JP4236595B2 - Magnetic resonance imaging system - Google Patents

Description

  The present invention relates to a magnetic resonance imaging (hereinafter abbreviated as MRI) apparatus that displays an arbitrary cross section of a subject by utilizing a nuclear magnetic resonance (hereinafter abbreviated as NMR) phenomenon, and in particular, whether or not a preamplifier is incorporated. The present invention relates to a technology that enables a receiving coil to be connected regardless of the case.

  The MRI apparatus uses the NMR phenomenon to measure the NMR signal from the nuclear spin at the desired examination site in the subject with the nuclear spin density distribution and relaxation time distribution information, and from the measurement data, The cross section of the specimen is displayed as an image.

In such a receiving system in an MRI apparatus, an NMR signal is received by a receiving coil, and the received signal is amplified by a preamplifier (preamplifier). Here, the preamplifier amplifies a weak NMR signal received by the receiving coil below microvolts to about millivolts, and a very low noise figure is used. With this high-performance pre-stage amplifier, an image with excellent SNR can be obtained.
In order to reduce the noise mixed between reception and amplification when receiving the NMR signal by the receiving coil, the pre-amplifier is used so that the NMR signal can be immediately amplified immediately after receiving the NMR signal by the receiving coil. It is necessary to arrange as close to the receiving coil as possible.

In view of this, a receiving coil has been developed in which a pre-amplifier is built in the receiving coil and the coil and the pre-amplifier are integrated (Patent Document 1). However, conventionally, there has not been a small-sized and high-performance preamplifier that can be built in the receiving coil, and there is also a receiving coil in which the receiving coil and the preamplifier are separated to form only a coil (Patent Document 2). That is, at present, the subject is imaged by the same MRI apparatus using the two types of receiving coils.
JP 2003-265432 A JP 2003-325476 A

  Since the above two types of receiving coils exist, the receiving system must be designed and manufactured on the assumption that these two types of receiving coils exist at the input end of the receiving system that processes received signals. is there. However, if the receiving system is designed and manufactured on the assumption that the receiving amplifier has a built-in pre-stage amplifier, a sufficiently amplified received signal can be obtained if a receiving coil without a pre-stage amplifier is used. Disappear. Conversely, if the receiving system is designed and manufactured on the assumption that the receiving coil does not have a built-in pre-stage amplifier, a problem arises because the receiving coil having the pre-stage amplifier cannot be used.

Therefore, a first object of the present invention is to enable processing of NMR signals from a receiving coil in the same MRI apparatus regardless of whether or not a pre-amplifier is incorporated in the receiving coil. is there.
The second object of the present invention is to prevent noise from being mixed into the NMR signal as much as possible in the amplification of the received NMR signal.

In order to achieve the above object, the present invention is configured as follows. That is, in a magnetic resonance imaging apparatus including a receiving coil for receiving a nuclear magnetic resonance signal from a subject and a receiving means having an amplifier for amplifying the nuclear magnetic resonance signal.
The receiving means includes a first path including the amplifier, a second path not including the amplifier, and a selection means for selecting one of the two paths.
The selecting means selects the second path when the receiving coil includes the amplifier, and selects the first path when the receiving coil does not include the amplifier.

As a result, it becomes possible to use a receiving coil that does not include the pre-stage amplifier and a receiving coil that includes the pre-stage amplifier in a mixed manner, thereby achieving the first object.
In a preferred embodiment, the selecting means includes means for recognizing the type of the receiving coil, and selects one of the two paths corresponding to the type of the receiving coil.
As a result, a route can be automatically selected in accordance with the type of receiving coil.
Further, in a preferred embodiment, control means for turning off the power supply of the amplifier is further provided, and the power supply of the amplifier is ON / OFF controlled in accordance with the use state of the amplifier.
As a result, it is possible to prevent the noise generated due to the pre-stage amplifier from propagating to the pre-stage amplifier being used or to other parts of the receiving system, thereby achieving the second object. it can.

  As described above, in the receiving system including the receiving coil and the pre-stage amplifier, by having the receiving coil switch, regardless of whether or not the pre-stage amplifier is built in the receiving coil, it does not depend on the form of the receiving coil. The same MRI apparatus can receive NMR signals and perform subsequent processing.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment of the invention, and the repetitive description thereof is omitted.

  First, an MRI apparatus to which the present invention is applied will be described. FIG. 4 is a block diagram showing the overall configuration of an embodiment of the MRI apparatus to which the present invention is applied. This MRI apparatus uses a NMR phenomenon to obtain a tomographic image of a subject.As shown in FIG. 4, the MRI apparatus includes a static magnetic field generation system 2, a gradient magnetic field generation system 3, a transmission system 5, The receiving system 6, the signal processing system 7, the sequencer 4, a central processing unit (CPU) 8, and a bed 26 on which the subject 1 is placed are configured.

  The static magnetic field generation system 2 generates a uniform static magnetic field in the direction perpendicular to the body axis in the space around the subject 1 in the vertical magnetic field method (or the body axis direction in the horizontal magnetic field method). Thus, a permanent magnet type, normal conducting type or superconducting type static magnetic field generating source is arranged around the subject 1.

  The gradient magnetic field generating system 3 includes a gradient magnetic field coil 9 wound in three axial directions of X, Y, and Z, and a gradient magnetic field power source 10 for driving each gradient magnetic field coil 9. By driving the gradient magnetic field power supply 10 of each coil in accordance with the above command, gradient magnetic fields Gx, Gy, and Gz in three axial directions of X, Y, and Z are applied to the subject 1. More specifically, a slice direction gradient magnetic field pulse (Gs) is applied in one of X, Y, and Z to set the slice plane for the subject 1, and the phase encode direction gradient magnetic field is applied to the remaining two directions. A pulse (Gp) and a frequency encoding direction gradient magnetic field pulse (Gf) are applied, and position information in each direction is encoded in the echo signal.

  The sequencer 4 is a control means that repeatedly applies a high-frequency magnetic field pulse (hereinafter referred to as “RF pulse”) and a gradient magnetic field pulse in a predetermined pulse sequence, and operates under the control of the CPU 8 to collect tomographic image data of the subject 1. Various commands necessary for the transmission are sent to the transmission system 5, the gradient magnetic field generation system 3, and the reception system 6.

  The transmission system 5 irradiates an RF pulse to cause nuclear magnetic resonance to the nuclear spins of atoms constituting the biological tissue of the subject 1, and includes a high frequency oscillator 11, a modulator 12, a high frequency amplifier 13, and a transmission side And a high frequency coil (transmitting coil) 14a. The high-frequency pulse output from the high-frequency oscillator 11 is amplitude-modulated by the modulator 12 at a timing according to a command from the sequencer 4, and the amplitude-modulated high-frequency pulse is amplified by the high-frequency amplifier 13 and then placed close to the subject 1. By supplying to the high frequency coil 14a, the subject 1 is irradiated with the RF pulse.

The receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the biological tissue of the subject 1, and receives a high-frequency coil (receiving coil) 14b on the receiving side and a preamplifier 15 And a quadrature detector 16 and an A / D converter 17. After the NMR signal of the response of the subject 1 induced by the electromagnetic wave irradiated from the high frequency coil 14a on the transmission side is detected by the high frequency coil 14b arranged close to the subject 1 and amplified by the preamplifier 15, The signal is divided into two orthogonal signals by the quadrature phase detector 16 at the timing according to the command from the sequencer 4, and each signal is converted into a digital quantity by the A / D converter 17 and sent to the signal processing system 7.
In the MRI apparatus to which the present invention is applied, the receiving coil includes a built-in pre-stage amplifier and a separate receiving coil.

  The signal processing system 7 performs various data processing and display and storage of processing results, and has an external storage device such as an optical disk 19 and a magnetic disk 18 and a display 20 composed of a CRT, etc. Is input to the CPU 8, the CPU 8 executes processing such as signal processing and image reconstruction, and displays the tomographic image of the subject 1 as a result on the display 20, and the magnetic disk 18 of the external storage device. Record in etc.

The operation system 25 is used to input various control information of the MRI apparatus and control information of processing performed by the signal processing system 7, and includes a trackball 23 and a keyboard 24. The operation unit 25 is disposed close to the display 20, and the operator controls various processes of the MRI apparatus interactively through the operation unit 25 while looking at the display 20.
In FIG. 4, the high-frequency coil 14a and the gradient magnetic field coil 9 on the transmission side are placed facing the subject 1 in the static magnetic field space of the static magnetic field generation system 2 into which the subject 1 is inserted. The high-frequency coil 14b on the receiving side is installed so as to face or surround the subject 1.

  Currently, the radionuclide to be imaged by the MRI apparatus is a hydrogen nucleus (proton) which is a main constituent material of the subject as widely used in clinical practice. By imaging information on the spatial distribution of proton density and the spatial distribution of relaxation time in the excited state, the form or function of the human head, abdomen, limbs, etc. is imaged two-dimensionally or three-dimensionally.

  Prior to describing the present invention, a conventional example of a receiving coil and a pre-stage amplifier will be described based on the MRI apparatus in FIG. 4 for comparison. 1A and 1B show an outline of a conventional receiving coil and a signal input unit of a receiving system. FIG. 1 (a) shows the case of a receiving coil that does not incorporate a pre-stage amplifier. As shown in FIG. 1 (a), the NMR signal obtained from the receiving coil 101 is input to the pre-amplifier 103 via the connector 102 and amplified, and then is a signal input terminal of the receiving system of the MRI apparatus. Input 1 (104-1) and input 2 (104-2) are input, subjected to quadrature detection and A / D conversion in the receiving system 6, and then sent to the signal processing system 7.

  On the other hand, FIG. 1 (b) shows a case of a receiving coil in which a pre-stage amplifier is incorporated. As shown in FIG. 1 (b), in the receiving coil 101 in which the pre-amplifier 103 is built, the NMR signal obtained by the receiving coil 101 is amplified by the built-in pre-amplifier 103 and passes through the connector 102. Input to input 1 (104-1) and input 2 (104-2), which are the signal input terminals of the receiving system of the MRI apparatus, and after being subjected to quadrature detection and A / D conversion in the receiving system 6, it is sent to the signal processing system 7. It is done.

In this way, when only the receiving coil not including the preamplifier 103 or only the receiving coil including the preamplifier 103 is used, the received NMR signal does not cause a problem in the path, and the receiving system It is sent to 6 quadrature detectors and A / D converters for image display.
However, as can be seen from the examples of FIGS. 1 (a) and 1 (b), it is not possible to use a reception coil that does not include the pre-amplifier 103 and a reception coil that includes the pre-amplifier 103 in a mixed manner.

Next, the present invention for solving the above problems will be described. An object of the present invention is to make it possible to use a reception coil that does not include a pre-stage amplifier and a reception coil that includes a pre-stage amplifier.
For this purpose, the MRI apparatus to which the present invention is applied further includes a path with a pre-stage amplifier, a path without the pre-stage amplifier, and a changeover switch for selecting these, and can be connected to any type of receiving coil. These are provided, for example, in the receiving system 6 in the MRI apparatus of FIG.

  First, a first embodiment of the present invention will be described. In this embodiment, two paths with a pre-stage amplifier and two paths without a pre-stage amplifier are prepared so that any type of receiving coil can be connected, and either one of them is placed before the signal input terminal of the receiving system. It is the form which comprises the switch which can select the path | route of this, and can select a desired receiving coil. This switch has a configuration in which switches having a pair of a switch that selects a path having a pre-stage amplifier and a switch that selects a path without a pre-stage amplifier are arranged in parallel by the number of input terminals.

  An example of this embodiment is shown in FIGS. 2 (a) and 2 (b). The switcher 201 shown in FIG. 2 has a configuration in which two switches each having a pair of a switch A that selects a path having a pre-stage amplifier and a switch B that selects a path without the pre-stage amplifier are arranged in parallel. It is an example.

  FIG. 2A shows a case where the receiving coil 101 not including the preamplifier 103 is used. The NMR signal received by the receiving coil 101 passes through the path 202 provided with the preamplifier 103 via the connector 102, and is amplified by the preamplifier 103 attached inside the bed, for example, and then input to the switch 201. . In the switch 201, the switch A side is turned on and the switch B side is turned off, and the receiving coil 101 not including the preamplifier 103 is selected.

On the other hand, FIG. 2B shows a case where the receiving coil 101 including the preamplifier 103 is used. The NMR signal received by the receiving coil 101 is amplified by the built-in preamplifier 103 and then input to the switch 201 via the connector 102 through the path 203 without the preamplifier 103. In the switch 201, the switch A side is turned OFF and the switch B side is turned ON, and the reception coil 101 including the pre-stage amplifier 103 is selected.
Here, the ON / OFF control of the switch in the switch 201 can be performed by a control signal from the sequencer 4, for example, as shown in FIG. Or it has a control part (illustration omitted) which recognizes a receiving coil automatically, and can control a switch by the recognition signal.

  Next, a second embodiment of the present invention will be described. In the present embodiment, in addition to the first embodiment, when the pre-stage amplifier on the path is not used, the power supplied to the pre-stage amplifier is turned off and the noise generated by the pre-stage amplifier is used. In this mode, the signal is prevented from propagating to other preamplifiers and other parts of the receiving system. As a result, it is possible to prevent deterioration in image quality.

  3A and 3B show an example of this embodiment. A preamplifier power supply switching unit 301 shown in FIG. 3 is an example of means for ON / OFF control of the power supply of the preamplifier 103 in the path 202 including the preamplifier. The preamplifier 103 in the path 202 including the preamplifier is When not in use, the power is turned off so that the noise generated by the unused preamplifier 103 is not propagated to the preamplifier 103 in use and other parts of the receiving system.

  FIG. 3A shows a case where one receiving coil 101 not including the preamplifier 103 is used. The NMR signal received by the receiving coil 101-1 passes through the path 202-1 provided with the preamplifier 103-1 through the connector 102, and is amplified by the preamplifier 103-1 attached inside the bed, for example. Is input to the switch 201. On the other hand, since the pre-stage amplifier 103-2 is not used, the pre-stage amplifier power supply switching unit 301 turns on the power of the pre-stage amplifier 103-1 and turns off the power of the pre-stage amplifier 103-2.

On the other hand, FIG. 3B shows a case where two receiving coils 101 each including the pre-stage amplifier 103 are used. The NMR signal received by the receiving coil 101 is amplified by the built-in preamplifier 103 and then input to the switch 201 via the connector 102 through the path 203 without the preamplifier 103. In this case, since both the pre-stage amplifiers 103 are not used, the pre-stage amplifier power supply switching unit 301 turns off the power supplies of both the pre-stage amplifiers 103.
Here, the control of the amplifier power supply switching unit 301 can be performed by a control signal from the sequencer 4, for example, as shown in FIG. Or it has a control part (illustration omitted) which recognizes a receiving coil automatically, and can control a switch by the recognition signal. This is the same as in the case of FIG.

In the above description of the embodiment of the present invention, one type of receiver coil connector is used. However, even when a plurality of types of connectors are used, the same switch can be operated to support the type of receiver coil. Thus, the received NMR signal can be amplified.
In addition, although the number of receiving coils is one or two, the received NMR signal can be amplified corresponding to the type of the receiving coil even when the number is three or more.

The figure which shows a prior art example. (a) shows the case of a receiving coil without a built-in pre-stage amplifier, and (b) shows the case of a receiving coil with a built-in pre-stage amplifier. The figure which shows the 1st Embodiment of this invention. (a) shows the case of a receiving coil without a built-in pre-stage amplifier, and (b) shows the case of a receiving coil with a built-in pre-stage amplifier. The figure which shows the 2nd Embodiment of this invention. (a) shows the case of a receiving coil without a built-in pre-stage amplifier, and (b) shows the case of a receiving coil with a built-in pre-stage amplifier. The block block diagram of one Example of the MRI apparatus with which this invention is applied.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Subject, 2 ... Static magnetic field generation system, 3 ... Gradient magnetic field generation system, 4 ... Sequencer, 5 ... Transmission system, 6 ... Reception system, 7 ... Signal processing system, 8 ... Central processing unit (CPU), 9 ... Gradient magnetic field coil, 10 Gradient magnetic field power source, 11 High frequency transmitter, 12 Modulator, 13 High frequency amplifier, 14 a High frequency coil (transmitting coil), 14 b High frequency coil (receiving coil), 15 Signal amplifier, 16 ... Quadrature detector, 17 ... A / D converter, 18 ... Magnetic disk, 19 ... Optical disk, 20 ... Display, 21 ... ROM, 22 ... RAM, 23 ... Trackball or mouse, 24 ... Keyboard, 25 ... Operation system

Claims (3)

In a magnetic resonance imaging apparatus comprising a receiving coil for receiving a nuclear magnetic resonance signal from a subject and a receiving means having an amplifier for amplifying the nuclear magnetic resonance signal,
The receiving means includes a first path including the amplifier, a second path not including the amplifier, and a selection means for selecting one of the two paths.
The magnetic resonance imaging apparatus characterized in that the selection means selects the second path when the receiving coil has the amplifier, and selects the first path when the receiving coil does not have the amplifier. The magnetic resonance imaging apparatus according to claim 1.
The magnetic resonance imaging apparatus according to claim 1, wherein the selection means includes means for recognizing the type of the receiving coil, and selects one of the two paths corresponding to the type of the receiving coil .   3. The magnetic resonance imaging apparatus according to claim 1, further comprising control means for turning on / off the power supply of the amplifier, wherein the power supply of the amplifier is controlled to be turned on / off in accordance with a use state of the amplifier. Magnetic resonance imaging apparatus.

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