JP3153572B2 - Magnetic resonance imaging - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resonance imaging apparatus for interactively setting photographing conditions and executing a continuous pulse sequence.

[0002]

2. Description of the Related Art In recent years, with the progress of medical image diagnostic apparatuses, magnetic resonance imaging apparatuses have been developed.

[0003] As is well known, magnetic resonance imaging uses the energy of a high-frequency magnetic field that rotates at a specific frequency when a group of nuclei having a unique magnetic moment is placed in a uniform static magnetic field. Utilizing the phenomenon of resonance absorption,
It is a method of imaging chemical and physical microscopic information of a substance. In this magnetic resonance imaging method, data acquisition time is much longer than in other medical image diagnostic apparatuses such as an ultrasonic diagnostic apparatus and an X-ray CT. Therefore, there is a problem that artifacts occur due to the movement of the subject such as respiration, and it is difficult to image a moving heart or vascular system. In addition, since the imaging time is long, the pain given to the subject is great.

Therefore, as a method of reconstructing an image at a high speed in the magnetic resonance imaging method, an echo planar method by Mansfield, an ultra-fast Fourier method by Hutcison et al., And the like have been proposed. FIG. 9 shows a pulse sequence for an image data acquisition method by an ultra-fast Fourier method (also called a multiple echo Fourier method). As a high-frequency magnetic field RF, after selectively excited simultaneously applying a selected excitation 90 ° RF pulse, the magnetization of the slice plane by applying a slice gradient magnetic field for G _s, further 180
° from application of RF pulses, by switching by applying a soup for gradient G _r read in a direction parallel to the slice plane at a high speed in the positive and negative gradient for phase encoding in the direction at the same time perpendicular to the G _s and G _r pulsed manner is applied to each of the switching of the magnetic field G out gradient magnetic field for reading _e G _r. The magnetic resonance signals generated thereby are collected, and a magnetic resonance image is reconstructed.

Recently, in addition to the above-mentioned methods, a Turbo FLASH method, which is a speedup of the conventional field echo method, has been proposed. The use of these ultra-high-speed sequences enables high-speed imaging.

[0006]

However, the conventional high-speed imaging method in the magnetic resonance imaging apparatus has the following disadvantages.

The conventional photographing method does not correspond to high-speed imaging. At the time of high-speed imaging, a new photographing condition input method corresponding to the photographing time is required.
For example, in the conventional method of designating an imaging section, a section necessary for diagnosis is determined from one or a plurality of images taken in advance, the parameters of the corresponding pulse sequence are statically rewritten, and an image of an arbitrary section is taken. Was getting. It is sufficient to set the pulse sequence slowly for each imaging condition.

However, in the case of a high-speed sequence, a method of real-time use, such as an operator changing sequence conditions interactively and immediately observing a corresponding image, can be considered. Settings cannot be made continuously. Further, when changing the imaging conditions between the executions of the sequence, it is necessary to rewrite the pulse sequence at high speed, but such a complicated control is impossible with a conventional sequence controller.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem. It is an object of the present invention to easily set a photographing surface and appropriately change photographing conditions in real time. To provide a magnetic resonance imaging apparatus capable of performing the above.

[0010]

According to the present invention, a high frequency magnetic field and a gradient magnetic field are applied to a subject placed in a uniform static magnetic field by a predetermined pulse. In a magnetic resonance imaging apparatus for applying according to a sequence and detecting and imaging a magnetic resonance signal from within the subject,
A first display unit for displaying a three-dimensional guide image, and a second display unit for displaying an imaging region on the guide image in an overlapping manner.
Display means, movement selecting means for moving and selecting the imaging area, imaging means for imaging the imaging area of the subject corresponding to the selected imaging area, and displaying the imaged imaging area And a third display unit, wherein the movement selection unit is operable during execution of a pulse sequence, and the third display unit is configured to change an imaging region captured in accordance with a change in an imaging region by the movement selection unit. Is displayed in conjunction with the change, and the magnetic resonance diagnostic apparatus is a solution.

Further, according to the present invention described in claim 2,
2. The system according to claim 1, further comprising: a plurality of event memories that store the pulse sequence; and an event memory control unit that selectively controls writing to each of the event memories and reading from each of the event memories. The magnetic resonance diagnostic apparatus described above is used as a solution. According to the third aspect of the present invention, when the selected imaging area deviates from the photographable area, there is provided a notifying means for notifying the fact.
Alternatively, the magnetic resonance diagnostic apparatus described in 2 is a solution.

[0012]

With the above arrangement, the entire image of the subject is displayed three-dimensionally, and the imaging region can be selected using the three-dimensional image as a guide image. Therefore, a desired photographing area can be easily set. In addition, the imaging region can be changed even during the execution of the pulse sequence, and the imaging region can be set according to the imaging speed of ultra-high-speed MRI. In addition, a desired area can be observed in real time.

[0013]

[0014]

FIG. 1 is a block diagram showing the configuration of a magnetic resonance imaging apparatus according to an embodiment of the present invention. In FIG. 1, a static magnetic field magnet 1 and a gradient magnetic field coil 3 are driven by an excitation power supply 2 and a drive circuit 4 controlled by a sequence controller 9, respectively.
, A uniform static magnetic field, and a gradient magnetic field whose magnetic field intensity changes in two orthogonal directions of read and encode in a desired cross section (slice plane) of interest and in a slice direction perpendicular thereto. In the present embodiment, a gradient magnetic field applied in a direction perpendicular to the slice plane is a slice gradient magnetic field G _s , a gradient magnetic field applied in an appropriate direction in the slice plane is read out, and a gradient magnetic field G _r is read out in a direction perpendicular thereto. the gradient magnetic field applied to explaining the gradient phase-encoding magnetic field G _e.

Under the control of the sequence controller 9, a high-frequency magnetic field generated from the probe 6 by a high-frequency signal from the transmission unit 7 is applied to the subject 5. In the present embodiment, the probe 6 is shared by a transmission coil for high-frequency transmission and a reception coil for receiving magnetic resonance signals related to various nuclei in the subject 5, but the transmission and reception coils are separately provided. It may be provided.

The magnetic resonance signal (echo signal) received by the probe 6 is amplified and detected by the receiving unit 8 and then sent to the data collecting unit 10 under the control of the sequence controller 9.

The data collecting unit 10 collects the magnetic resonance signals taken out via the receiving unit 8 under the control of the sequence controller 9, A / D converts them, and sends them to the data processing unit 11.

The data processor 11 is controlled by the computer 12 and performs image reconstruction processing by Fourier transform on the echo signal input from the data collector 10.
Obtain image data. Then, the image data is output to the image display 14.

The image display 14 includes the data processing unit 1
The image data given from 1 is displayed. Further, the display 14 has a plurality of independent display screens, and has a function of displaying the respective screens independently or overlapping and displaying them. Further, full color display is possible.

The computer 12 operates according to a command from the console 13 and controls the system controller 9. In addition, the image display 14 has frame buffers (not shown) for the number of display screens, and supplies, for example, an image to be overlapped on an MRI image to the image display 14 via the data processing unit 11.

Next, a method of specifying an imaging area will be described. Before performing imaging of a desired section, a magnetic resonance signal is collected from the entire subject 5 in advance, and a three-dimensional image is captured. Then, the three-dimensional image is displayed three-dimensionally on the display 14 as a guide image for positioning.
If a three-dimensional image of the subject cannot be captured, 3D images collected by an appropriate number of volunteers in advance are used.
A three-dimensional guide image may be created from a three-dimensional image based on the physique of the patient, such as height and weight, or may be created by computer graphics according to the physique of the subject.

FIG. 2A shows an example of display on the display 14. The guide image 21 is displayed three-dimensionally.
A cross section 22 indicating an imaging region is displayed on this image 21 in an overlapping manner. In addition, this display 14
A switch 23 for operating the enlargement / reduction, a switch 24 for operating the angle of the imaging area 22, and an imaging area 22
Are displayed, and a switch 26 for instructing the angle and the direction of the translation is displayed. Then, for example, when the “X” of the switch 26 is pressed and the translation switch 25 is pressed, the imaging region section 22 moves in parallel in the x-axis direction. In addition, the observation direction of the guide image 22 is not fixed, and can be arbitrarily changed using a mouse, a trackball, or the like (not shown).

Next, the procedure of the positioning operation will be described. First, a guide image suitable for a diagnostic region of a subject is displayed three-dimensionally on the display 14, and the operator changes the display position, angle, and the like so that the optimal observation position is obtained. Then, the guide image is fixed at this position, and FIG.
Each of the switches 23 to 26 shown in (a) is adjusted to select an imaging area. Thus, the initial setting of the positioning is completed.

When the imaging conditions such as the slice thickness are set on the console 13, the imaging is started according to a predetermined pulse sequence. When the photographing is started, the image display 14 is switched as shown in FIG. 2B, and the real-time MR image 27 is displayed. Further, an image 28 for indicating the imaging area of the MR image 27 is also displayed. By adjusting the translation switch 29, the angle switch 30, and the direction indication switch 31, the imaging area is displayed even during the execution of the sequence. Changes are possible. Therefore, if the imaging region is changed during the execution of the sequence, the MR image 27 changes every moment in real time.

Thus, the operator can interactively change the imaging area, and can observe a desired cross section in real time.

When performing the above operation, the computer 12 synchronizes with the change input of the imaging area,
Sequence parameters such as gradient magnetic field strength for making this change are sequentially calculated.

[0027] That is, when a larger imaging area, the encoding direction of the gradient field strength G _e, and it is necessary to increase the lead direction of the gradient field strength G _r, also in order to reduce the slice thickness Gradient magnetic field strength G _{s in} slice direction
Need to be larger. For example, slice thickness by multiplying the gradient field strength G _s A _s becomes 1 / A _s.

Further, in order to select an arbitrary cross section, the coordinate system (x, y, z) formed by the physically arranged gradient coil is changed from the coordinate system (s, e, r) for imaging. ), For example, to obtain a desired gradient magnetic field G _s , the gradient magnetic field strength G _x , applied to the x, y, z axes
It is _{sufficient that} the combination of the vectors of G _y and G _z is G _s .

[0029] That is, as shown in FIG. 3, the angle theta, to produce a G _s represented by φ is, G _x indicated by the following (1) ~ (3), G y, which determines the G _z I just need.

[0030] _{G x = A s · G s} · sinθ · cosφ ... (1) G y = A s · G s · sinθ · sinφ ... (2) G z = A s · G s · cosφ ... (3) The , G _r , G _e , G _x , G _y ,
G _z can be expressed. These sequence parameters A _s , θ, φ, etc. are continuously sent to the sequence controller 9 in real time, and the supply of current to the gradient coil 3 is actually controlled.

When the range specified in the section of the imaging region is a region where photographing is not possible, an alarm is issued by a bell sound or the like, or the input specified range is clipped at a limit value to allow the operator to perform the operation. Inform

FIG. 4 is a block diagram showing a specific configuration of the sequence controller 9. The host CPU 41 controls the sequence controller 9 as a whole, the SC-CPU 44 controls the operation of the sequence, and connects them. Interfaces 42 and 43 and an event memory 4 for storing the order of actual execution according to the sequence
6 and an RF waveform memory 47 for storing the waveform of the selective excitation pulse. Further, an RF control unit 50 for actually controlling the output of the selective excitation pulse in accordance with the contents stored in the RF memory 47, a data collecting unit 51 for collecting an MR signal generated on the imaging surface, and storing the data collected here. It has an acquisition data memory 48 and a gradient magnetic field control unit 52 for controlling the gradient magnetic field strength. Furthermore,
For example, an event control unit 49 that gives an execution command to the RF control unit 50, the data acquisition unit 51, and the gradient magnetic field control unit 52 in accordance with the execution order stored in the event memory 46 as shown in FIG. There is a clock circuit 45 for providing a timing clock to the clocks 50 and 51.

FIG. 4 shows the event memory 46 and the SC-C.
FIG. 3 is a block diagram showing a more detailed configuration of a PU 44. As shown, in this example, a plurality of (three in the figure) event memories 46 are provided, and writing and reading to and from each event memory 46 are controlled by switching the switches 53 and 54.

The SC-CPU 44 has an area setting table 56 for storing multi-slice areas, encoding steps, and the like, and an image area setting section 55 for determining an imaging area in accordance with designated parameters. .

For example, when a parameter to be changed is input to the imaging area setting section 55 while the sequence is being executed in accordance with the contents stored in the event memory 46a, a new imaging area is photographed. Is written into the event memory 46b, for example.
Thereafter, when the writing to the event memory 46b is completed, the switch 54 is switched to
Is read out, the photographing conditions such as the sequence can be changed immediately. Therefore, it is possible to set an imaging surface that follows the imaging speed of ultra-high-speed MRI, and the imaging region is changed in real time on the image display.

FIG. 6 is a block diagram showing the internal configuration of the gradient magnetic field control unit. The gradient magnetic fields G _r , G _e ,
When G _s is given, the set value A _s, theta, x-axis in accordance with such phi, y-axis, the gradient magnetic field in the direction of the z-axis G _x, G _y, G _z
And an image area setting unit 61 for calculating G _x , G
_y, a buffer 62a for temporarily storing the G _z, 62b, 62
c.

According to such a configuration, in particular, the setting of the oblique angle and the processing of enlargement / reduction, etc., which require a large amount of calculation, are performed in accordance with FIG.
Are performed in the gradient magnetic field control unit, not in the event memories 46a to 46c shown in FIG. Therefore, the time lag when changing the imaging area can be reduced.

FIG. 7 shows a hardware configuration of the gradient magnetic field control unit shown in FIG. 6, which includes an imaging area setting section 71, a plurality of registers 72 to 72, and a multiplier 73.
To 73 and adders 74 to 74. Each of the registers 72 to 72 has a weighting coefficient G _rx , G _ry ... Indicating the degree of dependence of the gradient magnetic field in the read, encode, and slice directions on the gradient magnetic field in the x-axis, y-axis, and z-axis directions.
G _sz is set by the imaging area setting unit 71. The calculation is performed by the multipliers 73 to 73 and the adders 74 to 74, and the gradient magnetic fields G _x , G _y , G in the respective axial directions are obtained.
_z is required. For example, G _x is obtained by the following equation (4).

G _x = G _rx · G _r + G _ex · G _e + G _sx · G _s (4) Even in such a configuration, the gradient magnetic fields G _x , G _y , G _z
Can be obtained quickly, and the calculation can be speeded up.

As described above, in the present embodiment, a three-dimensional guide image is displayed on the image display, and the imaging regions are displayed on the guide image in an overlapping manner.
Since the imaging section is determined by appropriately moving the imaging area, the imaging section can be easily determined. In addition, since a plurality of event memories are provided, and writing and reading of imaging conditions such as a sequence are performed simultaneously and in parallel, it is possible to change the imaging surface in real time.

[0041]

As described above, according to the present invention, the whole image of the subject is three-dimensionally displayed and the imaging region is selected using the three-dimensional image as a guide image, so that a desired imaging region can be easily set. . In addition, since the imaging region can be changed even during the execution of the pulse sequence, the imaging region can be set according to the imaging speed of ultra-high-speed MRI, and a desired region can be observed in real time.

[0042]

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a magnetic resonance imaging apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing an example displayed on an image display.

[3] The slice direction gradient magnetic field G _s, is an explanatory diagram showing x, y, z-axis direction of the gradient magnetic fields G _x, G _y, decomposing operation G _z.

FIG. 4 is a block diagram showing a detailed configuration of a sequence controller.

FIG. 5 is a block diagram showing a detailed configuration of an SC-CPU and an event memory.

FIG. 6 is a block diagram showing a first example of a detailed configuration of the gradient magnetic field control unit.

FIG. 7 is a block diagram showing a second example of the detailed configuration of the gradient magnetic field control unit.

FIG. 8 is an explanatory diagram showing stored contents of an event.

FIG. 9 is a pulse sequence diagram of the high-speed imaging method.

[Explanation of symbols]

 9 Sequence controller 10 Data processing unit 12 Electronic calculator 13 Console 14 Image display 44 SC-CPU 46 Event memory 49 Event control unit 52 Gradient magnetic field control unit 61 Imaging area setting unit

Continuation of the front page (56) References JP-A-4-71535 (JP, A) JP-A-1-131652 (JP, A) JP-A-64-64640 (JP, A) JP-A-63-192430 (JP) JP-A-3-258244 (JP, A) JP-B-2-36260 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 5/055 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. A magnetic resonance image in which a high-frequency magnetic field and a gradient magnetic field are applied to a subject placed in a uniform static magnetic field in accordance with a predetermined pulse sequence, and a magnetic resonance signal from inside the subject is detected and imaged. In the apparatus, first display means for displaying a three-dimensional guide image, second display means for displaying an imaging area on the guide image in an overlapping manner, and movement selection means for moving and selecting the imaging area, An imaging unit configured to image an imaging region of the subject corresponding to the selected imaging region; and a third display unit configured to display the captured imaging region. Wherein the third display means displays an imaging area taken in accordance with the change of the imaging area by the movement selection means in conjunction with the change. Cutting device. 2. An event memory for storing the pulse sequence, and event memory control means for selectively controlling writing to each of the event memories and reading from each of the event memories. The magnetic resonance diagnostic apparatus according to claim 1, wherein: 3. The magnetic resonance diagnostic apparatus according to claim 1, further comprising a notifying unit that notifies the user when the selected imaging area deviates from the photographable area.