JPS59122937A - Nuclear magnetic resonance apparatus - Google Patents

Abstract

PURPOSE:To make it possible to perform accurate tuning of a resonance circuit, by providing the resonance circuit, which detects an NMR signal, and a voltage control generator, which controls the capacity of a variable capacity diode, thereby controlling the control voltage based on the detected NMR signal. CONSTITUTION:In collecting a nuclear magnetic resonance (NMR) signal, a series circuit, which are formed by a variable capacity diode 51, whose electrostatic capacity is changed by an applied voltage in the reverse direction, and a capacitor 52 having large capacity that is provided in series on the cathode side of the diode 51, is provided in parallel with a coil 2. Thus an LC parallel resonance circuit is constituted. In parallel with said parallel circuit, reverse parallel diodes 53, which are connected in reverse parallel each other, are provided. A control voltage VC is imparted from a D/A converter part 14. In this case, since the control is performed by using the NMR signal obtained by a body under inspection, a special signal feeding system for tuning control is not required, and the NMR signal can be always obtained under the optimum tuning conditions.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention uses nuclear magnetic resonance (hereinafter referred to as "immediate") phenomenon to determine the spin density or relaxation time of a specific atomic nucleus present in a sample. NM to obtain an image that reflects constants, etc.
This relates to the R device.

[Technical background of the invention]

For example, in a diagnostic equipment, the part that detects the signal induced by the subject by the NMR phenomenon (this is called an "open signal") consists of a saddle-shaped coil installed around the subject and , and a capacitor that together forms a resonant circuit. - Since the NMR signal is very weak, a resonant circuit with a very large Q (quality factor) is required to efficiently detect the signal.

Therefore, the resonant characteristics of the resonant circuit become sharp.

Therefore, a slight change in the capacitance component of the resonant circuit significantly changes the amplitude of the detected signal, that is, the sensitivity of the detector. On the other hand, there is a stray capacitance between the test object and the detection coil, and this varies depending on the test object, so the capacitance of the capacitor is changed every time the test object changes, and the capacitance is accurately located at the resonance point. It is necessary to synchronize.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an NMR apparatus that makes it possible to automatically tune a detection section when collecting an open signal.

[Summary of the Invention] The present invention includes a resonant circuit configured using a receiving coil and a variable capacitance diode to detect an NMR signal, and a voltage for controlling the capacitance of the variable capacitance diode in this resonant circuit. and a tuning control means that receives a nine NMR signal detected by the resonant circuit and controls the control voltage generator based on the signal input to perform tuning control of the resonant circuit. 1 (Patented.

[Embodiments of the invention]

FIG. 1 shows the overall system configuration in an embodiment of the present invention.

In FIG. 1, 1 is a transmitting probe head consisting of a transmitting coil, 2 is a receiving globe head consisting of a receiving coil, and these transmitting/receiving probe heads 1.2 are as shown in the figure.
It constitutes a cross-coil type glove head in which saddle-shaped transmitting and receiving coils are arranged in directions orthogonal to each other. The transmission tuning unit 3 tunes to a high frequency of a specific frequency,
In response to the output of the transmitter 4, a high-frequency excitation signal that is tuned to a specific atomic nucleus in the subject is transmitted to the transmitter globe.
is applied to the subject as electromagnetic waves via the The signal from the subject is transmitted to the receiving tuning unit 5 via the receiving glove head 2.
It is received by a preamplifier 6, amplified by a preamplifier 6, and then output by two phase detectors 7A.
, 7B. These phase detectors 7 and 7B have a phase shifter 8 based on the signal generated in the transmitter 4, and a phase shifter 8 which has the same frequency as the NMR signal generated by the 90° phase shifter 9 and whose phases are 90° relative to each other. ° Two different types of reference waves are given. Phase detectors 7A and 7B receive the nine NMR signals and phase-detect them using the reference waves, respectively, and the detected outputs are sent to amplifiers 101 and 10B.
and amplify each separately, and each low and mother filter Ilk, 11
B via A/]) (analog-to-digital) converter 1
2A.

12B and input it into the computer 13. In the computer 13, a predetermined phase correction process is performed using the two digitized signals, and a Roux analog converter 14
constitutes a control voltage generator that provides a control voltage 1)c corresponding to the output of the computer 13 to the reception tuning section 5.

FIG. 2 shows in detail the reception tuning section 5 and its surrounding parts in the above-described configuration.

In FIG. 2, a series circuit formed by a variable capacitance diode 51 whose capacitance changes depending on a voltage applied in the reverse direction and a large capacitance capacitor 52 provided in series on the cathode side of this variable capacitance diode 51 is shown. It is provided in parallel to the receiving probe head 2 (coil) to constitute a parallel resonant circuit of LC. Here, the capacitance of the capacitor 52 is set to be sufficiently larger than that of the variable capacitance diode 5, so that the series combined capacitance of both is almost determined by the variable capacitance diode 5. In this case, the series circuit of the variable capacitance diode 51 and the capacitor 52 was connected with the anode side of the variable capacitance diode 51 as the ground side, but this series circuit could also be connected in the opposite direction to the illustration, with the capacitor 52 side as the ground side. good.

The parallel circuit is further provided with anti-parallel diodes (sometimes referred to as "crossover diodes") 53 consisting of 91 pairs of diodes connected in anti-parallel to each other. Further, the connection point between the variable capacitance diode 51 and the capacitor 52 is connected to the output side of the D/A converter 14 via a resistor 54, and
A control voltage tle from the /A converter 14 is applied. As the resistor 54, a resistor with a high resistance value is used to prevent a high frequency reception signal from flowing into the D/A converter 6 side. In addition, in the case shown, the signal line is connected to D by the capacitor 52.
/A converter 14 in terms of direct current. In addition, the anti-parallel diode 53 prevents damage to the input section of the preamplifier 6 due to leakage of high-power high-frequency excitation pulses applied to the subject from the transmitting side to the receiving side, and distortion generated by the variable capacitance diode 51. It is something to prevent. These variable capacitance diode 51, capacitor 52, anti-parallel diode 53, resistor 5
4 constitutes a reception tuning section 5. The control voltage τC applied to the variable capacitance diode 51 is applied from the D/A converter 14, and this voltage is set as follows.

First, with the subject placed inside the transmitting/receiving probe heads 1 and 2, a high-frequency excitation pulse (
990) Apply an arm thrust of 180° to the transmitting glove head 1 (coil), and apply N to the receiving glove head 1.
Obtain MR signal. At this time, the output control voltage τC of the D/A converter 14 is initially set to the minimum value vo as shown in FIG. 4(,). The nine NMR signals induced in the receiving probe head 1 are amplified and detected by the preamplifier 6, phase detectors 7A, 7B, etc., and are input to the computer 13 through the υ converters 121 and 12B. The peak value of the echo signal sampled here as shown in FIG. 4(b) is set as po, and this is
Record in the storage device within 3. Next, the output control voltage υC of the D/A converter 14 is changed to vt''vo+ΔV, echo signals are collected in the same manner as described above, and the peak value thereof is set as P!.Furthermore, sequentially v2=vl+ΔV, . . . vn=v
Let the peak values of the echo signal when the control voltage is increased such that n=1+ΔV be P, l, . . . , Pn.

Here, if the initial control voltage M c = V (1 is sufficiently small, this is the control voltage (obtainable The control voltage (control voltage) vc = VB is also smaller, and by increasing the control voltage υC sequentially, the resonance condition is approached, and the peak value of the echo signal increases monotonically until it reaches the resonance point. Applying the control voltage τc = Vm When the peak value Pm of the echo signal is obtained, this value is compared with the previous peak value Pm-1, and the operation of increasing the multi-control voltage vc, which is Pm)Pm-1, by ΔV. Repeat this until pk (pk-1) is reached.The control voltage vc=Vk-1 corresponding to the peak value Pk-1 at this time is the value that provides the resonance condition of the tuning section.Flowchart of the above process is shown in Figure 5.

While collecting signals for obtaining a tomographic image, the control voltage τC determined by this operation is applied to the variable capacitance diode 51 of the reception tuning section 5. By performing the above operations prior to the actual signal collection each time the subject changes, the synchronization of the receiving section is always maintained.

In this case, since control is performed directly using the open signal obtained from the subject, there is no need to prepare a special signal supply system for tuning control, and the recommended signal is always obtained under the optimal tuning conditions. be able to. Note that the present invention is not limited to the embodiments described above and shown in the drawings, but can be modified in various ways without changing the gist thereof.

For example, instead of the capacitor 52 shown in FIG.
Two variable capacitance diodes may be connected in series in the direction in which the candos are connected to each other to enable fine adjustment of the tuning. may be oriented in the opposite direction from that shown.

Furthermore, although the above-mentioned embodiment shows the case where a saddle-shaped receiving coil as shown in FIG. Is possible.

Furthermore, in the same embodiment, a case was shown in which a cross-coil method was used in which the transmitting coil and the receiving coil were orthogonal to each other, but as shown in FIG. Almost the same implementation as described above is also possible in a single coil system in which the probe head 15 is constructed. In FIG. 3, 16 is a power amplifier for transmission, 17 is an anti-parallel diode for preventing malfunction, 18 is a variable capacitor for tuning, and 19 is an auxiliary coil.

〔Effect of the invention〕

According to the present invention, it is possible to provide an NMR apparatus that allows automatic tuning of the detection section when collecting signals.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention, FIG. 2 is a circuit configuration diagram showing the main part configuration of the embodiment, and FIG.
The figure is a circuit configuration diagram showing the main part configuration of another embodiment of the present invention,
FIG. 4 is a timing chart of tuning control for explaining the operation of the above embodiment of the present invention, and FIG. 5 is a flowchart of tuning control. DESCRIPTION OF SYMBOLS 1... Transmission globe head, 2... Receiving block head, 3... Transmission tuning section, 4... Transmission section, 5...
Reception tuning section, 6... Preamplifier, 7A, 7B... Phase detector, 8... Phase shifter, 9... 90° phase shifter, 1
0, 10B...Amplifier, 11, 11B...Low 1? Filter, 12, 12B...ψ converter, 13
. . . Computer, 14 . . . D/A converter, 15 .
7.53...Anti-parallel diode (cross diode),
18... Variable capacitor, 19... Auxiliary coil, 5
1... Variable capacitance diode, 52... Capacitor,
54...Resistance. Applicant's representative Patent attorney Takehiko Suzue II! Figure 5 Kazuo Wakasugi, Commissioner of the Japan Patent Office1, Indication of the case, Patent Application No. 1983-2335062, Name of the invention, nuclear magnetic resonance apparatus 3, Person making the amendment, Relationship with the case, Patent applicant (3t) 7) Tokyo Shibaura Electric Co., Ltd. 4, agent 5, voluntary amendment

Claims (4)

[Claims] (1) In a nuclear magnetic resonance apparatus that images at least one of the spin density and relaxation time constant of a specific atomic nucleus in a subject using signals induced by nuclear magnetic resonance phenomena,
a resonant circuit configured using a receiving coil and a variable capacitance diode to detect a nuclear magnetic resonance signal; a control voltage generator that supplies a voltage for controlling the capacitance of the variable capacitance diode in the resonant circuit; Nuclear magnetic resonance characterized by comprising a tuning control means for inputting a nuclear magnetic resonance signal detected by the resonant circuit and controlling the control voltage generator based on the signal input to perform tuning control of the resonant circuit. Device. (2) The nuclear magnetism according to claim 1, wherein the resonant circuit has a configuration in which a capacitor is inserted in series on the cathode side of a variable capacitance diode and a control voltage is supplied to a connection point between these. Resonator. (3) The resonant d path is characterized by having a configuration in which another variable capacitance diode is inserted in series with the opposite direction to the cathode side of the variable capacitance diode, and a control voltage is supplied to the connection point between the two. A nuclear magnetic resonance apparatus according to claim 1. (4) The resonant circuit according to any one of claims 1 to 3, wherein the resonant circuit is configured by connecting a pair of antiparallel diodes to a receiving coil in parallel. Nuclear magnetic resonance apparatus.