JP4763429B2 - Magnetic resonance imaging system - Google Patents

Description

  The present invention relates to a magnetic resonance imaging apparatus (MRI apparatus), and more particularly to an MRI apparatus having a function of exciting a plurality of locations simultaneously.

  Currently, the imaging target of the magnetic resonance imaging apparatus is the main constituent substance of the subject, proton. By imaging the spatial distribution of the proton density and the spatial distribution of the relaxation phenomenon in the excited state, the form or function of the human head, abdomen, limbs, etc. is photographed two-dimensionally or three-dimensionally.

  Next, an imaging method of the MRI apparatus will be described.

  Different phase encodings are given depending on the gradient magnetic field, and echo signals obtained by the respective phase encodings are detected. As the number of phase encodings, values such as 128, 256, and 512 are usually selected for one image. Each echo signal is usually obtained as a time-series signal composed of 128, 256, 512, and 1024 sampling data. These data are two-dimensionally Fourier transformed to create one MR image.

  By the way, in recent years, a method (whole body MRI) for photographing the whole body while moving the bed on which the subject is placed in a continuous or stepwise manner is being performed. As typical methods, there are multi-station imaging and moving table imaging described in Patent Literature 1, Patent Literature 2, and Non-Patent Literature 1.

  These imaging methods are described in Non-Patent Document 2 as being effective techniques as whole body screening examination methods, and screening examinations that have been performed with a plurality of modalities such as CT, bone scintigraphy, and PET until now are performed by an MRI apparatus. The possibility of being able to do it alone is also shown.

  As shown in FIG. 13A, these imaging operations are performed while moving the bed 312 on which the subject 301 is placed in a continuous or stepwise manner to the imaging region 1201 that is the lower central region of the static magnetic field magnet 302. The whole body is photographed with multiple slices. Then, as shown in FIG. 13B, the whole body image is obtained by connecting these images to one image.

  However, when imaging the chest and abdomen, the subject may move due to body movement caused by respiration, and the connected whole body image may become a discontinuous image.

  In order to suppress such discontinuities, various respiratory motion navigation methods that acquire data in the same respiratory cycle have been proposed. Typical known techniques include those described in Patent Document 3, Non-Patent Document 3, and Non-Patent Document 4.

  In these radiographs, one location such as the diaphragm and chest surface is excited, and the position of the diaphragm and chest is tracked using signals obtained therefrom to detect respiratory motion. At this time, a received signal is referred to as a navigation signal, and a sequence executed for navigation is referred to as a navigation sequence.

JP-A-6-304153 Japanese Patent Laid-Open No. 2004-611 U.S. Pat. No. 4,937,526 Whole-Body MRI: A Simple Approach using Automatic Table Movement and Dedicated Post-Processing: ISMRM 10, (2002) Who1e Body-MRI imaging with a continuously moving table platform in detection of metastatic disease in cancer patients First Results of a feasibility study: ISMRM 11, P.1333 (2003) Journal of Magnetic Resonance imaging, 21,576-582 (2005) Magnetic Resonance in Medicine, 34.11-16 (1995)

  However, in the above-described whole-body MRI in the prior art, since the imaging region moves continuously or stepwise from the head of the subject to the lower limb, respiratory motion navigation generated from the excitation profile of the chest region of the subject. There are cases where the gate signal cannot be received.

  For this reason, data may not be acquired in the same respiratory cycle, and the connected whole body images may be discontinuous.

  An object of the present invention is to realize a magnetic resonance imaging apparatus capable of acquiring imaging data from a plurality of parts of a subject with the same respiratory cycle and avoiding discontinuity between images due to body movement of the subject.

Magnetic resonance imaging apparatus of the present invention includes a static magnetic field generating means, a gradient magnetic field generating means, and a high-frequency pulse generating means, a magnetic resonance signal receiving means, and a table Shimesuru display means a tomographic image of a subject, a predetermined sequence And a control means for controlling the magnetic resonance signal receiving means .

In the magnetic resonance imaging apparatus, the predetermined sequence includes a navigation sequence for detecting a navigation signal indicating body movement of the subject and an imaging sequence for imaging a desired region of the subject. to become, the navigation sequence, detecting a first navigation signal indicating the body movement of the first region of the subject, and the second navigation signal indicating the body movement of the second region, the To do . Control means, said first calculating a correlation between the navigation signal and the second navigation signal, such that the image of the image and a second region of the first region is continuous, the photographing The imaging of at least one of the first area and the second area by the sequence is controlled based on the navigation signal generated from the one area and the correlation.

Preferably, the first navigation signal is a chest navigation signal indicating body movement of the subject's chest region , and the second navigation signal is abdominal navigation indicating body movement of the subject's abdominal region. a gate signal.

Control means, a chest navigate signals, based on the correlation between the abdominal navigating signal, the body motion indicated by the chest navigating signal to determine when it is within a certain gate window. Then, in the region where only the abdominal navigation signal can be detected, it is determined based on the abdominal navigation signal when the body movement of the chest is within a certain gate window and the imaging start time is determined.

  Preferably, the navigation signal is generated by a 2D excitation method.

  According to the present invention, it is possible to realize a magnetic resonance imaging apparatus capable of acquiring imaging data from a plurality of parts of a subject with the same respiratory cycle and avoiding discontinuity between images due to body movement of the subject.

  In other words, even if the subject moves, the same effect as receiving a navigation signal from the same position can be obtained, so that no unlucky continuation occurs between imaging slices, and high-accuracy imaging is possible.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is an overall schematic configuration diagram of an MRI apparatus to which the present invention is applied.

  In FIG. 1, the MRI apparatus includes a magnet 302 that generates a static magnetic field around a subject 301 lying on a bed 312, a gradient magnetic field coil 303 that generates a gradient magnetic field in a static magnetic field space region, and a high-frequency magnetic field in this region. An RF coil 304 to be generated and an RF probe 305 for detecting an MR signal generated by the subject 301 are provided.

  The gradient magnetic field coil 303 is composed of gradient magnetic field coils in three directions of X, Y, and Z orthogonal to each other, and each generates a gradient magnetic field in response to a signal from the gradient magnetic field power supply 309.

  The RF coil 304 generates a high frequency magnetic field in accordance with a signal from the RF transmission unit 310. The signal from the RF probe 305 is detected by the signal detection unit 306, signal processed by the signal processing unit 307, and converted into an image signal.

  The image signal from the signal processing unit 307 is supplied to the image processing unit 313, the image processing unit 313 performs arithmetic processing on the captured image, and the captured image is displayed on the display unit 308.

  The gradient magnetic field power source 309, the RF transmission unit 310, and the signal detection unit 306 are controlled by the control unit 311. The control time chart is generally called a pulse sequence.

  In the embodiment of the present invention, a 2D excitation method for exciting a space two-dimensionally is used. This 2D excitation method includes spiral type 2D excitation in which the K space is spirally filled and EPI type 2D excitation in which the K space is filled in a comb shape.

  In an embodiment of the invention, column type 2D excitation is used. This column type 2D excitation is described in the document “Two-Dimens 1 onal Spatia 1ly-Selective RF Excitation Pulses in Echo-Planar Imaging: Magnetic Resonance in Medicine, 47: 1186-1193 (2002)”.

  FIG. 2 is a diagram showing a pulse sequence used for 2D excitation in the first embodiment of the present invention. FIG. 3 is a diagram showing an excitation profile when 2D excitation is performed using the pulse sequence shown in FIG.

  As shown in FIG. 3, when the 2D excitation method is used, the excitation size can be limited to the column type on the XY plane. Further, a folded excitation 106 having the same excitation profile in the Y direction is generated.

  FIG. 4 is an explanatory diagram of the movement of the imaging part accompanying the movement of the subject in the first embodiment of the present invention, and FIG. 5 is a flowchart showing an operation procedure and a data processing procedure in one embodiment of the present invention. . The processing shown in FIG. 5 is executed by a command signal from the control unit 311.

  4 and 5, imaging is started in step S1, and moved to the imaging region 101 (step S2). When an imaging region comes to the region 101 with respiratory motion, a navigation sequence is executed in steps S3 to S5. In the navigation sequence, the above-described column type 2D excitation method is used.

  The navigation signal generated by the excitation profile 104 is received using the chest coil 105. Then, the imaging sequence is executed in the same cycle of respiratory motion by the navigation sequence. Details of the synchronous measurement method will be described later.

  Subsequently, in step S6, the camera moves to the imaging region 102. When the imaging region is 102 in step S107, the AP direction profiles of the chest and abdomen are referred to. A photographed image is created by combining signals from two coils, the chest coil 105 and the abdominal coil 107.

  The range of the imaging region 102 includes two navigation excitation profiles of chest excitation 104 and abdominal excitation 106, but the navigation of respiratory motion uses only the signal emitted by the chest excitation 104, step S8, In S9, the same process as in steps S4 and S5 is performed.

  At the same time, a signal generated by the abdominal excitation 106 is received using the abdominal coil 107, and synchronization between the chest and the abdomen is measured (step S10). Details of the synchronous measurement method for the chest and abdomen will be described later.

  Subsequently, in step S11, the camera moves to the imaging region 103. Since this imaging region 103 is a region where the signal of the chest excitation 104 does not enter, the signal generated by the abdominal excitation 106 is received, and imaging is performed in the same manner as in steps S4 and S5 with the time obtained in step S10 as the synchronization signal output time. Is performed (step S12).

  FIG. 6 shows a navigation sequence and a timing chart of the shooting sequence in the first embodiment of the present invention, and FIG. 7 shows an explanatory diagram of the shooting sequence.

  The relationship between the abdominal position profile shown in FIG. 6 and the imaging timing will be described later.

  Subsequently, in step S13, the camera moves to the imaging region 108 that is not affected by the respiratory motion. Since this imaging area 108 is an area that is not affected by the respiratory motion of the subject, the navigation sequence is stopped and normal imaging is executed (step S14).

  Next, the above-described respiratory synchronization measurement method will be described. FIG. 8 is a diagram showing a timing chart of the navigation sequence and the imaging sequence in the respiratory synchronization measurement, and FIG. 9 is an explanatory diagram of the imaging sequence in the respiratory synchronization measurement method.

  8 and 9, first, a navigation sequence is executed to monitor the AP direction profile 501 of the chest. Next, a gate window is set from the chest profile 501.

  When it is determined that the chest profile 501 is included in the gate window, a synchronization signal is output to execute the imaging sequence.

  Next, the chest / abdomen synchronous measurement method described above will be described. FIG. 10 is a diagram illustrating a timing chart of the navigation sequence and the imaging sequence in the chest and abdominal synchronization measurement, and FIG. 11 is an explanatory diagram of the imaging sequence in the chest and abdominal synchronization measurement method.

  10 and 11, the AP direction profile 601 of the chest is monitored. At the same time, the abdominal AP direction profile 701 is also monitored.

  Next, similarly to the chest, a gate window is set for the abdomen, and it is determined that the chest position is included in the gate window from the time when the abdominal profile 601 is determined to be included in the gate window. Let T1 be the time until.

  Then, T1 hour after the time when the abdominal profile 701 is included in the gate window is set as the imaging start time in the imaging region 102.

  As shown in FIG. 11, the following means are required for chest and abdominal synchronization measurement.

  First, when the imaging region includes two coils 105 and 107, a means for receiving signals from the two coils and combining them to create an image.

  Second, when two excitations 104 and 106 are excited, each is received using different coils 105 and 107, and only one of them is used as a navigation signal.

  Third, there is a means for synchronizing the signals 601 and 701 received using another coil.

  As described above, according to the first embodiment of the present invention, in the imaging region in which the navigation signal from the chest can be received, imaging is started based on the navigation signal from the chest, and the navigation from the chest is performed. In the imaging area where it is difficult to receive the gate signal, and the imaging area operates in response to the chest movement, imaging starts based on the correlation between the navigation signal from this imaging area and the navigation signal from the chest To do.

  Therefore, in whole body MRI, it is possible to acquire data from the subject in the same breathing cycle and avoid discontinuities between images due to body movement of the subject.

  Next, a second embodiment of the present invention will be described.

  This second embodiment is different from the synchronous measurement method of the chest profile and the abdominal profile shown in steps S6 to S10 in FIG. 5 in the first embodiment, and the gate window is reset and will be described next. Synchronize in such a way.

  The setting method is shown in FIG. In this case, a gate window including both an expiration period and an inspiration period is set in the gate window.

  Therefore, the difference between the abdominal position 1101 at which the abdominal profile 701 is determined to be included in the gate window and the abdominal position 1102 immediately before the abdominal position 701 is taken. Judged as the period.

  Then, only the person who is determined to match the case where the chest profile 501 is included in the gate window, that is, only the case of the expiration period is adopted as the output time of the synchronization signal.

  As in the second embodiment, the same effect as that of the first embodiment can be obtained by the method of determining the inclination direction of the abdominal profile and starting imaging when the abdominal profile 701 is included in the gate window. Can be obtained.

  Next, a third embodiment of the present invention will be described.

  The above-described example is an example in which the subject is moved and the whole body is imaged. However, when a plurality of regions of the subject are imaged using a plurality of local coils instead of the whole body of the subject. Also, the present invention can be applied.

  In this case, column-type 2D excitation is used to simultaneously excite a plurality of locations such as the abdomen and heart, obtain navigation signals at a plurality of locations, and synchronize using the method described above, thereby achieving high accuracy. Position correction can be performed.

  In addition, although the example mentioned above is an example at the time of applying 2D excitation method, if a navigation signal is acquired from the several location of a subject and the correlation of these signals can be judged, it will not necessarily be 2D excitation. It is not necessary to use a method, and other excitation methods can be used.

1 is an overall schematic configuration diagram of an MRI apparatus to which the present invention is applied. It is a figure which shows the pulse sequence used for 2D excitation in the 1st Embodiment of this invention. It is a figure which shows the excitation profile at the time of performing 2D excitation using the pulse sequence shown in FIG. It is explanatory drawing of the movement of the imaging | photography site | part accompanying the subject movement in the 1st Embodiment of this invention. It is a flowchart which shows the operation procedure and data processing procedure in one Embodiment of this invention. It is a timing chart of the navigation sequence and imaging | photography sequence in the 1st Embodiment of this invention. FIG. 7 is an explanatory diagram of the navigation sequence shown in FIG. 6. It is a timing chart of the navigation sequence and imaging | photography sequence in the 1st Embodiment of this invention. It is explanatory drawing of the navigation sequence shown in FIG. 5 is a timing chart of a navigation sequence and an imaging sequence for chest and abdominal synchronization measurement in the first embodiment of the present invention. It is explanatory drawing of the navigation sequence shown in FIG. It is a figure explaining the synchronous measurement method of the chest profile and the abdominal profile in the 2nd Embodiment of this invention. It is explanatory drawing of whole body MRI.

Explanation of symbols

101 to 103, 108 Imaging region of subject 104 Excitation for chest navigation 105 Coil for chest 106 Excitation for abdominal navigation 107 Coil for abdomen 301 Subject 302 Static magnetic field magnet 303 Gradient magnetic field coil 304 RF coil 305 RF probe 306 Signal detection unit 307 Signal processing unit 308 Display unit 309 Gradient magnetic field power supply 310 RF transmission unit 311 Control unit 312 Bed 313 Image processing unit 501 Chest position profile 701 Abdominal position profile

Claims (6)

A static magnetic field generating means for applying a static magnetic field to a space where an imaging region of the subject is arranged;
A gradient magnetic field generating means for applying a gradient magnetic field to the space;
High-frequency pulse generating means;
A magnetic resonance signal receiving means for receiving magnetic resonance signals from the subject,
And Table Shimesuru display means a tomographic image rather based on magnetic resonance signals received by the magnetic resonance signal receiving means,
Based on a predetermined sequence, the gradient magnetic field generating means, the high frequency pulse generating means, in the magnetic resonance imaging apparatus and a control means for controlling the magnetic resonance signal receiving means,
The predetermined sequence includes a navigation sequence for detecting a navigation signal indicating body movement of the subject, and an imaging sequence for imaging a desired region of the subject.
The navigation sequence, detects a first navigation signal indicating the body movement of the first region of the subject, and the second navigation signal indicating the body movement of the second region, and
The control means calculates a correlation between the first navigation signal and the second navigation signal, and takes the photographing so that the image of the first area and the image of the second area are continuous. A magnetic resonance imaging apparatus, wherein imaging of at least one of the first area and the second area by a sequence is controlled based on a navigation signal detected from the one area and the correlation . The magnetic resonance imaging apparatus according to claim 1.
The first navigation signal is a chest navigating signal indicating the motion of the chest region of the subject,
The second navigation signal is abdominal navigating signal indicating the motion of the abdominal region of the subject,
The control means, based on the correlation between the chest navigate signal and the abdominal navigate signals, upper SL in the region capable of detecting the chest navigating signal, the chest portion navigate signal motion indicated by the constant gate window to determine when an inner controls the photographing according to the chest portion navigating signal, the chest navigate signals can not be detected, the region capable of detecting the abdominal navigating signal, based on the abdominal navigating signals, chest A magnetic resonance imaging apparatus characterized by determining when the body movement of the body is within a certain gate window and controlling imaging. The magnetic resonance imaging apparatus according to claim 2.
The control means measures the predicted time that the chest navigation signal is within the constant gate window from the time when the abdominal navigation signal becomes a constant value, and the chest navigation signal cannot be detected, In the region where the abdominal navigation signal can be detected, imaging is started after the predicted time from the time when the abdominal navigation signal becomes a constant value. The magnetic resonance imaging apparatus according to claim 2 or 3,
The subject is placed, a plurality of imaging area of the subject includes a moving means for sequentially moving to the space,
Said control means, a magnetic resonance imaging apparatus characterized by controlling said moving means to image a wide range of the subject. The magnetic resonance imaging apparatus according to claim 2.
The control means determines whether the value of the abdominal navigation signal is positive within a certain abdominal gate window and the value of the abdominal navigation signal measured immediately before entering the abdominal gate window. A magnetic resonance imaging apparatus characterized in that an imaging start time is determined according to whether it is negative. The magnetic resonance imaging apparatus according to any one of claims 1 to 5,
The magnetic resonance imaging apparatus, wherein the control means generates the navigation signal by a 2D excitation method.

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