JP2007236455A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve joining accuracy in the region of interest. <P>SOLUTION: A control part 107 sets the ROI to each of two master images obtained by imaging while changing an imaging position. The control part 107 extracts evaluation information (tangent vector) expressing the feature of the master image for evaluating the continuity of images from the ROI for each of the two master images. Then, the control part 107 generates a joined image for which the two master images are joined on the basis of the evaluation information. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic resonance imaging apparatus that images a wide area by performing imaging a plurality of times while changing the imaging position.

  In recent years, a method of imaging a wide area that cannot be captured by one imaging (hereinafter referred to as wide-area imaging) is used by performing multiple imaging while moving the bed between them. It has become to.

In this case, a single image corresponding to a wide area is generated by stitching together a plurality of images obtained individually for each shooting. Several techniques for joining images in this way have been conventionally considered. For example, there is a method of performing the joining by evaluating the correlation or the like for the entire region overlapped by imaging the FOV larger than the desired FOV in the joining direction.
JP 2000-268178 A

  In such a method, since joining is performed by evaluating a wide area, that is, the entire overlap region, the joining portion as a whole is appropriately joined.

  However, due to the influence of body movement or the like, the images in the overlap region of two adjacent images are different, so that an offset remains at the joined portion. In the above method, since this offset is distributed over a wide range, the offset occurs locally at any location. For this reason, there is a fear that the joining accuracy in the region of most interest in image diagnosis is not sufficient.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a magnetic resonance imaging apparatus capable of improving the joining accuracy in a region of interest. .

  The magnetic resonance imaging apparatus according to the first aspect of the present invention includes a setting means for setting a region of interest in each of a plurality of parent images obtained by imaging while changing an imaging position, and an image from the plurality of regions of interest. Extracting means for extracting a plurality of pieces of evaluation information respectively representing the characteristics of the plurality of parent images for evaluating the continuity of the image, and a joined image obtained by connecting the plurality of parent images based on the plurality of pieces of evaluation information And a joined image generating means for generating.

  The magnetic resonance imaging apparatus according to the second aspect of the present invention includes setting means for setting the first and second regions of interest in the first and second parent images obtained by imaging while changing the imaging position, respectively. Extraction means for extracting, from the first and second regions of interest, first and second evaluation information representing features of the first and second parent images for evaluating continuity of images, respectively; And a joined image generating means for generating a joined image obtained by joining the first and second parent images based on the first and second evaluation information.

  According to a third aspect of the present invention, there is provided a magnetic resonance imaging apparatus comprising: setting means for setting a region of interest in each of a plurality of parent images obtained by imaging while changing an imaging position; Evaluation image generation means for generating a plurality of evaluation images respectively representing the characteristics of the plurality of parent images for evaluating continuity, and a relative positional relationship between the plurality of evaluation images according to an operation by an operator Setting means, and a joined image generating means for creating a joined image by joining the plurality of parent images arranged in a positional relationship based on the positional relationship of the plurality of evaluation images.

  A magnetic resonance imaging apparatus according to a fourth aspect of the present invention includes setting means for setting the first and second regions of interest in the first and second parent images obtained by imaging while changing the imaging position, Evaluation image generation for generating first and second evaluation images respectively representing features of the first and second parent images for evaluating image continuity from the first and second regions of interest. Means, a means for setting a relative positional relationship between the first and second evaluation images according to an operation by an operator, and a positional relationship based on the positional relationship between the first and second evaluation images. And a joined image generating means for generating a joined image by joining the first and second parent images.

  According to the present invention, it is possible to improve the joining accuracy in a region of interest.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a magnetic resonance imaging apparatus (MRI apparatus) according to the present 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 supply 3, a bed 4, a bed control unit 5, a transmission RF coil 6, a transmission unit 7, a reception RF coil 8, a reception 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 magnetic field coil 2 is a combination of three types of coils corresponding to the X, Y, and Z axes orthogonal to each other. The gradient magnetic field 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 supply 3 and the magnetic field intensity changes along the X, Y, and Z axes. The Z-axis direction is, for example, the same direction as the static magnetic field. The gradient magnetic fields of the X, Y, and Z axes respectively correspond to, for example, the slice selection gradient magnetic field Gs, the phase encoding gradient magnetic field Ge, and the readout gradient magnetic field Gr. 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 change the phase of the magnetic resonance signal in accordance with the spatial position. The readout gradient magnetic field Gr is used for changing the frequency of the magnetic resonance signal in accordance with the spatial position.

  The subject P is inserted into the cavity (imaging port) of the gradient coil 2 while being placed on the top 41 of the bed 4. The top 41 of the bed 4 is driven by the bed control unit 5 and moves in the longitudinal direction and the vertical direction. Usually, the bed 4 is installed such that the longitudinal direction thereof is parallel to the central axis of the static magnetic field magnet 1.

  The transmission RF coil 6 is disposed inside the gradient magnetic field coil 2. The transmission RF coil 6 receives a high frequency pulse from the transmission unit 7 and generates a high frequency magnetic field.

  The transmission unit 7 includes an oscillation unit, a phase selection unit, a frequency conversion unit, an amplitude modulation unit, a high frequency power amplification unit, and the like. 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 conversion unit converts 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 7 transmits a high-frequency pulse corresponding to the Larmor frequency to the transmission RF coil 6.

  The reception RF coil 8 is disposed inside the gradient magnetic field coil 2. The reception RF coil 8 receives a magnetic resonance signal radiated from the subject due to the influence of the high frequency magnetic field. An output signal from the reception RF coil 8 is input to the reception unit 9.

  The receiving unit 9 generates magnetic resonance signal data based on the output signal from the reception RF coil 8.

  The computer system 10 includes an interface unit 101, a data collection unit 102, a reconstruction unit 103, a storage unit 104, a display unit 105, an input unit 106, and a control unit 107.

  The interface unit 101 is connected to the gradient magnetic field power source 3, the bed control unit 5, the transmission unit 7, the reception RF coil 8, the reception unit 9, and the like. The interface unit 101 inputs and outputs signals exchanged between these connected units and the computer system 10.

  The data collection unit 102 collects digital signals output from the reception unit 9 via the interface unit 101. The data collection unit 102 stores the collected digital signal, that is, magnetic resonance signal data in the storage unit 104.

  The reconstruction unit 103 performs post-processing, that is, reconstruction such as Fourier transform, on the magnetic resonance signal data stored in the storage unit 104, and obtains spectrum data or image data of the desired nuclear spin in the subject P. Ask.

  The storage unit 104 stores magnetic resonance signal data and spectrum data or image data for each patient.

  The display unit 105 displays various information such as spectrum data or image data under the control of the control unit 107. As the display unit 105, a display device such as a liquid crystal display can be used.

  The input unit 106 receives various commands and information input from the operator. As the input unit 106, a pointing device such as a mouse or a trackball, a selection device such as a mode change switch, or an input device such as a keyboard can be used as appropriate.

  The control unit 107 includes a CPU, a memory, and the like (not shown), and comprehensively controls the MRI apparatus according to the present embodiment. The control unit 107 has the following various functions in addition to a control function for realizing a well-known function in the MRI apparatus. One of these functions is to set a region of interest for each of two images (parent images) to be joined in response to an operator operation. One of the functions described above generates an edge image as an evaluation image representing the characteristics of the parent image for evaluating the continuity of the image from the region of interest for each of the parent images. One of the functions is to extract a tangent vector in the edge image. One of the functions described above generates a joined image by connecting parent images based on the extracted tangent vectors. One of the functions is to set the relative positional relationship between the edge images according to the operation by the operator. One of the functions described above generates a joined image by connecting parent images arranged in a positional relationship based on the positional relationship of edge images. One of the functions is to display the generated joint image on the display unit 105 by superimposing a maximum intensity projection (MIP) image or a spine image as necessary.

  Next, the operation of the MRI apparatus configured as described above will be described.

  Since the operation for imaging the subject P is the same as that of a conventional MRI apparatus, detailed description thereof is omitted here. And here, the operation | movement which joins the two parent images obtained by imaging twice while changing an imaging position, and produces | generates a joining image is demonstrated in detail.

  FIG. 2 is a flowchart showing a processing procedure of the control unit 107 for connecting two parent images to generate a joined image.

  In step Sa <b> 1, the control unit 107 causes the display unit 105 to display two parent images designated as stitching targets. At this time, if the overlap region is included in the two parent images, the control unit 107 displays the two parent images A and B in an overlapping manner as shown in FIG. If the overlap area is not included in the two parent images, the control unit 107 displays the two parent images C and D in contact with each other as shown in FIG. Note that here, the control unit 107 only displays the two parent images side by side in the positional relationship as described above, and does not consider a shift between the parent images. The overlap amount of the two images may be input by an operator, or may be automatically determined by the control unit 107 based on the conditions at the time of imaging.

  In step Sa2, the control unit 107 accepts designation of an area by the operator on the parent image displayed as described above. At this time, if the two parent images overlap each other, the control unit 107 displays a frame E indicating the overlap area as shown in FIG. Then, the control unit 107 accepts the designation of the area only within the overlap area. That is, the control unit 107 accepts a designated area such as the area F or the area G shown in FIG. 6 as an effective area. If the two parent images are not overlapped, the control unit 107 displays the boundary of the parent image, and accepts a designated area that crosses the boundary as an effective area.

  In step Sa3, the control unit 107 sets a region included in the specified region as a region of interest (ROI) for each of the two parent images.

  In step Sa4, the control unit 107 generates an edge image for each of the two parent images. Specifically, the control unit 107 generates an edge image as shown in FIG. 7 by performing edge enhancement filter processing and thinning processing on the entire parent image, for example. A well-known method can be applied to the edge enhancement filter process and the thinning process. The edge image may be generated only for the image in the ROI or the overlap region. In addition, a range that is a generation target of the edge image may be determined according to an operator instruction.

  In step Sa5, the control unit 107 confirms whether the auto mode or the manual mode is set as the joining mode. The joining mode may be set before the start of the process shown in FIG. 2 or may be selected by the operator at this timing.

  When the auto mode is set, the control unit 107 proceeds from step Sa5 to step Sa6. In step Sa <b> 6, the control unit 107 obtains a tangent vector for a line segment constituting the edge image that is included in the ROI. In step Sa7, the control unit 107 evaluates the tangent vector obtained for each of the two edge images, and connects the parent images to generate a joined image. A well-known method can be applied to the evaluation here, but in a typical method, a tangent unit vector is used to find the most matching pattern in the evaluation region, such as template matching.

  Thus, for example, when there are shifted line segments H and I as shown in FIG. 8A, the offset is obtained from the tangent vectors in the ROI of these line segments H and I as shown in FIG. 8B. The parent images are stitched together to eliminate this offset.

  On the other hand, if the manual mode is set, the control unit 107 proceeds from step Sa5 to step Sa8. In step Sa8, the control unit 107 causes the display unit 105 to simultaneously display the edge images in the ROI relating to the respective parent images. In step Sa9, the control unit 107 relatively moves the edge image displayed as described above in accordance with an operator operation. Therefore, the operator moves the edge image by a mouse operation or the like so that the line segments appearing in the two displayed edge images are in a satisfactory connection. Then, the operator inputs movement completion by a predetermined instruction operation. Then, in step Sa10, the control unit 107 generates a joined image by joining the two parent images in a state where the two parent images are arranged in a positional relationship determined based on the relative positional relationship of the moved edge images. To do.

  If the joined image is generated in step Sa7 or step Sa10, the control unit 107 proceeds to step Sa11. In step Sa11, the control unit 107 confirms whether the display setting of the MIP image is ON. If it is ON, the control unit 107 proceeds from step Sa11 to step Sa12. In step Sa12, the control unit 107 causes the display unit 105 to perform superimposed display of the joined image generated in step Sa7 or step Sa10 and the MIP image generated by separately known processing.

  If the MIP setting is OFF, the control unit 107 proceeds from step Sa11 to step Sa13. In step Sa13, the control unit 107 confirms whether or not the spine display setting is ON. If it is ON, the control unit 107 proceeds from step Sa13 to step Sa14. In step Sa14, the control unit 107 causes the display unit 105 to perform superimposed display of the joint image generated in step Sa7 or step Sa10 and the spine image generated by another well-known process.

  If the spine display setting is also OFF, the control unit 107 proceeds from step Sa13 to step Sa15. In step Sa15, the control unit 107 causes the display unit 105 to display the joint image generated in step Sa7 or step Sa10 alone.

  As described above, according to the present embodiment, images can be joined in consideration of only the continuity in the ROI, so that a joined image with very good joining accuracy in the ROI can be obtained. Such an image is very useful for interpretation of a local area including, for example, the ROI periphery.

  Further, according to the present embodiment, since the joining can be performed in either the auto mode or the manual mode, it is possible to reduce the labor of the operator by using the auto mode, or to reduce the operator's trouble by using the manual mode. It is also possible to realize more precise stitching by making use of experience, and flexible operation according to user needs is possible.

  Further, according to the present embodiment, since the MIP image and the spine image can be superimposed and displayed on the generated joint image, it can be easily confirmed by comparison with the MIP image and the spine image whether the joining state in the joint image is appropriate. can do.

  Further, according to the present embodiment, the operator only has to specify one area for setting two ROIs, and the operation is simple.

  This embodiment can be variously modified as follows.

  In step Sa1, the two parent images may be displayed separately from each other.

  The parent image can also be a volume image. In this case, ROI setting and splicing evaluation are also performed on the volume image. If the operator designates the area on the slice image in the same manner as in the above embodiment, the designated area is similarly applied to a plurality of slices arranged in the slice direction with respect to the display slice. Operator operations can be simplified. For example, when stitching together a volume image made up of 100 head coronal images and a volume image made up of 100 chest coronal images in the depth direction, the operator needs to designate 100 regions. Therefore, for example, the ROI set in the 50th head coronal image and the chest coronal image based on the region designated as the 1st slice (center slice) of the 50th image and the position in the x and y directions are the same. Are respectively copied as ROIs of the other 99 head coronal images and chest coronal images. Thereby, the burden on the operator related to the area designation can be reduced. Note that copying the ROI to all slice images included in the volume data takes extra time if the number of slice images is large. For example, copying to only 50 of the 100 images. The slice image for copying the ROI may be limited.

  It is also possible to perform stitching on images of some slices of a plurality of slices included in the volume image. In this case, image joining may be performed for each slice by the same processing as in the above embodiment. Also in this case, if the operator designates an area on an image related to one slice and the designated area is applied to other slices arranged in the slice direction with respect to the display slice, the operator The operation can be simplified.

  There may be three or more parent images. For example, when there are a head image, a chest (abdomen) image, and a lower limb image as the first, second, and third parent images, they may be connected in a line. In this case, first, the two parent images are joined together as in the previous embodiment, then the joined image is used as a single parent image, and another parent image is joined together as in the previous embodiment. Just add. However, in this case, it is necessary to repeat the unit process including the ROI setting and the joining process a plurality of times. Therefore, ROIs may be set from a plurality of areas designated on one screen, and the above-described images may be joined based on the images in this ROI. For example, in the case of the above specific example, the first to third images are displayed side by side, the first region straddling the first image and the second image, and the second region straddling the second image and the third image. The designation by the operator for the area 2 is accepted. Then, the first image and the second image are joined together by performing the same processing as in the first embodiment on the two ROIs set in the same manner as in the previous embodiment based on the first region. The second image and the third image may be joined by performing the same processing as in the first embodiment on two ROIs set in the same manner as in the previous embodiment based on the second region. .

  The parent images may be joined together in consideration of not only the features of the parent images to be joined but also the continuity in images of different slices in the vicinity of the parent images.

  The region designation by the operator for setting the ROI may be performed individually for each parent image.

  By performing the same processing as described above three-dimensionally, it is possible to generate a joined image obtained by joining three-dimensional images.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components 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.

The figure which shows the structure of the magnetic resonance imaging apparatus (MRI apparatus) which concerns on one Embodiment of this invention. The flowchart which shows the process sequence of the control part 107 in FIG. 1 for connecting two parent images and producing | generating a joining image. The figure which shows the example of a display of these parent images in case an overlap area | region is included in two parent images. The figure which shows the example of a display of these parent images in case an overlap area | region is not included in two parent images. The figure which shows an example of the display screen for accepting designation | designated of the area | region used as ROI. The figure which shows the example of designation | designated of the area | region used as ROI. The figure which shows an example of an edge image. The figure which shows the mode of the joining based on the tangent vector in ROI.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Static magnetic field magnet, 2 ... Gradient magnetic field coil, 3 ... Gradient magnetic field power supply, 4 ... Bed, 5 ... Bed control part, 6 ... Transmission RF coil, 7 ... Transmission part, 8 ... Reception RF coil, 9 ... Reception part, DESCRIPTION OF SYMBOLS 10 ... Computer system, 101 ... Interface part, 102 ... Data collection part, 103 ... Reconstruction part, 104 ... Memory | storage part, 105 ... Display part, 106 ... Input part, 107 ... Control part.

Claims (9)

Setting means for setting a region of interest in each of a plurality of parent images obtained by imaging while changing the imaging position;
Extraction means for extracting a plurality of pieces of evaluation information respectively representing features of the plurality of parent images for evaluating continuity of images from the plurality of regions of interest;
A magnetic resonance imaging apparatus comprising: a bonded image generating unit configured to generate a bonded image obtained by connecting the plurality of parent images based on the plurality of evaluation information. Setting means for setting the first and second regions of interest in the first and second parent images obtained by imaging while changing the imaging position;
Extraction means for extracting, from the first and second regions of interest, first and second evaluation information representing features of the first and second parent images for evaluating continuity of images, respectively;
A magnetic resonance imaging apparatus comprising: a bonded image generating unit configured to generate a bonded image obtained by connecting the first and second parent images based on the first and second evaluation information.   The magnetic resonance imaging apparatus according to claim 1, wherein the extraction unit extracts a tangent vector of an edge of a tissue shown in the parent image as the evaluation information. Setting means for setting a region of interest in each of a plurality of parent images obtained by imaging while changing the imaging position;
Evaluation image generation means for generating a plurality of evaluation images respectively representing features of the plurality of parent images for evaluating continuity of images from the plurality of regions of interest;
Means for setting a relative positional relationship between the plurality of evaluation images according to an operation by an operator;
A magnetic resonance imaging apparatus comprising: a bonded image generating unit configured to generate a bonded image obtained by connecting the plurality of parent images arranged in a positional relationship based on a positional relationship of the plurality of evaluation images. Setting means for setting the first and second regions of interest in the first and second parent images obtained by imaging while changing the imaging position;
Evaluation image generation for generating first and second evaluation images respectively representing features of the first and second parent images for evaluating image continuity from the first and second regions of interest. Means,
Means for setting a relative positional relationship between the first and second evaluation images according to an operation by an operator;
And a joined image generating unit configured to generate a joined image obtained by joining the first and second parent images arranged in a positional relationship based on a positional relationship between the first and second evaluation images. Magnetic resonance imaging device.   The magnetic resonance imaging apparatus according to claim 4, wherein the evaluation image generation unit generates an image representing an edge of a tissue shown in the parent image as the evaluation image.   The setting means selects a region belonging to each of the two parent images from among the one region designated by the operator on the display screen displaying the two adjacent parent images side by side. The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance imaging apparatus is set as a region of interest.   6. The magnetic resonance imaging apparatus according to claim 1, further comprising display means for displaying the bonded image on a display.   The said display means superimposes and displays the maximum value projection image or spine image each extracted from the said some parent image on the said joint image, The claim 1, 2, 4, and 5 characterized by the above-mentioned. The magnetic resonance imaging apparatus according to any one of the above.

Images