JPH01223943A - Receiving device of nuclear magnetic resonance tomographic imaging apparatus - Google Patents

Abstract

PURPOSE:To prevent the generation of mixed modulation strain even when the mu- factor of a preamplifier is sufficiently increased to a required value, by converting the electric signal as the output signal of an amplifier to a light signal by an electro- optical converter before setting the same to the output signal of the preamplifier. CONSTITUTION:The high frequency electric signal received by a receiving coil 400 is set to the input signal of a preamplifier 2 through a matching circuit 1. A light emitting diode 4 as an electro-optical converter means is allowed to emit light by the output signal of the preamplifier 2 to generate a light signal 41 which is, in turn, allowed to irradiate a photodiode 5 as a photoelectric converter means through an optical fiber 42 as a light transmission means to be converted to an electric signal. By this mechanism, the cable connecting a main amplifier 6 from the preamplifier 2 can be omitted and it is prevented that said cable picks up external noise. This cable becomes a transmission antenna to transmit a high frequency electromagnetic wave and feedback such that said high frequency electromagnetic wave is received by the wiring of the input circuit of the preamplifier 2 is generated and the mixed modulation strain generated owing to said feedback is not also generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-frequency electromagnetic wave receiving device for so-called MRI bag '1, which images a cross section of a subject such as a human body by utilizing nuclear magnetic resonance phenomena.

[Conventional technology]

The receiving coil of an MHI device is mainly a transmitting/receiving coil that also serves as a receiving coil to obtain cross-sectional images of body parts such as internal organs, and a transmitting/receiving coil that also serves as a receiving coil to obtain cross-sectional images of body parts such as internal organs. There are a reception-only coil called a body coil that is used in close contact with the body, and a head-only reception coil.

Since the head is often associated with particularly important diseases such as brain tumors, it is necessary to accurately image this, so the receiving coil must be able to get as close to the head as possible, and the transmitting/receiving coil has a voltage of several kilovolts. Since a high voltage is applied, it is better to be as far away from the subject as possible, and a receiving coil exclusively for the head is used for imaging a cross section of the head.

Fig. 2 mainly shows the various coils of the MRI apparatus. In this figure, the main coil 100 has a 0.1 T in the case of a normal conducting coil, and a 0.1 T in the case of a superconducting coil, and 0.1 T in the case of a superconducting coil, and around IT in the case of a superconducting coil. A coil that generates a uniform static magnetic field is used, and within this uniform magnetic field, a high-frequency IWI wave is irradiated by the transmitting/receiving coil 200 to cause nuclear magnetic resonance, and a receiving coil receives the high-frequency electromagnetic waves emitted by the resonated atomic nuclei. do. The frequency at which this atomic nucleus resonates varies depending on the type of nuclide and is proportional to the uniform magnetic field strength mentioned above. For example, when a hydrogen nucleus is in the IT uniform magnetic field space, the resonance frequency is approximately 43 M
It is 1.

When imaging a cross section of the body part of a subject, the transmitting/receiving coil 200 also serves as a receiving coil.
When imaging a cross section of the head, the head is placed in a uniform magnetic field space, and the high-frequency electromagnetic waves are irradiated by the transmitting/receiving coil 200 and received by the receiving coil 400 dedicated to the head. .

In this figure, each coil is placed at a different position in the axial direction of the human body.
ζ, but when obtaining a cross-sectional image of the head, the main coil 100.
Transmitting/receiving coil 200. In practice, the receiver coil 400 as well as the patient's head are all placed overlappingly within a uniform magnetic field.

What is received by the receiving coil is that the nuclei of hydrogen atoms that make up the human body undergo nuclear magnetic resonance due to the high-frequency electromagnetic waves transmitted by the transmitting coil, and after the transmission of the high-frequency electromagnetic waves is completed, the resonant atomic nuclei generate resonance energy in the form of electromagnetic waves. The emitted electromagnetic waves are called spin echo or FID (I) depending on the method, and are very low-intensity TS magnetic waves, so the transmission and reception system for these high-frequency electromagnetic waves should be placed in an environment with as little noise as possible. At the same time, it is necessary to amplify the minute electrical signals received by the receiving coil with low noise, and the signal-to-noise ratio in this receiving device is an important factor that determines the image quality of the MRI device. Therefore, the preamplifier that first amplifies the electrical signal received by the receiving coil is particularly required to be a low-noise amplifier, and is configured to suppress the intrusion of external noise.

There are two main routes for noise to enter from the outside, one of which is electromagnetic waves propagating through space. To counter this, an electromagnetic shield is installed to cover the test object, receiving coil, and preamplifier. . Another noise propagation path is the high frequency current that enters through the cable from the preamplifier's DC power supply.

In addition, this DC power cable also serves as an antenna that picks up high-frequency noise, which further causes a reduction in the No. 3 noise ratio.

Figure 3 is a circuit diagram of a conventional receiving device, where the receiving δ coil 40
The high frequency electric signal received by 0 passes through a matching circuit 1 consisting of two capacitors connected in series and parallel to the circuit and becomes a human input signal for the preamplifier 2A, but this electric signal is a weak signal on the order of μ■. Therefore, the two preamplifiers must amplify this weak (X field) to the required strength without reducing the noise ratio.Since the capacitors that make up matching circuit 1 are small, these capacitors The preamplifier 2A is installed in the receiving coil 400, and the two preamplifiers are also placed in the vicinity of the receiving coil, and the preamplifier 2A is structurally integrated with the receiving coil 400 in a fixed state.

In this way, by placing the matching circuit 1 and preamplifier 2A near the receiving coil, the wiring lengths of the input circuits of the receiving coil 400, matching circuit 1, and preamplifier IB2A can be shortened as much as possible. The circuit wiring is configured to suppress external noise from being picked up. The DC power supply for the preamplifier 2A is supplied from a DC power supply 21 through a cord 22, and this cord 22 is usually a coaxial cable in order to avoid picking up external noise.

Since the main amplifier 6A is provided under the bed on which the subject is placed (not shown in FIG. 2), it is located approximately 1 m away from the center of the main coil 100, where the receiving coil is placed. A coaxial cable connects the amplifier 2A and the main amplifier 6A.

This electrical signal is amplified by the preamplifier 2A to an electrical signal with a strength on the order of mV and then input to the main amplifier 6A, which converts the input electrical signal to an intermediate frequency and converts the frequency to an intermediate frequency. is further amplified after lowering the
The A/D converter 7 for converting the electric signal into a digital signal for input to the combiator amplifies the electric signal to a strength on the order of several square meters.

[Problem that the invention attempts to solve]

Since the high frequency signal received by the receiving coil is weak, this weak electric signal is first amplified to the required strength by a preamplifier. In order to make the output signal of this preamplifier the required strength, it is necessary to increase the amplification factor of the preamplifier, but the connection cable from the output side of this preamplifier to the main amplifier serves as an antenna. A feedback circuit is formed in which high-frequency electromagnetic waves are emitted into the surrounding space, and these high-frequency electromagnetic waves are received by the wiring of the input circuit of the preamplifier and fed back from the output side of the preamplifier to the input side, and the amplification of the preamplifier is completed. Since the ratio is high, a problem arises in that the effect of this feedback effect is large and causes intermodulation distortion in the output No. 13 of the preamplifier. Additionally, external noise intrudes from the preamplifier's DC source supply cable, further reducing the signal-to-noise ratio of the system amplifier.

This invention prevents the intrusion of external noise, sets the amplification factor of the preamplifier sufficiently large to achieve the required output signal strength, and also prevents fFA modulation distortion due to feedback of the output signal of the preamplifier. It is an object of the present invention to provide a reception VIW with excellent noise-to-noise t'r characteristics.

[Means to solve the problem]

In order to solve the above problems, the present invention includes a preamplifier that amplifies the high frequency electricity No. 43 received by the receiving coil, and converts the output No. 13 of this preamplifier into an intermediate frequency and further amplifies it. In a high-frequency electromagnetic wave receiving device for a nuclear magnetic resonance tomography device, which includes a main amplifier,
an electro-optical conversion means for converting the output signal of the preamplifier into an optical signal; an optical transmission means for optically transmitting the light No. 13 converted by the electro-optic conversion means; and an optical No. 13 optical signal transmitted by the optical transmission means. and a photoelectric conversion means for converting the signal into an electrical signal,
A solar cell that uses the output signal of the photoelectric conversion means as an input signal of the main amplifier to generate and supply DC power as a VL power source for the preamplifier, and a light emitting source that generates light to irradiate the solar cell. The solar cell is housed together with the preamplifier and the electro-optical conversion means in a common case, at least a part of the surface of the case is used as a light-receiving surface of the solar cell, and the light-emitting source is placed on the light-receiving surface. It is assumed that the generated light is irradiated.

[Effect]

In the configuration of this invention, since the power consumption of the preamplifier is small, a solar cell is used as the DC power source for this preamplifier, and by irradiating light with a dedicated light source, it takes a large amount of power to supply the required power. Thick area g4T! There is no need for a single pond, and a steady supply of power is possible.
Since the external power supply cord can be omitted, there is no external noise intruding from the power cord.Furthermore, the electrical signal as the output signal of the preamplifier is converted into an optical signal by an electro-optic converter, and then the preamplifier is converted into an optical signal. By using the output signal of a preamplifier, the output signal does not generate high-frequency electromagnetic waves in the surrounding area, so there is no phenomenon of feedback to the input side, so even if the amplification factor of the preamplifier is sufficiently increased to the required value, mixed modulation will not occur. No distortion occurs.

〔Example〕

The present invention will be explained below based on Example 'X. FIG. 1 is a circuit diagram showing an embodiment of the present invention, and parts common to those in the prior art are given the same reference numerals and detailed explanations will be omitted. The high-frequency electric signal received by the receiving coil 400 is passed through the matching circuit 1 as an input signal to the preamplifier 2, and the output signal of the preamplifier 2 causes the light emitting diode 4 as an electro-optical conversion means to emit light to generate an optical signal 41. This optical signal 41 is passed through an optical fiber 42 as an optical transmission means and irradiated onto a photodiode 5 as a photoelectric conversion means to convert it into an electric signal, and this electric signal is used as a human power signal of the main amplifier and is transmitted to the main amplifier X6. The signal is amplified and used as an input signal to the A/D converter 7. A solar cell 3 is used as a direct power source for the preamplifier 2, and an incandescent light bulb 32 dedicated to this solar cell 3 is used.
The required power is constantly supplied by irradiating the white light 31 with a white light 31.

The light emitting diode 4 and the solar cell 3 are housed together with the preamplifier 2 in a common case, and the light-receiving surface of the solar cell 3 is arranged as part of the surface of the case, and the white light of the incandescent light bulb 32 is placed on this light-receiving surface. The structure is such that the surface area of the solar cell 3 required to generate the required power can be reduced by concentrating the light 31 and irradiating it efficiently (by irradiating it), and at the same time can supply steady power.

By converting the output signal of the preamplifier 2 into the light 41 emitted by the light emitting diode 4, the cable connecting the preamplifier to the main amplifier can be omitted, so this cable will not pick up external noise. This cable also becomes a transmitting antenna and transmits high frequency '@ electromagnetic waves into the surrounding space, and this high frequency electromagnetic wave is transmitted to the preamplifier 20.
No cross-modulation distortion occurs due to feedback received by the wiring of the input circuit.

The solar cell 3 is used as a DC power source for the preamplifier 2, and the solar cell 3 is irradiated with white light 31 from a lamp or the like to constantly supply the required power to the solar cell 3. Since a cable for the DC power supply of the amplifier 2 is not required, noise intruding from this cable is eliminated, and the noise characteristics of the preamplifier 2 are improved.

Furthermore, the optical signal 41 is transmitted through an optical fiber 42 to the main amplifier 6, which is approximately 1 m away, but the main amplifier 6 is installed at a location far from high-frequency electromagnetic waves and has sufficient magnetic shielding. Therefore, the main amplifier, which is the circuit after the photodiode 5 that converts the optical signal 41 into an electrical signal, can be a low-noise amplifier that is not affected by external noise or high-frequency electromagnetic waves.

In this embodiment, the optical transmission means 42 is an optical fiber, but the transmission of optical signals by this optical fiber is a well-known technique widely used in optical communications. As mentioned above, the receiving coil to which this invention is applied includes a dual-purpose coil for transmitting and receiving, a receiving coil exclusively for the head, etc., but when using these coils, the position must be such that the center of both the uniform magnetic field and the uniform magnetic field generated by the main coil 100 is located. Since the light emitting position of the optical signal as the output signal of the preamplifier 2 is uniquely determined for each receiving coil, instead of using an optical fiber as the optical transmission means, It is also possible to use the light receiving section outside the main coil 100 and using space as a light transmission means, and by aligning the optical axes of the light emitting section and the light receiving section and using a lens, the optical signal emitted from the light emitting section can be transmitted to the light receiving section. An efficient optical transmission means can also be constructed by configuring the light beam to be focused.

Further, in the embodiment, an incandescent lamp was used as the light emitting source of the solar cell, but if the light wavelength characteristics of the solar cell are considered, the light emitting source is not limited to an incandescent lamp, and other light emitting sources may be used.

〔Effect of the invention〕

As mentioned above, this invention originates in a cable for transmitting the output signal of a preamplifier to the main amplifier by converting the electrical signal as the output signal of the preamplifier into an optical signal and then optically transmitting the signal to the main amplifier. This eliminates the possibility of cross-modulation distortion caused by the feedback effect caused by the feedback, and it is possible to use a solar cell as the source of the direct current of the preamplifier, and to integrate this solar cell with the preamplifier and the above-mentioned light emitting diode into a common case. By irradiating the light-receiving part of the solar cell provided on the surface of the case with light from the light-emitting source, the required DC power is constantly supplied.
The cable from the DC power supply no longer picks up noise and reduces the signal-to-noise ratio of the preamplifier. As a result of being able to significantly improve the signal-to-noise ratio in the high-frequency receiving device, which can be called the heart of the MHI device, we were able to create a high-performance MHI device that can obtain good images.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an embodiment of this invention, Figure 2 is a MH
FIG. 3 is a perspective view showing each coil of the I device, and a circuit diagram showing a conventional receiving device. 1... Matching circuit, 2.2A... Preamplifier, 3...
・Solar cell, 31...White light (light), 32...Incandescent light bulb (light source), 4...Light emitting diode (i! air conversion means), 41.
・・Optical signal, 42 ・・Optical fiber (optical transmission means), 5
・・・Photodiode (photoelectric conversion means), 6.6A・
...Main amplifier, 400...Reception coil. Figure 2 Yu Figure 3

Claims (1)

[Claims] 1) High-frequency electromagnetic waves of a nuclear magnetic resonance tomography imaging system consisting of a preamplifier that amplifies the high-frequency electrical signal received by the receiving coil, and a main amplifier that frequency-converts the output signal of this preamplifier to an intermediate frequency and further amplifies it. In the receiving device, there is provided an electro-optical conversion means for converting the output signal of the preamplifier into an optical signal, an optical transmission means for optically transmitting the optical signal converted by the electro-optic conversion means, and an optical transmission means using the optical transmission means. and a photoelectric conversion means for converting the optical signal into an electrical signal, the output signal of the photoelectric conversion means is used as an input signal of the main amplifier, and a solar power generator generates and supplies DC power as a DC power source for the preamplifier. The solar cell is housed in a common case together with the preamplifier and the electro-optical conversion means, and at least a part of the surface of the case is A receiving device for a nuclear magnetic resonance tomography imaging apparatus, characterized in that the light-receiving surface of the solar cell is used as a light-receiving surface, and the light-receiving surface is irradiated with light generated by the light emitting source.