JP4648686B2 - Surgery receiving coil and magnetic resonance imaging apparatus using the same - Google Patents

Description

  The present invention relates to a surgical receiving coil and a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus) using the same, and more particularly to a technique for suitably suppressing artifacts caused by eddy currents induced in a surgical receiving coil. .

  The MRI system utilizes the nuclear magnetic resonance phenomenon that occurs in the nuclei of the atoms that make up the subject when the subject is placed in a uniform static magnetic field and radiates electromagnetic waves. Hereinafter, an NMR signal is detected, and an image is reconstructed using the NMR signal, thereby obtaining a magnetic resonance image (hereinafter referred to as an MR image) representing the physical properties of the subject. In order to give this imaging position information, a gradient magnetic field is applied in a superimposed manner on the static magnetic field.

MRI equipment is not exposed to X-rays, can obtain arbitrary cross-sectional images by applying gradient magnetic fields, and has excellent resolution of soft tissues such as internal organs and brains. It is used for. For example, in an open MRI system in which magnets for generating a static magnetic field (superconducting magnets, permanent magnets, etc.) are placed facing each other up and down, surgery and treatment are performed from the side of the space where the subject is placed. There is an I-MR technique for performing (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2003-566

Patent Document 2 further discloses a technique related to stereotaxic surgery, which is a brain treatment method, which is one of I-MR procedures. Here, stereotactic brain surgery is a technique for treating a specific region without craniotomy using a craniotomy instrument. With a head fixture attached, tumor excision, aspiration, or A puncture or the like is performed. In Patent Document 2, in particular, a surgical reception coil used in stereotaxic surgery is arranged around the subject's head and is fixed around the head via a head-fixing bolt and U-shaped formed of a conductor. A fixed portion having a shape, a frame portion formed with a conductor on which a surgical jig is attached, and a connector portion that electrically connects the fixed portion and the end portions of the frame portion Has been proposed.
Japanese Patent Laid-Open No. 2003-126056

The present inventor has found the following problems as a result of studying the above prior art.
That is, when performing stereotaxic surgery with the surgical receiving coil disclosed in Patent Document 2, if an attempt is made to capture a diffusion-weighted image in order to detect minute movement of molecules in the tissue, that is, diffusion, the diffusion-weighted image Since imaging is an imaging method that is sensitive to factors that affect magnetic field inhomogeneity such as eddy currents, when eddy currents are induced by applying a gradient magnetic field to a surgical receiving coil, artifacts due to this are induced. The problem of occurring was not considered.

  An object of the present invention is to provide a surgical receiving coil and a magnetic resonance imaging apparatus using the same that can suitably suppress artifacts caused by eddy currents.

According to the first aspect of the present invention, there is provided a receiving coil used in the magnetic resonance imaging apparatus, the fixing unit being arranged in the circumferential direction of the imaging region of the subject and fixing the imaging region of the subject, and the surgical treatment A surgical receiving coil comprising a frame portion to which a tool is attached and a connector portion for electrically connecting the fixed portion and the frame portion to form a loop-shaped coil, wherein at least one of the surgical receiving coils part is a plate-like member of conductor and non-conductive body has become heavy I combined structure, the direction parallel to the plane of the plate-like member of the conductor and the non-conductive body to generate the magnetic resonance imaging apparatus A surgical receiving coil is provided that is substantially parallel to the direction of the static magnetic field.

  The present invention also provides a magnetic resonance imaging apparatus using the surgical receiving coil according to the first feature of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the receiving coil for a surgery which can suppress suitably the artifact resulting from an eddy current, and a magnetic resonance imaging apparatus using the same are provided.

Hereinafter, the system configuration of a general MRI apparatus will be described in detail with reference to FIG.
The MRI apparatus is roughly divided into a central processing unit (hereinafter abbreviated as CPU) 1, a sequencer 2, a transmission system 3, a static magnetic field generating magnet 4, a receiving system 5, a gradient magnetic field generating system 21, and a signal. It consists of a processing system 6.

  The CPU 1 controls the sequencer 2, the transmission system 3, the reception system 5, and the signal processing system 6 according to a predetermined program. The sequencer 2 operates based on a control command from the CPU 1, and sends various commands necessary for collecting image data of the tomographic plane of the subject 7 to the transmission system 3, the gradient magnetic field generation system 21, and the reception system 5. ing.

  The transmission system 3 includes a high-frequency oscillator 8, a modulator 9, and an irradiation coil 11. The reference high-frequency pulse from the high-frequency oscillator 8 is amplitude-modulated by the modulator 9 according to a command from the sequencer 2, and the amplitude-modulated high-frequency signal is transmitted. By amplifying the pulse through the high frequency amplifier 10 and supplying it to the irradiation coil 11, a predetermined pulsed electromagnetic wave is irradiated to the subject.

  The static magnetic field generating magnet 4 is for generating a uniform static magnetic field in a predetermined direction around the subject 7. In the static magnetic field generating magnet 4, an irradiation coil 11, a gradient magnetic field coil 13, and a receiving coil 14 are arranged. The gradient magnetic field coil 13 is included in the gradient magnetic field generation system 21 and receives a current supplied from the gradient magnetic field power supply 12 and generates a gradient magnetic field under the control of the sequencer 2.

  The receiving system 5 detects a high-frequency signal (NMR signal) emitted by nuclear magnetic resonance of the nucleus of the biological tissue of the subject, and includes a receiving coil 14, an amplifier 15, a quadrature detector 16, and an A / D converter. The high-frequency signal (NMR signal) of the response of the subject due to the electromagnetic wave irradiated from the irradiation coil 11 is detected by the receiving coil 14 disposed close to the subject, and the amplifier 15 and the orthogonal The signal is input to the A / D converter 17 via the phase detector 16, converted into a digital quantity, and the signal is sent to the CPU 1.

  The signal processing system 6 includes an external storage device such as a magnetic disk 20 and an optical disk 19 and a display 18 such as a CRT. When data from the reception system 5 is input to the CPU 1, the CPU 1 performs signal processing and image re-processing. Processing such as configuration is executed, and the resulting image of a desired tomographic plane of the subject 7 is displayed on the display 18 and stored in the magnetic disk 20 of the external storage device or the like.

  FIG. 2 is a diagram illustrating a state in which the subject's head is installed in the surgical receiving coil according to the first embodiment of the present invention, and FIG. 2 (a) is a view as seen from the side of the head. 2 (b) is a view of the AA ′ cross section (the cross section not passing through the conductor portion) in FIG. 2 (a) viewed from the top of the head. Although not shown, in this embodiment, stereotactic brain surgery is performed using an MRI apparatus that uses a vertical magnetic field type open MRI apparatus that generates a static magnetic field in the examination room from the ceiling to the floor or from the floor to the ceiling. An example of the receiving coil for surgery when performing the above is shown below. 2 (a) and 2 (b), 31 is a U-shaped fixing portion that is arranged around the head of the subject and fixes the head via a bolt 33 for fixing the head. As shown in FIG. 4, a surgical jig and a non-conductive body are provided on a laminated structure of a conductive body and a non-conductive body. The frame part 33 having a laminated structure, 33 is passed through the fixing part 31, and the head fixing bolt for fixing the head part, 34 is the machine between the ends of the fixing part 31 and the frame part 32 In addition, the conductor portions are also electrically connected to each other, a connector portion 35, a receiving coil base 35 for fixing the fixing portion 31 to the bed, and a head 36 of the subject. Reference numeral 37 denotes a conductor portion of the plate-like member constituting the surgical reception coil, and reference numeral 38 denotes a non-conductive portion of the plate-like member constituting the surgical reception coil.

  According to the present embodiment, the surgical receiving coil for the head used in stereotaxic surgery is a U-shaped loop that surrounds the head axis of the subject's head as described in Patent Document 2 above. The shape is a combination of a fixed portion, a frame portion, and a connector portion, but as described in Patent Document 2, not all of the receiving coils having a loop are made of a conductor. In the receiving coil of the present embodiment, a laminar structure in which one plate-shaped non-conductive body 38 having a plane parallel to the direction perpendicular to the head axis of the subject's head is sandwiched between two plate-shaped conductors 37 and stacked. It has a structure. With such a configuration, eddy currents generated in the receiving coil can be reduced. This is because a vertical magnetic field type MRI apparatus is used as an MRI apparatus in this embodiment, so that a gradient magnetic field pulse that applies a gradient magnetic field pulse in the X direction, the Y direction, and the Z direction is from the ceiling to the floor in the same direction as the static magnetic field. Alternatively, the eddy current generated along with the gradient magnetic field flows from the floor to the ceiling, but flows in a plane (horizontal direction) perpendicular to the gradient magnetic field pulse application direction (static magnetic field application direction). This is because the receiving coil for the head has a thin conductive plate in the vertical direction, so that no eddy current flows in the horizontal direction. Therefore, in the receiving coil for surgery exemplified in the present embodiment, when imaging is performed by an imaging method sensitive to a factor affecting magnetic field inhomogeneity such as eddy current as in diffusion-weighted images in MRI, eddy currents generated are not generated. Therefore, artifacts caused by eddy current can be reduced.

  When MRI imaging is performed using the surgical reception coil having such a configuration, when detecting an NMR signal generated on the head of the subject, a conductor member among the members constituting the surgical reception coil The current flowing through is detected and used as data for image reconstruction. Therefore, the thickness of the layer of the member constituting the conductor may be thin as long as the electrical resistance is small enough to detect the NMR signal. On the other hand, the non-conductive material sandwiched between the conductive materials must be strong because a surgical jig is mounted on the surgical receiving coil and is subjected to gravity. It should be hard enough and thick enough so that it will not bend even if it is mounted on top of it. In addition, two conductors arranged in parallel need to be sandwiched between non-conductors with an appropriate interval.If the non-conductor is thin and the distance between the conductors is too short, This is not preferable because the influence of a minute eddy current flowing in the thin thickness of the conductor is increased and artifacts are generated.

  FIG. 3 is a view showing a state where the head of the subject is installed in the surgical receiving coil according to the second embodiment of the present invention, and FIG. 3 (a) is a view as seen from the side of the head. Fig. 3 (b) is a view of the BB 'cross section (cross section not passing through the conductor) in Fig. 3 (a) as seen from the top of the head. It is different from the example. In the second embodiment, the frame portion 32 has the same configuration as that of the first embodiment, but the fixing portion 31 constituting the lower half of the surgical receiving coil is made of a conductive material and relatively hard. . By doing in this way, there exists an advantage that it becomes easy to attach the hole for attaching the volt | bolt inserted in order to attach a head from lower side.

  FIG. 4 is a view showing a state where the head of the subject is installed in the surgical receiving coil according to the third embodiment of the present invention, and FIG. 4 (a) is a view as seen from the side of the head. 4 (b) is a cross-sectional view taken along the line CC ′ in FIG. 4 (a) (a cross-section passing through a part of the conductor) as seen from the top of the head, and FIG. 4 (c) is the view in FIG. FIG. 4 (d) is a cross-sectional view taken along the line DD ′, and FIG. 4 (d) is a cross-sectional view taken along the line EE ′ in FIG. 4 (b). FIG. In the present embodiment, the cross-section taken along the line DD ′ in FIG. 4 (c) has a structure in which the non-conductive material sandwiched between them is surrounded from the horizontal direction, but the EE ′ shown in FIG. 4 (d). In the cross section, of the layered structure in which the non-conductor is sandwiched between the conductors, only one side that is not sandwiched between the conductors is covered with the conductor, and the other side is non-conductive, along the side of the square section The eddy current is prevented from flowing like a loop. Even in this embodiment, the occurrence of artifacts due to eddy currents can be reduced.

  The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention. In the above embodiment, the conductor is composed of two layers, and this is exemplified in the case where the conductor is sandwiched by one non-conductor. However, the present invention is not limited to this, and the conductor may be three or more layers. The non-conductor sandwiched between may be two or more layers. The outermost layer need not be a conductor and may be a non-conductor. However, if the distance between adjacent conductors becomes too short across a non-conductor, even a small amount of eddy current flowing in the conductor can cause artifacts due to a synergistic effect, so the distance should be as long as possible. good.

  Further, in the first embodiment, the upper frame portion of the surgical receiving coil having a loop, the lower fixing portion, and the connector portion connecting the frame portion and the fixing portion all have a layered structure made of a conductor and a non-conductor. In this case, in Example 2, only the upper frame part has a layered structure, and the lower fixing part has only a conductor structure, and these are connected by a connector. In this example, only one side of the layered structure of the upper frame part is covered with a conductor (see Fig. 4). The portion to be made only with the conductor is not limited to the embodiment shown in the above embodiment, and various ratios can be considered.

  Further, in the above embodiment, the reception of the surgical operation using the vertical magnetic field type open MRI apparatus in which the direction of the static magnetic field is the vertical direction (the direction from the ceiling to the floor or the direction from the floor to the ceiling) is shown. The receiving coil is not necessarily used only for the vertical magnetic field type open MRI apparatus, but is also used for the horizontal magnetic field type MRI apparatus. In such a case, the surgical receiving coil of the present invention horizontally aligns the conductive or non-conductive plate in a layered manner in accordance with the direction of the X, Y, and Z gradient magnetic fields applied horizontally. This is considered good for suppressing eddy currents. Further, in the above embodiment, the case where the subject's head is fixed to the surgical receiving coil and used as the imaging site or the surgical site is illustrated, but the present invention is not limited to this, and the portion other than the head (for example, the stomach) Needless to say, the present invention can be applied to the case where the foot is fixed. In the above embodiment, copper and aluminum are considered as examples of the material of the conductor, and acrylic is considered as an example of the material of the non-conductor. In addition, the surgical receiving coil of the present invention may be affected by eddy currents in normal imaging methods as well as diffusion-weighted images. Needless to say, there is an effect of reducing the above.

The figure which shows the system configuration | structure of a general MRI apparatus. FIG. 3 is a diagram showing a state in which the subject's head is installed in the surgical receiving coil according to the first embodiment of the present invention. FIG. 6 is a diagram showing a state where the head of a subject is installed in the surgical receiving coil according to the second embodiment of the present invention. FIG. 5 is a diagram showing a state in which a subject's head is installed in a surgical receiving coil according to Embodiment 3 of the present invention.

Explanation of symbols

  31 fixing part, 32 frame part, 33 bolt, 34 connector part, 35 receiving coil base, 36 subject head, 37 conductor part, 38 non-conducting part

Claims (3)

A receiving coil used in a magnetic resonance imaging apparatus, which is arranged in a circumferential direction of an imaging region of a subject and which fixes the imaging region of the subject, a frame portion to which a surgical jig is attached, and the fixing portion And a connector part for electrically connecting the frame part to a surgical receiving coil constituting a loop-shaped coil, wherein at least a part of the surgical receiving coil is made of a conductor and a non-conductive plate. the Jo member they become heavy I combined structure, the direction parallel to the plane of the plate-like member of the conductor and the non-conductive member is generally parallel to the direction of the static magnetic field generated in the magnetic resonance imaging apparatus A receiving coil for surgery. 2. The surgical receiving coil according to claim 1, wherein all of the fixed portion and the frame portion have a structure in which conductive and non-conductive plate-like members are overlapped. Magnetic resonance imaging apparatus using the surgical receiver coil according to claim 1 and 2 wherein.

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