JPH10234704A - Mri apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an MRI apparatus possible to test areas having different sizes of a plurality of subjects simultaneously with one magnetic circuit. SOLUTION: In an MRI test room 1, magnetic field generation sources 51, 52, 53, 54 are arranged at a determined distance with making the directions of magnetic force lines generated form them the same, which are connected circularly by materials 61, 62, 63, 64 letting magnetic flux pass through. Magnetic field generation sources 51, 52, 53, 54 have measurement spaces 71, 72, 73, 74, respectively, each having different size, and beds 81, 82, 83, 84 to locate the shooting parts of subjects 101, 102, 103, 104 are housed in them, respectively. Magnetic shielding materials 91, 92, 93, 94 are provided as part of the shield room to screen magnetic effects mutually generated among measurement spaces 71, 72, 73, 74 in order to simultaneously photograph in the measurement spaces 71, 72, 73, 74.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to nuclear magnetic resonance (NM)
R) The present invention relates to a magnetic resonance imaging (MRI) apparatus for obtaining a medical image to be used for image diagnosis of a subject using a phenomenon, and in particular, simultaneously photographs various examination sites of a plurality of subjects with one magnetic circuit. The present invention relates to an MRI apparatus capable of performing such operations.

[0002]

2. Description of the Related Art An MRI apparatus uses an NMR phenomenon to image the inside of a subject as an image. The MRI apparatus can capture an arbitrary cross section of the subject, and can capture a three-dimensional image or a blood vessel image. Further, the possibility of application to brain function measurement has been studied, and the importance as a medical image diagnostic device has been established.

Generally, an MRI apparatus includes a static magnetic field generator for generating a highly uniform static magnetic field in a space having a predetermined size, a gradient magnetic field generator for generating a gradient magnetic field in a space, and a test object. Radio frequency magnetic field irradiating means for irradiating the subject with a high frequency magnetic field in a pulsed manner, means for receiving an NMR signal generated from the body of the subject irradiated with the high frequency magnetic field, and reception signal processing means for processing the received signal Means for reconstructing an image using the processed signal, an image display for displaying the image, and a control device for controlling the components.

[0004] By the way, most of the MRI apparatuses currently on the market are whole-body apparatuses capable of imaging any part of a subject, and the static magnetic field generating apparatus has a cylindrical or prismatic shape. A space for subject insertion is provided, and only one uniform static magnetic field having a predetermined size is formed in the space. Therefore, in the conventional apparatus, one subject is put into the apparatus to perform imaging, and after the imaging of the subject is completed, the subjects are sequentially replaced by a method of imaging the next subject. To shoot. In addition to the whole-body device, there is also a device that targets an image of a specific part of the subject, but the static magnetic field generating device has only one uniform magnetic field space, and the imaging is performed in the same manner as the whole-body device. The examiners are sequentially replaced.

[0005] The MRI apparatus has a disadvantage that it takes a longer time to image one subject than an X-ray imaging apparatus, an X-ray CT apparatus, and an ultrasonic diagnostic apparatus. Although this shortcoming has been studied and overcome by various high-speed imaging methods, it has not been completely solved in view of image quality.

[0006] Attempts have been made to overcome this drawback. One of them is to install a bed in a plurality of directions toward the static magnetic field space, and to prepare the next subject to be photographed on another bed while the photographing of one subject is being performed, and wait for the next subject. . In addition, JP-A-61-15995
As disclosed in Japanese Patent Publication No. 0, two measurement spaces of the same size capable of accommodating the whole body of a subject in a single magnetic circuit are provided so that two subjects can be examined simultaneously. Things have been suggested.

[0007]

The MRI apparatus is not yet comparable to the X-ray imaging apparatus or the X-ray CT apparatus in terms of spatial resolution, but has an excellent contrast resolution with respect to the difference between tissues.
At present, in addition to the human brain, internal organs, cervical spine, spine,
It is used to obtain diagnostic images of parts such as ears and nose.

[0008] Nevertheless, as described above, the conventional MRI apparatus is configured for the whole body or for a certain extreme part, and the use efficiency of the apparatus is poor. That is, since the whole-body device has a large imaging space, it is necessary to generate a uniform and strong static magnetic field in that region.
The magnetic field source is configured to generate large magnetic energy. The RF probe that applies a high-frequency magnetic field to the subject also targets nuclear spins in the uniform magnetic field region to be excited, and the gradient magnetic field coil that applies a gradient to the static magnetic field naturally has a gradient over the entire uniform magnetic field region. It is large to create a magnetic field. If an attempt is made to image a limb with such a whole-body device, a living tissue that is not an imaging site is also exposed to a high-frequency magnetic field. At present, there is almost no theory that the high-frequency magnetic field irradiated by the MRI apparatus has an adverse effect on the living body, but it is desirable for safety if it is not necessary to irradiate the high-frequency magnetic field to a place other than the imaging site.

Therefore, if a device dedicated to a site such as a limb is to be prepared in addition to a device for the whole body, a static magnetic field generator is required.
You need one. Since the ratio of the static magnetic field generator in the cost of the MRI apparatus is very high, there is a problem that the economic burden on the hospital is increased in order to provide the apparatus for the whole body and the apparatus for the extreme part. Further, since the uniform magnetic field strength in the static magnetic field generator requires stability, two devices cannot be installed in the same room. Therefore, in order to install the apparatus for the whole body and the apparatus for the pole part, two magnetically shielded rooms are provided, which further increases the economic burden on the hospital.

In view of the above, the present invention forms a plurality of measurement spaces having different sizes including a whole body and a pole for a whole body in a single magnetic circuit (static magnetic field generating device), and makes these measurement spaces simultaneous. An object of the present invention is to provide an MRI apparatus which can be used and can shorten the waiting time for the examination of a subject.

[0011]

According to the present invention, there is provided a static magnetic field generator for use in an MRI apparatus.
At least one magnetic field generating source, magnetic flux passing means for guiding a magnetic flux generated by the magnetic field generating source to the magnetic field generating source in a loop, and a plurality of sizes provided in the middle of a magnetic flux passing path of the magnetic flux passing means. And a means for forming a uniform magnetic field region having a predetermined spatial size and magnetic strength corresponding to the size of the gap for each of these gaps. .

A magnetic flux shielding means is provided between the gaps of the static magnetic field generator, and the magnetic flux passing means penetrates the magnetic flux shielding means. Also,
The magnetic flux shielding means forms a part of the wall surface of the shield room. Further, the present invention is characterized in that the magnetic flux passing means is formed by a superconductor.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing the configuration and arrangement of an MRI apparatus according to one embodiment of the present invention. The embodiment shown in FIG. 1 is an example in which four measurement spaces are provided in one magnetic circuit.

In FIG. 1, reference numeral 1 denotes an MR examination room, in which four operation rooms 11, 12, 13, and 14 are disposed.
Inside the operation rooms 11, 12, 13, and 14, consoles 21, 22, 23 and 24, and MRI units 31 and 3 including a gradient magnetic field power supply, an image processing device, and the like, respectively.
2, 33 and 34 are arranged. These consoles and MR units are publicly known and will not be described.
Then, the operation rooms 11, 12, 13 of the MR examination room 1,
The part except 14 is four shield rooms 41, 42,
43 and 44. The shield room confines the stray magnetic field of the static magnetic field generator described in detail later in the room, shields the fluctuating magnetic field outside from entering the shield room where the static magnetic field generator is installed, and reduces the magnetic field in the measurement space. This is for maintaining the uniformity of 50 is a static magnetic field generator, 81, 82, 83 and 84 are examination beds, and subjects 101, 102, 103 and 104 are placed on each bed.
Is lying down for examination.

Next, the static magnetic field generator 50 of this embodiment will be described in detail. Conventionally, a static magnetic field generator of an MRI apparatus generates a static magnetic field having a predetermined magnetic field intensity and a high degree of uniformity in a predetermined area in a space having a size capable of accommodating a subject, Currently, as a method for generating a static magnetic field, a superconducting magnet method, a normal conducting magnet method, and a permanent magnet method are employed in products. The present invention can employ any of these methods, but the present embodiment will be described using a permanent magnet method as an example.

As shown in FIG. 1, a static magnetic field generator 50 according to the present embodiment includes magnetic field sources 51, 52, 53, 54 formed in pairs, and magnetic field sources 51 and 52.
, Between 52 and 53, between 53 and 54, and between 54 and 51, a magnetic circuit is formed by magnetic flux passing members 61, 62, 63 and 64 made of a material having high magnetic permeability such as pure iron. The four measurement spaces 71, 72, 7 are formed so that the subjects 101, 102, 103, 104 can be inspected simultaneously.
3, 74 are formed.

Although not shown in the drawings, conventionally known gradient magnetic field coils and coils for irradiating a high frequency magnetic field are accommodated in each of the four measurement spaces.

Each magnetic field generating source is arranged so that the directions of the magnetic fluxes generated by the magnetic field generating sources coincide with each other. As a result, the magnetic flux circulates in the magnetic circuit. Magnetic field source 51,
52, 53, and 54 are not shown in the drawings, but each include a permanent magnet block body having a predetermined magnetic energy and a pole piece, and the permanent magnet block body is provided in contact with the magnetic flux passing material; The pole piece is provided facing the measurement space. Magnetic field sources 51, 52, 5
The space between the pole pieces of the magnetic field sources is different from each other so that the subject accommodation spaces provided in the magnetic field sources 3 and 54 have different sizes. And the doctor 10 beside the subject 101
The magnetic field source 5 is arranged at an interval enough for 0 to enter.
The pole pieces of No. 2 are arranged at intervals enough to measure the extremities of the subject 102, and the pole pieces of the magnetic field source 53 are arranged at intervals only enough to measure the head of the subject 103. The pieces are arranged at intervals such that the whole body of the subject 104 can be measured.

As described above, since the four measurement spaces have different spatial sizes, the gradient magnetic field coil and the irradiation coil are also made to have a size corresponding to the size of each measurement space. When the magnetic field strength of the uniform magnetic field in each measurement space is made different, the magnetic resonance frequency of the nuclear spin in the subject differs for each measurement space.
It is necessary to set a reference frequency for the system.

Regardless of the static magnetic field generation method, a spherical uniform magnetic field space is formed in the measurement space of the current magnetic field generation source of the MRI apparatus. Since the size of the part is different, the size of the uniform magnetic field space may be different. For this reason, in the present invention, the facing area is made different in addition to the interval between the pole pieces for each magnetic field generating source. That is, as shown in the drawing, the larger the distance between the pole pieces of the respective magnetic field generating sources, the larger the facing area becomes.

As described above, when the distance between the pole pieces of the magnetic field source and the facing area are made different, the magnetic field strength of the uniform magnetic field formed in the measurement space by the magnetic energy of the magnetic field source can be changed. In other words, if the spacing between the pole pieces is reduced and the facing area is reduced, the diffusion of the magnetic field lines can be reduced and the number of magnetic flux lines per unit area can be increased, so the magnetic field strength of the uniform magnetic field can be increased, and the spacing and the facing area can be increased. Then, on the contrary, the magnetic field strength of the uniform magnetic field can be reduced. In addition, it is easy to improve the uniformity of the magnetic field by reducing the uniform magnetic field region as well as the magnetic field strength. Therefore, the measurement spaces 72 and 73 shown in FIG. 1 can have a static magnetic field region in which the magnetic field strength is higher and the uniformity is better than the measurement spaces 71 and 74.

Next, when a plurality of measurement spaces are provided in a single orbiting magnetic circuit as described above, adverse effects due to the interaction of the magnetic force lines from the respective magnetic field sources, for example, a magnetic field distortion in the measurement space may appear. It is conceivable that the high-frequency magnetic field or the pulsed gradient magnetic field applied to the subject during measurement in the measurement space has a small value but affects the magnetic field in another measurement space. In order to prevent such adverse effects, in the present invention, each measurement space is arranged in an independent shield room. That is, the magnetic shield material 9 shown in FIG.
The magnetic flux passing members 61, 62, 6
A hole that can be penetrated so that 3, 64 almost adheres is provided,
The magnetic flux passing members 61, 62, 63, 64 are made to penetrate through these holes, and these magnetic shielding members 91, 92, 93,
Reference numeral 94 designates the shield rooms 41, 42, 43, and 44 together with the magnetic shield members whose reference numerals are omitted. Note that the magnetic shield materials 91, 92, 93, and 94 need to be provided so as to intersect or closely contact each other at the center. The magnetic shield material may be a metal material generally used conventionally, for example, a copper plate, a stainless plate, or a mesh or honeycomb material thereof,
A superconducting multilayer composite manufactured by Nippon Steel Corporation can be used.

The superconducting multilayer composite comprises an NbTi layer (3
0 layer) and a Cu layer (31 layers) are alternately laminated so that both surfaces become Cu layers, and Nb is interposed between the NbTi layer and the Cu layer.
NbTi / Nb / Cu superconducting multilayer composite with a thickness of about 1 mm manufactured by hot rolling and cold rolling with interposed layers (60 layers), Conductivity,
Vol. 3, No. 1, March 1993, pp. 177-18
Page 0 (IEEE TRANSACTION ON AP
PLIED SUPER CONDUCTIVITY,
VOL. 3, NO. 1, MARCH 1993, pp1
77-180). Manufacturers have announced that this material, when immersed in liquid helium and subjected to an electric current, exhibits high shielding performance. When this is used, it is necessary to provide a heat insulating container structure for accommodating the shielding materials 91, 92, 93, 94 and for filling a cooling medium, for example, liquid helium, and a cooler for cooling liquid helium. is there.

Next, a method of using the MRI apparatus of this embodiment and the operation of the main part of the present invention will be described. A patient who needs an MRI examination at a hospital or the like is instructed at the reception of the MRI examination department in which shield room of the MRI apparatus to undergo the examination according to the examination site. For example, a patient undergoing an abdominal examination is guided to a shield room 44, a patient undergoing a head examination is guided to a shield room 43, and a patient undergoing a leg examination is guided to a shield room 42. Conventionally, in a hospital where there is only one MRI apparatus even if there is only one, each patient is sequentially examined. In the MRI apparatus of the present invention, up to four patients can be used in parallel with one MRI apparatus. Since a plurality of inspection areas are provided so that the inspection can be performed appropriately, the inspection can be performed by four persons simultaneously.

The patient guided to the shield room lies on the beds 84, 83, and 82, and after being fitted with a detection coil (not shown) for detecting NMR signals, is moved to the examination area by the bed. It is well known that an MRI apparatus detects an NMR signal by using a coil. If a dedicated detection coil is used in accordance with a part to be inspected, the signal reception sensitivity is high and the obtained image is also good. In the MRI apparatus described above, each of the plurality of examination regions has a different size so as to correspond to the size of the examination region of the subject, and thus the detection coil used in each examination region can be dedicated. Therefore, according to the present invention, the operation of selecting the detection coil by the operator is simplified.

In the patient's body, which is mounted on the detection coil and moved to the examination area, the nuclear spin in the body is directed toward the static magnetic field by the magnetic field in the measurement space. In this state, the operator performs positioning imaging, and refers to the positioning image displayed on the CRT display to determine the slice position and direction of the imaging region, the number of images to be imaged, and the imaging method (sequence) to be used. 23, 22, etc. Then, imaging is started individually in each inspection area.

Since the patient to be examined simultaneously in each examination region has a different imaging region, the imaging sequence is not always the same. Therefore, the magnitude and direction of the high-frequency magnetic field pulse and the gradient magnetic field pulse in the imaging sequence are variously disturbed in each examination region. However, since each inspection region is provided magnetically separated from each other in a shield room including the magnetic shield material, the magnetic influence caused by a high-frequency magnetic field pulse or a gradient magnetic field pulse generated in a certain inspection region causes another inspection. It does not appear in the territory. In other words, the inspection can proceed in the same manner as when one MRI apparatus is installed in each shield room. In the present invention, since the irradiation coil for irradiating the high-frequency magnetic field pulse during imaging has a size corresponding to the size of the measurement space,
The high-frequency magnetic field applied to the site excluding the inspection site can be reduced as compared with the conventional device.

Although the present invention has been described with reference to one embodiment, the present invention can be modified and implemented without changing the gist of the invention. For example, in the above-described embodiment, the magnetic circuit is arranged in a plane and the magnetic field direction of the measurement space is also arranged in the horizontal direction. However, this magnetic circuit extends vertically through, for example, the first and second floors. And the direction of the magnetic field can be provided horizontally or vertically in the magnetic circuit.

Further, in the above embodiment, the magnetic flux generated by the magnetic field source is passed through a material having a high magnetic permeability such as pure iron. In this case, however, the magnetic circuit may become very heavy. As a countermeasure against this, a modification example in which a magnetic flux generated by a magnetic field source is passed through the air to an adjacent magnetic field source is also possible. In the modified example, as a magnetic flux passing material,
The above-described superconducting multilayer composite is formed in a cylindrical shape with both ends open, a magnetic field source is fixed to the open end, and the magnetic flux passing material of the cylinder is surrounded by a refrigerant container, and liquid helium is sealed as a refrigerant in the refrigerant container. Such a structure is adopted. In addition,
The magnetic field source that can adopt this modification is limited to those that can excite the magnetic field source after assembling the magnetic circuit.

[0030]

As described above, according to the present invention, a plurality of measurement spaces having different spatial sizes and different magnetic intensities are formed in one magnetic circuit. Since the patient can be examined, the examination efficiency can be improved and the waiting time for the examination of the subject can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of an MRI apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 1 MR examination room 11, 12, 13, 14 Operation room 21, 22, 23, 24 Operation console 41, 42, 43, 44 Shield room 50 Static magnetic field generator 51, 52, 53, 54 Magnetic field source 61, 62, 63, 64 Magnetic flux passing material 71, 72, 73, 74 Measurement space 91, 92, 93, 94 Magnetic shielding material 100 Doctor 101, 102, 103, 104 Subject

Claims (4)

[Claims] At least one magnetic field generating source, magnetic flux passing means for guiding a magnetic flux generated by the magnetic field generating source to the magnetic field generating source, and a plurality of magnetic flux passing means provided in the middle of a magnetic flux passing path of the magnetic flux generating means. A static magnetic field generator having gaps having different sizes and means for forming a uniform magnetic field region having a predetermined spatial size and a magnetic intensity according to the size of the gaps provided for each of the gaps; An MRI apparatus characterized in that: 2. The MRI according to claim 1, wherein a magnetic flux shielding means is provided between gaps of the static magnetic field generator, and the magnetic flux passing means penetrates the magnetic flux shielding means. apparatus. 3. The MRI apparatus according to claim 2, wherein said magnetic flux shielding means forms a part of a wall surface of a shield room. 4. The MRI apparatus according to claim 1, wherein said magnetic flux passing means is formed of a superconductor.