JP5932393B2 - Magnetic resonance apparatus and program - Google Patents

Description

  The present invention relates to a magnetic resonance apparatus that executes a sequence for collecting data of an imaging region of a subject in synchronization with a respiratory signal of the subject, and a program for the magnetic resonance apparatus.

  As a method for imaging a part of the body that moves due to respiration, such as the liver, a respiratory synchronization imaging method using a navigator echo is known (see, for example, Patent Document 1).

JP 2011-036428 A

As an example of the respiratory synchronization imaging method, there is a method of generating image data by generating a respiratory synchronization trigger based on a respiratory signal. FIG. 21 shows an example of a method for generating a respiratory synchronization trigger. First, the reference level P _ref of the respiratory signal is set. The reference level P _ref is set, for example, at a position when the subject finishes exhaling. Then, the window width W is set with respect to the reference level _Pref . The position determined by the window width W is a trigger level used when determining whether or not to generate a trigger. When scanning the subject, a respiratory signal is acquired by the navigator sequence NAV, and a trigger is generated when the respiratory signal returns to the trigger level TL again after exceeding the trigger level TL. When the trigger occurs, a data collection sequence for collecting data is executed. Therefore, data can be acquired in synchronization with the respiratory signal of the subject.

  In the above method, the window width W is set in advance by the operator before scanning. However, since the value of the amplitude D of the respiratory signal varies depending on the subject, the window width W preset by the operator may be too wide or too narrow with respect to the amplitude D of the respiratory signal. In this case, the operator needs to change the value of the window width W during scanning, which increases the work load on the operator. Therefore, it is desired to reduce the work burden on the operator.

A first aspect of the present invention is a magnetic resonance apparatus that executes a sequence for collecting data of an imaging region of a subject in synchronization with a respiratory signal of the subject,
It is a magnetic resonance apparatus which has a trigger level setting means which sets the trigger level used when judging whether to generate the trigger for performing the sequence based on the amplitude of the respiration signal.

According to a second aspect of the present invention, there is provided a program for a magnetic resonance apparatus that executes a sequence for collecting data of an imaging region of the subject in synchronization with a respiratory signal of the subject,
A trigger level setting process for setting a trigger level used when determining whether to generate a trigger for executing the sequence based on the amplitude of the respiratory signal;
Is a program for causing a computer to execute.

  Since the trigger level is set based on the amplitude of the respiratory signal, a trigger level suitable for the amplitude of the respiratory signal can be set.

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 sequence performed with this form. It is a figure which shows an imaging | photography site | part schematically. It is explanatory drawing of the prescan A. FIG. 6 is an explanatory diagram of a main scan B. FIG. 3 is a diagram showing an operation flow of the MR apparatus 100. FIG. It is a figure which shows schematically the respiratory signal S obtained by the prescan A. FIG. FIG. 4 is a diagram illustrating an example of a reference level P _ref of a respiratory signal S. It is explanatory drawing of the setting method of a trigger level. 6 is an explanatory diagram of a main scan B. FIG. It is explanatory drawing of the scan in a 2nd form. It is explanatory drawing of simulation conditions. It is a figure which shows a simulation result. It is a figure which shows the simulation result of the trigger TG generate | occur | produced when the trigger level TL of window coefficient F = 0.9 is set with respect to the respiration signal. It is a figure which shows the simulation result of the trigger TG generate | occur | produced when the trigger level TL of window coefficient F = 0.6 is set with respect to the respiration signal. It is a figure which shows the operation | movement flow of the MR apparatus in a 3rd form. Is a diagram showing an example of pulse sequence IM has a plurality of preparation pulses _PR 1 to PR _m. It is a figure which shows roughly an example of the trigger level TL when the window coefficient F is small. It is a figure which shows a mode when a trigger stops generating when the subject fell asleep during the scan. It is a figure which shows a mode when a respiration signal has shifted _| deviated largely from the reference level _Pref . It is a figure which shows an example of the method of generating a respiration synchronous trigger.

  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 receiving coil 4, and the like.

  The magnet 2 has a bore 21 in which the subject 12 is accommodated, a superconducting coil 22, a gradient coil 23, a transmission coil 24, and the like. The superconducting coil 22 applies a static magnetic field, the gradient coil 23 applies a gradient magnetic field, and the transmission coil 24 transmits an RF pulse. In place of the superconducting coil 22, a permanent magnet may be used.

The table 3 has a cradle 3 a for supporting the subject 12. As the cradle 3a moves to the bore 21, the subject 12 is carried into the bore.
The receiving coil 4 is attached to the subject 12 and receives a magnetic resonance signal.

  The MR apparatus 100 further includes a sequencer 5, a transmitter 6, a gradient magnetic field power supply 7, a receiver 8, a control unit 9, an operation unit 10, and a display unit 11.

Under the control of the control unit 9, the sequencer 5 sends information for executing the pulse sequence to the transmitter 6 and the gradient magnetic field power supply 7.
The transmitter 6 supplies a current to the RF coil 24.
The gradient magnetic field power supply 7 supplies a current to the gradient coil 23.
The receiver 8 processes the magnetic resonance signal received by the receiving coil 4 and outputs it to the control unit 9.

  The control unit 9 transmits necessary information to the sequencer 5 and the display unit 11 and reconstructs an image based on data received from the receiver 8 so as to realize various operations of the MR apparatus 100. The operation of each part of the MR apparatus 100 is controlled. The control unit 9 is configured by, for example, a computer. The control unit 9 includes window coefficient setting means 91 to trigger generation means 94 and the like.

The window coefficient setting means 91 sets a window coefficient F (see formula (1) described later).
The reference level setting unit 92 sets the reference level of the respiratory signal of the subject.
The trigger level setting unit 93 sets a trigger level TL (see, for example, FIG. 9).
The trigger generation means 94 generates triggers TG _{1 to} TG _n (for example, see FIG. 10).

  The control unit 9 is an example that constitutes the window coefficient setting unit 91 to the trigger generation unit 94, and functions as these units 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.

FIG. 2 is an explanatory diagram of a sequence executed in this embodiment, and FIG. 3 is a diagram schematically showing an imaging region.
In this embodiment, pre-scan A and main scan B are executed.

  The prescan A is a scan for acquiring a respiratory signal including respiratory information of the subject, and the main scan M is a sequence for collecting image data from a site including an organ such as a liver or a kidney. Hereinafter, the pre-scan A and the main scan B will be described in order.

FIG. 4 is an explanatory diagram of the pre-scan A.
In prescan A, a navigator sequence NAV for detecting the position of the subject's diaphragm in the SI direction (see FIG. 3) is repeatedly executed. Since the diaphragm moves due to the breathing of the subject, the respiratory signal S of the subject can be obtained by repeatedly executing the navigator sequence NAV. In this embodiment, the trigger level TL is set based on the respiratory signal S acquired by the prescan A. The trigger level TL is used when determining whether or not to generate triggers TG _{1 to} TG _n for executing the data acquisition sequences AQ _{1 to} AQ _n (see FIG. 5) of the main scan B. . A method for obtaining the trigger level TL will be described in detail later. After executing pre-scan A, main scan B is executed.

FIG. 5 is an explanatory diagram of the main scan B.
In the main scan B, data collection sequences AQ _{1 to} AQ _n for collecting image data from a part including the liver and kidney are executed. In addition to the data collection sequences AQ _{1 to} AQ _n , a navigator sequence NAV is executed. The navigator sequence NAV is executed once or more immediately before each data collection sequence AQ _{1 to} AQ _n .

In the main scan B, the navigator sequence NAV is executed to acquire a respiratory signal. After the respiration signal exceeds a trigger level TL, when moved to the lower side of the trigger level TL again generates a trigger TG ₁ for performing data acquisition sequence AQ _1. When the trigger TG ₁ is generated, the data collection sequence AQ ₁ is executed.

After executing the data acquisition sequence AQ _1, again executes the navigator sequence NAV, When the next trigger TG ₂ is generated, executes a data acquisition sequence AQ _2. Similarly, the navigator sequence NAV is executed, and when a trigger occurs, the data collection sequence is executed. When the last data collection sequence AQ _n is executed, the main scan B is terminated.

  In this embodiment, a trigger level TL suitable for the respiratory characteristics of the subject can be set based on the respiratory signal S obtained by the prescan A. Hereinafter, this reason will be described with reference to FIGS.

FIG. 6 is a diagram showing an operation flow of the MR apparatus 100.
In step ST1, prescan A is executed. In the prescan A, a navigator sequence NAV for detecting the position of the diaphragm of the subject is executed. Therefore, the respiration signal S of the subject can be obtained by executing the prescan A. FIG. 7 schematically shows the respiratory signal S obtained by the pre-scan A. After performing the pre-scan A, the process proceeds to step ST2.

In step ST2, the reference level setting means 92 (see FIG. 1) sets the reference level P _ref of the respiration signal S based on the respiration signal S obtained by the prescan A. FIG. 8 shows an example of the reference level P _ref of the respiratory signal S. FIG. 8 shows a case where the position when the subject has finished breathing is set as the reference level P _ref of the respiratory signal S. After setting the reference level P _ref , the process proceeds to step ST3.

In step ST3, the trigger level setting means 93 (see FIG. 1) sets the trigger level. The trigger level is used when determining whether or not to generate a trigger for executing the data acquisition sequences AQ _{1 to} AQ _n of the main scan B. A method for setting the trigger level will be described below.

FIG. 9 is an explanatory diagram of a trigger level setting method.
First, the window width W for setting the trigger level TL is calculated. The window width W is calculated based on the amplitude D of the respiratory signal S. Specifically, it is calculated by the following formula.
W = D × F (1)
Where W: Window width
D: Amplitude of respiratory signal S
F: Window coefficient

  The window coefficient F is a value set in advance before executing the pre-scan A, and is a value set from the range of 0 <F <1. In this embodiment, before executing the pre-scan A, the operator operates the operation unit 10 (see FIG. 1) and inputs information indicating the value of the window coefficient F (for example, F = 0.5). When this information is input, the window coefficient setting unit 91 (see FIG. 1) sets the window coefficient F based on the information input from the operation unit 10. Therefore, the window coefficient F is a known value.

The amplitude D of the respiratory signal S can be obtained from the difference between the maximum value and the minimum value of the respiratory signal S. Therefore, the window width W can be obtained from the equation (1). The trigger level setting means 93 (see FIG. 1) calculates the window width W by substituting the amplitude D of the respiratory signal S and the window coefficient F into Expression (1). After calculating the window width W, a position separated from the reference level P _ref by the window width W is set as the trigger level TL. After setting the trigger level TL, the process proceeds to step ST4.

In step ST4, the main scan B is executed.
In the main scan B, as shown in FIG. 10, a navigator sequence NAV is executed to acquire a respiratory signal. Then, after the respiratory signal exceeds the trigger level TL, the trigger generation means 94 (see FIG. 1) triggers the trigger TG ₁ to execute the data collection sequence AQ ₁ when it moves again below the trigger level TL. Is generated. When the trigger TG ₁ is generated, the data collection sequence AQ ₁ is executed.

After executing the data acquisition sequence AQ _1, run again navigator sequence NAV, performs data acquisition sequence AQ ₂ When the next trigger TG ₂ is generated. Similarly, the navigator sequence NAV is executed, and when a trigger occurs, the data collection sequence is executed. Then, when the last data collection sequence AQ _n is executed, the flow ends.

In the first embodiment, since the trigger level TL is set based on the amplitude of the respiratory signal acquired in the pre-scan A, the trigger level TL is set too low with respect to the amplitude of the respiratory signal of the subject. It can be prevented from being too high. Therefore, it is not necessary for the operator to perform operations such as correcting the trigger level TL during scanning, and the operator's workload can be reduced. Also, by setting the trigger level TL based on the amplitude of the respiratory signal, the data collection sequences AQ _{1 to} AQ _n can be executed when the respiratory signal S is close to the reference level P _ref , so that the body motion artifact is A reduced high quality image can also be obtained.

In the first embodiment, the reference level P _ref is set to a position when the subject has finished exhaling. In general, when photographing the liver, body movement artifacts are reduced when photographing at the end of exhalation than when photographing at the end of breathing. Therefore, a higher quality image can be obtained by setting the position when the subject has exhaled as the reference level _Pref . However, if an image with sufficient quality can be obtained, the reference level P _ref may be set, for example, at a position when the subject has finished breathing, or while the subject is breathing in. It may be set at a position (while exhaling).

  In the first embodiment, the pre-scan A includes only the navigator sequence NAV. However, the pre-scan A may include a data collection sequence in addition to the navigator sequence NAV.

  In the first embodiment, the window width W is determined by the window coefficient F input by the operator. Therefore, depending on the value of the window coefficient F input by the operator, the window width W may be too wide or too narrow. If the window width W is too wide or too narrow, a trigger may not be generated or data may not be collected at an optimal timing. Therefore, an upper limit value and a lower limit value may be provided for the window width W so that the window width W is not too wide or too narrow (for example, the upper limit value of the window width W is 20 mm, the lower limit value is 2 mm, etc.).

(2) Second Embodiment FIG. 11 is an explanatory diagram of scanning in the second embodiment.
Also in the second mode, the pre-scan A and the main scan B are executed as in the first mode.

Since the prescan A is the same as the first embodiment, the description thereof is omitted.
In the main scan B, pulse sequences IM _{1 to} IM _n are executed. The pulse sequences IM _{1 to} IM _n have a preparation pulse PR and a data acquisition sequence AQ for collecting data from the subject. After preparation pulse PR is transmitted, when the waiting time T _W has elapsed, the data acquisition sequence AQ is executed. The preparation pulse PR is, for example, a 90 ° pulse and an inversion pulse. In addition, the navigator sequence NAV is executed once or more before each of the pulse sequences IM _{1 to} IM _n is executed. The hardware configuration of the MR apparatus is the same as that in the first embodiment.

  Next, the operation flow of the MR apparatus in the second embodiment will be described with reference to FIG.

  Steps ST1 to ST3 are the same as those in the first embodiment, and thus description thereof is omitted. After setting the trigger level TL, the process proceeds to step ST4.

In step ST4, the main scan B is executed.
In the main scan B, as shown in FIG. 11, the navigator sequence NAV is executed to acquire a respiratory signal. After the respiration signal exceeds a trigger level TL, when moved to the lower side of the trigger level TL again generates a trigger TG ₁ for executing a pulse sequence IM _1. When the trigger TG ₁ is generated, the preparation pulse PR of the pulse sequence IM ₁ is transmitted. After preparation pulse PR is transmitted, when the waiting time T _W has elapsed, the data acquisition sequence AQ is executed.

After executing the pulse sequence IM _1, run again navigator sequence NAV, preparation pulse PR pulse sequence IM ₂ When trigger TG ₂ is generated are transmitted. After preparation pulse PR is transmitted, when the waiting time T _W has elapsed, the data acquisition sequence AQ is executed. Similarly, the navigator sequence NAV is executed, and when a trigger is generated, the pulse sequence is executed. When the last pulse sequence IM _n is executed, the flow ends.

  In the second mode, since the trigger level TL is set based on the amplitude of the respiratory signal acquired in the pre-scan A, the operator corrects the trigger level TL during the scan as in the first mode. It is not necessary to perform such operations as the operator, and the operator's workload can be reduced.

In the second mode, the preparation pulse PR is transmitted before the data collection sequence AQ. Even when the preparation pulse PR is transmitted, by setting the trigger level TL based on the amplitude of the respiratory signal, the data collection sequence AQ of the pulse sequences IM _{1 to} IM _n when the respiratory signal S is close to the reference level P _ref Therefore, it is possible to obtain a high-quality image with reduced body motion artifacts.

(3) In the third embodiment the second embodiment, prior to data acquisition sequence AQ, since preparation pulse PR is transmitted, the waiting time T _W is generated between the preparation pulse PR and the data acquisition sequence AQ. Generally, the length of the waiting time T _W, result in different optimum values of the window coefficients F. Therefore, in the third embodiment, an example of setting the window coefficients F based on the waiting time T _W.

First, a simulation for examining the relationship between the waiting time _TW and the optimum value of the window coefficient F was performed.

FIG. 12 is an explanatory diagram of simulation conditions.
The pulse sequence was executed over 10 cycles of the respiratory signal, and two signal values of the respiratory signal were extracted during the execution of each data acquisition sequence. Next, an average value P _mean of the extracted signal values was calculated, and a deviation Δd (mm) between the average value P _mean and the reference level P _ref was calculated. The deviation Δd has determined how changes with latency T _W and the window coefficients F. The data collection time was 400 ms, and the respiratory signal obtained by actual measurement was used.

FIG. 13 is a diagram illustrating a simulation result.
Figure 13 (a) ~ (d) is the waiting time _{T W, respectively, T W = 200ms, 600ms,} 1000ms, when the 1400Ms, is a graph showing the relationship between the window coefficients F and displacement [Delta] d. In addition, the value of Δd in each graph is an average value of Δd calculated from the respiratory signals of five healthy persons.

The horizontal axis of the graph indicates the window coefficient F, and the vertical axis indicates the shift Δd. A smaller deviation Δd means that the data acquisition sequence AQ is executed when the diaphragm is closer to the reference level _Pref . Referring to the graphs of FIGS. 13A to 13D, when the waiting time T _W is T _W = 200 ms, 600 ms, 1000 ms, and 1400 ms, the window coefficients F are F = 0.1, 0.3, and 0, respectively. The deviation Δd is the minimum value when .5 and 0.9. Therefore, as the waiting time T _W becomes longer, the window coefficients F to the shift Δd to a minimum it can be seen that increase. In particular, when the waiting time T _W is T _W = 200 ms, 600 ms, and 1000 ms, the window coefficients F that minimize the deviation Δd are 0.1, 0.3, and 0.5, respectively. Therefore, considering from the simulation results of T _W = 200 ms, 600 ms, and 1000 ms, it can be seen that the following relational expression holds between the window coefficient F that minimizes the shift Δd and the waiting time T _W.
F = T _W / 2000 ms (2)

For example, if T _W = 200 ms, 600 ms, and 1000 ms are substituted into Equation (2), the window coefficients F are calculated as F = 0.1, 0.3, and 0.5, respectively. It can be seen that the results agree with the simulation results of (b) and (c).

On the other hand, when the waiting time T _W is T _W = 1400 ms, referring to the simulation result (FIG. 13D), the window coefficient F that minimizes the shift Δd is F = 0.9. However, when the window coefficient F is set to F = 0.9, there is a high possibility that the trigger TG for executing the pulse sequence IM will not occur. In order to verify this, a simulation for examining the occurrence of the trigger TG was performed.

  FIG. 14 is a diagram showing a simulation result of the trigger TG generated when the trigger level TL with the window coefficient F = 0.9 is set for the respiratory signal. In FIG. 14, the point where the trigger TG is generated is indicated by a symbol “▽”. In addition, the respiration signal used what was acquired by measurement.

The actual amplitude D of the respiratory signal is not constant and varies depending on the time t. Therefore, if the value of the window coefficient F is increased, the window width W is increased, so that the trigger level TL may exceed the peak of the respiratory signal. In this case, the trigger does not occur. Referring to FIG. 14, it can be seen that there are only three points where the trigger occurred, and the trigger failure rate is high. Therefore, when the waiting time T _W is T _W = 1400 ms, the window coefficient F needs to be set to F = 0.9 in order to reduce the shift Δd (see FIG. 13 (d)). If F = 0.9, the trigger failure rate increases. Therefore, in order to lower the trigger failure rate, it is desirable not to make the value of the window coefficient F too large. Hereinafter, when the waiting time _{T W} is _T W = _1400ms, it shows the simulation results of the occurrence of the trigger when the window coefficients F = 0.6.

  FIG. 15 is a diagram showing a simulation result of the trigger TG generated when the trigger level TL with the window coefficient F = 0.6 is set for the respiratory signal. A point where the trigger TG is generated is indicated by a symbol “▽”.

Referring to FIG. 15, since most of the peaks of the respiratory signal exceed the trigger level TL, the success rate of the trigger can be increased. Accordingly, when the waiting time T _W = 1400 ms, it is desirable to set the window coefficient F = 0.6.

14 and FIG. 15, the case where the waiting time T _W = 1400 ms is described. Generally, when the T _W is long (for example, T _W > 1200 ms), the value of the window coefficient F If the value is too large, the failure rate of the trigger increases. Therefore, in order to lower the failure rate of the trigger may be provided an upper limit value _{F Stay up-to} window coefficients F, if the waiting time _{T W} is long (for _example, T W> 1200 ms), the upper limit value F the window coefficients F It is desirable to set _up . As the upper limit value F _up , F _up = 0.6 can be used.

Therefore, judging from the simulation results of FIGS. 13 to 15, the waiting time _{T W} is the predetermined time _{T th (e.g.,} T th = 1200 ms) longer than the upper limit window coefficients F _{F Stay up-(e.g., F Stay up-=} set 0.6), whereas, if the waiting time _{T W} is shorter than the predetermined time _{T th,} it is desirable to calculate the window coefficients F using equation (2).

  In the third embodiment, the trigger level TL is set based on the simulation result and scanning is performed. Hereinafter, the operation of the MR apparatus according to the third embodiment will be described.

FIG. 16 is a diagram showing an operation flow of the MR apparatus in the third embodiment.
In step ST1, the window coefficient setting unit 91 (see FIG. 1), the waiting time _{T W} in the pulse sequence of the scan B determines whether it is _{T W} ≦ _{T th.} As an example, T _th = 1200 ms can be set. If T _W ≦ T _th , the process proceeds to step ST2, and if T _W > T _th , the process proceeds to step ST3. For example, if T _W = 600 ms and T _th = 1200 ms, T _W ≦ T _th , so the process proceeds to step ST2.

At step ST2, the window coefficient setting means _91, substituting F = T W / 2000 (see Equation (2)) latency _{T W,} to set the window coefficients F. For example, when the waiting time T _W = 600 ms, the window coefficient F = 0.3. After setting the window coefficient F, the process proceeds to step ST4.

On the other hand, if it is determined in step ST1 that T _W > T _th (for example, T _W = 1400 ms and T _th = 1200 ms), the process proceeds to step ST3. In step ST3, the window coefficient setting unit 91 sets the window coefficient F to F = 0.6. Then, the process proceeds to step ST4.

  In step ST4, prescan A is executed. FIG. 7 shows the respiratory signal S acquired by the pre-scan A. After performing the pre-scan A, the process proceeds to step ST5.

In step ST5, the reference level setting unit 92 (see FIG. 1) sets the reference level P _ref of the respiratory signal S based on the respiratory signal S obtained by the prescan A. FIG. 8 shows an example of the reference level P _ref of the respiratory signal S. After setting the reference level P _ref , the process proceeds to step ST6.

In step ST6, the trigger level setting means 93 (see FIG. 1) substitutes the amplitude D of the respiratory signal and the window coefficient F set in step ST2 or ST3 into W = D × F (see equation (1)). Then, the window width W is calculated. FIG. 9 shows the calculated window width W. After calculating the window width W, a position separated from the reference level P _ref by the window width W is set as the trigger level TL. After setting the trigger level TL, the process proceeds to step ST7.

  In step ST7, the main scan B is executed. Since the execution method of the main scan B is the same as that of the second embodiment, the description is omitted. When data is collected by the main scan B, the flow ends.

  In the third mode, since the trigger level TL is set based on the amplitude of the respiratory signal acquired in the pre-scan A, the trigger level TL is set during the scan by the operator as in the first and second modes. It is not necessary to perform work such as correcting the operation, and the work load on the operator can be reduced.

In the third embodiment, since the set of window coefficients F based on the waiting time T _W, it is possible to set the trigger level TL according to the waiting time T _W, motion artifacts are further reduced High quality images can be obtained.

  In the third embodiment, the window coefficient F is calculated based on the expression (2) in step ST2, but the window coefficient F is calculated using an expression different from the expression (2) according to the shooting conditions. May be calculated. In step ST3, the window coefficient F is set to 0.6, but may be set to another value (for example, F = 0.5).

In the third mode, each pulse sequence IM _{1 to} IM _n has only _one preparation pulse, but may have a plurality of preparation pulses. FIG. 17 shows an example in which the pulse sequence IM has a plurality of preparation pulses PR _{1 to} PR _m . In this case, the time from the first preparation pulse PR ₁ to the start of data acquisition sequence AQ as waiting time T _W, may execute a flow shown in FIG. 16.

In the third embodiment, since the window coefficient F is calculated based on F = T _W / 2000 (see Expression (2)), the value of the window coefficient F decreases as the waiting time T _W decreases. FIG. 18 is a diagram schematically illustrating an example of the trigger level TL when the window coefficient F is small. For example, when the waiting time T _W = 100 ms, F = 0.05, so W = 0.05D. In this case, since the window width W is only 5% with respect to the amplitude D of the respiratory signal, the trigger level TL is lowered. Therefore, the respiratory signal may exceed the trigger level TL during the scan due to a change in the respiratory rhythm of the subject. In this case, since no trigger is generated, the data of the subject cannot be collected. Therefore, a lower limit value F _low is provided for the window coefficient F, and when the window coefficient F calculated by Equation (2) is equal to or lower than the lower limit value F _low , the window coefficient F may be set to the lower limit value F _low Good. For example, F _low = 0.1 can be set.

In addition, the trigger may not be generated when the subject falls asleep during the scan. FIG. 19 shows a state where the trigger is not generated when the subject falls asleep during the scan. When the subject sleeps, the amplitude of the respiratory signal becomes small, so the respiratory signal may not exceed the trigger level TL. In this case, the trigger is not generated. Therefore, if the trigger does not occur after a certain period of time so that scanning can continue even if the subject has fallen asleep, it is determined that the subject has fallen asleep and the pulse sequence is executed. May be. However, when the subject falls asleep, the respiratory signal may deviate greatly from the reference level _Pref . This is shown in FIG. Collecting data in such cases can cause artifacts. Therefore, a respiration range AW in which the pulse sequence may be executed may be set in advance, and the pulse sequence may be executed only when the respiration signal is within this range AW.

In the third embodiment, based on the waiting time T _W, it was set window coefficients F, alternatively, may be set window coefficients F based on the period of the respiratory signal of the subject. Specifically, the window coefficient F is decreased when the period of the respiratory signal is long. Accordingly, since the data acquisition sequence AQ of the pulse sequences IM _{1 to} IM _n can be executed when the respiratory signal S is close to the reference level P _ref , a higher quality image can be obtained.

  In the above description, the case where an upper limit value and a lower limit value are provided for the window coefficient F has been described. Instead of providing an upper limit value and a lower limit value for the window coefficient F, an upper limit value and a lower limit value are set for the window width W. It may be provided (for example, the upper limit value of the window width W is 20 mm, the lower limit value is 2 mm, etc.).

2 Magnet 3 Table 3a Cradle 4 Receiving coil 5 Sequencer 6 Transmitter 7 Gradient magnetic field power supply 8 Receiver 9 Control unit 10 Operation unit 11 Display unit 12 Subject 21 Bore 22 Superconducting coil 23 Gradient coil 24 Transmitting coil 91 Window coefficient setting means 92 Reference level setting means 93 Trigger level setting means 94 Trigger generation means 100 MR apparatus

Claims (10)

A magnetic resonance apparatus for executing a first sequence having a preparation pulse and a data collection sequence for collecting data from the subject in synchronization with a respiratory signal of the subject ,
A window width is calculated by calculating a product of the amplitude of the respiratory signal and a window coefficient, and a trigger for executing the first sequence is performed based on the reference level of the respiratory signal and the window width. It has a trigger level setting means for setting a trigger level to be used when determining whether to generate,
The magnetic resonance apparatus , wherein the window coefficient is set based on a waiting time between the preparation pulse and the data acquisition sequence . The magnetic resonance apparatus according to claim 1 , further comprising a window coefficient setting unit that sets the window coefficient. The first sequence includes a plurality of preparation pulses and the data acquisition sequence;
The window coefficient setting means includes:
The magnetic resonance apparatus according to claim 2 , wherein the window coefficient is set based on a waiting time between a first preparation pulse of the plurality of preparation pulses and the data acquisition sequence. The magnetic resonance apparatus according to claim 1, wherein an upper limit value is set for the window coefficient. The window coefficient setting means includes:
5. The magnetic resonance apparatus according to claim 4 , wherein when the waiting time is longer than a predetermined time, the window coefficient is set to the upper limit value. Wherein the window coefficients, the lower limit value is set, the magnetic resonance apparatus according to any one of claims 1 to 5. The magnetic resonance apparatus according to any one of claims 1 to 6 , wherein an upper limit value or a lower limit value is set for the window width. Having a reference level setting means for setting a reference level of the respiratory signal, a magnetic resonance device according to any one of claims 1 to 7. The reference level setting means includes
The magnetic resonance apparatus according to claim 8 , wherein a position when the subject finishes exhaling is set as a reference level of the respiratory signal. A program for a magnetic resonance apparatus that executes a first sequence having a preparation pulse and a data collection sequence for collecting data from the subject in synchronization with a respiratory signal of the subject ,
A window width is calculated by calculating a product of the amplitude of the respiratory signal and a window coefficient, and a trigger for executing the first sequence is performed based on the reference level of the respiratory signal and the window width. It is a program for causing a computer to execute a trigger level setting process for setting a trigger level used when determining whether or not to generate ,
The window coefficient is set based on a waiting time between the preparation pulse and the data acquisition sequence .