JP6004924B2 - Magnetic resonance apparatus and program - Google Patents

Description

  The present invention relates to a magnetic resonance apparatus for imaging a subject and a program applied to the magnetic resonance apparatus.

  As a method for imaging a subject by the respiratory synchronization method, a method using a bellows and a method for collecting navigator echoes are known (see Patent Document 1).

JP 2011-036428 A

  However, in the method using the bellows, there is a problem that the imaging technician needs to wind the bellows around the abdomen of the subject, which is troublesome. In addition, the method of collecting navigator echoes requires the experience of a radiographer, and depending on the radiographic region, respiration may not be measured.

  Therefore, a method of laying a sheet with a plurality of pressure sensors built under the subject can be considered. Since the subject moves with the respiratory motion of the subject, the pressure signal detected by the pressure sensor of the seat changes with time. Therefore, it is possible to obtain respiratory information of the subject from the pressure signal detected by the pressure sensor. In addition, since such a sheet may be laid under the subject, it is possible to obtain the breathing information of the subject without taking time and effort like a bellows. However, since the gradient coil vibrates while scanning the subject, the pressure signal of the pressure sensor includes a frequency component due to the vibration of the gradient coil in addition to the frequency component due to the respiratory motion of the subject. Therefore, in order to obtain the respiratory signal of the subject, it is necessary to remove the frequency component due to the vibration of the gradient coil from the pressure signal. Therefore, it is conceivable to remove the frequency component due to the vibration of the gradient coil from the pressure signal by using a filter for removing the frequency component due to the vibration of the gradient coil. However, the frequency component due to the vibration of the gradient coil differs depending on the scanning conditions (for example, the magnitude of the gradient magnetic field applied when the pulse sequence is executed and the application time). Therefore, even if a filter that can remove only a certain frequency range is used, the frequency component due to the vibration of the gradient coil may not be removed depending on the scan condition of the subject. For this reason, there is a demand for a method that can remove the frequency component due to the vibration of the gradient coil from the pressure signal even when the frequency component due to the vibration of the gradient coil changes depending on the scanning condition or the like.

A first aspect of the present invention is a magnetic resonance apparatus for imaging a subject,
A sheet installed under the subject, the sheet having a pressure sensor for detecting the pressure that the sheet receives from the subject;
Scanning means for executing a first scan for applying a gradient magnetic field using a gradient coil, and executing a second scan for applying a gradient magnetic field using the gradient coil after the first scan When,
A signal processing unit that receives a first signal output from the sheet while the first scan is being executed, and a second signal output from the sheet while the second scan is being executed. And having
The signal processing unit
A filter that creates a filter for reducing the frequency component due to the vibration of the gradient coil included in the second signal based on the frequency component due to the vibration of the gradient coil included in the first signal. A magnetic resonance apparatus having a creating means.

A second aspect of the present invention is a sheet installed under a subject, the sheet having a pressure sensor for detecting the pressure that the sheet receives from the subject, and a gradient magnetic field using a gradient coil Scanning means for executing a first scan for applying a gradient magnetic field, and a second scan for applying a gradient magnetic field using the gradient coil after the first scan, and the first scan A signal processing unit that receives the first signal output from the pressure sensor while the second scan is being performed and the second signal output from the pressure sensor while the second scan is being performed. A program for a magnetic resonance apparatus,
A filter that creates a filter for reducing the frequency component due to the vibration of the gradient coil included in the second signal based on the frequency component due to the vibration of the gradient coil included in the first signal. A program for causing a computer to execute a creation process.

  Based on the first signal, a filter for reducing the frequency component due to the vibration of the gradient coil included in the second signal is created. Therefore, the frequency component due to the vibration of the gradient coil can be removed from the second signal.

It is the schematic of the magnetic resonance apparatus of one form of this invention. It is explanatory drawing of the internal structure of the body movement detection sheet | seat 5. FIG. It is a figure which shows the scan performed when image | photographing a subject. It is a figure which shows an example of the pulse sequence PSD performed by prescan PS1 and this scan MS1. It is a figure which shows the flow when performing the scan of FIG. It is a figure which shows a mode when a subject is carried into a bore. It is a figure which shows roughly the pressure signal obtained by step ST2. It is a figure which shows roughly the pressure signal obtained by step ST3. It is an explanatory diagram for creating a gradient coil 22x from the pressure signal by the pressure sensor P _pq outputs, 22y, a filter for removing frequency components caused by vibration of 22z. It is an explanatory diagram for creating a gradient coil 22x from a pressure signal by the pressure sensor P ₁₁ outputs, 22y, a filter for removing frequency components caused by vibration of 22z. It is an explanatory diagram for creating a gradient coil 22x from a pressure signal by the pressure sensor P _mn outputs, 22y, a filter for removing frequency components caused by vibration of 22z. It is a diagram showing the pressure signal _C 11 _{-C mn} detected before starting the main scan MS1. It is a figure which shows the pressure signal after a pulse sequence is started. It is a diagram illustrating an example of when sampling the pressure signal _C 11 _{-C mn} based on the pulse sequence PSD. It is a figure which shows the example which repeatedly performs the combination of a pre scan and a main scan.

  Hereinafter, although the form for inventing is demonstrated, this invention is not limited to the following forms.

FIG. 1 is a schematic view of a magnetic resonance apparatus according to one embodiment of the present invention.
A magnetic resonance apparatus (hereinafter referred to as “MR apparatus”, MR: Magnetic Resonance) 100 includes a magnet 2, a table 3, a receiving coil 4, and the like.

  The magnet 2 has a bore 21 in which the subject 12 is accommodated. Further, the magnet 2 incorporates gradient coils 22x, 22y, 22z and the like for applying a gradient magnetic field. The gradient coil 22x applies a gradient magnetic field in the x-axis direction, the gradient coil 22y applies a gradient magnetic field in the y-axis direction, and the gradient coil 22z applies a gradient magnetic field in the z-axis direction.

  The table 3 has a cradle 3 a that supports the subject 12. The cradle 3a is configured to be able to move into the bore 21. The subject 12 is transported to the bore 21 by the cradle 3a.

  The reception coil 4 is attached to the abdomen of the subject 12. The receiving coil 4 receives a magnetic resonance signal from the subject 12.

  A body movement detection sheet 5 is installed between the subject 12 and the cradle 3a. The subject 12 lies on the body movement detection sheet 5.

FIG. 2 is an explanatory diagram of the internal structure of the body movement detection sheet 5.
The body motion detection sheet 5 includes a plurality of pressure sensors P _{11 to} P _mn for detecting the pressure received by the sheet 5 from the subject 12. The pressure sensors P _{11 to} P _mn are arranged in m rows and n columns. In this embodiment, body movement due to breathing of the subject is detected using the body movement detection sheet 5. A method for detecting body movement due to breathing of the subject using the body movement detection sheet 5 will be described later.
Returning to FIG. 1, the description will be continued.

  The MR apparatus 100 further includes a transmitter 6, a gradient magnetic field power supply 7, a receiver 8, a control unit 9, an operation unit 10, a display unit 11, and the like.

The transmitter 6 supplies current to an RF coil (not shown), and the gradient magnetic field power supply 7 supplies current to the gradient coils 22x, 22y, and 22z.
The receiver 8 performs signal processing such as detection on the signal received from the receiving coil 4.
A combination of the magnet 2, the receiving coil 4, the transmitter 6, the gradient magnetic field power source 7, and the receiver 8 corresponds to the scanning means.

  The control unit 9 transmits necessary information to the display unit 11 and reconstructs an image based on the data received from the receiver 8 so as to realize various operations of the MR apparatus 100. Control the operation of each part. The control unit 9 includes filter creation means 91 to trigger generation means 94 and the like.

The filter creation unit 91 creates a filter for reducing the frequency component due to the vibration of the gradient coil included in the pressure signal.
The filter unit 92 uses the filter created by the filter creation unit 91 to execute a filter process for reducing the frequency component due to the vibration of the gradient coil included in the pressure signal.
The signal generator 93 generates a respiration signal based on the filtered pressure signal.
The trigger generation means 94 generates a trigger for starting a pulse sequence based on the respiratory signal.

  The control unit 9 corresponds to a signal processing unit. Moreover, the control part 9 is an example which comprises each of the filter preparation means 91-trigger generation means 94, and functions as these means by executing a predetermined program.

The operation unit 10 is operated by an operator and inputs various information to the control unit 9. The display unit 11 displays various information.
The MR apparatus 100 is configured as described above.
Next, a method for detecting body movement due to breathing of the subject using the body movement detection sheet 5 will be described.

FIG. 3 is a diagram illustrating a scan executed when imaging a subject.
In this embodiment, pre-scan PS1 and main scan MS1 are executed. The pre-scan PS1 is a scan that is executed to acquire vibration information of the gradient coils 22x, 22y, and 22z. The main scan MS1 is a scan for acquiring image data of an imaging region (a liver in this embodiment) of the subject. In this embodiment, the same pulse sequence is executed in the pre-scan PS1 and the main scan MS1. FIG. 4 shows an example of a pulse sequence PSD executed in the pre-scan PS1 and the main scan MS1. The number of steps N of the phase encoding gradient magnetic field of the pulse sequence PSD is, for example, N = 64.

FIG. 5 is a diagram showing a flow when the scan of FIG. 3 is executed.
In step ST1, the subject is carried into the bore (see FIG. 6).

FIG. 6 is a diagram showing a state when the subject is carried into the bore.
In this embodiment, since the imaging region of the subject is the liver, the cradle 3a moves so that the subject's liver is located at the center of the isocenter. In this way, the subject is carried into the bore. After carrying the subject into the bore, the process proceeds to step ST2.

In step ST2, pressure signals are acquired from the pressure sensors P _{11 to} P _mn of the body motion detection sheet 5 before executing the pre-scan PS1.

FIG. 7 is a diagram schematically showing the pressure signal obtained in step ST2. In FIG. 7, only pressure sensors P ₁₁ , P _pq , and P _mn are representatively shown among the pressure sensors P _{11 to} P _mn for convenience of explanation.

The subject moves by the breathing motion of the subject. From a certain pressure sensor (for example, pressure sensor P _pq ), a pressure signal (for example, pressure signal A _pq ) reflecting the respiratory motion of the subject can be obtained. On the other hand, from another pressure sensor (for example, pressure sensors P ₁₁ and P _mn ), a pressure signal (for example, pressure signals A ₁₁ and A _mn ) that is not significantly affected by the subject's respiratory motion can be obtained. After obtaining a pressure signal from each pressure sensor, the process proceeds to step ST3.

In step ST3, pressure signals are acquired by the pressure sensors P _{11 to} P _mn of the body movement detection sheet 5 while executing the pre-scan PS1 (see FIG. 8).

FIG. 8 is a diagram schematically showing the pressure signal obtained in step ST3.
In step ST3, pre-scan PS1 is executed. In the pre-scan PS1, since a gradient magnetic field is applied, vibrations of the gradient coils 22x, 22y, and 22z are generated. Therefore, the pressure signals B ₁₁ , B _pq , and B _mn include frequency components due to vibrations of the gradient coils 22x, 22y, and 22z.

In FIG. 8, only the pressure signals B ₁₁ , B _pq and B _mn obtained from the pressure sensors P ₁₁ , P _pq and P _mn are shown, but the pressure signals obtained from other pressure sensors are also shown. , Frequency components due to vibration of the gradient coils 22x, 22y, and 22z are included. After the pressure signal is acquired while executing the pre-scan PS1, the process proceeds to step ST4.

  In step ST4, the filter creating means 91 (see FIG. 1) calculates the gradient coil 22x from the pressure signal output from each pressure sensor based on the pressure signal obtained in step ST2 and the pressure signal obtained in step ST3. , 22y, and 22z to create a filter for removing frequency components.

In the following, for convenience of description, among the pressure sensors _P 11 _{to P mn,} representatively, by taking the pressure sensor _{P 11, P pq,} and _{P mn,} will be described an example of creating a filter, the other The filter of the pressure sensor can be created in the same way.

FIG. 9 is an explanatory diagram for creating a filter for removing frequency components due to vibrations of the gradient coils 22x, 22y, and 22z from the pressure signal output from the pressure sensor P _pq .
The filter creation means 91 first obtains the frequency component included in the pressure signal A _pq obtained in step ST2 and the frequency component included in the pressure signal B _pq obtained in step ST3. Hereinafter, the frequency component included in the pressure signal A _pq and the frequency component included in the pressure signal B _pq will be described in order.

(1) Frequency components included in the pressure signal A _{pq The} pressure detected by the pressure sensor P _pq changes under the influence of the respiratory motion of the subject. Accordingly, the pressure signal A _pq includes a frequency component ω1 due to the respiratory motion of the subject. However, since the pressure signal A _pq is acquired before the pre-scan PS1 is executed, the pressure signal A _pq does not include the frequency component ω2 due to the vibration of the gradient coils 22x, 22y, and 22z.

(2) On the other hand for the frequency components included in the pressure signal B _pq, the pressure signal B _pq is acquired while the prescan PS1 is running. Therefore, the pressure signal B _pq includes a frequency component ω2 due to the vibration of the gradient coils 22x, 22y, and 22z in addition to the frequency component ω1 due to the respiratory motion of the subject.

As described above, the main frequency component of the pressure signal A _pq is the frequency component ω1 due to the respiratory motion of the subject. Therefore, the frequency component ω1 due to the respiratory motion of the subject can be obtained from the information on the frequency component of the pressure signal A _pq . On the other hand, the main frequency component of the pressure signal _{B pq} is the frequency component ω1 by respiratory motion of the subject, gradient coils 22x, 22y, since the frequency components ω2 due to vibration of 22z, the pressure signal _{B pq,} two The frequency components ω1 and ω2 are mixed. However, since the frequency component ω1 due to the respiratory motion of the subject can be obtained from the information on the frequency component of the pressure signal A _pq, the two frequency components ω1 and ω2 included in the pressure signal B _pq can be separated. it can. Based on the two frequency components ω1 and ω2, the filter creation unit 91 creates a filter F _pq that passes the frequency component ω1 but removes the frequency component ω2.

  The frequency component ω1 due to the respiratory motion is a low frequency of about 0.25 Hz, while the frequency component ω2 due to the vibration of the gradient coils 22x, 22y, and 22z is a high frequency of about 2 kHz. Separation of ω2 can be easily performed.

Figure 10 is an explanatory diagram for creating a gradient coil 22x from a pressure signal by the pressure sensor P ₁₁ outputs, 22y, a filter for removing frequency components caused by vibration of 22z.

Filter creation unit 91 first obtains a frequency component included in the pressure signal A ₁₁ obtained in step ST2, the a frequency component contained in the pressure signal B ₁₁ obtained at step ST3. Hereinafter, the frequency component included in the pressure signal A _11, the frequency component included in the pressure signal B _11, will be described in order.

(1) pressure measured by the pressure sensor P ₁₁ for the frequency component contained in the pressure signal A ₁₁ is detected, little affected by respiratory motion of the subject. Therefore, the main frequency component of the pressure signal A _11, the noise is the frequency component ω3 due. The pressure signal _{A 11} is because it is acquired before the prescan PS1 is executed, the pressure signal _{A 11} is gradient coil 22x, 22y, frequency components ω2 due to vibration of the 22z is not included.

On the other hand the frequency components included in (2) pressure signals B _11, the pressure signal B ₁₁ is acquired during the prescan PS1 is running. Accordingly, the pressure signal _{B 11,} such as the other frequency components ω3 due to noise, the gradient coil 22x, 22y, frequency components ω2 due to vibration of the 22z also included.

Thus, by comparing the frequency component of the pressure signal A ₁₁ and the pressure signals B _11, and the frequency band of the frequency components ω3 such as noise, gradient coil 22x, 22y, and a frequency band of the frequency components ω2 due to vibration of the 22z Can be sought. Filter creation unit 91 based on the two frequency components .omega.2 and [omega] 3, but to pass the frequency component [omega] 3, to create a filter F ₁₁ for removing frequency components .omega.2.

Figure 11 is an explanatory diagram for creating a pressure signal the pressure sensor P _mn outputs gradient coil 22x, 22y, a filter for removing frequency components caused by vibration of 22z.

The pressure sensor P _mn is hardly influenced by the respiratory motion of the subject, like the pressure sensor P ₁₁ . Therefore, the frequency components of the pressure signals A _mn and B _mn can be considered in the same manner as the frequency components of the pressure signals A ₁₁ and B ₁₁ (see FIG. 10). Based on the two frequency components ω2 and ω3, the filter creation means 91 creates a filter F _mn that passes the frequency component ω3 but removes the frequency component ω2.

In the above description, the filter _{F 11} of the pressure sensor _{P 11,} filter _{F pq} of the pressure sensor _{P pq,} and has been described for filter _{F mn} of the pressure sensor _{P mn,} for other pressure sensor, similar in a way A filter is created. After creating each filter of the pressure sensors P _{11 to} P _mn , the process proceeds to step ST5.

In step ST5, the main scan MS1 is executed. The procedure for executing the main scan MS1 will be described below.
First, detection of a pressure signal is started before starting the main scan MS1 (see FIG. 12).

FIG. 12 is a diagram illustrating pressure signals C _{11 to} C _mn detected before starting the main scan MS1.
Before the start of the main scan MS1, the gradient coils 22x, 22y, and 22z do not vibrate. Therefore, before the start of the main scan MS1, the pressure signals C _{11 to} C _mn do not include frequency components due to vibrations of the gradient coils 22x, 22y, and 22z.

The pressure signals C _{11 to} C _mn are input to the filter means 92 (see FIG. 1). The filter means 92 filters the pressure signals C _{11 to} C _mn using the filters F _{11 to} F _mn created in step ST4. Specifically, the filters F _{11 to} F _mn respectively sample the pressure signals C _{11 to} C _mn at a predetermined sampling period, and remove frequency components due to vibrations of the gradient coils 22x, 22y, and 22z based on the sampling data. To perform filtering. As a filtering method, for example, an n-point moving average method is used. Incidentally, before the start of the scan MS1 is the pressure signal _C 11 _{-C mn,} gradient coil 22x, 22y, the frequency components caused by vibration of 22z is not included, the pressure signal _C 11 of the filtered '-C _mn ′ can be represented by a waveform substantially the same as the pressure signals C _{11 to} C _mn before filtering.

The signal generating means 93 (see FIG. 1) generates a respiration signal D based on the filtered pressure signals C ₁₁ ′ to C _mn ′. As a method for generating the respiration signal D, for example, there is a method of averaging the pressure signals C ₁₁ ′ to C _mn ′. Alternatively, the pressure signals C ₁₁ ′ to C _mn ′ may be weighted, and a respiratory signal may be generated based on the weighted pressure signal. As a weighting method, for example, there is a method in which the amplitudes of the pressure signals C ₁₁ ′ to C _mn ′ are compared, the pressure signal having a large amplitude is increased in weight, and the pressure signal having a small amplitude is decreased in weight.

  Next, the trigger generation means 94 (see FIG. 1) generates a trigger TG1 for starting the main scan MS1 based on the respiratory signal D. In the present embodiment, a reference range for generating a trigger is determined in advance, and when the respiratory signal D exceeds the reference range and then enters the reference range again, a trigger TG1 for starting the main scan MS1 is set. Occur. The reference range can be defined based on the minimum value of the respiratory signal D, for example. When the trigger TG1 is generated, the pulse sequence PSD is started.

FIG. 13 is a diagram illustrating the pressure signal after the pulse sequence is started.
When the pulse sequence PSD is executed, vibrations of the gradient coils 22x, 22y, and 22z are generated. Accordingly, the pressure signals C _{11 to} C _mn include frequency components due to vibrations of the gradient coils 22x, 22y, and 22z.

The pressure signals C _{11 to} C _mn are input to the filter means 92. The filters F _{11 to} F _mn of the filter unit 92 sample the pressure signals C _{11 to} C _mn at a predetermined sampling period, respectively, and remove frequency components due to vibrations of the gradient coils 22x, 22y, and 22z based on the sampling data. Filter processing is performed. Therefore, possible from the pressure signal _C 11 _{-C mn,} gradient coil 22x, 22y, is to remove the frequency components caused by vibration of 22z.
Note that when sampling the pressure signals C _{11 to} C _mn , information on the pulse sequence may be referred to (see FIG. 14).

FIG. 14 is a diagram illustrating an example when the pressure signals C _{11 to} C _mn are sampled based on the pulse sequence PSD. In the following, for convenience of explanation, the sampling method will be described by taking up the pressure signal C _pq output from the pressure sensor P _pq , but sampling of other pressure signals can also be performed by the same method.

  The repetition time TR of the pulse sequence PSD can be divided into a period a in which the pulse sequence is executed and a period b in which the pulse sequence is not executed. Therefore, only the data in the period b during which the pulse sequence is not executed may be sampled and the filtering process may be performed. By sampling only the data in the period b in which the pulse sequence is not executed, the filtering process can be performed using the sampling data when the influence of the vibration of the gradient coils 22x, 22y, and 22z is small.

  Further, the sampling frequency may be defined so that the number of samplings is as small as possible during the period a during which the pulse sequence is executed, and the number of samplings is as large as possible during the period b during which the pulse sequence is not executed.

Returning to FIG.
The signal generation means 93 generates a respiration signal D based on the filtered pressure signals C ₁₁ ′ to C _mn ′. The trigger generation means 94 checks whether or not the respiration signal D is within the reference range at the time t2 when the repetition time TR has elapsed from the trigger TG1. In FIG. 13, the trigger signal TG2 is generated because the respiration signal D is within the reference range at time t2. Therefore, the pulse sequence is executed in synchronization with the trigger TG2.

  Similarly, the trigger generation means 94 confirms whether or not the respiration signal D is within the reference range, and determines whether or not to generate a trigger. When necessary data is collected, the flow is terminated.

In this embodiment, the pre-scan PS1 is executed before the main scan MS1, and a pressure signal including a frequency component due to the vibration of the gradient coil is acquired during the execution of the pre-scan PS1. Then, and (see FIGS. 9 to 11) for creating a filter F ₁₁ to F _mn for removing frequency components due to the vibration of the gradient coil based on the pressure signal obtained when the pre-scan PS1. Therefore, since the filters F _{11 to} F _mn are created based on the pressure signal when the gradient coil is actually oscillating, a filter suitable for removing the frequency component due to the gradient coil oscillation is created. Can do.

  Further, in this embodiment, the body movement due to the respiration of the subject 12 can be detected simply by placing the body movement detection sheet 5 on the cradle 3 a and laying the subject 12 on the body movement detection sheet 5. Therefore, since the body motion detection sheet 5 does not need to be attached around the abdomen of the subject 12 like bellows or puffs, the burden on the operator can be reduced.

  In this embodiment, when the pre-scan PS1 is executed, the phase encoding gradient magnetic field of the pulse sequence PSD is changed by the number of steps N as in the main scan MS1. Accordingly, vibration close to that of the gradient coil generated in the main scan MS1 can be reproduced by the pre-scan PS1, so that a high-performance filter can be created. However, when the phase encode gradient magnetic field does not significantly affect the frequency component due to the vibration of the gradient coils 22x, 22y, and 22z, the number of steps of the phase encode gradient magnetic field of the pulse sequence PSD is made smaller than N in the pre-scan PS1. Also good. By making the number of steps of the phase encoding gradient magnetic field of the pulse sequence PSD less than N, the number of repetitions of the pulse sequence PSD in the prescan PS1 can be reduced, so that the scan time of the prescan PS1 can be shortened. For example, if a pre-scan PS1 that repeats the pulse sequence PSD only during the respiratory cycle T (for example, T = 4 seconds) of the subject is executed and a pressure signal is acquired during the respiratory cycle T, the pressure signal includes The frequency component information f1 due to the respiratory motion of the specimen and the frequency component information f2 due to the vibration of the gradient coil should be included. Therefore, theoretically, it is possible to shorten the scan time of the pre-scan PS1 to the respiratory cycle T (about 4 seconds) of the subject. If the pressure signal can include the information f1 and f2 of the above two frequency components, when executing the pre-scan PS1, a fixed value (for example, phase encoding) is used without changing the phase encoding gradient magnetic field. The gradient magnetic field may be set to zero).

In this embodiment, a filter is created for each pressure sensor. However, one filter may be created for a plurality of pressure sensors. For example, even if the pressure signals are output from different pressure sensors, if the frequency components included in these pressure signals are considered to be almost the same, these pressure signals may be filtered by a common filter. . For example, pressure sensors (for example, pressure sensors P ₁₁ and P _mn ) arranged at positions that are not easily affected by the subject's respiratory motion output pressure signals including substantially the same frequency components. The pressure signal output from the sensor may be filtered with a common filter.

  In this embodiment, an example in which the pre-scan PS1 and the main scan MS1 are executed is described (see FIG. 3). However, the combination of the pre-scan and the main scan may be repeatedly executed. FIG. 15 shows an example in which the combination of the pre-scan and the main scan is repeatedly executed. FIG. 15 shows an example in which z combinations of pre-scans and main scans are executed. The pre-scan PSi (i = 1 to z) is a scan executed for creating a filter in the main scan MSi. As described above, by executing the pre-scan for each main scan, it is possible to create a filter suitable for each main scan even if the gradient oscillation modes are different between the main scans MS1 to MSz. When the vibration modes of the gradient coils of the main scans MS1 to MSz are the same, only the prescan PS1 needs to be executed.

  Further, the filter F1 is calculated from the vibration of any one of the gradient coils 22x, 22y, and 22z, and the filters F2 and F3 of the other two gradient coils are estimated from the filter F1. F1 to F3 may be synthesized.

  The structure of the body motion detection sheet 5 is not limited to this embodiment, and various modifications can be made. For example, the pressure sensor may be provided so as to spread radially. Further, the shape of the pressure sensor may be a line or a spiral. Further, the pressure sensor may be configured using a fluid.

2 Magnet 3 Table 3a Cradle 4 Reception coil 5 Body motion detection sheet 6 Transmitter 7 Gradient magnetic field power supply 8 Receiver 9 Control unit 10 Operation unit 11 Display unit 12 Subject 21 Bore 22x, 22y, 22z Gradient coil 91 Filter creation means 92 Filter means 93 Signal generation means 94 Trigger generation means 100 MR apparatus

Claims (11)

A magnetic resonance apparatus for imaging a subject,
A sheet installed under the subject, the sheet having a pressure sensor for detecting the pressure that the sheet receives from the subject;
Scanning means for executing a first scan for applying a gradient magnetic field using a gradient coil, and executing a second scan for applying a gradient magnetic field using the gradient coil after the first scan When,
A signal for receiving a first signal output from the pressure sensor while the first scan is being executed and a second signal output from the pressure sensor while the second scan is being executed. A processing unit,
The signal processing unit
A filter that creates a filter for reducing the frequency component due to the vibration of the gradient coil included in the second signal based on the frequency component due to the vibration of the gradient coil included in the first signal. A magnetic resonance apparatus having a creating means. The filter creating means includes
2. The magnetism according to claim 1, wherein a frequency component due to body movement of the subject and a frequency component due to vibration of the gradient coil are obtained from the first signal, and the filter is created based on these frequency components. Resonator. The filter creating means includes
Based on the frequency component of the third signal output from the pressure sensor while the gradient magnetic field is not applied, the frequency component due to the body movement of the subject and the vibration of the gradient coil are derived from the first signal. The magnetic resonance apparatus according to claim 2, wherein a frequency component is obtained. The signal processing unit
Filter means for reducing a frequency component caused by vibration of the gradient coil included in the second signal using the filter;
Signal generating means for generating a body motion signal representing the body motion of the subject based on the second signal after being filtered by the filter means;
The magnetic resonance apparatus according to claim 1, comprising: The seat has a plurality of pressure sensors;
Each of the plurality of pressure sensors is
5. The magnetic resonance according to claim 4, wherein the first signal is output while the first scan is being executed, and the second signal is output while the second scan is being executed. apparatus. The filter means includes
Receiving a plurality of second signals, reducing a frequency component caused by vibration of the gradient coil included in each of the plurality of second signals;
The signal generating means includes
The magnetic resonance apparatus according to claim 5, wherein a body motion signal representing a body motion of the subject is generated based on the plurality of second signals after being filtered by the filter unit. The filter means includes
The magnetic resonance apparatus according to claim 4, wherein data of the second signal is sampled while a gradient magnetic field is not applied.   The magnetic resonance apparatus according to claim 4, wherein the body motion signal is a respiratory signal. The scanning means includes
The number of steps of the phase encoding gradient magnetic field of the pulse sequence executed in the first scan is the same as the number of steps of the phase encoding gradient magnetic field of the pulse sequence executed in the second scan. The magnetic resonance apparatus as described in any one of these. The scanning means includes
The number of steps of the phase encoding gradient magnetic field of the pulse sequence executed in the first scan is smaller than the number of steps of the phase encoding gradient magnetic field of the pulse sequence executed in the second scan. The magnetic resonance apparatus as described in any one of them. A sheet placed under a subject, the sheet having a pressure sensor for detecting the pressure received by the sheet from the subject, and a first scan for applying a gradient magnetic field using a gradient coil And, after the first scan, a scanning means for performing a second scan for applying a gradient magnetic field using the gradient coil, and the pressure while the first scan is being performed. A program of a magnetic resonance apparatus having a signal processing unit that receives a first signal output from a sensor and a second signal output from the pressure sensor while the second scan is being executed,
A filter that creates a filter for reducing the frequency component due to the vibration of the gradient coil included in the second signal based on the frequency component due to the vibration of the gradient coil included in the first signal. A program that causes a computer to execute creation processing.

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