Source: http://www.google.com/patents/US20040066195?ie=ISO-8859-1
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Patent US20040066195 - Antenna arrangement and coupling method for a magnetic resonance apparatus - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsAn antenna arrangement for a magnetic resonance device has a first antenna group, which includes at least one antenna element, and a second antenna group separated from the first antenna group, which likewise includes at least one antenna element. The antenna groups have respective cooperating coupler...http://www.google.com/patents/US20040066195?utm_source=gb-gplus-sharePatent US20040066195 - Antenna arrangement and coupling method for a magnetic resonance apparatusAdvanced Patent SearchPublication numberUS20040066195 A1Publication typeApplicationApplication numberUS 10/668,993Publication dateApr 8, 2004Filing dateSep 23, 2003Priority dateSep 23, 2002Also published asCN1490633A, CN100416290C, DE10244173A1, DE10244173B4, US7136023Publication number10668993, 668993, US 2004/0066195 A1, US 2004/066195 A1, US 20040066195 A1, US 20040066195A1, US 2004066195 A1, US 2004066195A1, US-A1-20040066195, US-A1-2004066195, US2004/0066195A1, US2004/066195A1, US20040066195 A1, US20040066195A1, US2004066195 A1, US2004066195A1InventorsArne ReykowskiOriginal AssigneeSiemens AktiengesellschaftExport CitationBiBTeX, EndNote, RefManReferenced by (11), Classifications (9), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetAntenna arrangement and coupling method for a magnetic resonance apparatusUS 20040066195 A1Abstract An antenna arrangement for a magnetic resonance device has a first antenna group, which includes at least one antenna element, and a second antenna group separated from the first antenna group, which likewise includes at least one antenna element. The antenna groups have respective cooperating coupler antenna parts that are fashioned and/or arranged such that, given a specific adjacent arrangement of the antenna groups with respect to one another, the coupler antenna parts form, by inductive coupling, a common boundary antenna element of the two antenna groups, which is inductively decoupled from the further antenna elements within the appertaining antenna groups. A corresponding method for coupling two antenna groups separated from one another employs such an antenna arrangement. Images(5) Claims(19)
DESCRIPTION OF THE PREFERRED EMBODIMENTS [0035]FIGS. 1 and 2 respectively show various practiced methods to couple with one another two separate antenna groups that are located in different housings G1, G2. The exact coupling methods, as well as their disadvantages, were already specified in detail above. [0036] As shown in FIG. 3, coupler antenna parts 2 a, 2 b (which are respectively associated with one of the two antenna groups 11, 12) are used in the inventive antenna arrangement to couple the antenna groups. The antenna groups 11, 12 are formed by a field of individual antenna elements 1, 3, 4. [0037]FIG. 3 illustrates the inside of the left antenna group 11, with only one antenna element 1 and one coupler antenna part 2 a being shown for better clarity, as well as two antenna elements 3, 4 and one coupler antenna part 2 b in the right antenna group 12. Typically, an antenna group includes further antenna elements which can again terminate in the shown left antenna group 11 at the far left antenna element 1 and in the right antenna group 12 at the far right antenna element 4. However, in principle an antenna group can also include only one antenna element and one coupler antenna part to couple with other antenna groups. [0038] The individual antenna elements 1, 3, 4 here each include a detuning circuit 5 in order to tune the self-resonant frequency of the appertaining antenna element antenna elements 1, 3, 4 to the frequency of the magnetic resonance signal to be received in the reception mode, and to detune with regard to this magnetic resonance frequency in the transmission mode. It is therefore ensured that the antenna elements 1, 3, 4 only acquire signals in the reception mode and are transparent to the transmission field in the transmission mode. [0039] The antenna groups 11, 12 each are arranged at the same height within their housings 13, 14, such that they are located substantially in an antenna plane E when the housing housings 13, 14 are placed together. The term �antenna plane� also encompasses configurations wherein the conductor loops of the antenna element 1, 3, 4 are arranged in two parallel planes, adjoining or lying a short distance from one another, that are adjacent to or overlapping one another. A typical example is the assembly of the antenna elements by means of conductor paths on a multilayer circuit board or multilayer conductor path film. The antenna plane can also be adapted in arbitrary form to an antenna housing and/or other environmental conditions, for example the body of the patient, meaning for example also wound around a cylinder or alternatively curved. [0040] The coupler antenna parts 2 a, 2 b of the antenna groups 11, 12 are each located at the edges 15, 16 facing one another of the housings 13, 14. A coupler antenna part 2 a of a first type (called the first coupler antenna part 2 a in the following) is located in the left shown antenna group 11, and a coupler antenna part 2 b of a second type (called the second coupler antenna part 2 b in the following) is located in the right shown antenna group 12. [0041] Both coupler antenna parts 2 a, 2 b have a first antenna section 7, 9, which proceeds substantially in the antenna plane E. Attached to it is a second antenna section 8, 10, running perpendicular to the antenna plane E, which protrudes downwardly from the antenna plane E. [0042] The second antenna sections 8, 10 lie parallel to one another in the shown coupled state of both antenna groups 11, 12. The first antenna sections 7, 9 in the antenna plane E overlap with the respective appertaining adjacent antenna elements 1, 3. [0043] As is later shown individually, given a suitable formation and arrangement of the two coupler antenna parts 2 a, 2 b, as well as the correct selection of the value of a capacitor C2 connected within the second coupler antenna parts 2 b, the two coupler antenna parts 2 a, 2 b form a common boundary antenna element 2 which receives magnetic resonance signals exactly like the other antenna elements 1, 3, 4, and is decoupled in the same manner by the overlap in the first antenna sections 7, 9 of the adjacent antenna elements 1, 3. [0044] The second coupler antenna part 2 b has no galvanic contact to any measurement device, ground potential, or the like. It is solely inductively coupled with the adjacent antenna elements 3 of its own antenna group 12 as well as in the coupled arrangement according to FIG. 3 with the first coupler antenna part 2 a in the left antenna group 11 as well as to the antenna element 1 adjacent thereto. [0045] In contrast, the first coupler antenna part 2 a has a tap 6 in order to tap a magnetic resonance signal that would be received by the boundary antenna element 2 formed by the two coupler antenna parts 2 a, 2 b. In addition, this first coupler antenna part 2 a, exactly like the remaining antenna elements 1, 3, 4, has a detuning circuit 5 in order to tune the boundary antenna element 2 as a whole to the frequency of the magnetic resonance signal to be received in the reception mode, and to detune with regard to the magnetic resonance signal in the transmission mode. Both the coupler antenna part 2 a of the first type and the coupler antenna part 2 b of the second type typically exhibit a self-resonant frequency that is detuned with regard to the magnetic resonance frequency. [0046] So that both coupler antenna parts 2 a, 2 b in the arrangement shown in FIG. 3 function as a common boundary antenna element, it is initially required that the current be approximately the same in both coupler antenna parts 2 a, 2 b. This means that the current I2b on the second coupler antenna part 2 b must correspond (as the case may be, except for a small, negligible coupler current) to the current I2a on the first coupler antenna part 2 a. This requirement can be fulfilled by suitable selection of the value of the capacitor C2. [0047] For this, reference is first made to the equivalent circuit diagram shown in FIG. 4, in which both coupler antenna parts 2 a, 2 b are isolated, meaning that they are considered without the influence of the adjacent antenna element 1, 3. In addition to the high-frequency currents I2a and I2b on the two-coupler antenna parts 2 a, 2 b and the current directions SR2a, SR2b, a gate voltage U2, which represents the voltage at the tap 6 given reception of a magnetic resonance signal, is also shown at the first coupler antenna part 2 a. In addition, the inductive coupling between the two-coupler antenna parts 2 a, 2 b is schematically shown by the mutual inductance M22. Due to the existing mutual inductance M22, the current I2a in the first coupler antenna part 2 a induces a current I2b in the second coupler antenna part 2 b. The level and the direction of the current I2b is substantially determined by the capacitor C2 connected in the coupler antenna part 2 b. [0048] In order to determine the value of this capacitor C2, at which the requirement is fulfilled that the currents 12 a and I2b are approximately the same magnitude in both coupler antenna parts 2 a, 2 b, the mesh equations for the equivalent circuit diagram according to FIG. 4 provide a starting point: [0049] Mesh 2 a: I 2a �jωL 2a −I 2b �jωM 22 =U 2 (1a) [0050] Mesh 2 b: - I 2  a � j   ω   M 22 + I 2  b � ( j   ω   L 2  b + 1 j   ω   C 2 ) = 0 ( 1  b ) [0051] L2a and L2b are the respective inductances of the two coupler antenna parts 2 a, 2 b, ω is the angular frequency of the high-frequency current (i.e. the frequency of the magnetic resonance signal to be received, and j designates an imaginary number. [0052] In order to determine the desired capacitance of the capacitor C2, the ideal condition can be established in a rudimentary fashion, normally that the currents I2a, I2b are exactly the same in both coupler antenna parts 2 a, 2 b. This means the condition I2a=I2b=I2 can be used. From this the equation (1a) becomes: - I 2 � j   ω   M 22 + I 2 � ( j   ω   L 2  b + 1 j   ω   C 2 ) = 0 ( 2 ) [0053] By solving this equation for C2, one obtains: C 2 = 1 ω 2  ( L 2  b - M 22 ) ( 3 ) [0054] Equation (3) consequently specifies the condition for the capacitance of C2 at which the currents I2a, I2b are equal in the isolated ideal case. [0055] It should be noted that, due to the minus sign in the denominator of the equation (3), the necessary value of the capacitor C2 can also be negative. An inductive component would then have to be used, or the capacitor would have to be replaced by a suitable coil. However, since inductors have lesser quality than comparable capacitors, a capacitor is preferably used. It is therefore preferably insured that the inductance L2b of the second coupler antenna part 2 b is always larger than the mutual inductance M22 between the two coupler antenna parts 2 a, 2 b. This is, as a rule, easily possible by a suitable arrangement and embodiment of the coupler antenna parts 2 a, 2 b. [0056] Given known values for the inductance of the second coupler antenna part 2 b, as well as the coupler inductance M22, it would be possible to precisely calculate the capacity C2. In reality, this inductance as well as the coupler inductance can be determined only with difficulty. Therefore, in the design phase a variable capacitor is used in an isolated assembly of both coupler antenna parts and is adjusted until the currents on both coupler antenna parts I2a, I2b are equal. The capacitance of C2 found in this manner can then be realized in the later serial production with a fixed capacitor. [0057] Additionally, in order to achieve a sufficient inductive decoupling of the common boundary antenna element 2, formed by the coupler antenna parts I2a, I2b, from the adjacent antenna elements 1, 3, it is necessary to overlap both coupler antenna parts I2a, I2b in a suitable manner with the appertaining adjacent antenna elements 1, 3. [0058] How the decoupling can be implemented by this overlap is shown in the following. It is sufficient, as an example, to describe the decoupling between the boundary antenna element 2 and the adjacent antenna element 3 in the right antenna group 12. The decoupling from the adjacent antenna element 1 in the left antenna group 11 ensues in a similar manner. [0059] For this, reference is made to the equivalent circuit diagram of these components in FIG. 5. The components shown in FIG. 5 are indicated in FIG. 3 with continuous lines, in contrast to which disregarded antenna elements are shown dashed in this equivalent circuit diagram. In this second equivalent circuit diagram, in addition to the parameters specified in the equivalent circuit diagram according to FIG. 4, the high-frequency current 13 and the current direction SR3 on adjacent antenna element 3 are shown, as well as the voltage U3 at the terminals of this antenna element 3. Furthermore, the mutual inductances M23a and M23b are shown between the first coupler antenna part 2 a, as well as the second coupler antenna part 2 b, and the antenna part 3. Additionally indicated are the voltages U23, U23 induced by the high-frequency currents I2a, I2b of the coupler antenna parts 2 a, 2 b in the antenna element 3 due to the mutual inductances M23a, M23b. These voltages U23a, U23b contribute to the terminal voltage U3 of the antenna element 3. A decoupling is then present precisely when both over-coupled voltage parts U23a, U23b mutually cancel. [0060] The mesh equations for the equivalent circuit diagram according to FIG. 5 are here again the starting point of the calculations: [0061] Mesh 2 a: I 2a �jωL 2a +I 3 �jωM 23a −I 2b �jωM 22 =U 2 (4a) [0062] Mesh 2 b: - I 2  a � j   ω   M 22 + I 3 � j   ω   M 23  b + I 2  b � ( j   ω   L 2  b + 1 j   ω   C 2 ) = 0 ( 4  b ) [0063] Mesh 3: I 2a �jωM 23a +I 3 �jωL 3 +I 2b �jωM 23b =U 3 (4 c) [0064] If, in equation (4c), the assumption is used for the third mesh formulated above that the currents I2a, I2b should be approximately equal in both coupler antenna parts 2 a, 2 b (i.e., that I2a≈I2b≈I2 is true), then the voltage U3 at the terminals of the antenna element 3 then depends precisely on the current I3 on this antenna element 3 alone, when the following is true: M 23a +M 23b=0 (5) [0065] This is the coupling requirement that is achieved by a suitable overlap between the coupler antenna part 2 b and the antenna element 3. [0066] The decoupling requirement according to equation 5 can also be written in the following form: M 23a =−M 23b =M 23 (6) [0067] If the constants M23a, M23b in the mesh equations (4a), (4b), (4c) are respectively replaced by the common constant M23 according to equation 6, the result is: I 2a �jωL 2a +I 3 �jωM 23 −I 2b �jωM 22 =U 2 (7a) - I 2  a � j   ω   M 22 - I 3 � j   ω   M 23 + I 2  b � ( j   ω   L 2  b + 1 j   ω   C 2 ) = 0 ( 7  b ) I 2a �jωM 23 +I 3 jωL 3 +I 2b �jωM 23 =U 3 (7c) [0068] By using the condition according to equation (3) for the capacitance of C2 in the equation (7b), the result is: −I 2a �jωM 22 −I 3 �jωM 23 +I 2b �jωM 22=0 (8) [0069] By solving this equation for I2b, one obtains: I 2  b = I 2  a + I 3 � M 23 M 22 ≈ I 2  a ( 9 ) [0070] Equation (9) shows that, given the presence of the adjacent antenna element 3, the current I2b in the second coupler antenna part 2 b does not correspond completely to the current I2a on the first coupler antenna part, even if the capacitance C2 were to be chosen according to equation (3). A lesser decoupling current, which is specified by the second term of the middle part of the equation (9), occurs in the second coupler antenna part 2 b. This decoupling current is dependent on the current 13 in the adjacent antenna elements 3. Additionally, the decoupling current is dependent on the identical coupling inductance M23 (according to the requirement according to equation (6)) of both coupler antenna parts 2 a, 2 b to the aforementioned antenna element 3 with regard to the coupling inductance M22 between the two coupler antenna parts 2 a, 2 b. [0071] The coupling inductance M22 between the coupler antenna parts 2 a, 2 b is set to be relatively strong. It is here a resonance coupling. Given a received magnetic resonance signal, modes form in the boundary antenna 2 formed from the coupler antenna parts 2 a, 2 b. In one mode, the currents flow in the same direction. This is known as the synchronous resonance mode, which is implemented at the desired magnetic resonance frequency given a tuning of the boundary antenna element 2 with the detuning device 5. The second mode, in which the currents flow in opposite directions, is in contrast uninteresting for the present application. [0072] In contrast, the coupling inductance M23 given by the inductive coupling between the coupler antenna parts 2 a, 2 b and the adjacent antenna element 3 is relatively small. It is significantly below 10% of the coupling inductance M22 between the coupler antenna parts 2 a, 2 b between each other. [0073] Since the internal coupling inductance M22 is implemented significantly larger than the coupling inductance M23 between the coupler antenna parts 2 a, 2 b and the adjacent antenna element 3, the decoupler current portion in equation (9) in relation to the current I2a on the first coupler antenna part 2 a is negligible. [0074] By using the equation (9) in equation (7a), one obtains for the requirements within the first coupler antenna part 2 a: I 2a �jωL 2a −I 2a �jωM 22 =U 2 (10) [0075] This equation shows that the gate voltage U2 of the first coupler antenna part 2 a no longer depends on current 13 on the antenna element 3 adjacent to the second coupler antenna part 2 b. A decoupling in this direction is thus achieved. [0076] By using the equation (9) in equation (7c), one obtains the following for the conditions within the adjacent antenna element 3: I 3 � j   ω   L 3 - I 3 � j   ω   M 23 2 M 22 = U 3 ≈ I 3 � j   ω   L 3 ( 11 ) [0077] This equation shows that the terminal voltage U2 of the adjacent antenna element 3 now depends only on the current I3 on this antenna element 3, and no longer depends on currents I2a, I2b on the coupler antenna parts 2 a, 2 b. A decoupling in this direction is thus also achieved. [0078] The coupler antenna parts 2 a, 2 b only have influence on the antenna element 3, inasmuch that the �normal� impedance jωL3 is somewhat decreased by the addition jω(M23 2/M22). Since the coupling inductance M23 between the coupler antenna parts 2 a, 2 b and the adjacent antenna element 3 is significantly less than the internal coupling inductance M22 of both coupler antenna parts 2 a, 2 b among each other, this change in impedance is also negligible in practice. [0079] Given a design of the antenna groups with the appertaining coupler antenna parts 2 a, 2 b, the requirements can be achieved by initially both coupler antenna parts 2 a, 2 b being assembled isolated, with the capacitance of C2 being adjusted by a variable capacitor until the current is equal in both coupler antenna parts 2 a, 2 b. In a second step, the overlap between the second coupler antenna part 2 b and the antenna element 3 can then be changed thus until the voltage U3 at the terminals of the antenna element 3 is zero in spite of a supplied voltage at the terminals of the first coupler antenna part 2 a. In this case, a decoupling exists. In the same manner, an antenna element can also be attached on the other side, i.e. adjacent to the coupler antenna part 2 a. [0080] The coupler antenna parts 2 a, 2 b and the antenna elements 1, 3, 4 are respectively arranged inside the housings 13, 14 such that the coupler antenna parts 2 a, 2 b are automatically located in the correct position with respect to one another when the housings 13, 14 are suitably placed with their edge surfaces 15, 16 one in front of the other. As a positioning aid, grooves 18 and tongues 17 fitting one another are disposed at these edge surfaces 15, 16 that interlock as soon as the housings 13, 14 are suitably placed one in front of the other. Alternatively, the antenna housings 13, 14 can have other positioning aids, for example interlocking pins and holes, position markings, or the like. [0081] The antenna groups 12, 11 each have at their other ends (not shown), a suitable coupler antenna part 2 a, 2 b, whereby the antenna group 11 shown on the left in FIG. 3 having a second coupler antenna part 2 b, and the antenna group shown on the right in FIG. 3 having at its end a first coupler antenna part 2 a. The individual antenna groups 11, 12 thus can be arbitrarily circuited as antenna modules like a chain one after the other, with the appertaining housings 13, 14 simply being placed together. [0082] At this point, it is once again noted the above-described assembly is only an exemplary embodiment, and the basic principle of the coupling of two antenna groups by means of the inventive coupler antenna parts can be modified in further fields by those skilled in the art. [0083] In particular, the proportions of both coupler antenna parts 2 a, 2 b can be shown other than as in FIG. 3. For example, the first antenna section 9 of the second coupler antenna part 2 b lying in the antenna plane E can be significantly longer, in order to implement at the same value the coupling inductance M23a between the first coupler antenna part 2 a and the adjacent antenna element 3, as well as the coupling inductance M23b of the inductive coupling between the second coupler antenna part 2 b itself and the antenna element 3 adjacent to it. [0084] Furthermore, in addition to the shown antenna elements arranged in a row, an antenna group can include still further antenna elements that are located in one or even more rows proceeding parallel to the shown row. In this case, corresponding coupler antenna parts 2 a, 2 b are again likewise located at the appertaining rows, in order to suitably decouple these rows of antenna elements. [0085] Likewise, the individual antenna elements of an antenna group can be positioned relative to one another in arbitrary other arrangements, whereby the coupler antenna parts must then likewise be suitably adapted. [0086] Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art. Referenced byCiting PatentFiling datePublication dateApplicantTitleUS7397245Aug 11, 2006Jul 8, 2008Siemens AktiengesellschaftSurface coil arrangement for magnetic resonance tomographsUS7579835 *Nov 28, 2006Aug 25, 2009Siemens AktiengesellschaftMulti-layer resonator for magnetic resonance applications with circuitry allowing equal magnitude current during active operationUS7579836 *Jan 30, 2007Aug 25, 2009Siemens AktiengesellschaftMulti-layer resonator for magnetic resonance applications with the resonator structure itself allowing equal magnitude current during active operationUS7602182Sep 28, 2006Oct 13, 2009Siemens AktiengesellschaftMagnetic resonance system having a base body and a patient bed and inductive or capacitive signal transmissionUS8228252 *Oct 16, 2008Jul 24, 2012Murata Manufacturing Co., Ltd.Data couplerUS8244328Oct 31, 2008Aug 14, 2012Siemens AktiengesellschaftHead coil for a magnetic resonance deviceUS8581588 *Sep 19, 2008Nov 12, 2013Max-Planck-Gesellschaft Zur Foerderung Der Wissenschaften E.V.Stripline antenna and antenna array for a magnetic resonance deviceUS20100213941 *Sep 19, 2008Aug 26, 2010Max-Planck-Gesellschaft zur Foerdering der Wissenschafften e.V.Stripline antenna and antenna array for a magnetic resonance deviceEP2772771A1 *Feb 25, 2014Sep 3, 2014Commissariat A L'energie Atomique Et Aux Energies AlternativesMulti-channel high-frequency antenna, in particular for a nuclear magnetic resonance imaging apparatusWO2007060052A1 *Sep 28, 2006May 31, 2007Siemens AgMagnetic resonance system having a base body and a patient bench and inductive or capacitive signal transmissionWO2009056622A1 *Oct 31, 2008May 7, 2009Siemens AgHead coil for a magnetic resonance device* Cited by examinerClassifications U.S. Classification324/319, 324/318, 324/322International ClassificationG01R33/3415, G01R33/36Cooperative ClassificationG01R33/3415, G01R33/365European ClassificationG01R33/36H1, G01R33/3415Legal EventsDateCodeEventDescriptionJan 4, 2011FPExpired due to failure to pay maintenance feeEffective date: 20101114Nov 14, 2010LAPSLapse for failure to pay maintenance feesJun 21, 2010REMIMaintenance fee reminder mailedSep 23, 2003ASAssignmentOwner name: SIEMENS AKTIENGESELLSCHAFT, GERMANYFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:REYKOWSKI, ARNE;REEL/FRAME:014548/0238Effective date: 20030922RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google