JP4751045B2 - Magnetic resonance imaging system - Google Patents

Description

  The present invention relates to a magnetic resonance imaging (MRI) apparatus that generates a magnetic resonance image using a magnetic resonance phenomenon.

    A magnetic resonance imaging apparatus utilizes a phenomenon in which energy of a high-frequency magnetic field rotating at a specific frequency is resonantly absorbed when a group of nuclei having a specific magnetic moment is placed in a uniform static magnetic field. It is a device that visualizes chemical and physical microscopic information of a substance or observes a chemical shift spectrum.

  Imaging of a diagnostic image by this magnetic resonance imaging apparatus is executed as follows, for example. That is, the subject is placed in a synthetic magnetic field composed of a static magnetic field formed by a magnet and a gradient magnetic field formed by a gradient magnetic field coil. A high frequency of a predetermined frequency for generating a magnetic resonance phenomenon is applied to the subject set in this way. The applied high frequency generates a magnetic resonance signal in the subject, which is received by the receiving high frequency coil and imaged.

  Patent Documents 1 and 2 are known as techniques for widening the imaging range with such an MRI apparatus.

  The MRI apparatus disclosed in Patent Document 1 fixes a vertically divided coil to an imaging area in a gantry in advance, and enables imaging of a wide area while a subject moves between the upper and lower coils. To.

  The MRI apparatus disclosed in Patent Document 2 places a table for holding a coil on an existing bed as a means for fixing the coil up and down. A movable second couch is placed on the table, and the subject is fed into the gantry so as to slide on the second couch.

Patent Document 3 discloses an MRI apparatus including a whole-body high-frequency coil and a movable surface coil.
US Pat. No. 5,808,468 US Pat. No. 5,808,468 JP-A-64-37939

  However, in the techniques of Patent Document 1 and Patent Document 2, since both coils are fixed, the distance between the coil and the subject increases, and the sensitivity cannot be increased efficiently.

  In the technique disclosed in Patent Document 3, imaging is performed after the surface coil is brought close to the imaging region, and the imaging range at one time becomes narrow.

  The present invention has been made in consideration of such circumstances, and the purpose of the present invention is to perform high-quality and wide-range imaging using a local high-frequency coil without mounting the probe on the subject. There is in doing so.

In order to achieve the above object, the first aspect of the present invention comprises a static magnetic field generating means for generating a static magnetic field in a gantry, and a gradient magnetic field generating means for applying a gradient magnetic field to a subject arranged in the static magnetic field. A high-frequency coil that receives a magnetic resonance signal from the subject to which the gradient magnetic field is applied, a subject moving unit that moves the subject, and the subject moving unit moving the subject in the first direction. A control unit that detects the outer shape of the subject based on the magnetic resonance signal received when the subject is moved , and the subject is moved in a second direction opposite to the first direction by the subject moving means. And generating a magnetic resonance image based on the received magnetic resonance signal and a coil moving means for moving the high-frequency coil in the perspective direction with respect to the subject based on the detected outer shape. With image generation means And a magnetic resonance imaging apparatus Te.

In order to achieve the above object, the second aspect of the present invention comprises a static magnetic field generating means for generating a static magnetic field in a gantry, a gradient magnetic field generating means for applying a gradient magnetic field to a subject arranged in the static magnetic field, A high-frequency coil that receives a magnetic resonance signal from the subject to which the gradient magnetic field is applied, a subject moving unit that moves the subject, and the subject moving unit moves the subject in a first direction. A control unit that detects an outer shape of the subject based on the magnetic resonance signal received at the time, and when the subject is moved in the same direction as the first direction by the subject moving means, based on the detected contour, the coil moving means for moving the high-frequency coil, a magnetic resonance imaging apparatus and an image generating means for generating a magnetic resonance image based on the previous Ki受 signal has been magnetic resonance signals Configured

In order to achieve the above object, the third aspect of the present invention comprises a static magnetic field generating means for generating a static magnetic field in a gantry, a gradient magnetic field generating means for applying a gradient magnetic field to a subject arranged in the static magnetic field, A high frequency coil that receives a magnetic resonance signal from the subject to which the gradient magnetic field is applied, a hall body coil that receives the magnetic resonance signal from the subject , and the magnetic resonance signal received by the hall body coil. A control unit for detecting an outer shape of the subject based on the coil, a coil moving means for moving the high-frequency coil in a perspective direction with respect to the subject based on the detected outer shape, and the received magnetic resonance signal And an image generating means for generating a magnetic resonance image on the basis of the magnetic resonance imaging apparatus.

  According to the present invention, high-quality and wide-range imaging using a local high-frequency coil can be performed without attaching a probe to a subject.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram showing the configuration of the MRI apparatus according to the first embodiment. The MRI apparatus shown in FIG. 1 includes a static magnetic field magnet 1, a gradient magnetic field coil 2, a gradient magnetic field power source 3, a high frequency coil 4, a transmission unit 5, a local probe 6, a position adjustment mechanism 7, a reception unit 8, a bed control unit 9, and A computer system 10 is provided.

  The static magnetic field magnet 1 has a hollow cylindrical shape and generates a uniform static magnetic field in an internal space. As the static magnetic field magnet 1, for example, a permanent magnet, a superconducting magnet or the like is used.

  The gradient magnetic field coil 2 has a hollow cylindrical shape and is disposed inside the static magnetic field magnet 1. The gradient coil 2 is a combination of three coils corresponding to the X, Y, and Z axes orthogonal to each other. The gradient coil 2 generates a gradient magnetic field in which the above three coils are individually supplied with electric current from the gradient magnetic field power source 3 and the magnetic field strength is inclined along the X, Y, and Z axes. The Z-axis direction is the same direction as the static magnetic field. The gradient magnetic fields of the X, Y, and Z axes correspond to the slice selection gradient magnetic field Gs, the phase encoding gradient magnetic field Ge, and the readout gradient magnetic field Gr, respectively. The slice selection gradient magnetic field Gs is used to arbitrarily determine an imaging section. The phase encoding gradient magnetic field Ge is used to encode the phase of the magnetic resonance signal in accordance with the spatial position. The readout gradient magnetic field Gr is used to encode the frequency of the magnetic resonance signal in accordance with the spatial position.

  The high frequency coil 4 has a hollow cylindrical shape and is disposed inside the gradient magnetic field coil 2. A subject P placed on the bed C is inserted inside the high-frequency coil 4. The high frequency coil 4 receives a high frequency pulse from the transmission unit 5 and generates a high frequency magnetic field. The high frequency coil 4 receives a magnetic resonance signal emitted from the subject due to the influence of the high frequency magnetic field. The high-frequency coil 4 has an inner diameter that allows the subject P to easily pass through, and thus functions as a whole-body RF probe.

  The transmission unit 5 includes an oscillation unit, a phase selection unit, a frequency conversion unit, an amplitude modulation unit, and a high frequency power amplification unit. The oscillation unit generates a high-frequency signal having a resonance frequency unique to the target nucleus in the static magnetic field. The phase selection unit selects the phase of the high-frequency signal. The frequency modulation unit modulates the frequency of the high-frequency signal output from the phase selection unit. The amplitude modulation unit modulates the amplitude of the high-frequency signal output from the frequency modulation unit, for example, according to a sync function. The high frequency power amplification unit amplifies the high frequency signal output from the amplitude modulation unit. As a result of the operation of each of these units, the transmission unit 5 transmits a high frequency pulse corresponding to the Larmor frequency to the high frequency coil 4.

  The local probe 6 incorporates a high frequency coil smaller than the high frequency coil 4. The local probe 6 is disposed inside the high-frequency coil 4 and is supported by the position adjusting mechanism 7. The high frequency coil built in the local probe 6 receives the magnetic resonance signal radiated from the subject P.

  FIG. 2 is a diagram showing a state in which the high-frequency coil 4 and the inside thereof are viewed from the left side of FIG. As shown in FIGS. 1 and 2, the position adjustment mechanism 7 is disposed inside the high frequency coil 4 and is fixed to the ceiling surface of the high frequency coil 4. Even if the position adjusting mechanism 7 is not directly fixed to the high frequency coil 4, it may be supported on the inside of the high frequency coil 4 by various methods. The position adjustment mechanism 7 moves the local probe 6 up and down as indicated by arrows in FIG.

  The receiving unit 8 includes a selector, a pre-stage amplifier, a phase detector, and an analog / digital converter. The selector selectively inputs magnetic resonance signals output from the high-frequency coil 4 and the local probe 6. The receiving unit 8 amplifies the magnetic resonance signal output from the selector. The phase detector detects the phase of the magnetic resonance signal output from the preamplifier. The analog-digital converter converts the signal output from the phase detector into a digital signal.

  The bed control unit 9 includes a movement mechanism unit and a movement control unit. The moving mechanism unit reciprocates the bed C in the axial direction of the high-frequency coil 4, that is, in the left-right direction in FIG. The movement control unit controls the movement mechanism unit so as to perform forward movement and backward movement described later.

  The computer system 10 includes an interface unit 10a, a data collection unit 10b, a reconstruction unit 10c, a storage unit 10d, a display unit 10e, an input unit 10f, and a control unit 10g.

  A gradient magnetic field power source 3, a transmission unit 5, a position adjustment mechanism 7, a reception unit 8, and a bed control unit 9 are connected to the interface unit 10a. The interface unit 10a inputs and outputs signals exchanged between these connected units and the computer system 10.

  The data collection unit 10b collects digital signals output from the reception unit 8 via the interface unit 10a. The data collection unit 10b stores the collected digital signal, that is, magnetic resonance signal data in the storage unit 10d.

  The reconstruction unit 10c performs post-processing, that is, reconstruction such as Fourier transform, on the magnetic resonance signal data stored in the storage unit 10d, and obtains spectrum data or image data of the desired nuclear spin in the subject P. Ask.

  The storage unit 10d stores magnetic resonance signal data and spectrum data or image data for each patient.

  The display unit 10e displays various information such as spectrum data or image data under the control of the control unit 10g. As the display unit 10e, a display device such as a liquid crystal display can be used.

  The input unit 10f receives various commands and information input from the operator. As the input unit 10f, a pointing device such as a mouse or a trackball, a selection device such as a mode switch, or an input device such as a keyboard can be used as appropriate.

  The control unit 10g includes a CPU, a memory, and the like, and comprehensively controls each of the above units. The control unit 10g detects the outer shape of the subject P based on the image data reconstructed according to the magnetic resonance signal output from the high frequency coil 4. Further, the control unit 10g compensates for a change in the distance between the surface of the subject P and the local probe 6 due to the movement of the subject P, and maintains the local probe 6 in a state close to the surface of the subject P. Thus, the position adjusting mechanism 7 is controlled.

Next, the operation of the MRI apparatus configured as described above will be described.
When the whole body of the subject P is to be imaged, the subject P is placed on the bed C pulled out from the high frequency coil 4. The operator then operates the input unit 10f to instruct the start of whole body imaging.

This command is transmitted from the input unit 10f to the control unit 10g. Upon receiving the above command, the control unit 10g starts processing as shown in the flowchart of FIG.
In step Sa1, the control unit 10g designates “whole body” for the receiving unit 8. In response to this designation, the receiving unit 8 inputs a magnetic resonance signal output from the high-frequency coil 4. Subsequently, in step Sa2, the control unit 10g instructs the bed control unit 9 to start the forward movement of the bed C. Upon receiving this instruction, the bed control unit 9 moves the bed C in the forward direction (for example, the direction toward the left side in FIG. 1). The couch controller 9 may move the couch C at a constant speed or may move it intermittently at every pitch. In step Sa3, the control unit 10g starts the outer shape detection.

  This outer shape detection is processing for detecting the outer shape of the subject. Specifically, the cross-sectional shape of the subject is determined based on the magnetic resonance signal data output from the receiving unit 8, that is, the magnetic resonance signal data generated by the receiving unit 8 from the magnetic resonance signal received by the high frequency coil 4. Find the outer shape. The outer shape is detected for each predetermined position of the bed C. While performing this outer shape detection, in step Sa4, the control unit 10g waits for the forward movement to be completed.

  If the bed C moves to the end of the predetermined moving range, the bed control unit 9 stops the forward movement and notifies the control unit 10g that the forward movement is completed. Upon receiving this notification, the control unit 10g proceeds from step Sa4 to step Sa5. In step Sa5, the control unit 10g ends the outer shape detection.

  Subsequently, in step Sa6, the control unit 10g designates “local” for the reception unit 8. In response to this designation, the receiving unit 8 receives a magnetic resonance signal output from the local probe 6. Subsequently, in step Sa7, the control unit 10g instructs the bed control unit 9 to start the backward movement of the bed C. Upon receiving this instruction, the bed control unit 9 moves the bed C in the reverse direction (for example, the direction toward the right side in FIG. 1). In step Sa8, the control unit 10g starts position control of the local probe 6.

  The position control is a process of adjusting the position of the local probe 6 so that the subject P and the local probe 6 are kept close to each other without interfering with each other. That is, the distance between the subject P and the local probe 6 changes due to a change in the portion of the subject P facing the local probe 6 as the subject P moves, so that the change in the interval is compensated. Then, the position of the local probe 6 is adjusted. Specifically, in synchronization with the movement of the bed C, the control unit 10g drives the position adjustment mechanism 7 while referring to the outer shape of the subject P detected by the above-described outer shape detection.

  FIG. 4 is a diagram illustrating an example of a change in the position of the local probe 6 under position control. As shown in FIG. 4, the distance from the base of the position adjusting mechanism 7 to the local probe 6 is set to be different L1, L2, and L3 according to the height of the portion facing the local probe 6. ing.

  As described above, after the backward movement of the bed C and the position control of the local probe 6 are started, the control unit 10g starts the main imaging process in step Sa9. This main imaging process is a process for obtaining spectrum data or image data relating to the entire subject P. Specifically, the main imaging process is based on magnetic resonance signal data output from the receiving unit 8, that is, based on magnetic resonance signal data generated by the receiving unit 8 from the magnetic resonance signal received by the local probe 6. Done. Based on the magnetic resonance signal data, processing for obtaining local spectrum data or image data for the subject P is periodically performed in synchronization with the movement of the bed C. Then, by accumulating these local spectrum data or image data, spectrum data or image data relating to the entire subject P is obtained.

  While performing this main imaging process, in step Sa10, the control unit 10g waits for the entire imaging of the subject P to be completed. When the entire imaging of the subject P is completed, the control unit 10g proceeds from step Sa10 to step Sa11. In Step Sa11, the control unit 10g stops the main imaging process and stops the position control of the local probe 6. And with this, the control part 10g complete | finishes the process shown in FIG.

  As described above, according to the first embodiment, first, the outer shape of the subject P is detected using the high-frequency coil 4 that is a whole-body probe. The whole body of the subject P is imaged using the local probe 6 while maintaining the state where the local probe 6 is brought close to the subject P with reference to the detected outer shape. As a result, it is possible to take high-quality images by making full use of the characteristics of the local probe 6. Further, since the local probe 6 is not attached to the subject P, no extra burden is placed on the subject P. In addition, since both the outer shape detection and the main imaging are performed while the bed C is reciprocated, the imaging can be efficiently completed in a short time.

The first embodiment can be variously modified as follows.
A configuration may be adopted in which a high frequency coil 4 is exclusively used for reception and a cross coil system in which a high frequency coil for transmission is separately provided is employed.
As shown in FIG. 5, the local probes 6a and 6b are provided in place of the local probe 6, and the position adjusting mechanisms 7a and 7b are provided in place of the position adjusting mechanism 7. The position may be adjusted individually.
Although the whole body imaging has been described above as an example, the present invention can also be applied to a wide range imaging including the movement of the subject P even if not the whole body. Alternatively, the present invention can also be applied to a case where a plurality of parts of a subject that cannot be imaged without moving the subject are imaged .

(Second Embodiment)
FIG. 6 is a block diagram showing the configuration of the MRI apparatus according to the second embodiment. 7 and 8 are diagrams showing the configuration of the moving mechanism of the receiving coil in FIG. For convenience of explanation, the X, Y, and Z axis directions are defined as shown.

  As shown in FIG. 6, the MRI apparatus of the second embodiment includes a gantry 21, a bed 22, a static magnetic field magnet 23, a gradient magnetic field coil 24, a high frequency coil 25, receiving coils 26a, 26b, 26c, 26d, and a first movement. Mechanism 27, second moving mechanism 28, distance measuring sensor 29, sensor control unit 30, gradient magnetic field driving unit 31, transmitting unit 32, moving mechanism control unit 33, receiving unit 34, data collecting unit 35, computer 36, console 37 , A display 38 and a sequence controller 39.

  The gantry 21 shows a cross section cut along the YZ plane in FIG. The gantry 21 is provided with a static magnetic field magnet 23, a gradient magnetic field coil 24, a high frequency coil 25, receiving coils 26a, 26b, 26c, and 26d, a first moving mechanism 27, a second moving mechanism 28, and a distance measuring sensor 29. .

  The bed 22 conveys the subject P into the gantry 21.

  The static magnetic field magnet 23 applies a uniform static magnetic field to the subject P. The gradient magnetic field coil 24 applies a gradient magnetic field to the subject P. The high frequency coil 25 applies a high frequency magnetic field to the subject P. The receiving coils 26a to 26d receive magnetic resonance signals radiated from the subject P.

  The first moving mechanism 27 moves the receiving coil 26a in the Y direction. The second moving mechanism 28 moves the consultation coil 26a in the X direction. The distance measuring sensor 29 measures the body thickness of the subject P.

  The sensor control unit 30 controls the distance measuring sensor 29 so that the body thickness is measured in synchronization with the subject P being transported into the gantry 21. The gradient magnetic field drive unit 31 drives the gradient magnetic field coil 24. The transmitter 32 applies a high frequency pulse to the high frequency coil 25. The movement mechanism control unit 33 controls the operations of the first movement mechanism 27 and the second movement mechanism 28. The receiving unit 34 amplifies and detects the magnetic resonance signal received by the receiving coils 26a to 26d. The data collection unit 35 collects the magnetic resonance signals output from the reception unit 34 by A / D conversion. The computer 36 performs image reconstruction processing based on the magnetic resonance signal output from the data collection unit 35. The console 37 captures information input by the operator to the computer 36. The display 38 displays various information under the control of the computer 36. The sequence controller 39 controls the gradient magnetic field drive unit 31, the transmission unit 32, the movement mechanism control unit 33, the reception unit 34, the data collection unit 35, and the computer 36.

  The receiving coil 26a is an upper coil, and the receiving coils 26b to 26d are lower coils. In the second embodiment, when a plurality of receiving coils are provided, at least one receiving coil is set on the upper side and the rest is set on the lower side, like the receiving coil 26a. A wide imaging region can be obtained by detecting a signal by pairing the upper coil and the lower coil. The number of coils placed on the lower side may be determined according to the required area of the imaging area. At the time of imaging, the receiving coil 26a is arranged at the center of the imaging area. The reception coil 26 a moves up and down according to the body thickness of the subject P under the control of the movement mechanism control unit 33. When the imaging range in the Z direction is designated by the imaging area designation method described later, the receiving coils 26b to 26d move sequentially below the receiving coil 26a accordingly.

  The internal space of the gantry 21 is called a bore. The gantry 21 is provided with an opening 21a through which the top 22a of the bed 22 on which the subject P is placed can be taken in and out of the bore. A second moving mechanism 28 is provided on the upper surface of the inner wall of the bore.

  In addition, a holding means, which will be described later, connected to the back side of the receiving surface (the surface facing the subject P) of the receiving coil 26 a is connected to one end of the first moving mechanism 27. The other end of the first moving mechanism 27 is attached to the second moving mechanism 28.

  As shown in FIG. 7, the first moving mechanism 27 includes a bellows mechanism 27a. The first moving mechanism 27 also includes a compressor. The compressor expands and contracts the bellows mechanism 27a by sending air to the bellows mechanism 27a through the inflow pipe 27b arranged in the gantry 21 or sucking air from the bellows mechanism 27a. The bellows mechanism 27a is arranged with its expansion / contraction direction in the Y direction. Data indicating the correlation between the displacement of the first moving mechanism 27 in the Y direction and the pressure value in the bellows mechanism 27a is stored in the data collecting unit 35. The sequence controller 39 refers to the data to determine the atmospheric pressure in the bellows mechanism 27a according to the required displacement.

  The second moving mechanism 28 includes a rail 28a. A groove 28b is formed in the Z direction on the rail 28a. When the holding member 40 formed in a rectangular shape is engaged with the groove 28b, the receiving coil 26a is guided by the rail 28a and can move in the Z direction. This is a mechanism for changing the imaging position in the bore. The holding member 40 has a structure in which the engagement with the groove 28b is released when the receiving coil 26a is moved in the Y direction by the first moving mechanism 27.

  The second moving mechanism 28 also includes a power source for moving the receiving coil 26a in the Z direction as described above. As this power source, a motor may be provided on the first moving mechanism 27 side, or a mechanism for moving the receiving coil 26a via a tow string by a motor arranged away from the first moving mechanism 27 is provided. May be.

  The distance measuring sensor 29 is disposed above the opening 21a. As the distance measuring sensor 29, for example, it is desirable to apply a sensor that measures the distance by reflecting the surface of the top plate 22a or the subject P using a distance measuring laser or ultrasonic wave.

  Next, the operation of the MRI apparatus of the second embodiment configured as described above will be described. For imaging, first, the subject P placed on the bed 22 is sent into the gantry 21. This is because the bed 22 moves the top plate 22a in the Z direction at a predetermined speed. At this time, when the imaging region of the subject P is positioned directly below the distance measuring sensor 29, the operator presses a distance measurement start button provided on the console 37 and sends a start signal to the sequence controller 39. Send. Next, when the imaging region of the subject P has passed just below the distance measuring sensor 29, the operator presses a distance measurement end button provided on the console 37 and transmits an end signal to the sequence controller 39. For this reason, it is convenient to attach the distance measurement start button and the distance measurement end button to the side of the gantry 21.

  When the start signal is transmitted to the sequence controller 39, the sequence controller 39 instructs the sensor control unit 30 to start body thickness measurement. Thereafter, when the end signal is transmitted to the sequence controller 39, the sequence controller 39 instructs the sensor control unit 30 to end the body thickness measurement. The sensor control unit 30 causes the distance measuring sensor 29 to measure the body thickness of the subject P after the start is instructed as described above and until the end is instructed as described above. The distance measuring sensor 29 transmits information obtained by the measurement to the sequence controller 39 via the sensor control unit 30.

  A uniform static magnetic field is applied to the subject P conveyed in the bore by the static magnetic field magnet 23. At this time, the direction of the applied static magnetic field is the Z direction.

  Next, the moving mechanism control unit 33 causes the second moving mechanism 28 to move the receiving coil 26a from the position shown in FIG. 8A to the center of the static magnetic field magnet 23 as shown in FIG. 8B. . Thereafter, the bed 22 is moved so that the receiving coil on which the part of the subject P corresponding to the starting point of the imaging region is placed is positioned below the receiving coil 26a. Here, the description will be made assuming that the start point of the imaging region is the head side end of the reception coil 26b and the end point is the foot side end of the reception coil 26d. That is, first, the bed 22 is moved so that the receiving coil 26b is positioned under the receiving coil 26a.

  Thereafter, the movement mechanism control unit 33 releases the engagement between the holding member 40 and the groove 28b. Further, the moving mechanism control unit 33 draws air into and out of the bellows mechanism 27a based on the information on the movement displacement in the Y direction transmitted from the sequence controller 39, and the Y of the receiving coil 26a as shown in FIG. 8C. The direction position is adjusted, and the receiving surface of the receiving coil 26a is brought close to the body surface of the subject P.

  Thereafter, the gradient magnetic field coil 24 is driven by the gradient magnetic field drive unit 31 under the control of the sequence controller 39, and receives the gradient magnetic fields Gx, Gy, and Gz whose magnetic field strength changes linearly in the X, Y, and Z directions, respectively. Applied to the specimen P. The high-frequency coil 4 applies a high-frequency magnetic field to the subject P when a high-frequency pulse is applied from the transmission unit 32 under the control of the sequence controller 39. And a magnetic resonance signal is received using the receiving coil 26a and the receiving coil 26b.

  After that, the sequence controller 39 transmits information on the movement displacement of the first moving mechanism 27 to the moving mechanism control unit 33 to instruct the movement of the receiving coil 26a.

  Subsequently, the receiving coil 26c is positioned below the receiving coil 26a by the movement of the bed 22. In this state, the magnetic resonance signal is received using the receiving coil 26a and the receiving coil 26c in the same manner as described above. Further, the receiving coil 26d is positioned below the receiving coil 26a. In this state, the magnetic resonance signal is received using the receiving coil 26a and the receiving coil 26d in the same manner as described above. Thereby, a magnetic resonance signal in a wide area over the positions of the receiving coils 26b to 26d can be acquired. Since the receiving coil 26a moves up and down according to the body thickness of the subject P at each position of the receiving coils 26b to 26d, the receiving coil 26a is close to the subject P, and magnetic resonance is satisfactorily performed at any position. A signal can be obtained.

  The magnetic resonance signals respectively received by the reception coils 26 a to 26 d are amplified and detected by the reception unit 34, A / D converted, and sent to the data collection unit 35 under the control of the sequence controller 39. The data collection unit 35 collects and stores magnetic resonance signals under the control of the sequence controller 39. The data collection unit 35 sends the stored magnetic resonance signal to the computer 36 under the control of the sequence controller 39. The computer 36 performs image reconstruction based on the magnetic resonance signal sent from the data collection unit 35 under the control of the sequence controller 39. The image reconstructed by the computer 36 is displayed on the display 38.

The second embodiment can be variously modified as follows.
In the specific example described above, the end of the region to be imaged is aligned with the coil ends of the receiving coils 26b to 26d. In such a case, for example, when the receiver coil 26a is imaged across both the receiver coils 26b and 26c, the receiver coils 26a, 26b, and 26c are used. What is necessary is just to receive a magnetic resonance signal. If the receiving coils 26b to 26d are fixed to the bed 22 in advance, when the imaging start point and the imaging end point are designated, the image data is collected by any combination of the receiving coils 26b to 26d. You should plan accordingly.

  The second moving mechanism 28 can be omitted. In this case, the receiving coil 26a is fixed with respect to the Z direction. Therefore, when the start signal is transmitted to the distance measuring sensor 29, the imaging region of the subject P on the bed 22 is specified. Then, the displacement of the bed 22 in the Z direction may be controlled so that the imaging region is directly below the receiving coil 26a.

  The second embodiment may be modified to have a configuration as shown in FIG. That is, the mechanism for moving the receiving coil 26 a in the gantry 21 is changed to one using the L-shaped support tool 41. The receiving coil 26 a is attached to one end of the support tool 41. The other end of the support tool 41 is attached to the outside of the gantry 21. And the support tool 41 is moved by the power source provided in the base 21 side, and the receiving coil 26a is moved.

  The receiving coil 26a may be removable so that the examiner can use it in a probe-like manner. The receiving coils 26a, 26b, 26c, and 26d may each be an array coil having a plurality of coils in one unit.

  You may provide the bed 22 with the 3rd moving mechanism which moves the top plate 22a up and down. When the subject P is small or the body thickness is small, it is necessary to move the receiving coil 26a largely with respect to the subject P. This means that the imaging area is lowered too much from the center of the magnet, which is a suitable imaging area for the magnetic field magnet, and sensitivity is lowered. However, if the third moving mechanism as described above is used, the amount of movement of the receiving coil 26a can be kept small, and the above-described problems can be solved.

  It is also possible to receive a magnetic resonance signal only by the receiving coil 26a without using the receiving coils 26b to 26d.

  The distance measuring sensor 29 may be attached to the receiving coil 26a. In this case, the top plate 22a is first moved so that the imaging part of the subject P faces the receiving coil 26a. Thereafter, the distance from the receiving coil 26 a to the subject P is measured by the distance measuring sensor 29. Based on the measurement result, the receiving coil 26a may be moved up and down. In this case, the attachment position of the distance measuring sensor 29 should be determined with sufficient consideration so as not to reduce the reception sensitivity of the reception coil 26a. The distance measuring sensor 29 is preferably shielded by a radio wave shielding material such as aluminum. Further, it is desirable that the timing of distance measurement by the distance measuring sensor 29 be outside the period in which the pulse sequence for imaging is not executed or the period of signal reception.

(Third embodiment)
FIG. 10 is a diagram showing a configuration of an MRI apparatus according to the third embodiment. For convenience of explanation, the X, Y, and X axis directions are defined as shown.
As shown in FIG. 10, the MRI apparatus of the third embodiment includes a gantry 51, a bed 52, receiving coils 53 and 54, wires 55, pulleys 56 and 57, a winding device 58, a sensor 59, and a control unit 60.

  In FIG. 10, the gantry 51 shows a cross section broken at the YZ plane. Although the gantry 51 is provided with a static magnetic field magnet, a gradient magnetic field coil, a high frequency coil, and the like, these are not shown. The MRI apparatus according to the third embodiment includes various other well-known elements for performing imaging. In FIG. 10, only characteristic elements are illustrated, and other elements are not illustrated. Omitted.

  The bed 52 includes a double top plate including an upper top plate 52a and a lower top plate 52b. The couch 52 moves the subject P placed on the upper couchtop 52a to the internal space of the gantry 51 by moving the upper couchtop 52a in the Z direction. There is a gap between the upper top plate 52a and the lower top plate 52b, and the RF coil 53 is disposed in this gap. During the whole body scan, the upper top plate 52a moves, and the lower top plate 52b does not move. That is, the subject P placed on the upper top plate 52 a is transported between the RF coils 53 and 54.

  The RF coil 53 is a multi-type receiving coil. The RF coil 53 receives a magnetic resonance signal radiated from the subject P.

  The RF coil 54 is a multi-type receiving coil. The RF coil 54 is disposed in the internal space of the gantry 51. One end of a wire 55 is connected to the RF coil 54. The other end of the wire 55 is guided to the outside of the gantry 51 by pulleys 56 and 57 and connected to a winding device 58. The RF coil 54 is suspended by the wire 55. The pulleys 56 and 57 are attached to the gantry 51 by a support member.

  The winding device 58 moves the RF coil 54 in the Y direction by winding or unwinding the wire 55.

  The sensor 59 is fixed to the RF coil 54 and moves together with the RF coil 54. The sensor 59 detects the proximity state between the RF coil 54 and the subject P.

  The control unit 60 controls the winding device 58 so that the RF coil 54 is brought close to the subject P while referring to the output of the sensor 59.

FIG. 11 is a diagram showing a detailed configuration of the control unit 60 in FIG.
The control unit 60 includes an ultrasonic drive unit 60a, a multiplexer 60b, a reception unit 60c, and a winding drive unit 60d. This configuration is for the case where an ultrasonic transducer 59 a is used as the sensor 59.

  The ultrasonic drive unit 60a outputs a transmission signal for causing the ultrasonic transducer 59a to transmit ultrasonic waves. The multiplexer 60b outputs the transmission signal output from the ultrasonic driving unit 60a to the ultrasonic transducer 59a. The multiplexer 60b outputs the signal output from the ultrasonic transducer 59a to the receiving unit 60c. The receiving unit 60c determines whether or not the distance between the RF coil 54 and the subject P is equal to or less than a predetermined distance based on the output signal of the ultrasonic transducer 59a input via the multiplexer 60b. When the distance is less than or equal to the distance, a detection signal is output to the winding drive unit 60d. The winding drive unit 60d drives the winding device 58 based on the detection signal and the control signal sent from the computer system.

  Next, the operation of the MRI apparatus configured as described above will be described. Note that the operation for obtaining a reconstructed image may be the same as that in the first embodiment or the second embodiment, and thus description thereof is omitted. Here, the position control of the RF coil 54 will be described.

  Every time imaging of a portion corresponding to the reception range of the RF coils 53 and 54 is performed, the movement of the subject P by the upper top plate 52a is repeated.

  Now, before the upper top plate 52a is moved, a lifting instruction is given to the winding drive unit 60d by a control signal. In response to this, the winding drive unit 60d drives the winding device 58 to wind up the wire 55 in order to sufficiently raise the RF coil 54. Thus, after separating the RF coil 54 from the subject P, the upper top plate 52a is moved.

  When the movement of the upper top plate 52a is completed, a proximity instruction is given to the winding drive unit 60d by a control signal. In response to this, the winding drive unit 60d drives the winding device 58 so as to feed out the wire 55.

  Now, when the winding device 58 sends out the wire, the RF coil 54 descends and approaches the subject P. At this time, the ultrasonic drive unit 60a intermittently outputs a transmission signal, and transmits ultrasonic waves from the ultrasonic transducer 59a. Then, the signal reflected by the subject P and received by the ultrasonic transducer 59a is received by the receiving unit 60c. The receiving unit 60c determines whether or not the delay time from when the ultrasonic wave is transmitted from the ultrasonic transducer 59a to when the reflected signal is received is equal to or shorter than a predetermined time corresponding to a predetermined distance. The predetermined time may be determined in advance by calculation, or may be calibrated by measuring with a phantom, for example. The receiving unit 60c outputs a detection signal when the delay time becomes equal to or shorter than the specified time. The winding drive unit 60d stops the winding device 58 when a detection signal is output from the reception unit 60c.

  That is, the control unit 60 stops the movement of the RF coil 54 when the RF coil 54 is close to the subject P to a predetermined distance. Thereafter, the magnetic resonance signals are received by the RF coils 53 and 54.

  As described above, according to the third embodiment, the RF coil 54 is moved so that the distance to each imaging region becomes the predetermined distance while moving the subject P and changing the imaging region. Imaging is performed by receiving magnetic resonance signals by the RF coils 53 and 54.

As a result, it is possible to take high-quality images by making full use of the characteristics of the RF coil 54. Further, since the RF coil 54 is not attached to the subject P, no extra burden is placed on the subject P.

  In addition, it is desirable to arrange the ultrasonic transducer 59a so that it does not come into each element so as not to affect the performance of the RF coil 54. The ultrasonic transducer 59a is preferably shielded by a radio wave shielding material such as aluminum. The frequency used for transmitting and receiving ultrasonic waves is a relatively low frequency so that attenuation in air is reduced. The ultrasound transmission / reception timing is set to a period in which the MRI pulse sequence is not executed, or the signal reception period is excluded even during the execution of the pulse sequence.

The third embodiment can be variously modified as follows.
FIG. 12 is a diagram showing another configuration of the control unit 60 in FIG. In addition, the same code | symbol is attached | subjected to FIG. 11 and an identical part, and the detailed description is abbreviate | omitted.
The control unit 60 shown in FIG. 12 includes a winding drive unit 60d, a laser drive unit 60e, and a reception unit 60f. This configuration is for the case where the sensor 59 is constituted by a laser oscillator 59b and a light receiver 59c.

  The laser driver 60e outputs a transmission signal for causing the laser oscillator 59b to oscillate the laser. The receiving unit 60f determines whether or not the distance between the RF coil 54 and the subject P is equal to or less than the predetermined distance based on the output signal of the light receiver 59c, and becomes equal to or less than the predetermined distance. Sometimes a detection signal is output to the winding drive 60d.

  In the configuration shown in FIG. 12, it is detected that the RF coil 54 has approached the subject P based on the intensity of light reflected from the subject P when the subject P is irradiated with laser light.

  The subject P may be affixed with a sheet that enhances the reflection efficiency of laser light, or may be coated with a paint or the like. Instead of laser light, other light such as infrared light may be used. Further, the laser beam does not have to be continuous, and is transmitted and received intermittently at a time that does not hinder MRI data collection.

FIG. 13A is a diagram showing another configuration of the control unit 60 in FIG. In addition, the same code | symbol is attached | subjected to FIG. 11 and an identical part, and the detailed description is abbreviate | omitted.
The control unit 60 illustrated in FIG. 13A includes a winding drive unit 60d and a reception unit 60g. This configuration is for the case where the sensor 59 is constituted by a pressure sensor 59d and a pressure probe needle 59e. The pressure probe 59e contacts the subject P and transmits the pressure to the pressure sensor 59d.

  The receiving unit 60g determines whether or not the distance between the RF coil 54 and the subject P is equal to or smaller than a predetermined distance based on the output signal of the pressure sensor 59d, and winds up the detection signal when the distance is equal to or smaller than the predetermined distance. It outputs to the drive part 60d.

  In the configuration shown in FIG. 13A, the proximity of the RF coil 54 to the subject P is detected based on the pressure transmitted to the pressure sensor 59d when the pressure probe 59e contacts the subject P. The receiving unit 60g outputs a detection signal when a pressure greater than a certain value is sensed by the pressure sensor 59d.

  As shown in FIG. 13B, the pressure sensor 59d may be attached to the tip of a support member 59f attached to the RF coil 54 so that the pressure sensor 59d contacts the subject P. The pressure exploration needle 59e may have a planar shape or a plurality of needles. Further, the pressure sensors 59d may be installed at a plurality of locations. The pressure sensor 59d may have a planar shape (sheet shape), a grid shape that avoids the element portion of the RF coil 54, or the like.

FIG. 14 is a diagram showing another configuration of the control unit 60 in FIG. In addition, the same code | symbol is attached | subjected to FIG. 11 and an identical part, and the detailed description is abbreviate | omitted.
The control unit 60 shown in FIG. 14 includes a winding drive unit 60d and a determination unit 60h. This configuration is for the case where the sensor 59 is configured by a micro switch 59g and a probe needle 59h. The probe 59h is displaced when it contacts the subject P and turns on the micro switch 59g.

  The determination unit 60h determines whether or not the distance between the RF coil 54 and the subject P is equal to or less than a predetermined distance based on the output signal of the micro switch 59g, and winds up the detection signal when the distance is equal to or less than the predetermined distance. It outputs to the drive part 60d.

  In the configuration shown in FIG. 14, it is detected that the RF coil 54 has approached the subject P based on the fact that the micro switch 59 g is turned on when the probe 59 h contacts the subject P.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a diagram showing a configuration of a magnetic resonance imaging apparatus according to a first embodiment of the present invention. The figure which shows a mode that the high frequency coil 4 in FIG. 1 and its inner side were seen from the left side of FIG. The flowchart which shows the process sequence of the control part 10g. The figure which shows an example of the change of the position of the local probe 6 under position control. The figure which shows the modification of arrangement | positioning of the local probe and the position adjustment mechanism. The block diagram which shows the structure of the MRI apparatus which concerns on the 2nd Embodiment of this invention. The figure which shows the structure of the moving mechanism of the receiving coil in FIG. The figure which shows the moving mechanism of the receiving coil in FIG. The figure which shows the modification structural example of the moving mechanism of a receiving coil. It is a figure which shows the structure of the MRI apparatus which concerns on 3rd Embodiment. It is a figure which shows the detailed structure of the control part 60 in FIG. It is a figure which shows another structure of the control part 60 in FIG. It is a figure which shows another structure of the control part 60 in FIG. It is a figure which shows another structure of the control part 60 in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Static magnetic field magnet, 2 ... Gradient magnetic field coil, 3 ... Gradient magnetic field power supply, 4,25 ... High frequency coil, 5, 32 ... Transmitter, 6, 6a, 6b ... Local probe, 7, 7a, 7b ... Position adjustment Mechanism: 8: Receiving unit, 9: Bed control unit, 10: Computer system, 21: Base, 21a ... Opening, C, 22, 34 ... Bed, 22a ... Top plate, 23 ... Static magnetic field magnet, 24 ... Gradient magnetic field coil , 26a, 26b, 26c, 26d ... receiving coil, 27 ... first moving mechanism, 28 ... second moving mechanism, 29 ... distance measuring sensor, 30 ... sensor control unit, 31 ... gradient magnetic field driving unit, 33 ... moving Mechanism control unit, 35 ... data collection unit, 36 ... computer, 37 ... console, 38 ... display, 39 ... sequence controller, 40 ... holding member, 41 ... support, 51 ... stand, 52 ... bed, 52b ... bottom plate 52a ... top plate 53, 54 ... Coil, 55 ... Wire, 56, 57 ... Pulley, 58 ... Winding device, 59 ... Sensor, 59a ... Ultrasonic vibrator, 59b ... Laser oscillator, 59c ... Light receiver, 59d ... Pressure sensor, 59e ... Pressure Search needle, 59f ... support member, 59g ... micro switch, 59h ... search needle, 60 ... control section, 60a ... ultrasonic drive section, 60b ... multiplexer, 60c, 60f, 60g ... receive section, 60d ... winding drive section, 60e ... Laser drive unit, 60h ... determination unit.

Claims (14)

A static magnetic field generating means for generating a static magnetic field in the gantry,
A gradient magnetic field generating means for applying a gradient magnetic field to a subject arranged in the static magnetic field;
A high frequency coil for receiving a magnetic resonance signal from the subject to which the gradient magnetic field is applied;
Subject moving means for moving the subject;
A control unit for detecting an outer shape of the subject based on the magnetic resonance signal received when the subject is moved in the first direction by the subject moving means ;
When the subject is moved in the second direction opposite to the first direction by the subject moving means , the high-frequency coil is moved away from the subject based on the detected outer shape. Coil moving means for moving in the direction;
Image generating means for generating a magnetic resonance image based on the received magnetic resonance signal;
A magnetic resonance imaging apparatus comprising: A hall coil for receiving the magnetic resonance signal from the subject;
The magnetic resonance imaging apparatus according to claim 1 , wherein the control unit detects an outer shape of the subject based on the magnetic resonance signal received by the whole body coil. The image generation means generates a pre-scan image of the subject based on a magnetic resonance signal received by the whole body coil,
The magnetic resonance imaging apparatus according to claim 2 , wherein the control unit detects an outer shape of the subject based on the prescan image. Condition detection for detecting an imaging condition when the subject is moved in the second direction by the subject moving means when the subject is moved in the first direction by the subject moving means Further comprising means,
The magnetic resonance imaging apparatus according to claim 1 , wherein the high-frequency coil receives the magnetic resonance signal under the detected imaging condition. The magnetic resonance imaging apparatus according to claim 4 , wherein the condition detection unit detects transmission power data of the magnetic resonance signal. The magnetic resonance imaging apparatus according to claim 4 , wherein the condition detection unit detects shimming data. The magnetic resonance imaging apparatus according to claim 4 , wherein the condition detection unit detects sensitivity distribution data. The magnetic resonance imaging apparatus according to claim 4 , wherein the condition detection unit detects tuning data. A static magnetic field generating means for generating a static magnetic field in the gantry,
A gradient magnetic field generating means for applying a gradient magnetic field to a subject arranged in the static magnetic field;
A high frequency coil for receiving a magnetic resonance signal from the subject to which the gradient magnetic field is applied;
Subject moving means for moving the subject;
Wherein a control unit for detecting a contour of the subject on the basis of the received magnetic resonance signal when the subject by the subject moving unit is moved in a first direction,
Coil moving means for moving the high-frequency coil based on the detected outer shape when the subject is moved in the same direction as the first direction by the subject moving means;
Image generating means for generating a magnetic resonance image based on the received magnetic resonance signal;
Magnetic resonance imaging apparatus characterized by comprising a.   The magnetic resonance imaging apparatus according to claim 1, wherein the high-frequency coil is a high-frequency coil for local imaging. A static magnetic field generating means for generating a static magnetic field in the gantry,
A gradient magnetic field generating means for applying a gradient magnetic field to a subject arranged in the static magnetic field;
A high frequency coil for receiving a magnetic resonance signal from a subject to which the gradient magnetic field is applied;
A hall body coil for receiving the magnetic resonance signal from the subject;
A control unit for detecting an outer shape of the subject based on the magnetic resonance signal received by the whole body coil;
Coil moving means for moving the high-frequency coil in a perspective direction with respect to the subject based on the detected outer shape;
Image generating means for generating a magnetic resonance image based on the magnetic resonance signal received by the high-frequency coil moved by the coil moving means;
A magnetic resonance imaging apparatus comprising: A subject moving means for moving the subject;
The magnetic resonance imaging apparatus according to claim 11 , wherein the coil moving unit moves the high-frequency coil according to the movement of the subject. The control unit detects an outer shape of the subject based on the magnetic resonance signal received when the subject is moved in the first direction by the subject moving means;
The magnetic resonance imaging apparatus according to claim 12 , wherein the coil moving unit moves the high-frequency coil when the subject is moved in the same direction as the first direction. The magnetic resonance imaging apparatus according to claim 11 , wherein the high-frequency coil is a high-frequency coil for local imaging.

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