pictorial illustration of how a semi-toroidal rf field coil such as ~hat shown in ~igures 1 and
NUCLEAR MAGNETIC RESONANCE APPARATUS HAVING
SEMITOROIDAL RF COIL ~OR USE IN TOPICAL NMR
AND NMR IMAGING
~he invention disclosed herein is generally related to the analytical and diagnostic applications of nuclear mag-netic resonanCe (NMR). More specifically, this invention is related to topical magnetic resonance (TMR) spectros-copy~ NMR imaging, and other NM~ applications.
Topical magne~ic resonance ~TM~ spectroscopy and NMR
imaging are variations of NMR spectroscopy in which an N~R
signal is obtained from material located inside an objeck. In recent years ~he development o~ TMR spectros-copy and of closely related NMR imaging have greatl~
lncreased the appli~ations of NMR in the fields of biology and medicineO 5pecifically, TMR has been shown to be use-~Ul as a non-invasive method of obtaining biochemical and physiological in~ormation ~rom localized regions inside living animals, particularly in~luding human sub jects. In actual demonstrations of the method, ~pecific metaboli~es have been identified, and from such information diseases and me~a~olic disorders have b~en diagnosed.
NMR ~pectroscopy has also been employed in a three-dimensional ~canning mode to provide NMR imaging. Such imaging has been shown to be comparable with x-ray com-puter tomoyraphy ~CT) imaging with respect to ~he quality of picture resolution tha~ can be ob~ained. ~nlike CT
imaging, however, NMR ~maging can distinguish regions hav-ing the same probe nucleu~ den~ity but having different ~l2~6~
local molecular environments. ~he major advantage of both NMR and CT imaging is that the internal tissues of a live animal can be studied without resorting to surgery or otherwise disturbing the metabolism of the animal. NMR
imaging offers an addltional advantage over CT imaging techniques in that no ioni~ing x-ray radiation is employed.
In all NMR instruments, the sample or article to be analyzed is positioned in the static magnetic field of a large magnet. A radio-frequency (rf) coil irradia~es the sample with an alterna~ing magnetic field, which ls absorbed at certain resonant frequencies that are charac-teristic of the chemical structure and composition of the sample. The absorbed energy is re-radiated by the sample and detected with a suitable receiving coil. In most mod-ern instruments, this ~ignal is detected by ~he rf irradi-ation coil, which serves in such ins~ruments in a duplex mode as bo~th transmitter and receiver.
In ty~ical NMR instruments th2 rf coil is a cylindri cal solenoidal coil which surrounds a small sample. ~n TMR applications, however, the object to be analyzed is ordinarily large and the rf coil must necessarily be located outside the object. ~ccordingly, remote sensing rf coils have been sought which can be placed against the 2S exterior surface of a sample object and selectively pro-ject an alternating magnetic field into the interior of the object, and which can ~urther operate to detect the induced rf signal~ all wi~hin ~he spatial confines imposed by the ~hape of the external electromagnet. Remote sens-ing studies to date have employed what is known as a sur-fac~ coil~ or pancake coil, which is a planar multi-turn coil that is placed flat against the surfa~e o~ an object.
There are sevaral disadvantages associated with ~uch a planar surface coil. First, the surfare coil gener~tes a large amount of undesirable rf electric field in addition 6 ~
to the rf magnetic field. The electric field is undesir-able because it induces dielectric as well as ohmic heat-ing of the ~ample, whioh must be avoided, particularly in hum~n and other living subjects. Further, a large rf 5 ~lectric field can present an electrical .shock hazard.
Addi~ionally, ~he surface coil is not very efficient in producing a deeply penetrating rf magnetic field because the rf field is shaped such that its strength diminishes rapidly with distance from the coil, resulting in proportionately stronger signals from regions near the coil an~ weaker signals from regions deeper in the sam-ple. Ano~her disadvantage is that the rf field from a planar surface coil projects in both directions from the plane of the coil, so that ~he stzength and shape of the field projected into the sample i5 affected by any metal components located behind ~he surface coil, such as the magnet polepieces, the magnet dewars in a liquid-helium-cooled superconducting magnet, or other components of the NMR spectrometer. Also, nearby metal objects may cause noise in the signal received by the rf coil.
SUMMARY OF THE INVENTION
Accordingly, it is an object and purpose of the pres-ent invention to provide an improved NMR apparatus for use in topical magnetic resonance spectroscopy and NMR imag-ing, ~herein the improvemen~ comprises an rf coil that iscapable of projec~ing an alternating magnetic field into an article from a location ou~side the article. It is also an object to provide su~h an rf coil which produces a minimum of r~ electric field, thereby minimizing adverse dielectric heating effects on the sample object.
I~ is also an object of he present invention to pro-vide, for use in an NMR spectrometer, an improved rf coil that projects an rf magnetic field at a distance from ~he coil, the intensity and shape of which are largely free of adverse effects from nearby metallic components~
Additional objects, advantages and novel features of the invention wlll be set forth in part in the de.scription which follows, and in part will beco~e apparent to those skilled in the art upon examination of the following or may be learned by practice of th~ invention~ The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combina-tions particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as embodied and broadly described herein, the present inven-tion provides an improved ~MR apparatus in which the improvement comprises an rf coil having a shape that is topologically equivalent to that of a truncated toroid, or semitoroid, and including open ends from which an alter-nating magnetic field may be projected. In application, the truncated ends of the semitoroidal coil are placed adjacent t-o or 1ush against the surface of an object to be studied. The semitoroidal rf coil produces an rf mag-netic field that is projected into the interior of theobject to a depth which is on the order of the diameter of the semitoroidal coil.
The semitoroidal rf coil is relatively insensitive to metallic objects located behind the coil, since the compo-nent of the rf magnetic field located behind the plane ofthe open coil ends is contained substantially within the confines of the semitoroid, where it is effectively shielded from effects of any nearby metallic objects.
The semitoroidal rf coil can be made relatively insen-sitive to NMR ~ignals from those regions of ~he sampleclosest to the coil~ i.e. t close ~o the surface o~ the object, by orienting the coil so that the axis of the ~tatic magnetic field extends parallel to ~he ~wo~fold rotation 3ymmetry axis of the coil. Since ~he nuclear magnetic resonance effect is proportional to ~he intensity of the component of the rf magnetic field extending pe~-pendicular to the axis of the static magnetic field/ NMR
signals produced in the sample object near ~he end~ of the semitoroid, where ~he rf magnetic field is approximately parallel to the static magnetic field, are attenuated.
The effective region ~rom which an NMR signal is obtained with such an arrangement is ~ volume centered about the aforementioned t~!o-fold symmetry axis and extending some dlstance away from the open ends of the coil~ This effec-tive region is more distinctly defined than the effectiveregion of siqnal generation for the previously known planar surface coils or, for that matter, ~or the semi-toroid with the magnetic fields arranged in ~ny other way.
In accordance with another aspect of the invention, a small semitoroidal shim coil can be nested concentrically inside the semitoroidal rf coil~ The shim coil is wound in the direction opposite to that of the rf coil (or, alternatively, the coil is wound in the same directlon and the current flow is in the opposite direction) so as to produce an rf magnetic shim field which ~ounteracts and partially cancels the primary rf field at short dis-tances. At greater distances ~he primary rf field is relatively unaffected by ~he field from the shim coil.
With such an arrangement the effective volume of signal generation within the sample is even more naxrowly define~
and is located at a distance from the coil~ The useful rf ~ignal is thus concentrated at a dis~ance from the nested pair of coils so that there can be obtained an NMR signal ~rom an isolated region at some distance ~rom the surface wlthin a living ~nimal.
In accordance with ano~her aspect of the invention~
the semitoroidal rf coil is employed as a deooupling coil in an NMR spectrometer. Decoupling coils are used to sup-press the NMR ~pec~rum of one class of nuclei ln a sample ~21~6~
so as ~o simplify and enhance the NMR spectrum of anotherclass of nuclei in the same sample. This is done by irra~
diating the sample at the resonant frequency of the nuclei which are to be suppressed. For exampley the carbon-13 NMR spectrum from a biological sample ~an be significantly simplified and enhanced by irradiating the sample with a magne~ic field alternating at the resonance frequency of hydrogen, thereby suppressing the hydrogen NMR spectrum that would otherwise obscure the mu~h weaker carbon-13 spectrum.
Previously known decoupling coils have suffered from the disadvantaqe of producing substantial stray electric rf fields and thereby causing dielectric heating of the sample. A semitoroidal r~ coil, and in particular a split semitoroidal rf coil coupled to a yrounded conductive plate, as described further below, can be used as a decou-pling coil with substantially redueed dielectric heating.
These and other aspects of the present invention will be apparent to one of ordinary skill in the art upon con-sideration of khe more detailed description of the inven-tion set forth below.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, whi~h are incorporated in and form a part of the specification~ illustrate several embodiments of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:
FIGURE 1 is an isometric view of a ~emitoroidal rf coil ~onstructed in accordance with the present invention ~0 FIG~RE 2 is a plan view of the coil shown in Figure 1, with field llnes to illustrate the shape o ~he magnetic ~ield produced by the coil;
~ IGURE 3 is ~chematic view of a ~emitoroi~al coil as in Figures 1 and 2, oriented with its two-fold symmetry ~xis parallel to an external ~tatic magnetic ield, and illustrating regions of different ~ensitivities;
6~
FIGURE 4 a pictorial isometric view illustrating how a semitoroidal rf coil such as that shown in Fi~ures 1 and 2 may be employed in the bore of a solenoidal superconduct-lng magnet to obtain an NMR signal from tissue inside the arm of a human subject, with a portion of the electromag-net removed for purposes of illustration;
FIGURE 5 i5 another isometric view of the semitoroidal rf coil and superconducting NMR e~ectromagnet shown in Figure 4;
FIGURE 6 is a pictorial illustration of how a semi-toroidal rf field coil such as ~hat shown in ~igures 1 and
2 might be used in an even larger superconducting NMR mag-net ~o o~tain diagnostic NM~ signals from tissue deep inside a human subject, with part of the electromagnet removed for purposes of illustration:
FIGURE 7 is an iRometric illustration of a ~emitoroi-- dal ~f coil, such as that shown in Figures 1 and 2, posi-tloned between th~ polepieces of a con~entional iron core NMR electromagnet:
FI~URE 8 is a side elevation view of the NMR system shown in Figure 7, illustrating how an NMR signal migh~ be obtained from tissue inside a person' 5 hand placed ~etween the polepi~ces of the NMR electromagne~, FIGUR~ 9 is an isometric illustration of an al~erna-tive embodiment of the semitoroidal rf coil of Figures 1 and 2, wherein the open ends of the semitoroidal coil are flattened in directions radial to the coil;
FIGURE 10 is an isometric view of another alternative embodiment of the semitoroidal rf coil shown in FigureS 1 and 2, wherein the open ends of the semitoroidal coil are p~nched in directions radial to the circumference of the coil:
~IGURE 11 is ~n isometric ~llustration o~ another alternative embodiment of the semi~oroi~al rf coil of the present invention, wherein the ~emitoroidal form is wound 6~
with two coil windings in parallel, with the sense of the windings opposed to each other, and with the far end of each coil winding connected to a grounded conductive plate which includes openings centered on the faces of the coil;
FIGURE 12 il~ustrates a further alternative ernbodiment o~ the invention consisting of two crossed semitoroidal coils of the type i11ustrated in Figure ll, with each of the four individual ~oil windings being connected to a common srounded plate, FIGURE 13 illustrates another alternative embodiment of the invention, which utilizes a small, oppositely wound shim coil nested concentrically inside a primary semito-roid~l rf coil7 and FIGURE 14 is a graphical representation of the net magnetic field strength as a function of distance away from the shimmed semi~oroidal rf coil of Figure 13; and FIGURE 15 illustrates the use of a semitoroidal coil as a decoupling coil in an otherwise conventional super-conducting NMR spectrometer.
DETAILED VESCRIPTION OF THE INVENTION
Figures l and ~ illustra~e in i~s simplest form a semitoroidal rf coil 10 such as might be used in an NMR
spectrometer. As illustrated; the coil consists simply of an electrical conductor 12 wrapped around a semitoroidal 2~ tubular form l4. The form l4 may be constructed of any suitable dielectric material, provided the material does not contain an element to be analyzed with the spectrom-eter and does not have a significant dielectric 2bsorption at the operat7ng frequency of the ~oil. Under certain conditions, the form 14 may be omitted if the c~il itself ~an be constructed wi~h a conductor that has sufflcient ~truc~ural rigidity ~o maintain i~s shape during ordinary use.
- It should be understood that the shape of the rf coil need not be that of a perfect semitoroid. Other similar shapes which are topologically equivalent may be equally or more suitable, depending on circumstance~.
Figure 2 includes magnetic field lines l6 which indi-cate the general shape of the magnetic field produced by the coil l0. As indicated, the field emerges from one end of the coil and returns to the o~her end. ~he complete field may be described as consisting of ~wo portions - a first, or internal, portion which is enclosed entirely within the tubular confines of ~he coil l0 and a second, or external portion which is external to the coil and which emerges from and returns through the o~en ends of the coil in the manner shown. It i5 the latter portion of the field that is useful in the NMR applications described below.
Figure 3 illustrates the relationship between the mag-netic field of the semitoroidal rf coil 10, as indicated by the field lines 16, and a static, homogenous magnetic field which ex~ends parallel to the two-fold symmetry axis of the coil. NMR siynals are most effectively obtained from regions in which the magnetic field produced by the coil is approximately perpendicular ~o the static field.
These regions are designated by ~he cross hatched areas of Figure 3. As indicated, such regions define a horn-shaped volume which generally extend-~ along the two-fold symmetry axis of the coil. The intensity of the rf mag-netic field decreases with distance from ~he r~ coil, how-ever, so that the portion of the region 18 ~losest tc the rf coil is most effective in producing NMR signals.
Conversely~ NMR signals are least effec~ively obtained ~om regions in which the static field and the rf coil field are ~pproximately parallel~ which are indicated as two cross-hatched regions 19 extending outwardly and away from the end fa~es of the coil.
Figures 4 and 5 illustrate how a semitoroidal rf coil 10 such as that shown in Figures 1 and 2 miyht be used in the bore of a large superconducting NMR magnet 20 ~o obtain TMR measu ements from tissue inside the forearm of a human subject. In the illustrated system, the sizes of both the bore of the magnet and the rf coil are selected so as to permit a person to insert his or her arm into the bore of the magnet and place the forearm in close proxim-ity to o~ in contact with the open ends of the coil 10.
Fur~her, the coil 10 of ~igures 4 and 5 is oriented such that it lies in a plane extendin~ perpendicular to the static magnetic field (which extends along the bore of the magnet), in contrast to the orientation shown in Fig-ure 3. With such an orientation, most of the magnetic 1~ fleld produced by the coil is perpendicular to the static magnetic field, thus making the coil sensitiYe to a greater volume of the sample. This orientation is desir-able where it is merely sought to obtain a signal from a relatively homogenous sample object, without regard to distinguishing among signals obtained from different loca-tions within the object.
Another possible configuration is one in which the plane of the semitoroid is parallel to the static field lines and the two-fold ~xis of symmetry is perpendicular to the static field. This configuration obtains maximum sensitivity in regions near the ends of the semitoroidal coil and minimum sensitivity away from the ends. Appro-priate comparison of signals from the various orientations of the coil ~elative to the static field enables one to . 30 differentiate signals obtained from portions of the sample whlch are close to the ~oil from portions which are deeper within the sample.
~ As noted above, the effectiYe magnetic ~ield generated by the ~emitoroidal coil can be described ~8 ~onsistln~ of two parts; namely, that portion ~xisting inside ~he tubu-lar ~emitoroid, and that portion which is external to the 6~
toroid and which penetrates a sample such as the forearm illustrated in Figures 3 an~ 4. The portion of the may netic field contained inside the semitoroid is effectively isolated from the effects of nearby metallic objectsD for example the inner surface of the superconducting magnet.
As a result, ~he portions of ~he rf magnetic field inside the coil as well as outslde the coil are largely unaffected by ~he proximity of ~he metallic surface behind the coil~ This isolation of the rf magnetic field repre-~ents a subs~antial improvement over previously known rfcoils, which are susceptible to the ef~ects of nearby metallic objects. In this regard, it is noted that any-thing which affects the unused portion of ~he magnetic field also affects the shape and strength of the used por-tion, thereby affecting the performance of the instru-ment.
Figure 6 illustrates another application of the inven-tion which is similar to that shown in Figures 4 and 5, but on a larger scale. In this application a semitoroidal rf coil 10 is used in combination with a very large super-conducting NMR elec~roma~net 21 to ob~ain diagnostic NMR
measurements from ~issue inside the abdomen of a human subject. Again, as with the embodiment described above, the sizes of the superconducting electromagnet and the semitoroidal rf coil are selected so as to obtain an opti-mum configuration for a person of ordinary slze.
~ igure 7 illustrates an applica~ion of he present invention in an NMR spectrometer having a conventional iron core electromagnet 22 consisting of a pair of spaced magnet coils 24 and associated iron polepieces 24a. A
semitoroidal rf coil 10 is positioned between the polepieces 24a of the electromagnet. In thP ~llustrated embodiment~ the rf coil is centered between ~he polepieces and is positioned such that it lies orthogonal to a longi-~udinal central axis 24b extending through the pole-pieces. Further, the rf coil is preferably offset from the axis 24b of the polepieces, such that the effective rf field from the semitoroidal coil is located at a central point on the axis 24b midway between the polepieces, where the magnetic field from the NMR electromagnet ls most S uniform.
Figure 8 illustrates a use of the arrangement shown in Figure 7D ~ person's hand i~ inserted between the pole-pieces 24a and placed edgewise against the faces of the semitoroidal coil lO. In this manner, an NMR measurement is obtained from tissue deep inside the person's hand.
With an actual prototype semitoroidal coil having an over-all dimension of 5 cm and a ~ros~-section 1.5 x 1.5 cm arranged in this manner, the single~shot proton NMR signal from an adult human hand at 5 cm distance and at a fre-quency of 10 MRz has a signal-to-noise ratio o about 10.
This type of application, because of its simplicity of use~ is particularly suited to dlagnostic applications requiring quick biochemical or physiochemical determina-tions, particularly where such determinations need not be obtained from any particular part of a person's body.
Figures 9 and lO illustrate certain modifications of the basic semitoroidal rf coil. In Figure 9, the open ends of a semitoroidal coil 30 are flattened, as by oom-pressing the open ends in direc~ions radial to the coil.
This shapes the magnetic field so as ~o improve the homo-geneity of the field in the direction perpendicular to the plane of the semi~oroid. ~owever~ the major portion of the ~emitoroid is circular ~n cross sec~ion to maximize the quality factor of ~he coil and therefore the intensity of the field produced.
~ igure 10 illustrates a ~oil 32 whi~h is flattened and pinched at its open ~nds to Purther improve ~e Pield homogeneity in ~he direction parallel ~o the plane of the ~emitoroid. One ~an visualize this effect by ~on~idering a case where ~he elongation was carried out ~o the point ~3 such that the ooil has been spl~t lnto two coils. Then, clearly there would be a region between the coil~ where the field ls a relatlve minimum. The minimum can be raised to be a flat dependence, ~.e., uniform field~ by a ~udicious adjustment of the effective distance between the ooils.
Fisure 11 illustrates another embodiment in which a coil 36 includes two coil windings 38 and 40O The wind-ings _ and 40 are driven ~rom a common central point and are reversed in direetion. Further, the windings 38 and 40 are oonnected to an electrically conductive grounded plate 42 The grounded plate 42 includes clrcular open-ings (not ~hown) whi~h coincide with the openings o~ the semitoroidal coil 36. ~ith this configuration~ the sample is not exposed to any stray electri~ field ~ha~ may arise due to voltage differences across the ends of ~he coilf since ~he ends of the coil are maintained at the same electrical po~ential. The apparatus is used simply by placing the grounded plate against an object, such as a part of a person's body, in the same manner as in the applica~ions described above~
The configura~ion shown in Figure 11 renders the appara~us safer in clinical applications, because there is no direc~ shock hazard from the ends of the coil. Addi-?5 tionallyt diele~tric heating of a ~amp}e due ~o stray rfelectric field is minimiæedO This advantage also has lmportant ramifications for ~he u~e of the coil as a decoupling coil for the second ~rradiation in a double resonance experimen~ ~or example, ln order to obtain NMR
signals from carbon-13 nuclei, lt is usually necessary to continuously irradia~e the protons ~t their resonant fre quency in order ~4 decouple the ef ect of the protons on the ~ar~on~13 resonance. Because of the high proton fre-quency ~s well a~ ~he large duty cycle of lrradiation, thi proton irradiation readily heats living ~lssue unless 6~
the rf electric fleld accompanying the rf magnetic field can be suppressed~ Another advantage is ~hat the signal to noise ratio is not adversely affected by the coupling of the dielectric noise to the coil. The si~3nal to noise ratio can be improved even more over a coil with identical dimensions because the parallel electrical connections permit a larger number of turns for the same inductance.
Finally, ~he tuning parameters are less affected by the electric field interaction of the sample with the coil, thus simplifying the operation of the coil For further improved performance, additional semito-roidal coils as shown in ~igure 11 may be utilized, as shown for example in Figure 12. Figure 12 illustrates a second semitoroid _ place~ at a righ~ angle ~o a first semitoroid 46, with the coils including a total o~ ~our electrical windings 4B, 50, 52 ad 54. The four windings are driven from a ~ommon center at the top of ~he arrange-ment, and are each connected to a grounded plate 56. In this way, 1.4 times the field from each coil is avail-able. In this embodiment, the two coils 44 and 46 may bedriven with rf currents that are phase shifted by 90 so that th~ contributions ~rom the ~wo co-ils are added con-structively ~o yield a circularly polarized rf field~
Figure 13 illustrates the use of a shim coil 60 ~o ~5 ~urther enhance the per~ormance of a semitoroidal primary rf coil. The shim coil 60 consists of a smal} semitoroi-dal rf coil which is ne~ted concentrically inslde the pri-mary rf coil 62. The shim coil 60 is driven with an rf electrical current so as to produce a co~nteracting rf magnetic fieldO The field from the shim coil ~0 is ad~usted to partially cance} the field from the primarY
coil 62 at some di~tance close to ~he common center plane ~ of the coils. At greater distances, however, the ield of ~he shim coil i~ weaker and has less effect, such ~hat ~he
FIGURE 7 is an iRometric illustration of a ~emitoroi-- dal ~f coil, such as that shown in Figures 1 and 2, posi-tloned between th~ polepieces of a con~entional iron core NMR electromagnet:
FI~URE 8 is a side elevation view of the NMR system shown in Figure 7, illustrating how an NMR signal migh~ be obtained from tissue inside a person' 5 hand placed ~etween the polepi~ces of the NMR electromagne~, FIGUR~ 9 is an isometric illustration of an al~erna-tive embodiment of the semitoroidal rf coil of Figures 1 and 2, wherein the open ends of the semitoroidal coil are flattened in directions radial to the coil;
FIGURE 10 is an isometric view of another alternative embodiment of the semitoroidal rf coil shown in FigureS 1 and 2, wherein the open ends of the semitoroidal coil are p~nched in directions radial to the circumference of the coil:
~IGURE 11 is ~n isometric ~llustration o~ another alternative embodiment of the semi~oroi~al rf coil of the present invention, wherein the ~emitoroidal form is wound 6~
with two coil windings in parallel, with the sense of the windings opposed to each other, and with the far end of each coil winding connected to a grounded conductive plate which includes openings centered on the faces of the coil;
FIGURE 12 il~ustrates a further alternative ernbodiment o~ the invention consisting of two crossed semitoroidal coils of the type i11ustrated in Figure ll, with each of the four individual ~oil windings being connected to a common srounded plate, FIGURE 13 illustrates another alternative embodiment of the invention, which utilizes a small, oppositely wound shim coil nested concentrically inside a primary semito-roid~l rf coil7 and FIGURE 14 is a graphical representation of the net magnetic field strength as a function of distance away from the shimmed semi~oroidal rf coil of Figure 13; and FIGURE 15 illustrates the use of a semitoroidal coil as a decoupling coil in an otherwise conventional super-conducting NMR spectrometer.
DETAILED VESCRIPTION OF THE INVENTION
Figures l and ~ illustra~e in i~s simplest form a semitoroidal rf coil 10 such as might be used in an NMR
spectrometer. As illustrated; the coil consists simply of an electrical conductor 12 wrapped around a semitoroidal 2~ tubular form l4. The form l4 may be constructed of any suitable dielectric material, provided the material does not contain an element to be analyzed with the spectrom-eter and does not have a significant dielectric 2bsorption at the operat7ng frequency of the ~oil. Under certain conditions, the form 14 may be omitted if the c~il itself ~an be constructed wi~h a conductor that has sufflcient ~truc~ural rigidity ~o maintain i~s shape during ordinary use.
- It should be understood that the shape of the rf coil need not be that of a perfect semitoroid. Other similar shapes which are topologically equivalent may be equally or more suitable, depending on circumstance~.
Figure 2 includes magnetic field lines l6 which indi-cate the general shape of the magnetic field produced by the coil l0. As indicated, the field emerges from one end of the coil and returns to the o~her end. ~he complete field may be described as consisting of ~wo portions - a first, or internal, portion which is enclosed entirely within the tubular confines of ~he coil l0 and a second, or external portion which is external to the coil and which emerges from and returns through the o~en ends of the coil in the manner shown. It i5 the latter portion of the field that is useful in the NMR applications described below.
Figure 3 illustrates the relationship between the mag-netic field of the semitoroidal rf coil 10, as indicated by the field lines 16, and a static, homogenous magnetic field which ex~ends parallel to the two-fold symmetry axis of the coil. NMR siynals are most effectively obtained from regions in which the magnetic field produced by the coil is approximately perpendicular ~o the static field.
These regions are designated by ~he cross hatched areas of Figure 3. As indicated, such regions define a horn-shaped volume which generally extend-~ along the two-fold symmetry axis of the coil. The intensity of the rf mag-netic field decreases with distance from ~he r~ coil, how-ever, so that the portion of the region 18 ~losest tc the rf coil is most effective in producing NMR signals.
Conversely~ NMR signals are least effec~ively obtained ~om regions in which the static field and the rf coil field are ~pproximately parallel~ which are indicated as two cross-hatched regions 19 extending outwardly and away from the end fa~es of the coil.
Figures 4 and 5 illustrate how a semitoroidal rf coil 10 such as that shown in Figures 1 and 2 miyht be used in the bore of a large superconducting NMR magnet 20 ~o obtain TMR measu ements from tissue inside the forearm of a human subject. In the illustrated system, the sizes of both the bore of the magnet and the rf coil are selected so as to permit a person to insert his or her arm into the bore of the magnet and place the forearm in close proxim-ity to o~ in contact with the open ends of the coil 10.
Fur~her, the coil 10 of ~igures 4 and 5 is oriented such that it lies in a plane extendin~ perpendicular to the static magnetic field (which extends along the bore of the magnet), in contrast to the orientation shown in Fig-ure 3. With such an orientation, most of the magnetic 1~ fleld produced by the coil is perpendicular to the static magnetic field, thus making the coil sensitiYe to a greater volume of the sample. This orientation is desir-able where it is merely sought to obtain a signal from a relatively homogenous sample object, without regard to distinguishing among signals obtained from different loca-tions within the object.
Another possible configuration is one in which the plane of the semitoroid is parallel to the static field lines and the two-fold ~xis of symmetry is perpendicular to the static field. This configuration obtains maximum sensitivity in regions near the ends of the semitoroidal coil and minimum sensitivity away from the ends. Appro-priate comparison of signals from the various orientations of the coil ~elative to the static field enables one to . 30 differentiate signals obtained from portions of the sample whlch are close to the ~oil from portions which are deeper within the sample.
~ As noted above, the effectiYe magnetic ~ield generated by the ~emitoroidal coil can be described ~8 ~onsistln~ of two parts; namely, that portion ~xisting inside ~he tubu-lar ~emitoroid, and that portion which is external to the 6~
toroid and which penetrates a sample such as the forearm illustrated in Figures 3 an~ 4. The portion of the may netic field contained inside the semitoroid is effectively isolated from the effects of nearby metallic objectsD for example the inner surface of the superconducting magnet.
As a result, ~he portions of ~he rf magnetic field inside the coil as well as outslde the coil are largely unaffected by ~he proximity of ~he metallic surface behind the coil~ This isolation of the rf magnetic field repre-~ents a subs~antial improvement over previously known rfcoils, which are susceptible to the ef~ects of nearby metallic objects. In this regard, it is noted that any-thing which affects the unused portion of ~he magnetic field also affects the shape and strength of the used por-tion, thereby affecting the performance of the instru-ment.
Figure 6 illustrates another application of the inven-tion which is similar to that shown in Figures 4 and 5, but on a larger scale. In this application a semitoroidal rf coil 10 is used in combination with a very large super-conducting NMR elec~roma~net 21 to ob~ain diagnostic NMR
measurements from ~issue inside the abdomen of a human subject. Again, as with the embodiment described above, the sizes of the superconducting electromagnet and the semitoroidal rf coil are selected so as to obtain an opti-mum configuration for a person of ordinary slze.
~ igure 7 illustrates an applica~ion of he present invention in an NMR spectrometer having a conventional iron core electromagnet 22 consisting of a pair of spaced magnet coils 24 and associated iron polepieces 24a. A
semitoroidal rf coil 10 is positioned between the polepieces 24a of the electromagnet. In thP ~llustrated embodiment~ the rf coil is centered between ~he polepieces and is positioned such that it lies orthogonal to a longi-~udinal central axis 24b extending through the pole-pieces. Further, the rf coil is preferably offset from the axis 24b of the polepieces, such that the effective rf field from the semitoroidal coil is located at a central point on the axis 24b midway between the polepieces, where the magnetic field from the NMR electromagnet ls most S uniform.
Figure 8 illustrates a use of the arrangement shown in Figure 7D ~ person's hand i~ inserted between the pole-pieces 24a and placed edgewise against the faces of the semitoroidal coil lO. In this manner, an NMR measurement is obtained from tissue deep inside the person's hand.
With an actual prototype semitoroidal coil having an over-all dimension of 5 cm and a ~ros~-section 1.5 x 1.5 cm arranged in this manner, the single~shot proton NMR signal from an adult human hand at 5 cm distance and at a fre-quency of 10 MRz has a signal-to-noise ratio o about 10.
This type of application, because of its simplicity of use~ is particularly suited to dlagnostic applications requiring quick biochemical or physiochemical determina-tions, particularly where such determinations need not be obtained from any particular part of a person's body.
Figures 9 and lO illustrate certain modifications of the basic semitoroidal rf coil. In Figure 9, the open ends of a semitoroidal coil 30 are flattened, as by oom-pressing the open ends in direc~ions radial to the coil.
This shapes the magnetic field so as ~o improve the homo-geneity of the field in the direction perpendicular to the plane of the semi~oroid. ~owever~ the major portion of the ~emitoroid is circular ~n cross sec~ion to maximize the quality factor of ~he coil and therefore the intensity of the field produced.
~ igure 10 illustrates a ~oil 32 whi~h is flattened and pinched at its open ~nds to Purther improve ~e Pield homogeneity in ~he direction parallel ~o the plane of the ~emitoroid. One ~an visualize this effect by ~on~idering a case where ~he elongation was carried out ~o the point ~3 such that the ooil has been spl~t lnto two coils. Then, clearly there would be a region between the coil~ where the field ls a relatlve minimum. The minimum can be raised to be a flat dependence, ~.e., uniform field~ by a ~udicious adjustment of the effective distance between the ooils.
Fisure 11 illustrates another embodiment in which a coil 36 includes two coil windings 38 and 40O The wind-ings _ and 40 are driven ~rom a common central point and are reversed in direetion. Further, the windings 38 and 40 are oonnected to an electrically conductive grounded plate 42 The grounded plate 42 includes clrcular open-ings (not ~hown) whi~h coincide with the openings o~ the semitoroidal coil 36. ~ith this configuration~ the sample is not exposed to any stray electri~ field ~ha~ may arise due to voltage differences across the ends of ~he coilf since ~he ends of the coil are maintained at the same electrical po~ential. The apparatus is used simply by placing the grounded plate against an object, such as a part of a person's body, in the same manner as in the applica~ions described above~
The configura~ion shown in Figure 11 renders the appara~us safer in clinical applications, because there is no direc~ shock hazard from the ends of the coil. Addi-?5 tionallyt diele~tric heating of a ~amp}e due ~o stray rfelectric field is minimiæedO This advantage also has lmportant ramifications for ~he u~e of the coil as a decoupling coil for the second ~rradiation in a double resonance experimen~ ~or example, ln order to obtain NMR
signals from carbon-13 nuclei, lt is usually necessary to continuously irradia~e the protons ~t their resonant fre quency in order ~4 decouple the ef ect of the protons on the ~ar~on~13 resonance. Because of the high proton fre-quency ~s well a~ ~he large duty cycle of lrradiation, thi proton irradiation readily heats living ~lssue unless 6~
the rf electric fleld accompanying the rf magnetic field can be suppressed~ Another advantage is ~hat the signal to noise ratio is not adversely affected by the coupling of the dielectric noise to the coil. The si~3nal to noise ratio can be improved even more over a coil with identical dimensions because the parallel electrical connections permit a larger number of turns for the same inductance.
Finally, ~he tuning parameters are less affected by the electric field interaction of the sample with the coil, thus simplifying the operation of the coil For further improved performance, additional semito-roidal coils as shown in ~igure 11 may be utilized, as shown for example in Figure 12. Figure 12 illustrates a second semitoroid _ place~ at a righ~ angle ~o a first semitoroid 46, with the coils including a total o~ ~our electrical windings 4B, 50, 52 ad 54. The four windings are driven from a ~ommon center at the top of ~he arrange-ment, and are each connected to a grounded plate 56. In this way, 1.4 times the field from each coil is avail-able. In this embodiment, the two coils 44 and 46 may bedriven with rf currents that are phase shifted by 90 so that th~ contributions ~rom the ~wo co-ils are added con-structively ~o yield a circularly polarized rf field~
Figure 13 illustrates the use of a shim coil 60 ~o ~5 ~urther enhance the per~ormance of a semitoroidal primary rf coil. The shim coil 60 consists of a smal} semitoroi-dal rf coil which is ne~ted concentrically inslde the pri-mary rf coil 62. The shim coil 60 is driven with an rf electrical current so as to produce a co~nteracting rf magnetic fieldO The field from the shim coil ~0 is ad~usted to partially cance} the field from the primarY
coil 62 at some di~tance close to ~he common center plane ~ of the coils. At greater distances, however, the ield of ~he shim coil i~ weaker and has less effect, such ~hat ~he
3~ effective magnetic field from the primary coil 6~ is 6~
lS
located at a distance from the common plane. The effect of the shim coil is further lllustrated in Figure l~, which indicates graphically how the field rom the Rhim coil ~nd the field from th~ primary coil cancel one another at close distance~ leaving a net field which is greatest at a distance from the assembly.
Pigure 15 illustr~tes the use of a ~emitoroidal rf coil 64 as ~ decoupling coil in the am~ient temperature bore of a superconducting magnet S6~ A ~ample 6B is enclosed in a conYentional solenoidal rf coil 7~ and is rotated abou~ a horizontal axis that extends perpendicular to the axis of two-fold ~ymmetry of the ~emitoroidal decoupling ~oil 64. Although ~he primary rf coil 70 is illustrated as beiny a conventional ~olenoidal coil, i~
should be understood that both the primary and decoupling coil~ could be semitoroidal. The decoupling coil 64 of Figure 15 includes split windings of the ~ype shown in Figure ll, and also includes a ground plate 64a to mini-mize stray electric field and minimize dielec~ric heating of the sample.
The foregoing description of various embodiments of the invention has been presented for purpose~ of illustra-tion ~nd descrip~ion. It is not intended to be exhaustive or ~o limit the invention to the precise forms disclosed, and there are various ~odific~tions, substitutions and ~lter~tion~ tha~ will be ~ppa~ent to one of ordinary ~kill in the ~rt in view of the above teaching. The embodiments disclosed were chosen and described in order ~o best explain the principles of the invention and it~ practical ~ appli~ation ~o a~ to ~hereby ~nable o~hers 3killed ~n the art ~o best u~ilize the ~nven~ion in variou~ ~mbodiments and with various modifi~ations as ~re suited ~o ~he par-ticular u3e ~ontemplated. I~ i~ in~ended eha~ ~he ~cope o the invention be defined by the claims appended hereto.
lS
located at a distance from the common plane. The effect of the shim coil is further lllustrated in Figure l~, which indicates graphically how the field rom the Rhim coil ~nd the field from th~ primary coil cancel one another at close distance~ leaving a net field which is greatest at a distance from the assembly.
Pigure 15 illustr~tes the use of a ~emitoroidal rf coil 64 as ~ decoupling coil in the am~ient temperature bore of a superconducting magnet S6~ A ~ample 6B is enclosed in a conYentional solenoidal rf coil 7~ and is rotated abou~ a horizontal axis that extends perpendicular to the axis of two-fold ~ymmetry of the ~emitoroidal decoupling ~oil 64. Although ~he primary rf coil 70 is illustrated as beiny a conventional ~olenoidal coil, i~
should be understood that both the primary and decoupling coil~ could be semitoroidal. The decoupling coil 64 of Figure 15 includes split windings of the ~ype shown in Figure ll, and also includes a ground plate 64a to mini-mize stray electric field and minimize dielec~ric heating of the sample.
The foregoing description of various embodiments of the invention has been presented for purpose~ of illustra-tion ~nd descrip~ion. It is not intended to be exhaustive or ~o limit the invention to the precise forms disclosed, and there are various ~odific~tions, substitutions and ~lter~tion~ tha~ will be ~ppa~ent to one of ordinary ~kill in the ~rt in view of the above teaching. The embodiments disclosed were chosen and described in order ~o best explain the principles of the invention and it~ practical ~ appli~ation ~o a~ to ~hereby ~nable o~hers 3killed ~n the art ~o best u~ilize the ~nven~ion in variou~ ~mbodiments and with various modifi~ations as ~re suited ~o ~he par-ticular u3e ~ontemplated. I~ i~ in~ended eha~ ~he ~cope o the invention be defined by the claims appended hereto.
Claims (15)
1. In a nuclear magnetic resonance (NMR) spectrometer, the improvement comprising a semitoroidal radio frequency (rf) coil for irradiating a sample with an alternating magnetic field.
2. The improvement defined in Claim 1 wherein said coil is a primary NMR coil.
3. The improvement defined in Claim 1 wherein said coil is a decoupling coil.
4. The improvement defined in Claim 2 wherein said semitoroidal rf coil has a two-fold axis of symmetry and wherein said spectrometer has a static magnetic field, and wherein said two-fold axis of symmetry extends parallel to the direction of the static magnetic field of the NMR
spectrometer.
spectrometer.
5. The improvement defined in Claim 2 further comprising a semitoroidal shim coil nested concentrically inside said primary coil, and wherein said primary and shim coils are wound in opposite directions such that the rf magnetic field of the shim coil partially cancels the field of the primary soil at close distances, thereby enabling the acquisition of an NMR signal from an isolated region at depth within a sample.
6. The improvement defined in Claim 2 wherein said coil includes a plurality of semitoroidal coils, each having an axis of two-fold symmetry, and wherein said axes of two-fold symmetry extend parallel go one another and are coaxial.
7. The improvement defined in Claim 2 wherein said semitoroidal rf coil is flattened in directions radial to the coil.
8. The improvement defined in Claim 2 wherein said semitoroidal rf coil is pinched in directions radial to the coil.
9. The improvement defined in Claim 2 wherein said semitoroidal rf coil includes two coil windings which are wound in opposite directions.
10. The improvement defined in Claim 9 further comprising a ground plate, and wherein the faces of the coil open through openings in said ground plate, and wherein each of the two coil windings is electrically connected at one end to said ground plate.
11. The improvement defined in Claim 2 wherein said semitoroidal rf coil is operable in a duplex mode to alternately irradiate a sample and receive the induced NMR
signal from the sample.
signal from the sample.
12. The improvement defined in Claim 3 wherein said semitoroidal rf decoupling coil has a two-fold axis of symmetry and wherein said spectrometer has a static magnetic field, and wherein said two-fold axis of symmetry of said decoupling coil extends parallel to the direction of the static magnetic field of the NMR spectrometer.
13. The improvement defined in Claim 3 wherein said decoupling coil includes a grounded plate for minimizing stray rf electric field, and wherein the faces of said coil open through openings in said ground plate.
14. The improvement defined in Claim 3 wherein said semitoroidal decoupling coil includes two coil windings wound in opposite directions.
15. The improvement defined in Claim 13 wherein said semitoroidal decoupling coil includes two coil windings wound in opposite directions, and wherein each of said two coil windings is electrically connected at one end to said grounded plate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US479,581 | 1983-03-28 | ||
| US06/479,581 US4590427A (en) | 1983-03-28 | 1983-03-28 | Nuclear magnetic resonance apparatus having semitoroidal rf coil for use in topical NMR and NMR imaging |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1210061A true CA1210061A (en) | 1986-08-19 |
Family
ID=23904590
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000449961A Expired CA1210061A (en) | 1983-03-28 | 1984-03-20 | Nuclear magnetic resonance apparatus having semitoroidal rf coil for use in topical nmr and nmr imaging |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4590427A (en) |
| JP (1) | JPS59197845A (en) |
| CA (1) | CA1210061A (en) |
| DE (1) | DE3411521A1 (en) |
| FR (1) | FR2562250B1 (en) |
| GB (1) | GB2137757B (en) |
Families Citing this family (35)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8329196D0 (en) * | 1983-11-02 | 1983-12-07 | Bydder G M | Nuclear magnetic resonance apparatus |
| GB8331501D0 (en) * | 1983-11-25 | 1984-01-04 | Picker Int Ltd | Nuclear magnetic resonance |
| US4728896A (en) * | 1984-07-31 | 1988-03-01 | Oxford Research Systems Limited | Method and apparatus for obtaining N.M.R. spectra and coils for use therein |
| JPS61115958U (en) * | 1984-12-30 | 1986-07-22 | ||
| DE3515190A1 (en) * | 1985-04-26 | 1986-11-06 | Siemens AG, 1000 Berlin und 8000 München | CORE SPIN TOMOGRAPHY UNIT |
| US4793356A (en) * | 1985-08-14 | 1988-12-27 | Picker International, Inc. | Surface coil system for magnetic resonance imaging |
| US4784146A (en) * | 1986-08-14 | 1988-11-15 | University Of Florida | Angled segment receiver coil for NMR imaging of a human head |
| FR2612641B1 (en) * | 1987-03-19 | 1989-06-09 | Oreal | APPARATUS FOR EXAMINING A BODY BY NUCLEAR MAGNETIC RESONANCE BY SLOW AND FAST METHODS, PARTICULARLY FOR EXAMINING THE SURFACE LAYER OF THIS BODY, DEVICE FOR CREATING A GRADIENT OF MAGNETIC FIELD FOR SUCH APPARATUS, AND APPLICATION TO THE SAME HUMAN BODY SKIN IMAGING |
| SE8702160L (en) * | 1987-05-25 | 1988-11-26 | Hoek Instr Ab | STETOSCOPE BEFORE USING MAGNETIC RESONANCE DIAGNOSTICS M M |
| ES2026257T3 (en) * | 1987-06-23 | 1992-04-16 | Hafslund Nycomed Innovation Ab | IMPROVEMENTS INTRODUCED IN THE PRESENTATION OF IMAGES BY NUCLEAR MAGNETIC RESONANCE. |
| US5162736A (en) * | 1987-08-14 | 1992-11-10 | National Research Development Corporation | NMR imaging |
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| US23769A (en) * | 1859-04-26 | Improvement in seeding-machines | ||
| US1594273A (en) * | 1925-07-20 | 1926-07-27 | Martin G Sateren | Radiofrequency transformer |
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-
1983
- 1983-03-28 US US06/479,581 patent/US4590427A/en not_active Expired - Fee Related
-
1984
- 1984-03-19 GB GB08407106A patent/GB2137757B/en not_active Expired
- 1984-03-20 CA CA000449961A patent/CA1210061A/en not_active Expired
- 1984-03-27 JP JP59059299A patent/JPS59197845A/en active Pending
- 1984-03-28 DE DE19843411521 patent/DE3411521A1/en not_active Withdrawn
- 1984-05-29 FR FR848408416A patent/FR2562250B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS59197845A (en) | 1984-11-09 |
| US4590427A (en) | 1986-05-20 |
| GB8407106D0 (en) | 1984-04-26 |
| FR2562250A1 (en) | 1985-10-04 |
| DE3411521A1 (en) | 1984-10-25 |
| GB2137757A (en) | 1984-10-10 |
| FR2562250B1 (en) | 1989-11-03 |
| GB2137757B (en) | 1986-07-30 |
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