JP2004202143A - Magnetic resonance imaging instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging (MRI) instrument for automatically allowing the part of a subject to be photographed to correctly meet the center of a magnetic field without using a positioning light. <P>SOLUTION: The MRI instrument is equipped with a position detection receiving means at a prescribed place facing an RF coil in the front surface part of a bore constituting the instrument. The RF coil includes a position detection transmitting means for transmitting a prescribed laser signal to the position detection receiving means. Thus, the part of the subject to be photographed is made to be coincide with the center of the magnetic field in a magnet assembly based on a distance L1 which is calculated by a distance calculation control means for calculating the distance L1 between the position detection transmitting and receiving means. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides an irradiation coil for irradiating an RF coil mounted on a subject placed in a static magnetic field with an electromagnetic wave of a predetermined frequency, and a magnetic resonance signal emitted by the subject. The present invention relates to an MRI (Magnetic Resonance Imaging) apparatus for imaging a subject, and more particularly, to a magnetic resonance imaging apparatus capable of automatically and reliably aligning an imaging target portion of a subject with a center position (scan center) of a magnetic field.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a magnetic resonance imaging apparatus (hereinafter, referred to as an “MRI apparatus”) that images an internal structure of an imaging target using a nuclear magnetic resonance phenomenon is known. Since the nuclear magnetic resonance phenomenon is harmless to the living body, the MRI apparatus is particularly useful for medical use, and is used for detailed examination of the whole body and diagnosis of brain tumor.
[0003]
This nuclear magnetic resonance phenomenon refers to a frequency in which a spin direction of nuclei of atoms constituting an object is uniform in an object to which a uniform static magnetic field is applied, and which is proportional to the strength of the static magnetic field (hereinafter, referred to as “resonance frequency”). ) Absorbs and emits electromagnetic waves. The MRI apparatus can image an arbitrary tomographic plane of an imaging target with an arbitrary thickness by using a nuclear magnetic resonance phenomenon for a specific nuclide (mainly, a hydrogen atom).
[0004]
When imaging the internal structure of an imaging target using the nuclear magnetic resonance phenomenon, a spatially and temporally varying gradient magnetic field is applied to the imaging target separately from the static magnetic field in order to check positional information. . By applying the gradient magnetic field to the imaging target site in this manner, the magnetic field applied to the imaging target varies depending on the location, and the resonance frequency of each atom constituting the imaging target changes depending on the location.
[0005]
Therefore, by examining the resonance frequency by applying a gradient magnetic field, it is possible to know what atom exists at which position on the imaging target. Specifically, a high-frequency magnetic field and a gradient magnetic field are applied in a predetermined pulse sequence to a subject placed in a uniform static magnetic field, and a magnetic resonance signal generated by the application is received. Can be used to create a magnetic resonance image.
[0006]
Here, when performing imaging with an MRI apparatus, it is important to position the imaging target site of the subject in a region where the magnetic field intensity is uniform (the center of the magnetic field, which is a magnet center) in the magnet assembly. Is required to make the MRI apparatus recognize the center of sensitivity (center position). The center position of the RF coil is substantially the same as the position of the subject to be imaged of the subject.
[0007]
More specifically, the MRI apparatus is usually provided with a positioning light for irradiating a subject mounted on a table with a light beam such as a laser beam or a halogen light to perform positioning of the subject. I have. Then, the position of the subject is moved until the intersection of the positioning lights and the center of the RF coil (the center of sensitivity) match, a mark (landmark) is attached to the matching part, and this position is set to the center of the magnetic field. The photographing is performed in accordance with.
[0008]
That is, first, an RF coil is attached to a subject to be imaged of a subject placed on a cradle of a table as a preparation, and a positioning positioning light or laser provided on an apparatus main body (gantry) of the MRI apparatus is used. Turn on the light. Next, the table is moved so that the irradiation position of the positioning light matches the center position (imaging target part) of the RF coil mounted on the subject.
[0009]
Here, since the distance L2 (FIG. 2) from the positioning light to the center of the magnetic field in the magnet assembly is a fixed numerical value set in advance, by moving (loading) the position of the table by this distance L2, the object can be moved. The imaging target part of the sample can be made to coincide with the center of the magnetic field (for example, see Patent Document 1).
[0010]
[Patent Document 1]
JP 2001-78980 A
[Problems to be solved by the invention]
However, in the case of the above-described alignment using the MRI apparatus in the related art, there are the following problems. That is, as described above, conventionally, the position of irradiation of the positioning light or the laser beam and the center position of the RF coil (the center of sensitivity) are visually checked, but this positioning with the naked eye is troublesome from the viewpoint of visibility. In addition, there is a problem that the photographer has to move between the scan room in which the MRI apparatus is installed and the radiographing operation room every time the positioning is performed.
[0012]
In addition, when the positioning by the positioning light is inaccurate, there is a problem that it is not possible to acquire a good MRI image having a proper (uniform) contrast and a high resolution.
[0013]
The present invention has been made in view of the above-described drawbacks of the related art, and automatically sets the imaging target portion of the subject with respect to the center of the magnetic field of the magnet assembly without using a positioning light or the like for positioning. It is an object of the present invention to provide a magnetic resonance imaging apparatus capable of performing accurate alignment.
[0014]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve the object, an invention according to a first aspect is directed to a magnet assembly including a gradient magnetic field generation unit that generates a gradient magnetic field, and a static magnetic field generation unit that generates a static magnetic field. A gantry composed of an irradiation coil for irradiating a predetermined electromagnetic wave to the subject placed in a static magnetic field, and emitted from an imaging target site of the subject via an RF coil mounted on the subject. In a magnetic resonance imaging apparatus for creating a magnetic resonance image based on a magnetic resonance signal to be provided, a position detection receiving means is provided at a position facing a front surface of a bore portion constituting the gantry and facing the RF coil. The RF coil includes a position detection transmitting unit that transmits a predetermined signal to the position detection receiving unit. Distance calculation control means for calculating a separation distance from the position detection reception means is provided, and based on the separation distance calculated by the distance calculation control means, the imaging target site of the subject is set at the center of the magnetic field of the magnet assembly. It is characterized by matching.
[0015]
According to the first aspect of the present invention, when the subject is placed on the table, a predetermined signal is transmitted from the position detecting transmitting means embedded in the RF coil to the position detecting receiving means. Is received by the receiving means for position detection, and the distance between the transmitting means for position detection and the receiving means for position detection is calculated by the distance calculation control means, and automatically based on the calculated distance. The MRI apparatus can recognize the imaging target site of the subject, and can control the amount of movement of the table so that the imaging target site is aligned with the center position of the magnetic field.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a magnetic resonance imaging apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 1 is a perspective view showing a positional configuration of an MRI apparatus and a subject on which an RF coil is mounted. FIG. 2 is a diagram showing an outline of an internal configuration and functional blocks of the MRI apparatus according to the embodiment of the present invention. FIG. 3 is an explanatory diagram showing the internal configuration of the RF coil and the state of attachment to the subject. Here, MRI imaging by an MRI apparatus is performed by a photographer (operator) operating an operation console in an imaging room adjacent to a scan room in which the MRI apparatus is installed.
[0018]
As shown in FIGS. 1 and 2, a static magnetic field generating magnet 16 that generates a static magnetic field, a gradient magnetic field generating coil 17 that generates a gradient magnetic field, and An irradiation coil 18 for irradiating a predetermined electromagnetic wave to a subject placed in the static magnetic field. The static magnetic field generating magnet 16 and the gradient magnetic field generating coil 17 constitute a magnet assembly.
[0019]
Further, a cylindrical irradiation coil 18 is disposed inside the gradient magnetic field generating coil 17. Then, a table 20 on which a subject 19 (patient) is placed can be carried inside the irradiation coil 18.
[0020]
Here, the feature of the present invention is that the position (center of sensitivity) of the RF coil 30 attached to the subject 19 is automatically recognized by the MRI apparatus 10 so that the moving amount of the table 20 for transporting the subject 19 is reduced. The object is to accurately move the imaging target part to the center position of the magnetic field (point A in FIG. 1) by control so as to match them.
[0021]
For this reason, a pair of photodiodes 31 and 31 (reception means for position detection) are provided on the front surface of the bore 15 a (Bore) constituting the gantry 15 of the MRI apparatus 10 and at a position facing the RF coil 30. Have been.
[0022]
On the other hand, as shown in FIG. 3, an infrared laser diode 32 (transmission means for position detection) for emitting an infrared laser is embedded in the RF coil 30 mounted on the subject 19 with respect to the photodiode 31. I have. That is, the RF coil 30 has two coil portions 30a and 30b on the upper side and the lower side, and the infrared laser diode 32 is buried in a substantially central portion of the coil portion 30a. Further, a four-channel type TORSO coil is employed for each of the coil portions 30a and 30b.
[0023]
The MRI controller 40 that controls the MRI apparatus 10 includes an RF transmitter 41, a magnetic controller 42, an RF receiver 43, an image processor 44, a signal transmission driver 45, a position detection controller 46, and a table drive controller. And a part 47. Here, the MRI control device 40 can be provided in an operation console for operating the MRI device 10 installed in the imaging operation room.
[0024]
The RF transmission unit 41 has a function of irradiating a high-frequency electromagnetic wave from the irradiation coil 18 in order to cause a nuclear magnetic resonance phenomenon to occur in a primitive nucleus constituting a living tissue such as a human body. The magnetic control unit 42 is connected to the static magnetic field generating magnet 16 and the gradient magnetic field generating coil 17, respectively, and supplies electric power to the static magnetic field generating magnet 16 and the gradient magnetic field generating coil 17 so that the static magnetic field and the gradient magnetic field Is performed.
[0025]
The RF coil 30 has a function of receiving an electromagnetic wave emitted by the subject due to a nuclear magnetic resonance phenomenon and transmitting the electromagnetic wave to the RF receiving unit 43. The image processing unit 44 has a function of creating an MRI image based on the electromagnetic waves received by the RF receiving unit 43.
[0026]
The position detection control section 46 has a function of calculating a separation distance L1 (FIG. 2) between the photodiode 31 and the infrared laser diode 32. The separation distance L1 between the photodiode 31 and the infrared laser diode 32 can be calculated based on the principle of triangulation. Here, since the distance L2 is predetermined as a fixed numerical value, the distance L to the magnetic center A (FIG. 2) can be calculated by “L = L1 + L2”, and the table 20 moves by this distance L. Then, the subject is transported.
[0027]
The table drive control unit 47 transports the table 20 until the center position of the RF coil 30 mounted on the subject 19 matches the center of the magnetic field of the magnet assembly based on the distance L calculated by the distance calculation control unit 46. It has the function of performing
[0028]
In this example, the transmitting means for detecting the position is an infrared laser diode. However, when the transmitting means for detecting the position is a wireless device, the wireless device uses an RF wave different from the resonance frequency of the RF coil 30. Shall be used. The position detecting transmitting means may be an electromagnetic wave generating means having directivity other than the infrared laser diode used in the present embodiment, and an electromagnetic wave sensor or the like may be used as the position detecting receiving means.
[0029]
Hereinafter, a processing procedure by the magnetic resonance imaging apparatus of the present invention will be described with reference to a flowchart shown in FIG. That is, first, preparations for performing MRI imaging by the MRI apparatus 10 are performed. More specifically, this preparation involves placing the subject 19 on the table 20 and attaching the RF coil 30 to a portion (in this example, the abdomen) of the subject 20 that is to be imaged. (Step S410).
[0030]
Next, in the imaging room, it is determined that the mounting of the RF coil 30 has been completed (Yes at Step S420), and a set command of the RF coil 30 is input by operating the control console (operation panel) (Step S430). This command is a command indicating that the attachment of the RF coil 30 to the subject has been completed.
[0031]
As a result, a drive ON signal is transmitted from the signal transmission drive unit 45, which is a drive power source for the infrared laser diode 32 (step S440), and the infrared laser diode 32 embedded in the RF coil 30 transmits infrared light by transmitting the drive ON signal. The laser is emitted toward the photodiode 31 (Step S450), and the laser signal from the infrared laser diode 32 is received by the photodiode 31 (Step S460).
[0032]
Thereby, the position of the RF coil 30 is detected, and the separation distance L1 between the RF coil 30 and the photodiode 31 is calculated (step S470). As described above, the calculation of the separation distance L1 is performed by the position detection control unit 46 using the principle of triangulation.
[0033]
Here, the principle of triangulation employed in the present invention will be briefly described with reference to FIG. That is, as shown in FIG. 5, the separation distance L1 based on the distance F1 obtained by equally dividing the pair of photodiodes 31 into two equal parts and the known angle θ is:
L1 = F1 · tan θ. Here, the distance d from the photodiode 31 to the infrared laser diode 32, which is the measurement point, is t, where the time for the infrared ray to reciprocate is t, and the propagation speed of the infrared ray is c,
Since the distance d is calculated from d = ct / 2, the angle θ is calculated from the distance d and the distance F1.
[0034]
Returning to the flowchart of FIG. 4, the table drive control unit 47 is driven by a drive signal based on the separation distance L1 calculated by the position detection control unit 46 in step S480, and the imaging target portion of the subject 19 is magnetized. The table 20 is moved to the magnetic field center A.
[0035]
On the other hand, in the imaging room, it is determined whether or not the imaging target part matches the center of the magnetic field (step S490). If the imaging target part matches the center of the magnetic field (step S490: YES), the operation of the operation console is performed. When the scan button on the panel is turned on (step S491), the MRI apparatus 10 performs MRI imaging (step S492). As described above, according to the present invention, the MRI imaging can be performed only by performing the operation of placing the subject on the table, and the subsequent operations are performed only by the operation console in the imaging room.
[0036]
When the photodiode 31 serving as the position detection receiving means is provided inside the gantry 15, the movement of the subject 19 can be grasped by using a monitor or the like.
[0037]
Further, in the present embodiment, the example in which the RF coil is mounted on the abdomen of the subject has been described. However, the present invention is not limited to the abdomen, but the head RF coil for the head and the arm for imaging the arm. It can be applied when mounting an RF coil used for any purpose such as an RF coil for use.
[0038]
Further, in the present embodiment, an MRI apparatus utilizing a nuclear magnetic resonance phenomenon has been described as an example, but the present invention may be applied to, for example, a CT (Computed Tomography) apparatus which performs tomography by X-rays, in addition to the MRI apparatus. It can be applied preferably. In this case, the infrared laser diode can be attached to the inspection gown worn by the subject, so that the subject can be automatically positioned similarly to the MRI apparatus of the present embodiment.
[0039]
As described above, in the magnetic resonance imaging apparatus according to the present embodiment, since the infrared coil is embedded in the RF coil, the RF coil is automatically set only by setting the RF coil to the imaging target portion of the subject. The positioning of the subject can be performed. In the case of this automatic alignment, since the center position of the RF coil and the center of the magnetic field (scan center) surely coincide with each other, the MRI image acquired at this imaging position has good contrast and image quality without imaging unevenness. An MRI image can be obtained.
[0040]
【The invention's effect】
As described above, according to the present invention, when performing imaging by a magnetic resonance imaging apparatus, simply performing the work of placing the subject on the table, automatically sets the imaging target site of the subject to the position of the center of the magnetic field. Since the alignment can be performed, there is an effect that the operability at the time of the MRI inspection can be improved without the trouble of attaching the landmark.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a positional configuration of an MRI apparatus according to the present invention and a subject on which an RF coil is mounted.
FIG. 2 is an overall schematic diagram showing an internal configuration and functional blocks of an MRI apparatus according to the present invention.
FIG. 3 is an explanatory diagram showing an internal configuration of an RF coil and a state of attachment to a subject.
FIG. 4 is a flowchart showing a processing procedure in the magnetic resonance imaging apparatus according to the present invention.
FIG. 5 is a diagram illustrating the principle of triangulation.
[Explanation of symbols]
Reference Signs List 10 MRI apparatus 15 Gantry 15a Bore section 16 Static magnetic field generating magnet 17 Gradient magnetic field generating coil 18 Irradiation coil 19 Subject 20 Table 30 RF coil 30a, 30b Coil section 31 Photodiode 32 Infrared laser diode 40 MRI controller 41 RF transmitter 42 Magnetic control unit 43 RF reception unit 44 Image processing unit 45 Signal transmission drive unit 46 Position detection control unit 47 Table drive control unit

Claims (1)

A gradient magnetic field generating means for generating a gradient magnetic field, a magnet assembly including a static magnetic field generating means for generating a static magnetic field, and an irradiation coil for irradiating a predetermined electromagnetic wave to a subject placed in the static magnetic field. A magnetic resonance imaging apparatus that creates a magnetic resonance image based on a magnetic resonance signal emitted from an imaging target portion of the subject via an RF coil mounted on the subject,
Position detection receiving means is provided at a position facing the RF coil on a front surface of a bore portion constituting the gantry,
The RF coil includes a position detection transmission unit that transmits a predetermined signal to the position detection reception unit,
Distance calculation control means for calculating a separation distance between the position detection transmission means and the position detection reception means,
A magnetic resonance imaging apparatus, wherein an imaging target portion of the subject is matched with a center of a magnetic field of the magnet assembly based on the separation distance calculated by the distance calculation control means.

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