JPS63215956A - High frequency probe for nmr - Google Patents

Abstract

PURPOSE:To enable a probe to be used both as a transmitter and a receiver by controlling the application of a bias to a first pin diode group by turning ON or OFF a second pin diode group. CONSTITUTION:When a probe is used for transmission, first pin diodes 30a and 30b are held in a reverse bias condition while transmitted pulses are applied to an input/output terminal 40. For this end, a forward current is made flow from a driver 72 to second pin diodes 71a and 71b. Since an NMR signal is detected after the transmission of transmitting pulses, the diodes 30a and 30b are held in a forward bias condition during detection. When the probe is used both for transmission and reception, the diodes 30a and 30b are always held in the reverse bias condition. That is, a forward current is made flow in the diodes 71a and 71b. Thus, a capacitor short circuit composed of the diodes 30a and 30b and resistors 60a and 60b does not operate and the probe can be used as a normal probe.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transmitting probe in which a high frequency NMR probe is separately provided with a receiving probe. To be more specific, there are so-called surface coils that receive signals using a surface coil and transmit using a large transmitting probe.
This relates to transmitting probes used in imaging.

[Prior Art] FIG. 4 is a circuit configuration diagram showing a conventional high-rise high-frequency probe for NMR, particularly a transmitting probe, described in, for example, Japanese Patent Application Laid-open No. 124854/1983. In the figure, (1)
is a high-frequency coil, (2a) and (2b) are capacitors for resonance and impedance matching, respectively, (3) is a diode connected in antiparallel, (4a) and (4b)
is a terminal connected to a transmitter (not shown).

Next, the operation will be explained. A resonant circuit is formed by the high frequency coil (1) and the capacitors (2a) (2b). When a transmission pulse is applied to the terminals (4a) and (4b) from a high frequency transmitter (not shown), the diode (3) becomes conductive and a resonant current flows through the high frequency coil (1). As a result, a high frequency magnetic field is transmitted, and immediately after the transmission pulse is cut off, an NMR signal is generated from a sample placed in a receiving probe (not shown), and the NMR signal is detected by the receiving probe. When the transmit pulse is cut off, the diode (3) becomes non-conductive, preventing the transmission of unwanted noise due to high frequency transmitter noise. Furthermore, since the above-mentioned resonant circuit becomes an open circuit, magnetic coupling with the resonant circuit of the receiving probe is almost eliminated, and the quality Q (quality factor) of the resonant state of the receiving probe is maximized.

[Problems to be solved by the invention] Since it is configured like a conventional high-rise high-frequency probe for NMR, it has a transmitting probe and a receiving probe (here, the probe includes the coil, capacitor, etc.). If these are provided separately, the operation will be satisfactory. However, it was not possible to configure a probe for both transmitting and receiving purposes. For example, if the transmitting coil is a large whole-body coil and the receiving coil is a small surface coil, the problem is that only the large whole-body coil is used for both transmission and reception, making it impossible to obtain NMR signals. was there.

This invention was made to solve the above-mentioned problems, and can be used both for transmitting and receiving, or for transmitting only, and when used only for transmitting, it can be used for both receiving and receiving probes provided separately. The purpose is to create a high-rise high-frequency probe for NMR that does not cause any adverse effects.

[Means for Solving the Problems] There is a high-rise high-frequency probe for NMR having an inductance component part of the high-rise high-frequency probe for NMR according to the present invention and a resonant capacitor part including at least one variable capacitor. A parallel circuit consisting of one or more pairs of first pin diodes (PIN diodes) connected in anti-series and one or more pairs of series-connected resistors is connected in parallel at one location, and the first
A bias application terminal for the first pin diode group was provided between the midpoints of the pin diode group and the resistor group, and one end was connected to this bias application terminal, and the other end was connected in parallel. terminated with a second pin diode consisting of at least one pin diode;
A transmission line whose electrical length is an odd number multiple of a quarter wavelength is installed, and the second
The bias application to the first pin diode group is controlled by turning on and off the pin diode group.

[Function] The high-rise high-frequency probe for NMR in this invention can be used as a probe for both transmission and reception, and can also be used only as a transmission coil. In this case, this By opening the resonant circuit of the transmitting coil, the Q of the receiving coil is not reduced. Also, unnecessary noise is not generated by the transmitting coil.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a circuit configuration diagram showing an embodiment of the high-rise high-frequency probe for NMR according to the present invention. (20a) is a resonance variable capacitor with a variable capacitance, and (20c) is a matching variable capacitor for matching the circuit.
are the input and output terminals of the probe.

Further, (30a) and (30b) are first pin diodes connected in anti-series, for example, t1M7010B manufactured by Unitroad. (50a) and (50b)
are the first pin diodes (30a) and (30b)
This is a bias application terminal for applying bias to
Resistors (60a) and (60b) are connected. (70) is a transmission line with an electrical length of 1/4 wavelength, one end of which is connected to the bias application terminals (50a) and (50b), and here it is a coaxial cable. There are (71a) and (71b)
is a second pin diode inserted in parallel to the other end of the coaxial cable (70), (72) is a driver that drives the second pin diode (71a) (71b), and (73) is a driver (72). ), into which, for example, a TTL level control signal is input.

Next, the operation will be explained. First, a case will be described in which the present probe is used for transmission and an NMR signal is acquired by a separately provided receiving coil (not shown). While applying a transmission pulse to the input/output terminal (40) (in this case used only as an input terminal), the first pin diodes (30a) (30b) are reverse biased. For this purpose, a forward current is caused to flow from the driver (72) to the second pin diode ()la) (71b). At high frequencies, the impedance looking from the bias application terminals (50a) (50b) to the coaxial cable (70) side is typically 100 J (Ω). , that is, depending on the characteristics of the coaxial cable (70).At this time, the first pin diode (30a)
(30b) is in a reverse bias state of approximately IV. It is preferable to make the characteristic impedance of the coaxial cable (70) as large as possible and to make the on-resistance of the second pin diode (71a) (71L+) as small as possible. For example,
A coaxial cable (70) with a characteristic impedance of 100 Ω is used, and Unitrode's 1 is used as the second pin diode.
It is recommended to connect about 4 784001 in parallel (only 2 are shown in the drawing), and resistors (80a) (60b)
) was selected to be 100KΩ, and the Q of the probe was measured and found to be approximately 400. After transmitting the transmission pulse, the NMR signal is detected, so the pin diode (30a) in the detection tube 1
(30b) is placed in a forward bias state. Experiments have shown that when a bias current of 0.45 mA is passed through the bias application terminals (50a) (50b), the resonance current is reduced by 38 dB. The output voltage of the driver (72) is -45
V, 100 KΩ resistance (60a) (60b)
through the first pin diode (30a) (30b)
A current of 0.45 ni flows through. Therefore, during signal detection,
Magnetic coupling with other receiving coils was almost negligible, and noise from the transmitter was also prevented from entering the receiving coil.

Next, when this probe is used for both transmission and reception, the first pin diodes (30a) (30b) are always reverse biased. That is, the second pin diode (71a) (
71b>, and thereby,
The capacitor short circuit consisting of the first pin diode (30a) (30b) and the resistor (60a) (Sob) is not activated and can be used as a normal 10-b.

In addition, FIG. 2 and FIG. 3 show circuit configuration diagrams of other embodiments of the present invention, and the difference in FIG. 2 from FIG. 1 is that two sets of resonant variable capacitors (20a)
The difference in Fig. 3 from Fig. 1 is that fixed capacitors (20d) (20e
) is added.

Note that FIGS. 1 to 3 are shown in terms of equivalent circuits, and the specific configuration is not particularly limited.

In addition, if the first pin diodes (30a) (30b) have insufficient withstand voltage, each can be connected in series with N number of pin diodes to increase the withstand voltage9. The anti-series connection can be made by connecting the anodes together or the cathodes together; in this case, the polarity of the bias application may also be reversed. Also,
Although the transmission line, ie, the coaxial cable (70), is shown as having an electrical length of a quarter wavelength, it may be an odd number multiple of a quarter wavelength.

[Effects of the Invention] According to the present invention, in a high frequency probe for NMI"j having an inductance component and a resonance capacitor section including at least one variable capacitor, a A parallel circuit consisting of one or more pairs of anti-series-connected first pin diodes and one or more series-connected resistors is connected to , and each of the first pin diodes and resistors is One end is connected to a bias application terminal for the first pin diode group provided between the midpoints,
A transmission line having an electrical length that is an odd multiple of a quarter wavelength is provided, the other end of which is terminated with a second pin diode consisting of at least one pin diode connected in parallel. Since the bias application to the first pin diode group is controlled by turning it on and off, it can be used for both transmitting and receiving, and when used only as a transmitting coil, it will not adversely affect the receiving coil. N
The effect of being able to supply a high frequency probe for MR can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a high frequency probe for NMR according to the present invention, FIG. 2 is a circuit diagram showing another embodiment of the invention, and FIG. 3 is a circuit diagram showing yet another embodiment of the invention. FIG. 4 is a circuit diagram of a conventional high frequency NMR probe, particularly a transmission probe. In the figure, (10) is the inductance, (20a) is the variable capacitor for resonance, (20b) is the capacitor for resonance, (20c) is the variable capacitor for matching, (20d
) and (20e) are fixed capacitors, (30a) and (30
b) is the first pin diode, (40) is the input/output terminal,
(50a) and (5011) are bias application terminals, (8
0a) and (60b) are resistors, (70) is a coaxial cable,
(71a) and (71b) are the second pin diodes, (7
2) is a driver, and (73) is an input terminal. In the drawings, the same reference numerals indicate the same or corresponding parts. Figure 1 Figure 2

Claims (3)

[Claims] (1) NM having an inductance component and a resonant capacitor section including at least one variable capacitor
The R high-frequency probe includes one or more pairs of anti-series connected first pin diodes and one or more series-connected resistors, which are connected in parallel to at least one location of the resonance capacitor section. A parallel circuit, a bias application terminal provided between the midpoints of the first pin diode group and the resistor group, and a bias application terminal with an electrical length of 1/4 wavelength connected to this bias application terminal. A second transmission line consisting of an odd-numbered transmission line and at least one pin diode inserted in parallel at the other end of the transmission line.
A high frequency probe for NMR, characterized in that the bias application to the first pin diode group is controlled by turning on and off the second pin diode group. (2) When using the above high-frequency probe for NMR for transmission, a separately provided receiving probe
The high frequency NMR device according to claim 1, wherein a current is caused to flow through the second group of pin diodes so as to turn on the first group of pin diodes during R signal detection. probe. (3) When the high-frequency NMR probe is used for both transmission and reception, a current is caused to flow through the second pin diode group so that the first pin diode group is always in an OFF state. A high frequency probe for NMR according to claim 1.