• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The invention relates to an electronic interface (10) between a pure NMR receiving resonator (RO) and a preamplifier, which is for transforming the impedance of the NMR receiving resonator to the preamplifier during the receiving process and for opening or detuning the resonator during the Transmission is set up, wherein one or more switching diodes (D open) are provided for opening or detuning of the resonator, which are durchgestromt during the transmission process. This interface is characterized in that one or more drive diodes (D match 1, D tune 1) are provided, by means of which the current for flowing through the switching diodes can be fed into this, and that the drive diodes directly or via one or more additional series impedances are connected to the switching diodes. As a result, during the receiving process, the impedance of the resonator is transformed to the required preamplifier or line impedance with little loss. In particular, the adaptation can be adjusted during the receiving process, during the transmission process the current caused by the B 1 field of the transmitting resonator in the inductance of the resonator is minimized and all components are protected against destruction.
    公开号:CH706312B1
    申请号:CH00655/13
    申请日:2013-03-22
    公开日:2017-05-15
    发明作者:Daniel Marek Dr；Schwilch Arthur；Luke Martin
    申请人:Bruker Biospin Ag；
    IPC主号:
    专利说明:

    Description: The invention relates to an electronic interface between an NMR reception resonator and at least one preamplifier for transforming the impedance of the NMR reception resonator to the preamplifier during the reception process and for opening or detuning the NMR reception resonator during the reception Transmission process by means of one or more switching diodes, which are thereby durchgestromt.
    Such an arrangement is known from the article "Cryogénie Varactor-Tuned 4-element Array and Cryostat for μ-MRI of Trabecular Bone in Distal Tibia" by J. Wosik, K. Nesteruk, MR Kamel, F. Ip1, L. Xue, A. C, Wright, and FW Wehrli in Proc. Intl. Soc. Mag. Reson. Med. 16 (2008) (= reference [1]).
    In NMR, especially in MRI, resonators are often used for the reception of the high-frequency signals. These are often also designed as so-called receive-only resonators (RO resonators). Such resonators are, as the name implies, used exclusively for receiving the NMR signals. During the transmission process, the nuclear spins are excited by an additional separate transmit resonator (TX resonator). This type of arrangement is particularly suitable for the realization of arrays of RO resonators in MRI [4]. For operation, the RO resonator for signal conditioning and amplification must be connected to a preamplifier. This is done in the embodiment discussed here by means of an electronic interface. The electronic interface for such a RO resonator must fulfill four main tasks: First, the terminal impedance (A1, A2 in FIG. 1) of the RO resonator must be as low-loss as possible to a defined second impedance (points P1, P2 in FIG Fig. 1) is transformed, so a noise and power adjustment of the preamplifier or a compromise thereof be made. This is done with or without line in between. This impedance transformation is commonly referred to as "matching."
    Second, because of the resonant characteristic of the resonator, matching is possible only at a certain frequency. Therefore, the resonance frequency must be able to be adjusted to the frequency ω of the NMR signals. This frequency adjustment is commonly referred to as "tuning". The two above terms together are often referred to as "impedance matching" or just as "adaptation".
    Third, the virtually unavoidable coupling of the RO resonator to the TX resonator induces a voltage during the transmission process in inductor L (see FIG. 1) of the RO resonator. Without further measures, this would lead to a resonant and therefore very high induced current in L, which would retroactively affect the Br field of the NMR arrangement in the vicinity of the RO resonator. To prevent this, the RO resonator must be "detuned" during the transmission process. This process, generally referred to as "detuning," can be realized by "opening" the RO resonator, i. by connecting such additional impedance (typically inductance) in parallel with C, so that the resulting total impedance across the terminals (A1, A2 in Fig. 1) of L becomes very high (parallel resonant circuit of C and the additional impedance) to coL. Thus, an induced voltage in L only generates negligible current in this L and thus in the RO resonator.
    However, there are also arrangements which, instead of opening the RO resonator (as in [1]) merely shift its resonant frequency (as in [2] and [3]), resulting in a reduced but still significant one Current in the RO resonator during the transmission process leads.
    Fourthly: It should be noted that in the transmission case, the electronic interface itself as well as the subsequent preamplifier must be protected from destruction.
    If you want in operation in a simple manner, the impedance transformation of a RO resonator with changing load (typically caused by a change in the load by the object to be measured (= sample) by the position, size or high-frequency characteristics at the same or also by changing the sample), offers itself as a very elegant possibility to use varactor diodes instead of fixed capacitors or mechanical trimmers. Their capacity can be electronically varied by a DC voltage.
    Known devices, such as e.g. described in [1], consist of an electronic network of varactor diodes, PIN diodes, inductors and capacitors. FIG. 4 shows a schematic of such an arrangement with the electronic interface 40. The tuning of the RO resonator is adjusted by means of a varactor diode (Dtune) and a corresponding DC voltage UT. The DC potential is supplied to the varactor diode via two reactors (RFC1, RFC2). The matching takes place in this arrangement via two further varactor diodes (DmatChi, DmatCh2), which are controlled by a DC voltage UM. The supply of the DC potential is again via two reactors (RFC3, RFC4).
    It is desirable to keep the potentials as symmetrical as possible with respect to the high-frequency ground in order to minimize capacitive fault currents and thus undesirable couplings with adjacent RO resonators. By "symmetrical" is generally understood an antisymmetric potential, so that no potentials are present at symmetry points and thus can not cause common mode currents.
    As an example, the inventive arrangement in Fig. 1 is not symmetrical in this sense. The known arrangement in Fig. 4 is only partially symmetrical, since the connection to the preamplifier (RX) is asymmetrical. By contrast, the arrangements in FIGS. 2 or 3 are largely symmetrical.
    The opening of the resonant circuit is in the prior art according to document [1] via two PIN diodes (Dopeni, Doperà) · Thus, the inductance L 'is connected in parallel to the capacitor C of the RO resonator. Viewed from the inductance L of the RÖ resonator, the connected circuit (parallel resonant circuit L 'and C) now appears much higher impedance (compared to the impedance (oL), with the result that almost no current can flow through the inductance L. , and thus the RO resonator appears as "open".
    This known arrangement according to FIG. 4 has the following disadvantages: 1. The throttles (RFC1, RFC2) in this arrangement hang directly on the two points of the RO resonator and additionally damp it, which is especially the case with very high grades of RO Resonator (especially in cryogenically cooled or even superconducting RO resonator, [1]) can lead to significant loss of sensitivity. However, reference [1] deals with a cryogenic resonator - even with HTS coils, which have a very high quality and are therefore very sensitive to unwanted attenuation due to the wiring. 2. Due to the passage through the PIN diodes, a DC current flows through the inductance L of the RO resonator to ground. This current generates a B0 inhomogeneity locally around the resonator, which may interfere with NMR and MRI. 3. Such an arrangement provides only insufficient protection against destruction of the varactor diodes. In the case of a strong external Br field, a high voltage is induced in the inductance L of the RO resonator, which lies to a large extent directly above the diode Dtune and somewhat attenuated via the diodes Dmatchi and DmatCh2.
    In another arrangement - such as e.g. described in reference [2] (not shown here as a figure) - is achieved by means of varactor diodes also an electronic adjustment. This arrangement also has disadvantages: 1. Again, the control signals are connected via chokes at points of high impedance, which leads to the attenuation of the RO resonator during the receiving process. 2. The RO resonator is not opened during the transmission, but only its resonant frequency is shifted. This has the consequence that during the transmission process by the induced voltage in the inductors Lcoii of the RO resonator still a considerable unwanted current flows through them and thus the Br field is also affected retroactively here.
    In a still further arrangement according to reference [3] (also not shown here as a figure), although a symmetrical circuit is shown. However, this arrangement also has serious disadvantages: 1. The circuit contains no effective provisions for opening the resonator, but detuning only this, so that during a transmission process still flow significant currents in the receiving coil. 2. In addition, none of the varactor diodes are protected against overvoltage, and are destroyed above a certain induced voltage in the receiving coil.
    Therefore, the whole arrangement works, as already mentioned in the title of the document, only for tuning the transmitting coil, with only low powers are applied and tolerated. The circuit does not protect against TX transmitter power and therefore appears unusable for actual operation.
    In a still further arrangement according to reference [5] (also not shown here as a figure), a passive detuning circuit with improved linearity is described. With this arrangement, no external bias current is necessary for the detuning. The bias current is obtained by rectification from the RF signal induced by the TX resonator in the RO resonator. However, the arrangement has the following disadvantages: 1. For very small transmission signals, the detuning does not work and the RO resonator couples with the TX resonator. 2. The arrangement has no impedance transformation to match the preamplifier, this must be resolved separately. The arrangement is therefore in the strict sense no interface between the RO resonator and preamplifier.
    Object of the present invention is in contrast to improve a technically simple and inexpensive means a device of the type described above in such a way that during the receiving process, the impedance of the RO resonator low loss as possible to the required preamplifier or line impedance is transformed , At the same time the other necessary conditions (see above under «Second» to «Fourth») should be fulfilled. In particular, the adjustment should be adjustable during the receiving process, and during the transmission process, the current caused by the Β-ι field of the transmitting resonator in the inductance of the RO resonator should be minimized and all components protected against destruction.
    This complex problem is solved in a surprisingly simple yet effective manner in that one or more drive diodes are provided, by means of which the current for the passage of the switching diodes can be fed into this, and that the one or more Drive diodes are connected directly or via one or more additional series impedances to the switching diodes. As a result, a low-loss adaptation is achieved, whereby the other requirements («second» to «fourth») are fulfilled.
    Particularly preferred is an embodiment of the invention in which one or more of the switching diodes are designed as PIN diodes. This has the advantage that the detuning behaves independently of the transmit power, since the PIN diode for the RF signal behaves like a very small and linear resistor.
    Embodiments of the electronic interface according to the invention which are distinguished by the fact that one or more of the drive diodes are designed as varactor diodes and connected in such a way that they conduct during the transmission process and act as capacitors during the reception process are particularly advantageous. This allows on the one hand to open the RO resonator via the same control signals, on the other hand, by reversing the polarity of the control signals to transform the impedance of the RO resonator to the preamplifier and to tune the resonant frequency.
    In advantageous developments of these embodiments, at least one of the varactor diodes (DmatChi, Dmatoh2) is designed so that it can be used for matching. This ensures that the impedance of the RO resonator is matched to the preamplifier.
    In other developments, at least one of the varactor diodes can be used for tuning, whereby the resonant frequency of the RO resonator can be tuned to the center frequency of the NMR signals.
    Further advantageous embodiments of the invention are characterized in that one or more switching diodes are connected in anti-parallel to one or more switching diodes. In this way, the switching diodes are additionally protected against overloading, in particular against unwanted DC potentials which can arise due to rectification effects in the PIN diodes at high powers.
    Also of particular advantage are embodiments of the inventive electronic interface, in which the device is designed symmetrically and thus has two signal outputs by the circuit is duplicated and the second circuit part, all diodes are reversed. This reduces coupling to and from neighboring components.
    In preferred embodiments of these embodiments, one or more of the series-connected identical electronic components of the circuit are replaced with the omission of a ground terminal by a single one of these components, which has the advantage that fewer of these components are required and thereby their serial loss resistances are smaller ,
    A class of developments of the above-defined embodiments is characterized in that a preamplifier is provided for each signal output. Thus, much stronger signals can be amplified without distortion.
    In an alternative class of developments, the two signal outputs are designed so that the signals are combined phase-correct and are guided to only one preamplifier. This allows a symmetrical design of the interface and still as few active components in the immediate vicinity of the RO resonator.
    In addition, the above-defined embodiments of the invention can also be improved by the fact that the varactor diodes and / or tuning diodes are multiplied by parallel or anti-parallel circuits. In this way, the tuning and matching areas can be enlarged and / or adapted to the respective RO resonator.
    Finally, in particularly preferred embodiments, the inventive electronic interface for operation at temperatures below 100 K designed so that the interface in the immediate vicinity of the also cooled RO resonator can be realized and thus the sensitivity of the device can be increased.
    Further advantages of the invention will become apparent from the description and the drawings. Likewise, the features mentioned above and those listed further can be used individually or in any combination. The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.
    [0034] In the drawings:
    1 shows a schematic circuit diagram of a particularly simple variant of the device according to the invention;
    2 shows a simple symmetrical embodiment of the device according to the invention;
    3 shows a more extensive symmetrical variant of the device according to the invention; and FIG. 4 shows a prior art electronic interface according to reference [1], [0035] With reference to FIGS. 1, 2 and 3, specific embodiments of the invention are described: FIG. 1 is a simplified diagram of the invention electronic interfaces 10 shown. A special feature is the low-loss feeding of the control signals for the varactor and PIN diodes at "low-resistance" points, that is, at points with a low RF impedance, as explained below: The tuning of the RO resonator takes place by means of a varactor diode Dtunei · The corresponding blocking voltage to control the capacitance of the varactor diode is fed via the resistor Rt1. The capacitor Ck serves as a short circuit of the high frequency at the feed point. This supply is thus at a point with low RF impedance and so hardly loaded the RO resonator. Only the resistor Rs1 is connected at a point of high impedance of the RO resonator. The resistor Rsi serves only to define the DC potential at the anode of Dtunei and can therefore be very high impedance (in the mega-ohm range), whereby, however, the RO resonator is not significantly loaded.
    The matching is carried out by a further varactor diode DmatChi · The reverse voltage UM + for controlling the capacity of the diode is supplied via the RFC1 from the low-side (port P1, P2, line to RX, e.g., 50 ohms). As a result, an additional load on the RO resonator is avoided.
    To open the resonator, a short circuit is generated with the switching diode Dopen, thus now the coil L | ' switched parallel to C. At the inductance L of the RO resonator, a high-impedance parallel resonant circuit (L and C) is now connected. Even with strong external Bp field, caused by the transmit resonator, thus flows in the coil L hardly a current. This does not affect the Β, - field generated by the TX resonator. The coupling capacitor Cki, which serves only for DC decoupling of the components located in the figure to the left, forms a high-frequency short circuit or can be offset with the inductance L / and does not need to be considered further for RF considerations.
    The passage through the switching diode Dopen is best achieved by reversing the matching voltage Um +. As a result, a current flows through Dopen, DmatCM and RFC1.
    The varactor diode Dtunei can be durchgestromt the transmission process by reversing the tuning voltage and thereby cause the «opening» of the RO resonator.
    Advantageously, during the transmission process, both varactor diodes are durchgestromt, resulting in a largest-possible current at the diode Dopen, resulting in a PIN diode to a lower RF resistance.
    In the switching diode Dopen a current of many amperes can flow during the transmission process. In general, a PIN diode is used as the switching diode. Although a PIN diode is generally understood to be a controllable high frequency resistor, a ripple effect may occur from certain RF currents or in the absence of the control current, in particular by charging the capacitor Ck1 to the peak during the negative half cycle. During the subsequent positive half cycle, twice the peak voltage is therefore across the diode Dopen, which can lead to their destruction. To prevent this, the PIN diode Dopen a protection diode Ddc can be switched in anti-parallel. Thus, the entire circuit is protected from destruction by large potentials even in the complete absence of the control current.
    2, a simple symmetrical embodiment of the inventive electronic interface 20 is shown. It is formed by a reflection of the circuit according to FIG. 1 and has been simplified in that the identical components then connected in series are replaced by a single one, namely omitting the earth connection.
    A special feature is the low-loss feed of the control signals for the varactor and switching diodes at low-resistance points, which also minimizes the losses, as well as the symmetry of the circuit, whereby (in particular capacitive) couplings to adjacent elements (eg further RO- Resonators) are minimized.
    The tuning of the RO resonator is carried out by means of two varactor diodes Dtunei and DtUne2 · The corresponding blocking voltage to control the capacitance of the varactor diodes, is fed via the capacitor Ck, which represents a short circuit for the high frequency. Due to the symmetrical design and the high-frequency short-circuit of Ck, this supply takes place at a low-impedance point with a practically vanishing RF potential and thus hardly loads the RO resonator. Only the two resistors Rsi and RS2 are connected to the high-resistance points of the RO resonator. They only serve to define the DC potential at the anode of Dtunei or at the cathode of Dtune2 and can therefore be very high-impedance (in the mega-ohm range), whereby the RO resonator is not additionally loaded.
    The matching is carried out by two additional varactor diodes DmatChi and DmatCh2 · The blocking voltages UM + and Um_ for controlling the capacitance of the diodes are two throttles RFC1, RFC2 from the low-side (port P1 and P2, line to RX, eg 50th Ohm) ago supplied. As a result, an additional load on the RO resonator is avoided.
    To open the resonator, a short circuit is generated with the switching diode Dopen, thereby now the two coils (series circuit of L-ι 'and L2') are connected in parallel to C. At the inductance L of the RO resonator, a high-impedance parallel resonant circuit (L-, '+ L2' and C) is now connected. Even with strong external Brfield, caused by the transmit resonator, thus flows in the coil L hardly a current. As a result, the Br field generated by the TX resonator is not affected.
    The two coupling capacitors Ck1 and Ck2, which are used only for DC decoupling of the components located to the left, form a high-frequency moderately short circuit or can be charged with the inductors Li 'and L2' and therefore need not further for RF considerations get noticed.
    The passage of the switching diode Dopen is achieved on the one hand by reversing the matching voltage UM +, UM- A current flows through RFC2 -> Dmatch2 -> Dopen -> Dmatchi -> RFC1. On the other hand, the two varactor diodes can also be bypassed by reversing the tuning voltage and also effect the "opening" of the RO resonator.
    Advantageously, all varactor diodes are durchgestromt in the transmission case, resulting in the largest possible current at the diode Dopen.
    Finally, FIG. 3 shows a more detailed variant of the electronic interface 30 according to the invention: [0053] With further diodes DCmi. DCm2, the Schaltang can be additionally protected from other possibly occurring common-mode voltages. These can also be reversely polarized as shown in Fig. 3.
    To increase the tuning range more varactor diodes (not shown here) can be connected directly parallel to the existing (Dtunei, Dtune2), or even the whole branch can be implemented multiple times (parallel or anti-parallel, in Fig. 3). Such a branch with the varactor diodes Dtune3, Dtune4, which is connected in antiparallel to the first branch (Dtunei, DtUne2), increases not only the tuning range but also the linearity during the reception process.
    On the other hand, a reduction of the tuning range and / or the matching range desired, this can be achieved by additional parallel and / or series circuits (taking into account the DC potentials) of fixed capacitors (not shown in Fig. 3rd ).
    According to practice in MRI receiving systems, parts or the entire supply line may be equipped with common mode filters (Balun B) to reduce unwanted common mode currents in the supply lines.
    The transmission to the preamplifier RX may be symmetric or asymmetrical, with the latter requiring a corresponding balun (e.g., the 180 degree electrical length line TL).
    The entire circuit, which should be located in the immediate vicinity of the RO resonator to avoid long lines to the RO resonator and associated unnecessary RF losses, in the inventive circuits (Fig. 1 to 3) very highly integrated and on very little space can be realized because no throttles are necessary, which are on the one hand bulky and on the other hand, without further countermeasures can also have unwanted couplings to the TX resonator itself. This enables the realization of robust and efficient RO arrays.
    Particularly suitable is the inventive electronic interface for use with cryogenically cooled and superconducting RO resonators. Here, the fully electrically controllable tuning and matching control is very advantageous, since the mechanical access to cryogenic systems in operation is usually severely restricted (for example, access to trimmers). By cryogenic temperatures we mean temperatures below 100 K, in particular around 77 K (= LN2). Even lower temperatures are possible and extend at a reasonable cost down to 4.2 K (= LHe) down. But also arbitrary temperatures in between are easily accessible with appropriate cooling device and common (cryocooler). Such RO resonators have very high grades, which have been unnecessarily attenuated in the circuits of the prior art used to date, and thus a considerable part of the gain in quality was once again lost by prior art electronic interfaces. The electronic interface according to the invention avoids this problem in an elegant and effective manner and makes it possible to realize practicable and highly efficient arrangements with cryogenic or even superconducting RO resonators. The electronic interface is advantageously also operated at cryogenic temperatures in order to further minimize electrical losses as well as the unwanted noise performance occurring in the process.
    Reference List [1] J. Wosik, K. Nesteruk, MR Kamel, F. Ip1, L. Xue, AC Wright, and FW Wehrli «Cryogénie Varactor-Tuned 4-element Array and Cryostat for μ-MRI of Trabecular Bone in the distal tibia »
    Proc. Intl. Soc. Mag. Reson. Med. 16 (2008)
    权利要求:
    Claims (13)
    [1]
    1. Circuit arrangement for arranging as an electronic interface (10; 20; 30) between a pure NMR reception resonator (RO) and at least one preamplifier, which on the one hand for transforming the impedance of the NMR receiving resonator (RO) to the Preamplifier is set during a receiving operation and on the other hand for opening or detuning the NMR receiving resonator (RO) during a transmission process, wherein one or more switching diodes (Dopen) are provided for opening or detuning the NMR receiving resonator (RO) , which are durchgestromt during the transmission process, characterized in that one or more drive diodes (Dmatch1, Dtunei, Dmatch2, Dtune2, Dtune3, Dtune4) are provided, by means of which the current for the passage of the switching diodes (Dopen) fed into this and that the one or more drive diodes (DmatChi, Dtunei, DmatCh2, Dtune2, Dtune3, Dtune4) directly or through one or more additional series I impedances are connected to the one or more switching diodes (Dopen).
    [2]
    2. Circuit arrangement according to claim 1, characterized in that one or more of the switching diodes (dopes) are designed as PIN diodes.
    [3]
    3. Circuit arrangement according to one of the preceding claims, characterized in that one or more of the drive diodes (Dmatch1, Dtune, Dmatch1, Dmatch2, Dtune3, Dtune4) are designed as varactor diodes and are connected so that they conduct during the transmission process and act as capacity during the reception process.
    [4]
    4. Circuit arrangement according to claim 3, characterized in that at least one of the varactor diodes (DmatChi> Dmatciö) can be used for matching.
    [5]
    5. Circuit arrangement according to claim 3 or 4, characterized in that at least one of the varactor diodes (Dtunei> DtUne2, Dtune3, Dtune4) can be used for tuning.
    [6]
    6. Circuit arrangement according to one of the preceding claims, characterized in that one or more further protection diodes (Ddc) are connected in anti-parallel to the one or more switching diodes (Dopen).
    [7]
    7. Circuit arrangement according to one of the preceding claims, characterized in that the circuit arrangement is symmetrical and thus has two signal outputs by the circuit double-circuit parts, called first and second circuit part includes, wherein the second circuit part all diodes over those in the first circuit part are reversed.
    [8]
    8. Circuit arrangement according to claim 7, characterized in that a preamplifier is provided for each signal output.
    [9]
    9. Circuit arrangement according to claim 7, characterized in that the two signal outputs are designed so that the signals are combined phase-correct and are guided to only one preamplifier.
    [10]
    10. Circuit arrangement according to one of claims 7 to 9, characterized in that the varactor diodes and / or tuning diodes are multiplied by parallel or anti-parallel circuits.
    [11]
    11. Circuit arrangement according to one of the preceding claims, characterized in that the circuit arrangement is designed for operation at temperatures below 100 K, in particular by the circuit arrangement can be cooled for operation.
    [12]
    12. Use of the circuit arrangement according to one of the preceding claims as an electronic interface (10; 20; 30) between a pure NMR receiving resonator (RO) and at least one preamplifier, preferably characterized in that as NMR receiving resonator (RO) a cryogenically cooled NMR receiving resonator (RO) is used, more preferably characterized in that a cryogenically cooled superconducting NMR receiving resonator (RO) is used.
    [13]
    13. Use according to the preceding claim 12, characterized in that the circuit arrangement is likewise operated at cryogenic temperatures, in particular in a temperature range below 100 K, preferably below 77 K.
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    法律状态:
    2019-10-31| PFA| Name/firm changed|Owner name: BRUKER SWITZERLAND AG, CH Free format text: FORMER OWNER: BRUKER BIOSPIN AG, CH |
    优先权:
    申请号 | 申请日 | 专利标题
    DE102012204798A|DE102012204798B3|2012-03-26|2012-03-26|Electronic interface for NMR reception resonators|
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