JP4007839B2 - Open MRI system - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus), and in particular, employs an open-type magnet that does not give a feeling of pressure to a subject, and means suitable for setting in the magnet of the subject. The present invention relates to an open MRI apparatus.
[0002]
[Prior art]
MRI examination methods that obtain tomographic images of the human body using the nuclear magnetic resonance (NMR) phenomenon are widely used in medical institutions. Since this MRI examination method needs to accurately reflect the internal structure of the examination region of the subject, a magnet that generates a uniform magnetic field strength in the space including the examination region is required. Since a uniform magnetic field space can be obtained in an infinitely long solenoid coil, many of the magnets used in an MRI apparatus have a structure that incorporates an elongated cylindrical air-core solenoid coil and a shim mechanism that improves magnetic field uniformity. ing.
[0003]
The magnetic structure MRI apparatus in which the subject is arranged in an elongated space gives a feeling of pressure to the subject and is not suitable for the examination of claustrophobic persons and children. In view of this, an MRI apparatus employing a magnet provided with an opening on the side surface or having a wide subject carrying part on the front side of the magnet has been developed and has recently become widespread.
[0004]
As the magnet of this open type MRI apparatus, a normal conducting magnet or a permanent magnet having a relatively low magnetic field strength is used because of the ease of making an open structure. These magnets constitute a magnetic circuit using an iron yoke, which constitutes a structure that supports the open type structure, and also works to improve magnetomotive force and leakage magnetic field, which are magnetic characteristics. Japanese Patent No. 2759185 is known as a related technique.
[0005]
On the other hand, in order to increase the position accuracy of the examination part, it is necessary to accurately arrange the examination part of the subject at the center of the magnet. It is substantially difficult to align the examination site of the subject at the center of the magnet. The reason is that it is difficult to move the subject's body in a relatively narrow magnet space, that there is a distance from the operator standing around the magnet to the vicinity of the magnet center, and that the examination site occupies the magnet center. This is because the magnet center cannot be specified. Therefore, a plurality of projectors for guiding the center of the magnet are attached to the peripheral positions of the magnet, and the examination site of the subject is adjusted according to the guide light of the projector. After this alignment operation, the inspection site of the subject is aligned with the magnet center through a moving process that removes the offset distance between the magnet peripheral position and the magnet center position.
[0006]
[Problems to be solved by the invention]
As the usefulness of MRI devices using open-structured magnets is established, it is easier to care for pediatric subjects during examinations and to further reduce the feeling of pressure felt when patients are carried into magnets. Thus, an open-type magnet structure has been proposed in which the openings on the front and side surfaces of the magnet are as wide as possible. Thus, by enlarging the examinee's entrance, the installation location of the projector installed around the magnet is restricted, causing a problem that the projector cannot be installed at the optimum position. This is because there is no structure to install a projector that emits guide light from the lateral direction for offset alignment that sets the inspection site and detection coil of the subject at the front position of the magnet, or There is also a consideration that the machine itself does not want to sacrifice the open space on the side of the magnet.
[0007]
As one solution to this problem, a proposal has been made to attach a projector to the wall of a room where a magnet is installed. In this case, it is necessary to accurately measure the relative position of the magnet and the room, and if an operator is interposed between the projector and the magnet, the guide light is blocked and the subject's target site is blocked. There was a problem that was not projected.
[0008]
The present invention has been made in view of the above-described viewpoints, and an object of the present invention is to arrange a projector that is suitable for alignment of an examination site of a subject without obstructing the open structure even with an open magnet structure. The purpose is to improve the position accuracy of the examination site.
[0009]
[Means for Solving the Problems]
The open MRI apparatus of the present invention that achieves the above object comprises a static magnetic field generating means for generating a uniform static magnetic field in a space where a subject is placed, a transport means for carrying in and out of the subject, and the subject. A plurality of guide means for moving a desired part of the specimen to the center of the space, and obtaining a tomographic image of the subject, wherein the static magnetic field generation means is located above and below the space. In the open-type MRI apparatus provided with the arranged magnetic field generation source and one structure that holds the upper and lower magnetic field generation sources with a predetermined interval, the guide means includes the space of one of the magnetic field generation sources. And a first guide means for irradiating the subject with a line spectrum on a straight line passing through the center of the space and a line spectrum perpendicularly intersecting the line spectrum, and the structure Arranged on the surface of the space, the center of the space and the first Second guide means for irradiating planar guide light substantially parallel to the space-side surface of the magnetic field generation source at an angle in a range including an intersection of the guide means inside, the transport means, The object is achieved by carrying the subject so that the position of the intersection of the first guide means and the second guide means outside the space is at the center of the space .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0011]
FIG. 1 is a diagram showing an overall outline of an open structure MRI apparatus to which the present invention is applied. This MRI apparatus includes a static magnetic field generating magnet 2 that generates a uniform magnetic field in a space where a subject 1 is installed, a gradient magnetic field coil 3 that is disposed inside the static magnetic field generating magnet 2, and an inner side thereof. A high-frequency coil 5 disposed and a detection coil 7 for detecting an NMR signal generated from the subject 1 are provided. A patient table 13 for arranging the subject 1 in the central space of the static magnetic field generating magnet 2 is provided. Furthermore, the power source for driving each coil, the amplifier for the NMR signal, the sequencer 9 for controlling the operation timing thereof (the power source and the sequencer 9 are housed in an integral housing 16) and the device are controlled. And a computer 10 for processing and imaging NMR signals. Normally, the static magnetic field generating magnet 2, each coil, and the patient table 13 are installed in a shield room 14 having an electromagnetic wave shielding effect, so that electromagnetic noise generated by the outside or the computer 10 of the MRI apparatus is prevented from being mixed into the detection coil 7. It is out. For this reason, connection to a power source for driving each coil and an amplifier for NMR signals (connection cables are not drawn in the figure) is made through a filter circuit 15 incorporated in a part of the shield room 14.
[0012]
In the illustrated embodiment, the static magnetic field generating magnet 2 is composed of a pair of upper and lower permanent magnets, which generate a uniform static magnetic field in the vertical direction in the space in which the subject 1 is disposed. Further, each of the pair of permanent magnets 2 has an iron plate on the outside, and an iron yoke including a support for connecting the upper and lower iron plates is combined to constitute a magnetic circuit. For example, the static magnetic field strength is 0.4 Tesla and is adjusted to generate a uniform magnetic field in the space where the subject is placed. The static magnetic field generating magnet 2 of the present embodiment is composed of a single support that supports upper and lower permanent magnets. Further, projectors 25 and 28 for emitting guide light are attached around the magnet and at one place of the support column.
[0013]
The gradient magnetic field coil 3 is composed of three sets of coils wound so as to change the magnetic flux density in three axial directions of x, y, and z orthogonal to each other, and each is connected to the gradient magnetic field power source 4. The gradient magnetic field power supply 4 (x axis 4a, y axis 4b, z axis 4c) is driven in accordance with the control signal from the sequencer 9 to change the value of the current flowing in the gradient coil 3 to change the gradient magnetic field Gx, Gy consisting of three axes. , Gz is superimposed on the static magnetic field in the placement space of the subject 1. This gradient magnetic field is used to identify the spatial distribution of NMR signals obtained from the examination site of subject 1. The gradient magnetic field coil 3 is composed of a pair of flat plates so as not to obstruct the open structure of the static magnetic field generating magnet 2, and is incorporated in the upper and lower magnets.
[0014]
The high-frequency coil 5 is connected to a high-frequency power amplifier 6 for flowing a high-frequency current through the high-frequency coil 5, and generates a high-frequency magnetic field for resonantly exciting the nucleus of the examination site of the subject 1. Since hydrogen nuclei are usually used as the nuclei, the high frequency coil 5 and the high frequency power amplifier 6 are tuned to 17 MHz. The high frequency power amplifier 6 is also controlled by the control signal of the sequencer 9. Further, the high-frequency coil 5 is also composed of a pair of flat plates so as not to obstruct the open structure of the static magnetic field generating magnet 2, and is incorporated inside the gradient magnetic field coil 3, respectively.
[0015]
The detection coil 7 is connected to a high-frequency amplifier 8. The high-frequency amplifier 8 amplifies and detects the NMR signal detected by the detection coil 7, and converts it into a digital signal that can be processed by the computer 10. The operation timing of the high-frequency amplifier 8 is also controlled by the sequencer 9.
[0016]
The computer 10 performs operations such as image reconstruction using the NMR signals converted into digital quantities, and controls the operation of each unit of the MRI apparatus via the sequencer 9 at a predetermined timing. The computer 10, the display device 11 that displays the processed data, and the console 12 that performs operation input constitute an arithmetic processing system.
[0017]
FIG. 2 is a view showing the appearance of the static magnetic field generating magnet 2 and the patient table 13 shown in FIG. In the drawing, the iron plates (not shown in the figure) that constitute the permanent magnet and the magnetic circuit are accommodated in the containers of the upper part 21 and the lower part 22. The outer appearance of the static magnetic field generating magnet 2 is made up of the support pillar 23 that incorporates a yoke (not shown in the figure) that constitutes a magnetic circuit with the iron plate of the upper part 21 and the iron plate of the lower part 22 and structurally supports the upper part 21 and the lower part 22 It is configured.
[0018]
A part of the lower part 22 has a straight surface 24 to which the patient table 13 is combined. A laser projector 25 is attached to the position of the upper portion 21 facing the surface 24. The laser beam of the projector 25 is projected onto the end of the top plate 27 of the patient table 13 through the slit of the cross 26. On the other hand, a laser projector 28 is attached at a position facing the magnet center of the column 23. The slit light (not shown in the figure) of the laser projector 28 is attached to the center of the column 23 and adjusted so as to coincide with the horizontal plane passing through the center of the magnet space.
[0019]
FIG. 3a is a side view of the static magnetic field generating magnet 2 and the patient table 13 of FIG. The cross point 31 of the light of the laser projector 25 indicates the position on the patient table 3 side that is offset by, for example, 65 cm from the spatial center 32 of the static magnetic field generating magnet 2. That is, one slit light of the laser projector 25 passes through the surface 33 and the other slit light passes through the surface 34. When the detection coil or the examination site of the subject is placed at the point 31 (shown by the plane 35 in FIG. 3b), the slit light 36 and the slit light 37 cross at the position of the point 31, and this crossing point 31 is static. It can be seen that the point is a distance of 65 cm from the space center 32 of the magnetic field generating magnet 2. Here, the surface 33 and the surface 34 of the slit light are projected with a certain spread. By this spread, the bending of the body axis of the subject can be corrected using the projection line of the surface 33, and the left-right positional balance of the subject can be corrected using the projection line of the surface 34. By this correction, the image of the MRI examination shows an accurate position and the diagnostic accuracy is improved. In particular, it is an extremely effective means for improving examination accuracy when acquiring a plurality of images simultaneously by the multi-slice imaging method or acquiring an image along the spine.
[0020]
Next, FIG. 4a is a diagram showing an AA ′ cross section of the static magnetic field generating magnet 2 of FIG. 3a. The slit light of the laser projector 28 attached to the curved surface 41 facing the magnet of the support 23 is a surface 42 indicated by oblique lines in the figure, and passes through points 31 and 32. When the detection coil or the examination site of the subject is placed at the point 31 (shown by the vertical plane 43 on the patient table in FIG. 3b), the slit light 44 is displayed through the point 31. The slit light 44 coincides with a horizontal plane passing through the space center 32 of the static magnetic field generating magnet 2. Moreover, since the slit light 44 exists in the space of the static magnetic field generating magnet 2, the slit light is not blocked by the operator or the nurse.
[0021]
Here, the subject 1 is set on the top plate 27 of the patient table 13, and a suitable detection coil is attached to the examination site. When the two laser projectors 25 and 28 are operated in this state, the red slit light line of the laser is projected onto the surface of the detection coil. FIG. 5 shows the laser beam projected on the surface of the head coil in this state. According to the figure, the centers of the detection coil are displayed three-dimensionally, that is, the front, back, left, right, top and bottom centers . Here, by moving the top plate 27 of the patient table 13 so that the center part of the examination matches the point where the laser beams intersect, the examination part of the subject is arranged at the center of the magnet space.
[0022]
According to the present embodiment, the three-dimensional position can be indicated with the minimum number of laser projectors (two in this embodiment). Furthermore, there is nothing intervening between the examination target site including the laser projector and the detection coil, and the laser beam projects the central position of the examination site regardless of the position of the operator or nurse. There is no shadow of people. Further, even when the subject is brought into the center of the magnet, at least one of the laser light is continuously projected on the examination site of the subject, so that it is possible to check a positional deviation caused by the subject's movement or the like.
[0023]
【The invention's effect】
According to the present invention, there is an effect that even an open-type magnet structure can be performed with high accuracy in alignment of a test site of a subject.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of an MRI apparatus to which the present invention is applied.
FIG. 2 is an external view of a static magnetic field generating magnet and a patient table used in an MRI apparatus to which the present invention is applied.
FIG. 3 is an explanatory diagram of a laser projector.
FIG. 4 is an explanatory diagram of a laser projector.
FIG. 5 is an explanatory diagram of alignment by a head detection coil.
[Explanation of symbols]
1 …… Subject
2 …… Static magnetic field generating magnet
3 …… Gradient field coil
5 …… High frequency coil
13 …… Patient table
25, 28 …… Laser projector

Claims (3)

A static magnetic field generating means for generating a uniform static magnetic field in a space in which the subject is placed, a transport means for loading / unloading the subject into / from the space, and a desired part of the subject to move to the center of the space A plurality of guide means for obtaining a tomographic image of the subject, wherein the static magnetic field generating means includes a magnetic field generating source disposed above and below the space, and upper and lower magnetic field generating sources. In an open-type MRI apparatus provided with one structure that is held at a predetermined interval,
The guide means is disposed on a side of the one magnetic field generation source facing the space, and a line spectrum on a straight line passing through the center of the space and a line spectrum perpendicularly intersecting the line spectrum are formed on the subject. The first guide means for irradiating and the surface of the structure is disposed on the space-side surface, and has an angle within a range including the intersection of the center of the space and the first guide means. Second guide means for irradiating planar guide light substantially parallel to the space side surface,
The open type MRI apparatus, wherein the transport means carries the subject in such a way that the position of the intersection of the first guide means and the second guide means outside the space is at the center of the space.   The open MRI apparatus according to claim 1,
  The open type MRI apparatus, wherein the second guide means is attached to the center of the structure.   In the open type MRI apparatus according to claim 1 or 2,
  The open type MRI apparatus, wherein the second guide means is one.

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