JP5315556B2 - NMR detector - Google Patents

Description

  The present invention relates to an NMR detector used in an NMR apparatus, and more particularly to an NMR detector including a plurality of tuning circuits that resonate at different frequencies.

Usually, in an NMR detector for multinuclear observation, a coil (hereinafter referred to as HF coil) that resonates at a high frequency f ₁ (for example, 700 MHz, hereinafter referred to as HF frequency) for measuring hydrogen nuclei ( ¹ H nuclei), etc. Low frequency f ₂ for measuring carbon nuclei ( ¹³ C nuclei), nitrogen nuclei ( ¹⁵ N nuclei), phosphorus nuclei ( ³¹ P nuclei), etc. (for example, 176 MHz for ¹³ C nuclei, 71 MHz for ¹⁵ N nuclei, ³¹ P nuclei for ³¹ P nuclei) 284MHz, and a coil which resonates them in later referred to as LF frequency) (hereinafter referred to as LF coil), the HF coil, the frequency f ₃ of the lock measuring the deuterium nuclei ⁽² D nucleus) ( For example, a double tuning circuit is provided so that resonance is possible even at 123 MHz (hereinafter referred to as a lock frequency).

  FIG. 1 is a diagram showing an example of a conventional multiple-tuned NMR detector. First, the resonance mode of HF will be described. In FIG. 1, L1 is a sample coil. RF having the HF frequency is introduced from the HF input port f1. The RF introduced from f1 resonates in an LC resonance circuit composed of the sample coil L1, the HF tuning capacitors C0, C2, and C3, and the HF matching capacitor C1, and is not shown in the figure placed near the sample coil L1. The sample is irradiated with an RF magnetic field having an HF frequency. As a result, if magnetic resonance occurs in the NMR sample, the NMR signal generated from the sample is detected by the sample coil L1 and taken out through the port f1. In this mode, the helical coils L3 and L4 act as distributed inductances and act as HF quarter-wave resonators. For example, when HF is 700 MHz, the quarter wavelength is about 102 to 107 mm. Therefore, the HF has an electromagnetic field distribution in which the electric field amplitude becomes maximum at the nodes 1 and 2 and the electric field amplitude becomes zero at the ground ends of the capacitors C4 and C6. As a result, HF is reflected from the node 1 closer to the helical coil L3 side and from the node 2 closer to the helical coil L4 side, and is not involved in resonance. The HF wavelength resonator is generally operated as a quarter wavelength resonator, but may be operated as an n / 4 wavelength resonator (n is an odd number).

  Next, the resonance mode of the lock frequency will be described. In FIG. 1, the combination of the sample coil L1, the helical coil L3, and the helical coil L4 is a resonance coil that resonates at the lock frequency. In this mode, the helical coils L3 and L4 function as concentrated inductances. Since the inductances of L3 and L4 are several times larger than the inductance of L1, the inductance of L1 hardly contributes to resonance. The RF having the lock frequency is introduced from the lock RF input port f2. The RF introduced from the port f2 resonates in a balanced manner in an LC resonance circuit composed of L1, L3, L4, locking tuning capacitors C4 and C6, and locking matching capacitor C5, and is placed in the vicinity of the sample coil L1. A non-illustrated NMR sample is irradiated with an RF magnetic field having a lock frequency. As a result, if magnetic resonance occurs in the NMR sample, the lock signal generated from the sample is detected by the sample coil L1 and taken out to the outside via the port f2.

  FIG. 2 shows an NMR detector in which a first LC parallel resonant circuit composed of L3 and C7 and a second LC parallel resonant circuit composed of L4 and C8 are employed in the HF reject circuit instead of the helical coils L3 and L4 in FIG. It is a NMR detector shown by these. In addition, instead of the helical coils L3 and L4 in FIG. 1, an NMR detector employing a first wavelength resonator TL1 (eg, helical resonance, quarter wavelength resonator) and a second wavelength resonator TL2 in the HF reject circuit. Is the NMR detector shown in FIG.

FIG. 4 is a DCPL (abbreviation for decoupling circuit) generally used for the helical coil of FIG. 1, the LC parallel resonance circuit of FIG. 2, and the wavelength resonator of FIG. 3, and is a more general NMR detector. A standard NMR detector having a function capable of observing a certain multinuclear (a so-called LF frequency nuclide such as ¹³ C nucleus, ¹⁵ N nucleus, ³¹ P nucleus) is shown.

  The resonance mode of LF will be described. In FIG. 4, L2 is an LF coil (second sample coil). RF having the LF frequency is introduced from the LF input port f4. The RF introduced from the port f4 resonates in an LC resonance circuit composed of the LF coil L2, the LF tuning capacitors C00, C11 and C12, and the LF matching capacitor C10, and is placed in the vicinity of the LF coil L2 (not shown) An NMR sample is irradiated with an RF magnetic field having an LF frequency. As a result, if magnetic resonance occurs in the NMR sample, the NMR signal generated from the sample is detected by the LF coil L2, and taken out through the port f4.

  FIG. 5 shows the relative arrangement of the sample coils L1 and L2 of this standard probe when they are arranged concentrically. The observation coil is an L2 coil located inside, and the irradiation coil is an L1 coil located outside. In general, when observing a nucleus for which sensitivity is to be obtained, the nucleus is tuned to a sample coil that is positioned closest to the sample (that is, located inside). Therefore, depending on the case, the arrangement of L1 and L2 may be reversed.

  In the example of FIG. 5, the nuclide of the port f4 is the nucleus that wants the most sensitivity. The circuit on the f4 side is a single tuning circuit. The reason why the example of the balanced circuit and the example of the unbalanced circuit are written together is that, when it is considered appropriate in the usage method, any one is selected and used.

  Since it is the technical content related to this subject, here we will briefly explain balanced and unbalanced circuits. A balanced resonance circuit constitutes a circuit in which both ends of the sample coil are floated by capacitors. Conversely, a balanced resonance circuit constitutes a circuit in which one end of the sample coil is grounded and the other end is floated by a capacitor. The difference is about two, and one is that in the case of a balanced resonant circuit, it floats from ground, so the proportion of the sample coil and its surrounding stray capacitance contributing to the resonant capacitance is reduced, and the higher frequency range. It can cover the range.

Secondly, if the resonance voltage at both ends of the sample coil is 4 kV _pp , the voltage applied to one capacitor is reduced because the balanced resonance circuit can perform voltage division with the capacitors at both ends of the sample coil. Assuming the circuit shown in FIG. 5, if C11 and C12 have substantially similar capacitances, the voltage applied to each capacitor is 2 kV _pp . However, in an unbalanced circuit, 4 kV _pp is directly applied to C11. That is, in the unbalanced circuit, the withstand voltage specification of the capacitor becomes very strict, and in such a circuit, it is worried about discharge, and a large RF voltage cannot be applied to the detector.

  Conversely, in a balanced circuit, twice as much RF power can be applied. The fact that the withstand voltage specification is only half means that the square of the voltage ratio, that is, four times the power can be input in the balanced circuit. This is a feature that is greatly superior to an unbalanced circuit.

  FIG. 6 and FIG. 7 describe the prior art for a detector including a triple resonance circuit (HF / LF / LF) with one additional circuit, unlike the double resonance (HF / LF) described so far. doing. As described above, a tuning circuit having a desired frequency can be sequentially added via the separation circuit. However, in a configuration incorporating a balanced circuit, an unnecessary signal resonance mode called a ghost is always generated as a secondary.

  6 and 7, based on the S-parameter analysis graph of the network analyzer measuring instrument used for such a network analysis, a rough background of the ghost signal that appears, that is, what range it is in, etc. The relative relationship with the frequency group is schematically understood. By the way, the vertical axis of the graph is a reflection characteristic frequency distribution indicated by an arbitrary index, which shows the help of the positional relationship in which the ghost signal is output with respect to the topic frequency.

  If we talk with a device having an HF of 600 MHz, it can be imagined that the ghost signal affects adjacent frequencies in either case of FIG. 6 or FIG.

JP 2006-208216 A

Returning to the standard probe, suppose that there are LF observation (or LF irradiation), HF irradiation (or HF observation) ² D (deuterium) NMR-lock as an example. Here, since the LF circuit side falls within a range that can be explained by words, the illustration is omitted. However, in the description, the discussion will proceed assuming that the LF circuit is always present.

^{Examples, f1 (HF: 1 H)} , f2: the separation circuit of the double tuned circuit to obtain the (lock ² D) is described in the example is composed of wavelength resonant circuit. This is shown in FIG. As described above, various circuits are assumed as the separation circuit. Here, an appropriate characteristic impedance and an appropriate length (generally, the line is designed to resonate a quarter wavelength, but the odd number thereof is used. The frequency is separated by resonating the wavelength with a deformation such as double.

In FIG. 8, the HF resonance circuit is configured with L ₁ , C ₀ , C ₂ , and C ₃ as main elements, and the lock resonance circuit is configured with TL ₁ , TL ₂ , C ₄ , and C ₆ as main elements. . The ghost signal resonance circuit described above is generated from the element groups of TL ₁ , TL ₂ , C ₄ , C ₆ , C ₂ , and C ₃ and interferes with LF.

  When the circuit configured as shown in FIG. 8 is used in a 600 MHz NMR apparatus, the frequency characteristics are as shown in FIG. The left figure shows the reflection characteristic (line shown by a straight line) at the f1 terminal and the passing characteristic from the f1 terminal to the f2 terminal. The right figure shows the reflection characteristic (line indicated by a straight line) at the f2 terminal and the passing characteristic from the f2 terminal to the f1 terminal.

In this example, the ghost signal appears at 326 MHz. When the omitted frequency f4 on the LF side is, for example, ³¹ P (243 MHz), the ghost signal interferes with the ³¹ P resonance frequency. In this example, the device constant arrangement is set to be relatively gentle. However, in an extreme case, the position where the ghost signal appears is around 270 MHz. As shown in FIG.

In Figure ^{10, f1 (1 H: HF} ), f2 indicates the S parameter characteristics of each frequency of the network specifications, including ⁽² D:: lock), f3 (ghost), f4 (LF ³¹ P Example) . Only those relevant to this plan will be described.

The ghost signal appears around 270 MHz and interferes with 31P (243 MHz). If the sensitivity of ³¹ P when no interference occurs is 100%, the sensitivity is reduced to about 50 to 70% even with this level of interference. When the pulse width is set, the length becomes 1.4 to 2 times longer.

Most of the tuning on the HF side covers the tuning range up to ¹⁹ F nuclei (565 MHz in the 600 MHz NMR apparatus). In such a case, as shown in FIG. 11, the ghost signal is completely covered by f4. Therefore, the sensitivity is significantly reduced. The pulse width is also significantly increased.

  The conventional technology has such a problem. Such a ghost signal does not appear in an unbalanced circuit, which is a rather old technology. It is shown in FIG. 12 and FIG. However, as explained above, in the era when ultra-high magnetic field NMR devices appear as in modern times and a wide excitation band is desired and high sensitivity is required, a large RF power can be input, and 700/800/900 MHz. The superiority of the balanced circuit that can handle the design up to the high frequency of the class is tremendous, and the old technology such as the unbalanced circuit becomes obsolete.

  The reason why such a ghost signal is generated in the balanced circuit will be described. This will be described with reference to the circuit shown in FIG. When TL1 and TL2 are simply approximated by induction components, they are L (TL1) and L (TL2). It is assumed that the resonant capacitance component is rounded including the related peripheral capacitance, C2 is C2 *, C3 is C3 *, C4 is C4 *, and C6 is C6 *.

  Although f1, f2, and f3 are related, since f1 is HF, it is a signal generated by parallel resonance composed of L1, C0, C3 *, and C2 *. Now, f2 and f3 are signals as schematically shown in FIGS.

  In FIG. 14, the sample coil L1 originally enters between two coils. However, considering HF resonance, the value of L1 as an inductance is only about ˜20 nH, and is ignored here. That is, in order to balance with FIG. 15, it is omitted intentionally.

  In the balanced circuit of FIG. 15, two parallel resonances can be made, and when the capacitance is coupled between them, the frequency characteristic is split into two peaks. Further, when a sample coil is inserted instead of the capacitor, it becomes equivalent to the direct connection state as shown in FIG. 15, and thus a single combined frequency is generated. This is called a ghost, and will inevitably appear when taking such a balanced circuit configuration.

  For this reason, if either the tuning capacity of HF, C2 * or C3 *, is changed, this combined frequency will move greatly. This is why the ghost moves as shown in FIG. FIG. 16 shows the change of the ghost when the HF tuning equivalent C is appropriately changed as described above.

  As is clear from FIG. 16, the ghost signal that was initially in the range of three hundred and several tens of megahertz has changed to the 219 MHz region, causing a very large change. The existence of a ghost signal having such a problem is serious, and it has long been expected that an idea of a circuit configuration that does not output such a ghost signal is proposed.

  In view of the above points, the present invention is to provide a balanced circuit type NMR detector capable of preventing a ghost signal from appearing in the vicinity of the LF.

In order to achieve this object, the NMR detector according to the present invention comprises:
The sample coil L1, the first capacitive element C0 connecting both ends of the L1, and the capacitive elements C2 and C3 having substantially the same capacitance each grounding both ends of the L1,
The first high-frequency HF for resonating an observation nucleus having a high resonance frequency such as a hydrogen nucleus ( ¹ H nucleus) or a fluorine nucleus ( ¹⁹ F nucleus) and the resonance frequency of a deuterium nucleus ( ² D nucleus) Construct a balanced resonant circuit that can be double-tuned for two high frequencies (lock frequency),
The HF is an NMR detector that is input and output from a port connected to one end of the L1,
The portion that resonates with the lock frequency of the balanced resonant circuit is:
Connected to both ends of the L1 to provide an inductance component to the lock frequency resonance circuit, and an end opposite to the end connected to the L1 is connected to the lock frequency input / output port to connect to the lock frequency input / output port. Separation circuits DCPL1, DCPL2 that block the entry of the HF into the port;
A capacitive element C100 that connects ends of the DCPL1 and DCPL2 opposite to the L1 side connection ends;
With
The end of the DCPL1 and DCPL2 opposite to the connection end on the L1 side is characterized by floating from the ground potential.

  The capacitive element C100 is composed of a plurality of capacitive elements.

  Further, a lock frequency is inputted / outputted from one end of the capacitive element constituting the capacitive element C100.

According to the NMR detector according to the present invention,
The sample coil L1, the first capacitive element C0 connecting both ends of the L1, and the capacitive elements C2 and C3 having substantially the same capacitance each grounding both ends of the L1,
The first high-frequency HF for resonating an observation nucleus having a high resonance frequency such as a hydrogen nucleus ( ¹ H nucleus) or a fluorine nucleus ( ¹⁹ F nucleus) and the resonance frequency of a deuterium nucleus ( ² D nucleus) Construct a balanced resonant circuit that can be double-tuned for two high frequencies (lock frequency),
The HF is an NMR detector that is input and output from a port connected to one end of the L1,
The portion that resonates with the lock frequency of the balanced resonant circuit is:
Connected to both ends of the L1 to provide an inductance component to the lock frequency resonance circuit, and an end opposite to the end connected to the L1 is connected to the lock frequency input / output port to connect to the lock frequency input / output port. Separation circuits DCPL1, DCPL2 that block the entry of the HF into the port;
A capacitive element C100 that connects ends of the DCPL1 and DCPL2 opposite to the L1 side connection ends;
With
Since the end of the DCPL1 and DCPL2 opposite to the L1 side connection end is floating from the ground potential,
It has become possible to provide a balanced circuit type NMR detector capable of preventing a ghost signal from appearing in the vicinity of the LF.

It is an example of the conventional NMR detector. It is an example of the conventional NMR detector. It is an example of the conventional NMR detector. It is an example of the conventional NMR detector. It is an example of the conventional NMR detector. It is an example of the conventional NMR detector. It is an example of the conventional NMR detector. It is an example of the conventional NMR detector. It is the S para characteristic of the conventional NMR detector. It is the S para characteristic of the conventional NMR detector. It is the S para characteristic of the conventional NMR detector. It is an example of the conventional NMR detector. It is the S para characteristic of the conventional NMR detector. This is a mechanism in which a conventional NMR detector resonates at a lock frequency. This is a mechanism in which a conventional NMR detector resonates at a ghost frequency. It is the S para characteristic of ghost resonance. It is one Example of the NMR detector concerning this invention. It is a S para characteristic of the NMR detector concerning this invention. It is a S para characteristic of the NMR detector concerning this invention. It is another Example of the NMR detector concerning this invention. It is another Example of the NMR detector concerning this invention. It is another Example of the NMR detector concerning this invention. It is another Example of the NMR detector concerning this invention.

  FIG. 17 shows an embodiment of the NMR detector according to the present invention. As shown in FIG. 17A, in this embodiment, the terminals of the two separation circuits DCPL1 and DCPL2 are connected to each other in a form floating from the ground via the capacitor C100. Further, FIG. 17B is an example described as C101 in consideration of the stray capacitance, in consideration of the adjustment auxiliary capacitance α in order to optimize the operation.

  Of course, since DCPL1 and DCPL2 generally have substantially the same circuit configuration in such a balanced circuit, the input / output coupling capacitance C102 as f2 is opposite to the position in the figure, That is, the * side corresponding to the common node of DCPL1 and C100 may be the coupling position of the input / output coupling capacitor C102 as f2.

  Further, in some cases, C100 may be a plurality of serially connected capacitors, and input / output coupling of f2 may be performed as C102 from any connected node. This is the scope of the design.

  In short, it is important not to create a parallel resonance condition such as C6 * or C4 * shown in FIG.

  Further, it is needless to say that the separation circuit is a general generic name and is composed of various reactance circuits as described above.

The ghost described in FIG. 15 has a C6 * equivalent capacity and a C4 * equivalent capacity connected in series so that it does not exist or forms a composite frequency that resonates with a very small value of stray capacitance. The frequency of the region, that is, the frequency range considered as a target by the present application is shifted to a high region that is completely unrelated, and the influence on LF ( ³¹ P) is eliminated.

  The operation of this circuit is as follows. C100 can be set to a value substantially close to a value obtained by connecting capacitors corresponding to C4 and C6 in the prior art of FIG. In this example, since the series capacitance of C4 and C6, it can be considered as a combined capacitance of C100≈C4 × C6 / (C4 + C6).

FIG. 18 shows the S-para characteristic in the circuit of the present embodiment by network specifications. f1 (HF: ¹ in this case H nuclei), f2 (Rock: In this case ² D nucleus), f4: when the (LF in this case ³¹ P nuclei), the frequency characteristic of the 3 mode frequency. Ghosts such as those shown in FIGS. 9, 10, and 11 no longer exist.

As a simple example, let us change the tuning on the HL side to the resonance frequency of the ¹⁹ F nucleus as shown in FIG. In FIG. 11, the ghost shifts to around 250 MHz, causing proximity interference at the resonance frequency 243 MHz of the ³¹ P nucleus, and the two frequencies are double-peaked. In this embodiment, there is no interference. Therefore, the performance on the LF side is guaranteed 100%. That is, it can be said that the device sensitivity is not spoiled. At the same time, the pulse width does not increase significantly.

  FIG. 20 shows another embodiment of the NMR detector according to the present invention. In this embodiment, one of the capacitors constituting the balanced resonant circuit in the HF circuit is not clearly grounded by the capacitor with respect to the ground. This is a stray capacitance and is grounded.

  FIG. 21 shows another embodiment of the NMR detector according to the present invention. The present embodiment specifically describes the modification described in the first embodiment.

  FIG. 22 shows another embodiment of the NMR detector according to the present invention. The present embodiment also specifically describes the modification described in the first embodiment.

  FIG. 23 shows another embodiment of the NMR detector according to the present invention. In this embodiment, the circuit impedance on the NMR detector side changes due to the impedance condition of the circuit such as a cable or a filter connected to the probe terminal and the outside due to crosstalk between the LF side and the HF / lock side, and the performance deteriorates. For example, a filter circuit is added as an example.

  When the impedance change is significant, the impedance may be maintained by inserting a fixed resistor R100 or the like at a predetermined location in the NMR detector. In R100, for example, the system impedance may be set to 50Ω.

  In the present embodiment, an inductive device or a wavelength resonator may be added to the capacitive device added for the purposes of the first to fifth embodiments. is there.

  Since the LF side of the present invention is not main, only an example of a balanced circuit form is shown, but an unbalanced circuit or a triple tuning circuit already disclosed in FIG. 7 may be included.

  Widely applicable to multiple resonance NMR detectors.

Claims (3)

The sample coil L1, the first capacitive element C0 connecting both ends of the L1, and the capacitive elements C2 and C3 having substantially the same capacitance each grounding both ends of the L1,
The first high-frequency HF for resonating an observation nucleus having a high resonance frequency such as a hydrogen nucleus ( ¹ H nucleus) or a fluorine nucleus ( ¹⁹ F nucleus) and the resonance frequency of a deuterium nucleus ( ² D nucleus) Construct a balanced resonant circuit that can be double-tuned for two high frequencies (lock frequency),
The HF is an NMR detector that is input and output from a port connected to one end of the L1,
The portion that resonates with the lock frequency of the balanced resonant circuit is:
Connected to both ends of the L1 to provide an inductance component to the lock frequency resonance circuit, and an end opposite to the end connected to the L1 is connected to the lock frequency input / output port to connect to the lock frequency input / output port. Separation circuits DCPL1, DCPL2 that block the entry of the HF into the port;
A capacitive element C100 that connects ends of the DCPL1 and DCPL2 opposite to the L1 side connection ends;
With
An NMR resonator characterized in that the end of the DCPL1 and DCPL2 opposite to the L1 side connection end is floating from the ground potential. The NMR detector according to claim 1, wherein the capacitive element C100 includes a plurality of capacitive elements. 3. The NMR detector according to claim 1, wherein a lock frequency is inputted / outputted from one end of the capacitive element constituting the capacitive element C100.

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