JP6554719B2 - Magnetic resonance apparatus and program - Google Patents

Description

  The present invention relates to a magnetic resonance apparatus for obtaining body movement information of a subject and a program applied to the magnetic resonance apparatus.

  In abdominal imaging, an imaging method using a respiratory synchronization method is executed in order to reduce motion artifacts. As an imaging method of the respiratory synchronization method, an imaging method is known in which a navigator region for detecting the movement of the edge of the liver is set at the boundary between the lung and the liver, and navigator echoes are collected (see Patent Document 1). .

JP 2010-155021 A

  In Patent Document 1, a navigator region for setting an excitation region is positioned at a boundary portion between a lung and a liver. Then, a pencil beam type navigator sequence for performing excitation in a cylindrical shape in the navigator region is executed, and navigator echoes are collected from the region excited in the cylindrical shape. Based on the navigator echo, a profile representing the signal intensity of the navigator echo is created, and the movement of the edge of the liver is detected.

However, it is difficult for the pencil beam type navigator sequence to be excited in a cylindrical shape due to the influence of B0 non-uniformity. In practice, the excitation region expands as the distance from the boundary between the lung and the liver increases. Therefore, unnecessary signals of fat existing near the body surface of the subject may be mixed in the navigator echo, and the signal intensity due to the unnecessary signals may appear in the profile. There is a problem that the detection accuracy of the position of the edge of the liver is deteriorated due to the signal intensity due to such an unnecessary signal.
Therefore, a technique capable of improving the detection accuracy of the body movement of the subject is desired.

A first aspect of the present invention is a sequence having a phase encoding gradient magnetic field applied in a first direction and a frequency encoding gradient magnetic field applied in a second direction, and includes a moving part of a subject. A magnetic resonance apparatus that executes a sequence for acquiring MR signals from a scan plane that crosses one region and acquires an image of the scan plane,
Distance calculating means for calculating a distance between the position in the first direction of the isocenter representing the reference point of the gradient magnetic field and the position in the first direction of the moving part;
Data specifying means for specifying data at the position of the moving portion in the first direction from the image of the scan plane based on the position of the isocenter in the first direction and the distance;
Detecting means for detecting a position of the moving portion in the second direction based on the data;
This is a magnetic resonance apparatus.

According to a second aspect of the present invention, there is provided a sequence having a phase encoding gradient magnetic field applied in a first direction and a frequency encoding gradient magnetic field applied in a second direction, which includes a moving part of a subject. A sequence for collecting MR signals from a scan plane crossing one region is executed, and a first signal including frequency and phase information of the MR signal is included in the first signal using a reference signal A magnetic resonance apparatus for performing detection for conversion into a second signal including information of a frequency different from a frequency to be detected,
Distance calculating means for calculating a distance between the position in the first direction of the isocenter representing the reference point of the gradient magnetic field and the position in the first direction of the moving part;
Phase calculating means for calculating the phase of the reference signal based on the distance;
Detection means for performing detection for converting the first signal into the second signal using the reference signal including information on the phase calculated by the phase calculation means;
Image generating means for generating an image of the scan surface based on the second signal;
Data specifying means for specifying data at the position of the moving part in the first direction from the image of the scan surface;
Detecting means for detecting a position of the moving portion in the second direction based on the data;
This is a magnetic resonance apparatus.

A third aspect of the present invention is a sequence having a phase encoding gradient magnetic field applied in a first direction and a frequency encoding gradient magnetic field applied in a second direction, and includes a moving part of a subject. A program that is applied to a magnetic resonance apparatus that executes a sequence for acquiring MR signals from a scan plane that crosses one region and acquires an image of the scan plane,
A distance calculation process for calculating a distance between the position in the first direction of the isocenter representing the reference point of the gradient magnetic field and the position in the first direction of the moving part;
A data specifying process for specifying data at the position of the moving part in the first direction from the image of the scan plane based on the position of the isocenter in the first direction and the distance;
A detection process for detecting a position of the moving part in the second direction based on the data;
Is a program for causing a computer to execute.

A fourth aspect of the present invention is a sequence having a phase encoding gradient magnetic field applied in a first direction and a frequency encoding gradient magnetic field applied in a second direction, and includes a moving part of the subject. A sequence for collecting MR signals from a scan plane crossing one region is executed, and a first signal including frequency and phase information of the MR signal is included in the first signal using a reference signal A program applied to a magnetic resonance apparatus that performs detection for conversion into a second signal including information of a frequency different from the frequency to be detected,
A distance calculation process for calculating a distance between the position in the first direction of the isocenter representing the reference point of the gradient magnetic field and the position in the first direction of the moving part;
A phase calculation process for calculating the phase of the reference signal based on the distance;
A data specifying process for specifying data at the position of the moving part in the first direction from the image of the scan surface;
A detection process for detecting a position of the moving part in the second direction based on the data;
Is a program for causing a computer to execute.

  Data on the position of the moving part in the first direction is specified from the image of the scan plane, and the position of the moving part in the second direction is detected based on this data. Therefore, since it is not necessary to detect a position using a sequence for performing cylindrical excitation, it is possible to improve the detection accuracy of a moving part.

1 is a schematic view of a magnetic resonance apparatus according to a first embodiment of the present invention. It is explanatory drawing of the gradient magnetic field which the gradient coils 23x, 23y, and 23z apply. 3 is a diagram for schematically explaining the structure of a receiver 7. FIG. It is explanatory drawing of the process which the processor 9 performs. It is a figure which shows the scan performed with a 1st form. It is a figure which shows the flow for performing the scan shown in FIG. It is explanatory drawing of the scan of the axial surface performed by a localizer scan. It is explanatory drawing of the scan of the coronal surface performed by a localizer scan. FIG. 3 is a diagram schematically showing an imaging region R. It is explanatory drawing of step ST3. It is explanatory drawing of step ST4. It is explanatory drawing of step ST6. It is explanatory drawing of step ST7. It is a figure which shows schematically the sagittal surface SG which crosses the vertex V of a liver. It is explanatory drawing of the prescan A. FIG. Run the navigator scan A _1, it is a diagram showing a flowchart for determining the position information of the SI direction liver. Is a diagram showing an example of a sequence NS, which is used in the navigator scan A _1. It is explanatory drawing when performing the sequence NS of the 1st time. The sagittal image DS1 acquired by the navigator scan A ₁ is a diagram schematically showing. It is explanatory drawing of the method of specifying the data used in order to obtain | require the positional information on the SI direction of a liver from sagittal image DS1. The time variation of the detected position of SI direction liver edge E when executing each of the navigator scan A ₂ to A _d schematically shows. It is a figure which shows an example of the window W. FIG. 6 is an explanatory diagram of a main scan B. FIG. It is explanatory drawing of the process which the processor in a 2nd form performs. It is a figure which shows the flow for performing scanning in a 2nd form. It is explanatory drawing when performing the sequence NS of the 1st time. The sagittal image DS2 obtained by the navigator scan A ₁ is a diagram schematically showing. It is explanatory drawing of the method of specifying the data used in order to obtain | require the positional information on the SI direction of a liver from sagittal image DS2.

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

(1) First Embodiment FIG. 1 is a schematic view of a magnetic resonance apparatus according to a first 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 reception RF coil (hereinafter referred to as “reception coil”) 4, and the like.

The magnet 2 has a bore 21 in which the subject 13 is accommodated. The magnet 2 includes a superconducting coil 22 for generating a static magnetic field, gradient coils 23x, 23y, and 23z for applying a gradient magnetic field, and an RF coil 24 for transmitting an RF pulse. ing. FIG. 2 is an explanatory diagram of the gradient magnetic field applied by the gradient coils 23x, 23y, and 23z. The gradient coil 23x is a coil that generates a gradient magnetic field applied in the RL direction (left-right direction) of the subject, and the gradient coil 23y generates a gradient magnetic field applied in the AP direction (front-rear direction) of the subject. The gradient coil 23z is a coil that generates a gradient magnetic field applied in the SI direction (head-to-tail direction) of the subject. FIG. 2 also shows an isocenter C that represents the reference point of the gradient magnetic field. Specifically, the isocenter C represents a point where the gradient magnetic field becomes zero when a gradient magnetic field is applied in these three directions. In FIG. 2, the position in the RL direction, the position in the AP direction, and the position in the SI direction of the isocenter C are denoted by reference signs “x _rl ”, “y _ap ”, and “z _si ”, respectively.
Returning to FIG. 1, the description will be continued.

  The table 3 has a cradle 3a. The cradle 3a is configured to be able to move into the bore 21. The subject 13 is transported to the bore 21 by the cradle 3a.

  The receiving coil 4 is attached to the body of the subject 13. The receiving coil 4 receives a magnetic resonance signal from the subject 13.

  The MR apparatus 100 further includes a transmitter 5, a gradient magnetic field power supply 6, a receiver 7, a computer 8, an operation unit 11, a display unit 12, and the like.

  The transmitter 5 supplies current to the RF coil 24, and the gradient magnetic field power source 6 supplies current to the gradient coils 23x, 23y, and 23z. The receiver 7 performs signal processing such as detection on the signal received from the receiving coil 4.

FIG. 3 is a diagram for schematically explaining the structure of the receiver 7.
The receiver 7 includes an AD converter 7a, a detection circuit 7b, a digital filter 7c, and the like. The AD converter 7a converts the analog signal AS output from the receiving coil 4 into a digital signal DH. The detection circuit 7b performs detection for converting the high frequency contained in the digital signal DH into a low frequency using the reference signal S (f, φ). “F” of the reference signal S (f, φ) is a frequency, and “φ” is a phase. The values of f and φ are determined in advance. In an MR apparatus of 1.5T (Tesla), f = 63.86 MHz. By detecting the digital signal DH with the reference signal S (f, φ), the high frequency of the digital signal DH is converted to the low frequency, and thus the digital signal DL including the low frequency information is obtained. The digital filter 7c filters the digital signal DL and outputs a filtered digital signal DL ′. The filtered digital signal DL ′ is output to the computer 8.
Returning to FIG. 1, the description will be continued.

  The computer 8 transmits necessary information to the display unit 12 and reconstructs an image based on a signal received from the receiver 7 so as to realize various operations of the MR apparatus 100. Control the operation of each part. The computer 8 includes a processor 9 and a memory 10.

  FIG. 4 is an explanatory diagram of processing executed by the processor 9. The memory 10 stores a program executed by the processor 9. The processor 9 reads a program stored in the memory 10 and executes processing described in the program. The processor 9 configures an image creating unit 91 to a determining unit 99 by reading a program stored in the memory 10.

The image creating unit 91 creates an image based on the signal received from the receiver.
The center position specifying unit 92 specifies the center position in the AP direction of the in-vivo region of the subject.
The position selection means 93 selects the center position used as the position in the AP direction of the end of the liver from the plurality of center positions specified by the center position specifying means 92.
The distance calculation means 94 calculates a distance Δh (see FIG. 11) described later.
The scan plane setting unit 95 sets a scan plane (sagittal plane) when executing a navigator scan described later.
The data specifying unit 96 specifies data Di (see FIG. 20) at a position y _i described later from the sagittal image.
The detecting means 97 detects the position of the end of the liver in the SI direction based on the data Di.
The window setting means 98 sets a window W (see FIG. 22) described later.
The determination unit 99 determines whether or not to execute an imaging sequence (see FIG. 23) in the main scan.

  The processor 9 is an example constituting the image creating means 91 to the judging means 99, and functions as these means by executing a program stored in the memory 10. A combination of the center position specifying unit 92 and the position selection unit 93 corresponds to a unit for obtaining a position, and a combination of the digital filter 7c and the image generation unit 91 corresponds to an image generation unit.

The operation unit 11 is operated by an operator and inputs various information to the computer 8. The display unit 12 displays various information.
The MR apparatus 100 is configured as described above.

FIG. 5 is a diagram showing a scan executed in the first form.
In the first form, the localizer scan LX, the pre-scan A, and the main scan B are executed.

The localizer scan LX is a scan for acquiring an image used for setting a sagittal surface SG (see FIG. 14) described later. A method for setting the sagittal plane SG will be described later.
The prescan A is a scan for acquiring data necessary for obtaining a window W (see FIG. 22) described later.
The main scan B is a scan for acquiring an image of the imaging region.

  Hereinafter, a procedure for executing the localizer scan LX, the pre-scan A, and the main scan B will be described.

FIG. 6 is a diagram showing a flow for executing the scan shown in FIG.
In step ST1, a localizer scan LX is executed.

7 and 8 are explanatory diagrams of the localizer scan LX.
In the localizer scan LX, scans of a plurality of axial planes AX _{1 to} AX _m crossing a site including the liver (see FIG. 7) and scans of a plurality of coronal planes CO _{1 to} CO _n crossing the site including the liver (see FIG. 8). ) Is executed. Image creating device 91 (see FIG. 4), based on the data collected by the localizer scan LX, the image _DA 1 to DA _m axial planes _AX 1 _{~AX m,} coronal plane _CO 1 to CO _n image DC ₁ of to create a ~DC _n. Hereinafter, the image on the axial plane is referred to as “axial image”, and the image on the coronal plane is referred to as “coronal image”. After the axial images DA _{1 to} DA _m and the coronal images DC _{1 to} DC _n are created, step ST2 and steps ST3 to ST5 are executed. Hereinafter, step ST2 and steps ST3 to ST5 will be described in order.

In step ST2, the operator sets an imaging region in the main scan in step ST10 described later with reference to the axial images DA _{1 to} DA _m and coronal images DC _{1 to} DC _n . FIG. 9 schematically shows the set imaging region R. In the first embodiment, since the liver is photographed, the liver is included in the photographing region R.
Next, steps ST3 to ST5 will be described.

FIG. 10 is an explanatory diagram of step ST3.
In step ST3, based on the axial images DA _{1 to} DA _m , a process for determining the position of the end E on the lung side of the liver in the AP direction is executed. Hereinafter, a method of obtaining the position of the end E on the lung side of the liver in the AP direction will be described with reference to FIG.

The center position specifying means 92 (see FIG. 4) first specifies the center position y ₁ in the AP direction of the in-vivo region of the subject within the axial plane AX ₁ based on the axial image DA ₁ . When specifying the center position y ₁ in the AP direction of the in-vivo region of the subject, the center position specifying unit 92 first specifies the AP direction range T ₁ of the in-vivo region of the subject based on the axial image DA _1. . Although the extracorporeal area of the subject is low signal, the body area of the subject because a high signal, the difference in signal value, can be determined range T ₁ of the AP direction in the body area of the subject. After obtaining the range T ₁ in the AP direction of the in-vivo region of the subject, the center position specifying unit 92 determines the AP in the in-vivo region of the subject in the axial plane AX ₁ based on the range T ₁ in the AP direction of the in-vivo region. identifying a center position y ₁ direction.

Similarly, for other axial images DA _{2 to} DA _m , the range T2 to Tm in the AP direction of the in-vivo region of the subject is specified, and the center position y in the AP direction of the in-vivo region is determined based on the range T2 to Tm. seek ₂ ~y _m. Thus, each axial image _DA 1 to DA _m, it is possible to obtain the center position _y 1 ~y _m of the AP direction of the body region.

After determining the center position y ₁ ~y _m, obtains the AP position of the liver lung side of the end portion E. In general, the position in the AP direction of the end E on the lung side of the liver can be considered to be close to the center position in the AP direction of the in-vivo region of the subject. Accordingly, each of the center positions y ₁ ~y _m can be considered close to the AP position of the liver edge E. Therefore, the position selection means 93 (see FIG. 4) is one of the center position from the center position y ₁ ~y _m, selected as AP position of the liver edge E. In this embodiment, the position selection means 93 specifies the central value (median) from the center position y ₁ ~y _m, select a specified center position, as AP position of the liver edge E as the median To do. Here, it is assumed that the center position y _i obtained from the axial image DA _i is a median (median). Accordingly, the center position y _i is selected as the position of the end E of the liver in the AP direction. After obtaining the position y _i in the AP direction of the end E of the liver, the process proceeds to step ST4.

FIG. 11 is an explanatory diagram of step ST4.
In step ST4, the distance calculation means 94 (see FIG. 4) calculates the distance Δh between the position y _{i in} the AP direction of the end E of the liver obtained in step ST3 and the position y _{ap in} the AP direction of the isocenter C. To do. Δh is expressed by the following equation.
Δh = y _ap −y _i (1)

Since the position y _{ap in} the AP direction of the isocenter C is determined for each MR apparatus, it is known. Further, the position y _{i in} the AP direction of the end E of the liver is known in step ST3 and thus known. Therefore, the distance Δh can be calculated by using Expression (1). When Δh> 0, it means that y _i is located on the P side with respect to y _ap , and when Δh <0, y _i is located on the A side with respect to y _ap . It means that In addition, when Δh = 0, it means that y _i matches y _ap . After calculating the distance Δh, the process proceeds to step ST5.

  In step ST5, the scan plane setting means 95 (see FIG. 4) sets a sagittal plane SG (see FIG. 14) to be described later based on the image obtained by the localizer scan. The sagittal plane is a plane used as a scan plane (excitation plane) when navigator scan is executed in pre-scan and main scan described later. Hereinafter, step ST5 will be described. Since step ST5 includes steps ST6 and ST7, steps ST6 and ST7 will be described in order.

FIG. 12 is an explanatory diagram of step ST6.
In step ST6, the scan plane setting means 95 selects the coronal image closest to the position y _i in the AP direction of the end E of the liver from the coronal images DC _{1 to} DC _n . In FIG. 12, it is assumed that the coronal image DC _i is the closest to the position y _i in the AP direction of the end E of the liver among the coronal images DC _{1 to} DC _n . Accordingly, the scan plane setting unit 95 selects the coronal image DC _i . After selecting the coronal image DC _i, the process proceeds to step ST7.

FIG. 13 is an explanatory diagram of step ST7.
In step ST7, the scan plane setting unit 95 is, from the coronal image DC _i, determining the point for positioning the sagittal plane SG (see FIG. 14) described later. Hereinafter, a method for determining this point will be briefly described.

The scan plane setting unit 95 detects the vertex V of the liver closest to the position z ₀ in the SI direction from the coronal image DC _i and determines this vertex V as a point for positioning the sagittal plane SG. The lungs are affected by air and have a lower signal value than the liver. Therefore, based on the difference between the lung signal value and the liver signal value, the vertex V of the liver closest to the position z ₀ in the SI direction can be detected from the coronal image DC _i . A specific example of the detection method is described in the document "Examination of Navigator Tracker positioning in MRI liver scan, Takao Goto, Hiroyuki Serizawa, Japanese Society for Medical Imaging, 32nd Annual Meeting, OP4-9 (2013)". The method can be used. Position of the RL direction of the vertex V of the liver is represented by x _V, the position of the SI direction of the vertex V is represented by z _V. By determining the vertex V, a sagittal plane across the vertex V can be set. FIG. 14 schematically shows a sagittal plane SG crossing the vertex V of the liver. FIG. 14A is a perspective view of the sagittal surface SG, and FIG. 14B is a view of the sagittal surface SG viewed from the RL direction. The sagittal plane SG is set so as to cross both the liver and lung organs. This sagittal surface SG is used as a scan surface (excitation surface) when navigator scan is executed in pre-scan and main scan described later.
After performing Step ST2 to Step ST5, the process proceeds to Step ST8.

In step ST8, prescan A is executed (see FIG. 15).
FIG. 15 is an explanatory diagram of prescan A. FIG.
In prescan A, navigator scan A ₁ to A _d for acquiring an image of a sagittal plane SG is executed sequentially. The image of the sagittal plane SG is used to obtain position information in the SI direction of the liver. The following describes the navigator scan _A 1 to A _d. Note that the configuration of the navigator scan _A 1 to A _d is the same, in the following, among the navigator scan _A 1 to A _d, taken up navigator scan _{A 1} on behalf liver by executing the navigator scan _{A 1} A method for obtaining position information in the SI direction will be described.

Figure 16 executes the navigator scan A _1, is a diagram showing a flowchart for determining the position information of the SI direction liver.
In step ST11, the navigator scan _{A 1} is executed. Figure 17 shows an example of a sequence NS, which is used in the navigator scan A _1. Figure 17 is an example of a sequence NS, which is used in the navigator scan A _1, but the sequence of gradient echo system is shown, such as a sequence of spin echo system, may be other sequences. The repetition time of the sequence NS is represented by TR. The sequence NS has a slice selection gradient magnetic field applied in the slice selection direction, a phase encode gradient magnetic field applied in the phase direction, and a frequency encode gradient magnetic field applied in the frequency direction. The slice selection direction is set to the RL direction, the phase direction is set to the AP direction, and the frequency direction is set to the SI direction. The number of phase encodings of the sequence NS is n. Therefore, during the navigator scan A1, the _first to n-th sequence NS is executed while changing the phase encoding n times. Since the repetition time of the sequence NS is TR, the time length LT navigator scan A ₁ is expressed by the following equation.
LT = n × TR (2)

In navigator scan _{A 1,} first, first sequence NS is executed. FIG. 18 is an explanatory diagram when the first sequence NS is executed. By executing the first sequence NS, the MR signal H is generated from the sagittal plane SG (see FIG. 17). This MR signal H is received by the receiving coil 4. The MR signal H received by the receiving coil 4 is supplied to the receiver 7 as an analog signal AS. The receiver 7 converts the analog signal AS into a digital signal DH by the AD converter 7a. The digital signal DH includes frequency and phase information W of the MR signal H. The digital signal DH is supplied to the detection circuit 7b. The detection circuit 7b performs detection for converting the high frequency contained in the digital signal DH into a low frequency using the reference signal S (f, φ). By detecting the digital signal DH with the reference signal S (f, φ), the high frequency of the digital signal DH is converted to the low frequency, and thus the digital signal DL including the low frequency information is obtained. The digital signal DL is filtered by the digital filter 7 c, and the filtered digital signal DL ′ is output to the computer 8.

  Similarly, the magnitude of the phase encoding gradient magnetic field is changed, and the second to n-th sequence NS is executed. Therefore, each time the sequence NS is executed, a filtered digital signal DL ′ is obtained.

Image creating unit 91 based on the digital signal DL' obtained from each of the first ~n th sequence NS at navigator scan A _1, creating an image of a sagittal plane SG (hereinafter referred to as "sagittal image") to To do. Figure 19 shows a sagittal image DS1 acquired by the navigator scan A ₁ schematically. As will be described later, the sagittal image DS1 is not used as a medical diagnosis image, but is used to detect the position of the liver in the SI direction. Therefore, since the sagittal image DS1 does not need to have high quality, the value of the phase encoding number n of the sequence NS does not need to be set to a very large value. For example, n = 8 and n = 16. Since the repetition time TR is, for example, TR = 5 ms, when n = 8, the time length LT of the navigator scan A1 is LT = 8 × 5 = 40 ms from Equation (2). Therefore, the sagittal image DS1 can be acquired in a short time. After obtaining the sagittal image DS1, the process proceeds to step ST12.

  In step ST12, the data specifying means 96 (see FIG. 4) specifies data used for obtaining position information in the SI direction of the liver from the sagittal image DS1 (see FIG. 20).

FIG. 20 is an explanatory diagram of a method for specifying data used for obtaining position information in the SI direction of the liver from the sagittal image DS1.
Data specifying unit 96, first, from the range _y 0 ~y _p of the AP direction of the sagittal image DS1, identifies the AP direction position _{y i} of the liver edge E. In this embodiment, the distance Δh is calculated in step ST4 executed previously. Further, the position y _{ap in} the AP direction of the isocenter C is a known value. Therefore, y _i can be specified by substituting Δh and y _ap into equation (1). The data specifying unit 96 specifies the data Di at the position y _i from the sagittal image DS1. The profile of the data Di specified by the data specifying means 96 is schematically shown on the lower side of FIG. The horizontal axis of the profile of the data Di represents the position in the SI direction, and the vertical axis of the profile of the data Di represents the signal intensity. This data Di is used as data for obtaining position information in the SI direction of the liver. After specifying the data Di, the process proceeds to step ST13.

In step ST13, the detecting means 97 (see FIG. 4) detects the position of the end E of the liver in the SI direction based on the specified data Di. Since the area on the lung side of the data Di is affected by air, the signal intensity is lower in the area on the lung side of the data Di than in the area of the liver. Therefore, a position z ₁ where the signal intensity changes abruptly appears in the data Di. Detection means 97, the position z _1, is detected as the position of the SI direction liver edge E. In this embodiment, the position z ₁ is obtained as position information in the SI direction of the liver.

Similarly, even when executing each of the remaining navigator scan A ₂ to A _d, the flow shown in FIG 16 is executed. Therefore, it is possible to detect the SI position of the end portion E of the liver when executing each of the navigator scan A ₂ to A _d. Figure 21 shows the time change of the detected position of SI direction liver edge E when executing each of the navigator scan A ₂ to A _d schematically.
Therefore, the respiratory signal S _res of the subject can be obtained while the pre-scan A is being executed.
After executing the pre-scan A, the process proceeds to step ST9 (see FIG. 6).

In step ST9, the window setting means 98 (see FIG. 4) sets the window W based on the respiratory signal S _res . FIG. 22 shows an example of the window W. The window W represents a range used when determining whether or not to execute the imaging sequences DAQ _{1 to} DAQ _z (see FIG. 23) in the main scan B. Hereinafter, an example of a method for setting the window W will be briefly described.

The window setting means 98 obtains the position Pb in the SI direction of the end E of the liver when the subject _finishes exhaling from the respiration signal S _res . While the subject exhales, the end E of the liver moves in the S direction, but when the subject starts to inhale, the end E of the liver starts to move in the I direction. Therefore, by detecting the maximum value of the position in the SI direction of the end E of the liver, the position Pb in the SI direction of the end E of the liver when the subject finishes exhaling can be obtained. After obtaining the position Pb, the window setting means 98 sets a certain range as the window W with respect to this position Pb. How the window W is used when executing the main scan B will be described later. After setting the window W, the process proceeds to step ST10.

In step ST10, the main scan B is executed (see FIG. 23).
FIG. 23 is an explanatory diagram of the main scan B.
In the main scan B, a plurality of navigator scans and one imaging sequence are executed alternately. Hereinafter, the main scan B will be described. The navigator scan used in the main scan B is the same as the navigator scan used in the prescan A. The imaging sequence may be a 2D imaging sequence or a 3D imaging sequence.

In the main scan B, first, navigator scans A _{d + 1 to} A _e are executed. Each time each of the navigator scans A _{d + 1 to} A _e is executed, the position of the end E of the liver in the SI direction is detected according to the flow shown in FIG. In FIG. 23, the positions in the SI direction of the end E of the liver detected by executing the navigator scans A _{d + 1 to} A _e are denoted by symbols “z _{d + 1} ”, “z _{d + 2} ”,... “Z _e ”. It is shown.

The determination means 99 (see FIG. 4) determines whether or not the detected position of the end E of the liver is in the window W every time the navigator scans A _{d + 1 to} A _e are executed. Then, when the detected position of the end E of the liver enters the inside of the window W from the outside of the window W, the imaging sequence DAQ ₁ for collecting data of the imaging region R (see FIG. 9) is executed. .

In FIG. 23, in the navigator scans A _{d + 1 to} A _e−1 , the position of the end E of the liver is outside the window W, but the position of the end E of the liver enters the inside of the window W in the navigator scan A _e . . Therefore, immediately after the navigator scan _Ae is executed, the imaging sequence DAQ ₁ is executed.

After executing the imaging sequence DAQ _1, it executes the navigator scan _{A e} + 1 ~A _f, to detect the position of the liver edge E. Then, when the position of the end E of the liver enters the inside of the window W from the outside of the window W, the next imaging sequence DAQ ₂ for collecting the data of the imaging region R is executed. In FIG. 23, in navigator scans A _{e + 2 to} A _f−1 , the detection position of the end E of the liver is outside the window W, but the detection position of the end E of the liver in the navigator scan A _f is inside the window W. Get in. Thus, immediately after a navigator scan _{A f,} the imaging sequence DAQ ₂ is executed.

Thereafter, the navigator scan is similarly executed, and when the detection position of the end E of the liver enters the window W, an imaging sequence for collecting data of the imaging region R (see FIG. 9) is executed. When the last imaging sequence DAQ _z is executed, the main scan B is terminated and the flow is terminated.

In the first form, the distance Δh between the position y _ap of the isocenter C in the AP direction and the position y _i of the end E of the liver in the AP direction is obtained (see FIG. 11). Further, the detected (see FIG. 13) the vertex V of the liver from the coronal image DC _i obtained by the localizer scan to set the sagittal plane SG (scan surface) across the vertex V of the liver (see Fig. 14). And sagittal image DS1 is acquired by performing a navigator scan (refer FIG. 19). After acquiring the sagittal image DS1, data Di at the position y _i in the AP direction of the end E of the liver is specified from the sagittal image DS1 based on the distance Δh (see FIG. 20). Since the data Di represents data of a portion that crosses the liver and the lung, the position of the end E of the liver in the SI direction can be detected based on the data Di. In the first mode, in the navigator scan, a sequence NS (see FIG. 17) for performing sagittal surface excitation is executed instead of a sequence for performing cylindrical excitation. In general, a sequence for performing cylindrical excitation is easily influenced by B0 non-uniformity, so that the excitation region is spread over a wide range, and an unnecessary signal such as a fat signal is likely to be mixed into the MR signal. Therefore, when data for detecting the position of the liver in the SI direction is acquired using a sequence that performs cylindrical excitation, the waveform of the data is disturbed due to an unnecessary signal such as a fat signal, and the end of the liver This may cause the position to be erroneously detected. On the other hand, in the first embodiment, since the sequence NS that performs (sagittal) surface excitation instead of column excitation is used, it is difficult to be affected by B0 nonuniformity. Therefore, the waveform Di is small and data Di suitable for detecting the position of the end of the liver can be obtained.

(2) Second embodiment The MR device of the second embodiment is different from the MR device of the first embodiment in the processing executed by the processor, but the other configurations are the same as those of the MR device of the first embodiment. is there. Accordingly, a processor will be mainly described for the MR apparatus of the second embodiment.

FIG. 24 is an explanatory diagram of processing executed by the processor according to the second embodiment.
In the second embodiment, the processor 9 includes a phase calculation unit 991 in addition to the image creation unit 91 to the determination unit 99. Since the image creating means 91 to the judging means 99 are the same as those in the first embodiment, description thereof will be omitted. The phase calculating unit 991 calculates the phase of the reference signal based on the distance Δh.

The processor 9 is an example constituting the image creating means 91 to the phase calculating means 991 and functions as these means by executing a program stored in the memory 10.
Next, a scan executed in the second form will be described.

In the second mode, as in the first mode, the localizer scan LX, the pre-scan A, and the main scan B are executed. In the pre-scan A, navigator scans A _{1 to} A _d (see FIG. 17) are executed, and in the main scan B, a plurality of navigator scans and imaging sequences are executed alternately (see FIG. 23). The procedure for executing the localizer scan LX, the pre-scan A, and the main scan B in the second embodiment will be described below.

FIG. 25 is a diagram showing a flow for executing a scan in the second embodiment.
Steps ST1 to ST5 are the same as those in the first embodiment, and a description thereof will be omitted. After setting the sagittal plane SG (scan plane) in step ST5 (see FIG. 14), the process proceeds to step ST70.

In step ST70, the phase calculation means 991 (see FIG. 24) calculates the phase φk (see FIG. 26) of the reference signal used for detection in pre-scan A and main scan B described later. φk is used when detecting a digital signal obtained by the k-th (k = 1 to n) sequence of the first to n-th sequence NS (see FIG. 17) executed in each navigator scan. Represents the phase of the reference signal. In the second mode, the value of the phase φk is determined so that detection is performed with reference to the phase of the MR signal at the position y _i in the AP direction of the end E of the liver. The phase φk can be determined using the following equation.

φk = −γG _k ΔhΔt (3)
Here, γ: magnetic rotation ratio Gk: magnitude of phase encode gradient magnetic field of k-th sequence NS Δh: distance obtained in step ST4 Δt: application time of phase encode gradient magnetic field

Since γ, Gk, Δh, and Δt in equation (3) are known, the phase φk of the reference signal can be calculated by substituting these values into equation (3).
After obtaining the phase φk, the process proceeds to step ST8.

  In step ST8, pre-scan A is executed (see FIG. 17). Hereinafter, the pre-scan A will be described. Note that the pre-scan A in the second embodiment will be described with reference to the flow of FIG. 16 as in the first embodiment.

In step ST11, the navigator scan _{A 1} is executed.
In navigator scan _{A 1,} first, first sequence NS is executed. FIG. 26 is an explanatory diagram when the first sequence NS is executed. By executing the first sequence NS, the MR signal H is generated from the sagittal plane SG (see FIG. 14). This MR signal H is received by the receiving coil 4. The MR signal H received by the receiving coil 4 is supplied to the receiver 7 as an analog signal AS. The receiver 7 converts the analog signal AS into a digital signal DH by the AD converter 7a. The digital signal DH includes frequency and phase information W of the MR signal H. The digital signal DH is supplied to the detection circuit 7b. The detection circuit 7b performs detection for converting the high frequency included in the digital signal DH into a low frequency using the reference signal S (f, φk). The phase φk is set to a value calculated by the phase calculation means 991 using the equation (3). FIG. 26 shows an example in which the detection of the digital signal DH obtained by the first sequence NS is shown, so k = 1. Therefore, from equation (3), φk = φ1 = −γG ₁ ΔhΔt.

  The detection circuit 7b performs detection for converting the high frequency included in the digital signal DH into a low frequency using the reference signal S (f, φ1). By detecting the digital signal DH with the reference signal S (f, φ1), the high frequency of the digital signal DH is converted to the low frequency, and thus the digital signal DL including the low frequency information is obtained. The digital signal DL is filtered by the digital filter 7 c, and the filtered digital signal DL ′ is output to the computer 8.

After executing the first sequence NS, the magnitude of the phase encode gradient magnetic field of the sequence NS is changed, and the second sequence NS is executed. When the second sequence NS is executed, the phase φk of the reference signal is set to a value obtained by substituting k = 2 into k in Equation (3), that is, φk = φ2 = −γG ₂ ΔhΔt. Detection is performed. Similarly, the magnitude of the phase encode gradient magnetic field is changed, and the third to nth nasequence NS is executed. When the third to n-th nasequence NS is executed, the detection circuit performs detection using the reference signals (f, φ3) to S (f, φn). Therefore, each time the sequence NS is executed, detection is performed while adjusting the phase φk of the reference signal, and a filtered digital signal DL ′ is obtained.

Image creating device 91 (see FIG. 24) based on the digital signal DL' obtained from each of the first ~n th sequence NS at navigator scan A _1, to create a sagittal image. Figure 27 shows a sagittal image DS2 obtained by the navigator scan A ₁ schematically. In the second mode, the phase φk of the reference signal is set so that detection is performed with reference to the phase of the MR signal at the position y _i in the AP direction (phase direction) of the end E of the liver. Therefore, in the sagittal image DS2, the position y _i in the AP direction (phase direction) of the end E of the liver can be matched with the position y _ap in the AP direction (phase direction) of the isocenter. After obtaining the sagittal image DS2, the process proceeds to step ST12.

  In step ST12, the data specifying means 96 (see FIG. 24) specifies data used for obtaining position information in the SI direction of the liver from the sagittal image DS2 (see FIG. 28).

FIG. 28 is an explanatory diagram of a method for identifying data used for obtaining position information in the SI direction of the liver from the sagittal image DS2.
Data specifying unit 96, first, from the AP direction range _y 0 ~y _p sagittal image DS2, identifies the AP direction position _{y i} of the liver edge E. In the second form, in the sagittal image DS2, the position y _{i in} the AP direction of the end E of the liver coincides with the position y _ap in the AP direction of the isocenter. Therefore, the position y _i in the AP direction of the end E of the liver can be identified from the position information in the AP direction of the isocenter. After specifying the position y _i , the data specifying unit 96 specifies the data Di at the position y _i from the sagittal image DS2. FIG. 28 shows the identified data Di. After specifying the data Di, the process proceeds to step ST13.

In step ST13, the position of the end E of the liver in the SI direction is detected based on the specified data Di. The method for detecting the position of the end E of the liver in the SI direction is the same as in the first embodiment. Therefore, from the data Di, it is possible to detect the position z ₁ of the SI direction liver edge E.

After executing the navigator scan A1, the remaining navigator scans A _{2 to} A _f are executed. When each of the remaining navigator scans A _{2 to} A _f is executed, the flow shown in FIG. 16 is executed, and the position of the end E of the liver in the SI direction when each of the navigator scans A _{2 to} A _f is executed. Is detected. Therefore, as shown in FIG. 21, a respiratory signal S _res can be obtained.

  After performing the pre-scan A, the process proceeds to step ST9 (see FIG. 25), the window W is set, the main scan is executed in step ST10, and the flow ends.

In the second embodiment, based on the distance Δh, the phase φk of the reference signal is calculated so that detection is performed with reference to the phase of the MR signal at the position y _i in the AP direction of the end E of the liver. . Therefore, in the sagittal image DS2, the position y _{i in} the AP direction (phase direction) of the end E of the liver coincides with the position y _ap in the AP direction (phase direction) of the isocenter. Thus, the position y _i in the AP direction of the end E of the liver can be specified. After identifying the position y _i, from the sagittal image DS2, by identifying data Di at the position y _i, from the data Di, it is possible to detect the position z ₁ of the SI direction liver edge E.

  Further, in the second embodiment, as in the first embodiment, since the sequence NS that performs (sagittal) surface excitation is used instead of the sequence that performs column excitation, there is little waveform disturbance and the end of the liver Data Di suitable for the position detection can be obtained.

  In the first and second embodiments, the sagittal plane SG is set as the scan plane. However, in the present invention, the scan plane is not limited to the sagittal plane, and a plane different from the sagittal plane (for example, a coronal plane, an axial plane, or an oblique plane) can be set as the scan plane.

2 Magnet 3 Table 3a Cradle 4 Reception coil 5 Transmitter 6 Gradient magnetic field power supply 7 Receiver 8 Computer 9 Processor 10 Memory 11 Operation unit 12 Display unit 13 Subject 21 Bore 91 Image creation means 92 Center position specifying means 93 Position selection means 94 Distance calculating means 95 Setting means 96 Data specifying means 97 Detection means 98 Window setting means 99 Determination means 100 MR apparatus

Claims (15)

A sequence having a phase encoding gradient magnetic field applied in a first direction and a frequency encoding gradient magnetic field applied in a second direction, and MR from a scan plane that traverses the first part including the moving part of the subject A magnetic resonance apparatus that executes a sequence for collecting signals and acquires an image of the scan surface,
Means for determining the position of the moving part in the first direction based on a plurality of first images obtained by performing a scan of a plurality of first cross sections across the first part;
Distance calculating means for calculating a distance between the position in the first direction of the isocenter representing the reference point of the gradient magnetic field and the position in the first direction of the moving part;
Data specifying means for specifying data at the position of the moving portion in the first direction from the image of the scan plane based on the position of the isocenter in the first direction and the distance;
Detecting means for detecting a position of the moving portion in the second direction based on the data;
A magnetic resonance apparatus.   The magnetic resonance apparatus according to claim 1, wherein a sequence for collecting MR signals from the scan plane is executed. Converting a first signal including frequency and phase information of the MR signal into a second signal including information of a frequency different from the frequency included in the first signal by using a reference signal; A detection means for performing detection;
Image generating means for generating an image of the scan surface based on the second signal;
The magnetic resonance apparatus according to claim 2, comprising: A sequence having a phase encoding gradient magnetic field applied in a first direction and a frequency encoding gradient magnetic field applied in a second direction, and MR from a scan plane that traverses the first part including the moving part of the subject A sequence for collecting signals is executed, and a first signal including frequency and phase information of the MR signal is used as a reference signal and a frequency information different from the frequency included in the first signal is used. A magnetic resonance apparatus that performs detection for conversion into a second signal including:
Means for determining the position of the moving part in the first direction based on a plurality of first images obtained by performing a scan of a plurality of first cross sections across the first part;
Distance calculating means for calculating a distance between the position in the first direction of the isocenter representing the reference point of the gradient magnetic field and the position in the first direction of the moving part;
Phase calculating means for calculating the phase of the reference signal based on the distance;
Detection means for performing detection for converting the first signal into the second signal using the reference signal including information on the phase calculated by the phase calculation means;
Image generating means for generating an image of the scan surface based on the second signal;
Data specifying means for specifying data at the position of the moving part in the first direction from the image of the scan surface;
Detecting means for detecting a position of the moving portion in the second direction based on the data;
A magnetic resonance apparatus. Run the sequence multiple times so that the magnitude of the phase encoding gradient field is changed,
The detection means includes
Converting the first signal obtained for each sequence into the second signal;
The image generating means includes
5. The magnetic resonance apparatus according to claim 3, wherein an image of the scan plane is generated based on the second signal obtained for each sequence. 6. The means for determining the position is:
Based on the plurality of first images, for each of the first cross sections, obtain a range in the first direction of the in-vivo region of the subject,
Based on the range, for each of the first cross sections, to determine the center position of the body region of the subject in the first direction,
The first on the basis of the center position determined for each section, determining the position of the first direction of the moving parts, a magnetic resonance device according to any one of claims 1 to 5. The magnetic resonance apparatus according to claim 6 , wherein the first cross section is an axial plane. Having a scan plane setting means for setting the scan plane, the magnetic resonance apparatus according to any one of claims 1 to 7. The scan plane setting means includes
A second image closest to the position of the moving part in the first direction out of the plurality of second images obtained by performing a scan of a plurality of second cross sections crossing the first region; Select
The magnetic resonance apparatus according to claim 8 , wherein a point for positioning the scan plane is obtained from the selected second image. The magnetic resonance apparatus according to claim 9 , wherein the second cross section is a coronal surface. The image generating means includes
Filter means for filtering the second signal;
An image creating means for creating an image of the scan surface based on the filtered second signal;
The magnetic resonance apparatus according to claim 1 , comprising: The magnetic resonance apparatus according to claim 11 , wherein the first signal and the second signal are digital signals. The first direction is AP direction, the second direction is a SI direction, the magnetic resonance apparatus according to any one of claims 1 to 12. A sequence having a phase encoding gradient magnetic field applied in a first direction and a frequency encoding gradient magnetic field applied in a second direction, and MR from a scan plane that traverses the first part including the moving part of the subject A program applied to a magnetic resonance apparatus that executes a sequence for collecting signals and acquires an image of the scan surface,
Processing for determining the position of the moving portion in the first direction based on a plurality of first images obtained by performing a scan of a plurality of first cross sections across the first region;
A distance calculation process for calculating a distance between the position in the first direction of the isocenter representing the reference point of the gradient magnetic field and the position in the first direction of the moving part;
A data specifying process for specifying data at the position of the moving part in the first direction from the image of the scan plane based on the position of the isocenter in the first direction and the distance;
A detection process for detecting a position of the moving part in the second direction based on the data;
A program that causes a computer to execute. A sequence having a phase encoding gradient magnetic field applied in a first direction and a frequency encoding gradient magnetic field applied in a second direction, and MR from a scan plane that traverses the first part including the moving part of the subject A sequence for collecting signals is executed, and a first signal including frequency and phase information of the MR signal is used as a reference signal and a frequency information different from the frequency included in the first signal is used. A program applied to a magnetic resonance apparatus that performs detection for conversion into a second signal including:
Processing for determining the position of the moving portion in the first direction based on a plurality of first images obtained by performing a scan of a plurality of first cross sections across the first region;
A distance calculation process for calculating a distance between the position in the first direction of the isocenter representing the reference point of the gradient magnetic field and the position in the first direction of the moving part;
A phase calculation process for calculating the phase of the reference signal based on the distance;
A data specifying process for specifying data at the position of the moving part in the first direction from the image of the scan surface;
A detection process for detecting a position of the moving part in the second direction based on the data;
A program that causes a computer to execute.

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