JP2013230386A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus capable of continuing proper imaging regardless of a fluctuation of a respiration state of a subject.SOLUTION: A main control part 10g detects a respiration level of a subject 200. The main control part 10g controls each related part to image the subject 200 based on an imaging magnetic resonance signal collected in a state that the detected respiration level is within an allowable range. Furthermore, the main control part 10g obtains a peak value of the respiration of the subject from the detected respiration level, and changes the allowable range based on the peak value.

Description

  The present invention relates to a magnetic resonance imaging apparatus that obtains an image in a subject based on a magnetic resonance signal emitted from the subject.

  In order to image the coronary artery by the magnetic resonance imaging (MRI) method, a method of capturing images under breath holding or natural breathing using a three-dimensional (3D) SSFP (steady state free precession) sequence is used. In particular, in the case of WH MRCA (whole heart MR coronary angiography) which images the coronary artery running of the entire heart, a change in the position of the heart accompanying respiration may affect the image quality.

The rate of change of the position of the heart accompanying respiration is small when the respiration level is near the peak. Therefore, a method of controlling data collection according to the respiratory level is used. That is, for example, the position of the diaphragm in the body axis direction can be detected from a signal obtained by one-dimensional Fourier transform of the NMR signal collected for the region R as shown in FIG. Since the position of the diaphragm with respect to the body axis direction periodically rises and falls according to breathing, a monitor signal as shown in FIG. 22 synchronized with the respiratory motion is plotted by plotting the periodically detected diaphragm position in time series. Can be obtained. If the peak of the monitor signal is outside the allowable range between the upper threshold USL and the lower threshold LSL as shown in FIG. 21, data is not collected or the collected data is not used for image reconstruction. Then, the image is reconstructed using the collected data when the peak of the monitor signal is within the allowable range.

Japanese Patent Laid-Open No. 2000-041970 JP 2000-157507 A JP 2004-057226 A

  Conventionally, the allowable range is set according to the breathing state of the subject before or immediately after the start of the imaging operation, and is not changed until the imaging operation ends.

  However, if the respiration level is not constant, gradually decreases, or gradually increases, and the respiration level peak falls outside the allowable range as shown in FIG. 22, for example, the data collection efficiency effective for image reconstruction decreases. Therefore, there is a possibility that the imaging time becomes long or the inspection cannot be completed in the worst case.

  If the allowable range is sufficiently large, the period during which the data collection efficiency can be maintained can be extended. However, the influence of the movement of the heart is increased, and the image quality may be deteriorated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a magnetic resonance imaging apparatus capable of continuing proper imaging regardless of changes in the respiratory state of the subject. is there.

  A magnetic resonance imaging apparatus according to an aspect of the present invention applies a uniform static magnetic field to a subject, and applies a high-frequency magnetic field and a gradient magnetic field to the subject according to a predetermined pulse sequence, thereby magnetic resonance from the subject. A collecting means for collecting signals; an imaging means for imaging the subject based on the magnetic resonance signals collected by the collecting means; a detecting means for detecting a respiratory level of the subject; Control means for controlling the imaging means to image the subject based on the magnetic resonance signals for imaging collected by the collecting means in a state where the respiration level is within an allowable range; and detection Means for obtaining a peak value of respiration of the subject from the respiration level, and changing means for changing an allowable range based on the peak value.

The figure which shows the structure of the magnetic resonance imaging device (MRI apparatus) which concerns on the 1st thru | or 4th embodiment of this invention. The figure which shows an example of the sequence of WH MRCA using the RMC method. The figure which shows the process sequence of the main control part in 1st Embodiment. The figure which shows an example of the change of the respiration level referred in order to obtain | require an average peak value. The figure which shows a mode that the peak value was detected from the respiration level actually detected as shown in FIG. The figure which shows a mode that the peak value was detected by interpolation based on the respiration level actually detected as shown in FIG. The figure which shows the modification of a sequence in the case of performing WH MRCA. The figure which shows an example of a mode that a new tolerance | permissible_range is determined. The figure which shows another example of a mode that a new tolerance | permissible_range is determined. The figure which shows an example of a mode that a tolerance | permissible_range is changed. The figure which shows a mode that the deviation | shift amount referred for adjustment of an imaging range is calculated | required. The figure which shows an example of the change of a respiration level when respiration fluctuation | variation is small. The figure which shows an example of the change of a respiration level when respiration fluctuation | variation is large. The figure which shows the example of a setting of the tolerance | permissible_range when the respiratory fluctuation in 2nd Embodiment is small. The figure which shows the example of a setting of the tolerance | permissible_range when the respiration fluctuation | variation in 2nd Embodiment is large. The figure which shows the example of a setting of the tolerance | permissible_range when the respiration fluctuation | variation in 3rd Embodiment is small. The figure which shows the example of a setting of the tolerance | permissible_range when the respiratory variation in 3rd Embodiment is large. The figure which shows the process sequence of the main-control part in 4th Embodiment. The figure explaining the effect of 4th Embodiment. The figure which shows the area | region which collects the NMR signal for detecting a respiration level. The figure which shows an example of a monitor signal. The figure which shows an example of a mode that the peak of a monitor signal shift | deviates outside an allowable range.

  Hereinafter, first to fourth embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a magnetic resonance imaging apparatus (MRI apparatus) 100 according to the first to fourth embodiments. The MRI apparatus 100 includes a static magnetic field magnet 1, a gradient magnetic field coil unit 2, a gradient magnetic field power source 3, a bed 4, a bed control unit 5, a transmission RF coil 6, a transmission unit 7, a reception RF coil 8, a reception unit 9, and a computer system. 10. A video transmission system 11 and a display system 12 are provided.

  The static magnetic field magnet 1 has a hollow cylindrical shape and generates a uniform static magnetic field in an internal space. For example, a permanent magnet or a superconducting magnet is used as the static magnetic field magnet 1.

  The gradient magnetic field coil unit 2 has a hollow cylindrical shape and is disposed inside the static magnetic field magnet 1. In the gradient coil unit 2, three types of coils corresponding to the X, Y, and Z axes orthogonal to each other are combined. In the gradient magnetic field coil unit 2, the above three types of coils are individually supplied with current from the gradient magnetic field power supply 3, and generate gradient magnetic fields whose magnetic field strengths change along the X, Y, and Z axes. The Z-axis direction is, for example, the same direction as the static magnetic field. The gradient magnetic fields of the X, Y, and Z axes are arbitrarily used as, for example, a slice selection gradient magnetic field Gs, a phase encoding gradient magnetic field Ge, and a readout gradient magnetic field Gr. The slice selection gradient magnetic field Gs is used to arbitrarily determine an imaging section. The phase encoding gradient magnetic field Ge is used to change the phase of the NMR signal in accordance with the spatial position. The readout gradient magnetic field Gr is used to change the frequency of the NMR signal in accordance with the spatial position.

  The subject 200 is inserted into the cavity of the gradient coil unit 2 while being placed on the top 4 a of the bed 4. The couchtop 4a of the couch 4 is driven by the couch controller 5 and moves in the longitudinal direction and the vertical direction. Usually, the bed 4 is installed such that the longitudinal direction thereof is parallel to the central axis of the static magnetic field magnet 1.

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

  The transmission unit 7 transmits a high-frequency pulse corresponding to the Larmor frequency to the transmission RF coil 6.

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

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

  The computer system 10 includes an interface unit 10a, a data collection unit 10b, a reconstruction unit 10c, a storage unit 10d, a display unit 10e, an input unit 10f, and a main control unit 10g.

  The interface unit 10a is connected to the gradient magnetic field power source 3, the bed control unit 5, the transmission unit 7, the reception RF coil 8, the reception unit 9, the video transmission system 11, and the like. The interface unit 10a has an interface circuit corresponding to each of these connected units, and inputs and outputs signals exchanged between the respective units and the computer system 10.

  The data collection unit 10b collects digital signals output from the reception unit 9 via the interface unit 10a. The data collection unit 10b stores the collected digital signal, that is, NMR signal data, in the storage unit 10d.

  Thus, in the MRI apparatus 100, the static magnetic field magnet 1, the gradient magnetic field coil unit 2, the gradient magnetic field power source 3, the transmission RF coil 6, the transmission unit 7, the reception RF coil 8, the reception unit 9, and the data collection unit 10b are included in the subject 200. It functions as a collecting means for collecting magnetic resonance signals from.

  The reconstruction unit 10c performs post-processing, that is, reconstruction such as Fourier transform, on the NMR signal data stored in the storage unit 10d to obtain spectrum data or image data of a desired nuclear spin in the subject 200. .

  The storage unit 10d stores NMR signal data and spectrum data or image data for each patient.

  The display unit 10e displays various information such as spectrum data or image data under the control of the main control unit 10g. As the display unit 10e, a display device such as a liquid crystal display can be used.

  The input unit 10f receives various commands and information input from the operator. As the input unit 10f, a pointing device such as a mouse or a trackball, a selection device such as a mode switch, or an input device such as a keyboard can be used as appropriate. The input unit 10f accepts designation by an operator of an excitation slice or excitation slab as an imaging region such as the entire heart or a synchronization target region such as the diaphragm.

  The main control unit 10g includes a CPU, a memory, and the like (not shown), and controls the MRI apparatus 100 overall. The main control unit 10g generates a video signal indicating whether or not the respiration level is within the allowable range. This video signal is, for example, an NTSC (national television system committee) signal.

  The video transmission system 11 transmits the video signal generated by the main control unit 10g with light.

  The display system 12 displays an image based on the image signal so that the subject 200 placed in the imaging state can see the image.

(First embodiment)
In the first embodiment, the main controller 10g has a plurality of functions as follows. The plurality of functions can be realized by causing a processor included in the main control unit 10g to execute a program.

  One of the functions is to control each related unit so that the data acquisition unit 10b acquires an NMR signal (hereinafter referred to as a monitoring NMR signal) for detecting the respiration level of the subject 200. One of the functions described above detects the respiratory level of the subject 200 based on the monitoring NMR signal acquired by the data collection unit 10b. One of the above functions is to cause the data collection unit 10b to collect an NMR signal for reconstructing an image (hereinafter referred to as a reconstruction NMR signal) when the detected respiration level is within an allowable range. Control each part concerned. One of the functions is to detect the position of the diaphragm of the subject 200 based on the monitoring NMR signal. One of the functions is to measure the amount of deviation of the detected diaphragm position from the reference position. One of the above functions controls each related part so that the range in which the NMR signal for reconstruction is collected is moved by the movement amount corresponding to the measured deviation amount. One of the above functions changes the center level of the tolerance range based on the detected change in respiratory level.

  Next, the operation of the MRI apparatus 100 of the first embodiment will be described.

  In the MRI apparatus 100 of the first embodiment, WH MRCA using the RMC method is executed according to a known sequence.

  FIG. 2 is a diagram illustrating an example of a WH MRCA sequence using the RMC method.

  The RMC method is usually performed with electrocardiogram synchronization. That is, the sequence is performed in synchronization with an electrocardiogram signal output from an electrocardiograph (not shown) attached to the subject 200. Specifically, MPP (motion probing pulse) as a monitoring NMR signal is collected after a certain delay time has elapsed since the R wave appeared in the electrocardiogram signal. Immediately after this, a period for collecting data for photographing is set.

  The MPP is acquired for a region R as shown in FIG. 20 without applying a phase encoding gradient magnetic field, for example. Thus, the position of the diaphragm with respect to the body axis direction can be detected from the signal obtained by one-dimensional Fourier transform of this MPP. Since the position of the diaphragm in the body axis direction periodically rises and falls according to breathing, the position of the diaphragm detected as described above can be used as it is as a breathing level.

  Therefore, the main control unit 10g detects the position of the diaphragm (respiration level) based on the MPP. The main control unit 10g controls each related unit so that data collection is performed in the immediately subsequent data collection period only when the detected respiration level is within a predetermined allowable range. Alternatively, the main control unit 10g controls each related unit so as to collect data in the immediately following data collection period regardless of whether or not the detected breathing level is within the allowable range. Collected data is valid only if it is within range. When collecting data, the main control unit 10g measures the amount of deviation of the detected diaphragm position from a predetermined reference position, and collects a reconstruction NMR signal so as to compensate for the amount of deviation (imaging). Each part concerned is controlled to adjust (range). However, this adjustment of the imaging range can be omitted.

  Note that the allowable range is initially set based on the respiration level of the subject 200 before the start of imaging. This initial setting may be performed by the main control unit 10 in accordance with an instruction from the operator, or may be automatically performed by the main control unit 10g. The initial permissible range may be arbitrary, but is typically determined as a constant width around the average value of the peak respiratory level as the central level. The reference position is also initially set as the diaphragm position before the start of imaging. The initial setting of the reference position may be performed by the main control unit 10 in response to an instruction from the operator, or may be automatically performed by the main control unit 10g. Furthermore, the shooting range is also initialized before the start of imaging. The initial setting of the shooting range may be performed by the main control unit 10 in response to an instruction from the operator, or may be automatically performed by the main control unit 10g. Here, “before imaging” means before the operation for actually collecting the NMR signals for reconstruction is started. In order to detect the position of the diaphragm before the start of imaging, the sequence shown in FIG. 2 may be repeated several times before the sequence shown in FIG. 2 is started in order to collect NMR signals for reconstruction. . In this case, data collected during the data collection period is discarded, and only the MPP is used to detect the position of the diaphragm. Alternatively, only the MPP collection may be repeated several times without performing the data collection in FIG.

  In parallel with performing the imaging as described above, the main control unit 10g performs the process shown in FIG. 3 at every predetermined timing. The timing of performing this process may be arbitrary, but it is conceivable that, for example, every time a respiration level is newly detected or a certain time elapses.

  In step Sa1, the main control unit 10g detects a plurality of respiration level peak values based on the respiration level at point N as shown in FIG. N may be an arbitrary integer, but in order to be able to detect a plurality of peak values, it is necessary to include a plurality of breathing cycles within the time required to measure the breathing level at N points.

  The peak value of the respiration level can be detected as a respiration level greater than any of the previous and next respiration levels from the actually detected respiration levels.

  FIG. 5 is a diagram showing a state in which the peak value is detected from the actually detected respiration levels as shown in FIG. In FIG. 5, the detected peak value is represented by a white circle.

  However, when the sequence shown in FIG. 2 is adopted, the detection of the respiration level is performed only once per heartbeat. That is, the detection of the respiration level is performed only several times for each respiration, and there is no guarantee that the peak value of the respiration level is actually detected. For this reason, the method as described above is easy to process, but the error of the detected peak value may increase.

  Therefore, in order to reduce the error of the peak value, the peak value may be detected by interpolation using a polynomial approximation or a spline function.

  FIG. 6 is a diagram showing a state where the peak value is detected by interpolation based on the actually detected respiration level as shown in FIG. In FIG. 6, detected peak values are represented by white circles, and values detected by interpolation are represented by broken lines.

  In addition, you may increase the detection frequency of a respiration level by employ | adopting a sequence as shown in FIG. If the frequency of detecting the respiratory level is increased in this way, the error of the peak value can be reduced even when the peak value is detected by any of the above methods.

  In the sequence shown in FIG. 7, MPPs are collected a plurality of times within one heartbeat. The plurality of MPPs are classified into a main MPP collected immediately before the data collection period of the imaging region and a sub MPP collected at a timing different from the main MPP while avoiding the data collection period. The sub-MPP may be collected before or after the main MPP as long as it is a period excluding the data collection period of the imaging region. For example, a plurality of sub MPPs may be collected before the main MPP. A plurality of MPPs (including not only the sub MPP but also the main MPP) may be collected at regular intervals within one heartbeat. In this case, if any of the plurality of MPPs set at equal intervals is included in the data collection period of the imaging region, the MPP is not collected.

  In step Sa2, the main control unit 10g obtains an average value of a plurality of peak values detected in step Sa1 (hereinafter referred to as an average peak value).

  In step Sa3, the main control unit 10g checks whether or not the average peak value obtained in step Sa2 is within an allowable range.

  If the average peak value is within the allowable range, the main control unit 10g ends the processing of FIG. Therefore, in this case, the allowable range is not changed.

  If the average peak value is outside the allowable range, the main control unit 10g proceeds from step Sa3 to step Sa4. In step Sa4, the main control unit 10g changes the allowable range based on the average peak value.

  FIG. 8 is a diagram illustrating an example of how a new allowable range is determined.

  In the example shown in FIG. 8, a value obtained by adding the specified value a to the average peak value is set as the upper limit threshold value USL, and a value obtained by subtracting the specified value a from the average peak value is set as the lower limit threshold value LSL. The specified value a is ½ of the width of the allowable range set initially. Therefore, in the example shown in FIG. 8, the allowable range is shifted so that only the center level is combined with the newly obtained average peak value without changing the width of the allowable range.

  FIG. 9 is a diagram showing another example of how a new allowable range is determined.

  In the example shown in FIG. 9, a value obtained by adding the specified value a to the average peak value is set as the upper limit threshold USL, and a value obtained by subtracting the specified value b from the average peak value is set as the lower limit threshold LSL. The specified values a and b are values obtained by multiplying the initial set allowable range by the coefficients Ca and Cb. The coefficients Ca and Cb are determined in advance so that Ca <Cb. Therefore, in the example shown in FIG. 9, the allowable range is shifted so that only the center level is combined with the newly obtained average peak value without changing the width of the allowable range, as in the example shown in FIG. It is. However, in the example shown in FIG. 9, the allowable range is set so that the margin from the average peak value to the lower limit threshold LSL is larger than the margin from the average peak value to the upper limit threshold USL. The coefficients Ca and Cb may be fixed values or values arbitrarily designated by the user.

  When the method shown in FIG. 9 is adopted, the probability that the respiration level detected thereafter is within the allowable range can be increased as compared with the case where the method shown in FIG. 8 is adopted, and the examination efficiency can be improved.

  Thus, the allowable range is changed as shown in FIG. 10, for example, according to the change in the respiratory level.

  By changing the permissible range in this way, it is possible to make the breathing level once not within the permissible range reenter the permissible range as shown in FIG. Therefore, it is possible to continue imaging.

  The first embodiment can be applied to any of imaging under natural breathing, breath-holding imaging, or multi-breath hold imaging.

  In breath holding imaging and multi-breath hold imaging, conventionally, it is necessary to hold a breath so that the subject's breathing level is within an allowable range. If breath holding is performed in a state where the breathing level is outside the allowable range, valid data cannot be collected during the breath holding period. However, if the first embodiment and multi-breath hold imaging are used in combination, the allowable range is changed according to the breathing level at which the breath is held. Therefore, data can be collected as long as the breath is held. It becomes. Thereby, it is possible to shorten the imaging time. In addition, the subject can hold his / her breath without worrying about the allowable range. Furthermore, as a result of such shortening of the imaging time and improvement in the degree of freedom of breath holding, the burden on the subject can be greatly reduced.

  In this case, however, the larger the value of N, the greater the time lag from when the breath is held until the allowable range is changed. That is, the proportion of dead time during which data cannot be collected during the breath holding period increases. For this reason, it is preferable to set the value of N smaller when performing breath-holding imaging or multi-breath hold imaging than when performing imaging with natural breathing.

  If breath-hold imaging or multi-breath hold imaging is used, data can be collected in a state in which there is almost no change in the position of the heart due to breathing. Can be configured.

  In the case of multi-breath hold imaging, the data collection operation may be performed only during intermittent breath holding periods, and the data collection operation may not be performed during the natural breathing period. Regardless of this, the operation for collecting data may be continued. However, according to the latter, since the RF excitation is continuously performed, the contrast of the reconstructed image is stabilized.

  In addition, only data collected when the breathing level is within an allowable range within the breath holding period may be effective data for image reconstruction, and the breathing level may be set regardless of whether or not the breath holding period. Data collected when it is within the allowable range may be effective data for image reconstruction. However, according to the latter, data effective for image reconstruction can be collected even during a natural breathing period between breath holding periods, and the imaging time can be shortened.

  By the way, in breath holding imaging or multi-breath hold imaging, a subject may be instructed to start holding his / her breath using a sound generator. In this case, it is possible to quickly change the allowable range by executing processing for changing the allowable range in conjunction with the operation of the sound generator.

  Subsequently, some ideas in the first embodiment will be described.

  (1) As described above, the imaging range is adjusted by measuring the amount of deviation of the detected diaphragm position from a predetermined reference position and compensating for the amount of deviation. For example, the above-described measurement of the amount of deviation is performed by holding a Fourier transform signal obtained for detecting a respiration level when a reference imaging range is set as a reference signal, and each time data is collected, The shift amount is calculated by comparing the Fourier transform signal obtained for detecting the level with the reference signal as shown in FIG. In FIG. 11, the reference signal is represented by a solid line, and the Fourier transform signal when data is collected is represented by a one-dot chain line. In addition, specifically, a known method such as an edge detection method or a cross-correlation method is used to measure the deviation amount.

  Specifically, for example, the adjusted imaging range may be set as a range in which the initially set imaging range is moved by a movement amount corresponding to the shift amount. In this case, even if the allowable range is changed, the reference position is not changed. That is, even if the allowable range is changed, the reference signal is not reacquired. However, each time the allowable range is changed, the reference signal may be reacquired to update the reference position. However, in this case, the positional relationship between the reference position and the initially set imaging range changes before and after the update of the reference position. Therefore, when the reference position is updated, the correspondence relationship between the deviation amount and the movement amount is changed.

In addition, although the position of the heart changes in synchronization with the movement of the diaphragm, the moving amount of the diaphragm and the changing amount of the heart position do not necessarily match. Therefore, the movement amount is obtained by multiplying the deviation amount by the coefficient. That is, the movement amount in the initial state in which the reference position is not changed is obtained by, for example, multiplying the obtained deviation amount by a predetermined coefficient. However, after changing the reference position, it is obtained by multiplying the value obtained by adding the amount of movement of the latest reference position from the initial reference position to the obtained deviation amount and a predetermined coefficient.

  Incidentally, the coefficient here may be changed according to the respiration level. Specifically, when the respiration level is high and low compared to when the respiration level is medium, the amount of change in the position of the heart is reduced due to the influence of surrounding organs. Considering this, the coefficient is changed according to the respiration level.

  (2) Some imaging target parts such as the heart change not only in position but also in shape according to the respiration level. For example, the heart becomes larger as the diaphragm is located below. For this reason, before and after the change of the permissible range, data collection relating to imaging target parts having different shapes is performed. This does not require any countermeasure when the rate of change in the shape of the imaging target region is small or when the image quality is not important. However, it is desirable to take measures when the rate of change of the shape of the region to be imaged is large or when image quality is important.

  One of the countermeasures is based on the post-processing data after each data has been scaled, reduced, or affine transformed at a ratio corresponding to the amount of deviation of the allowable range when each data was collected. To reconstruct the image. Enlargement / reduction, affine transformation, or the like can be performed by, for example, the reconstruction unit 10c or the main control unit 10g.

  (3) The number N of breathing levels that are referred to in order to obtain the average peak value may be changed according to the degree of breathing fluctuations so that it can cope with the case where the state of breathing fluctuations becomes earlier in the middle. . That is, if the number of breathing levels referred to for obtaining the average peak value is represented as N1 when the breathing fluctuation is small as shown in FIG. 12, for example, N2 when the breathing fluctuation is large as shown in FIG. , N1> N2. In order to realize this, the main control unit 10g obtains an index value representing the degree of respiratory fluctuation. Then, either N1 or N2 is adopted by comparing this index value with a predetermined threshold value. N1, N2 and the threshold may be arbitrarily determined by the designer or user of the MRI apparatus 100. Specifically, the respiration variation includes a change in respiration depth, a change in average respiration level, a change in respiration rate, and the like. As an index value for the change in the depth of respiration, for example, the distribution of the respiration level detected during a predetermined period can be used. As an index value of the change in the average level of respiration, for example, an average value of respiration levels or a difference value of variance in each of two predetermined periods can be used. As the index value for the change in respiratory rate, for example, the number of peaks detected within a unit time can be used. Of course, M candidates (M is an integer equal to or greater than 3) and M-1 thresholds for the number of breathing levels to be referred to obtain the average peak value, and breathing to be referred to obtain the average peak value. It is also possible to change the number of levels to three or more levels. Or you may make it obtain | require the value of N based on the type | formula which determines the value of N according to an index value.

(Second Embodiment)
In the second embodiment, the main controller 10g has a plurality of functions as follows. The plurality of functions can be realized by causing a processor included in the main control unit 10g to execute a program.

  One of the functions is to control each related unit so that the data acquisition unit 10b acquires the NMR signal for monitoring. One of the functions described above detects the respiratory level of the subject 200 based on the monitoring NMR signal acquired by the data collection unit 10b. One of the above-described functions controls the related units so that the data collecting unit 10b collects the reconstruction NMR signal when the detected respiration level is within the allowable range. One of the functions is to detect the position of the diaphragm of the subject 200 based on the monitoring NMR signal. One of the functions is to measure the amount of deviation of the detected diaphragm position from the reference position. One of the above functions controls each related part so that the range in which the NMR signal for reconstruction is collected is moved by the movement amount corresponding to the measured deviation amount. One of the functions changes the tolerance range based on the detected respiratory variation.

  Next, the operation of the MRI apparatus 100 of the second embodiment will be described.

  The operation in the second embodiment is the same as that of the first embodiment in many respects. The operation of the second embodiment is different from that of the first embodiment in the allowable range changing method.

  In parallel with performing the imaging as described in the first embodiment, the main control unit 10g obtains an index representing the degree of respiratory fluctuation instead of performing the processing shown in FIG. As this index, the variance of the respiratory level detected during a predetermined period, the average value of the respiratory level or the difference value of the variance during each of the two predetermined periods can be used.

  The main control unit 10g changes the width of the allowable range according to the obtained index size. Specifically, as shown in FIGS. 14 and 15, the width of the allowable range when the respiratory fluctuation is large is made larger than the allowable range when the respiratory fluctuation is small.

  According to the second embodiment, it is possible to improve the adjustment accuracy of the imaging range when the respiratory fluctuation is small, and to continue data collection even when the respiratory fluctuation becomes large.

  This second embodiment is useful when the inspection efficiency is more important than the image quality.

(Third embodiment)
In the third embodiment, the main controller 10g has a plurality of functions as follows. The plurality of functions can be realized by causing a processor included in the main control unit 10g to execute a program.

  One of the functions is to control each related unit so that the data acquisition unit 10b acquires the NMR signal for monitoring. One of the functions described above detects the respiratory level of the subject 200 based on the monitoring NMR signal acquired by the data collection unit 10b. One of the above-described functions controls the related units so that the data collecting unit 10b collects the reconstruction NMR signal when the detected respiration level is within the allowable range. One of the functions is to detect the position of the diaphragm of the subject 200 based on the monitoring NMR signal. One of the functions is to measure the amount of deviation of the detected diaphragm position from the reference position. One of the above functions controls each related part so that the range in which the NMR signal for reconstruction is collected is moved by the movement amount corresponding to the measured deviation amount. One of the functions changes the tolerance range based on the detected respiratory variation.

  Next, the operation of the MRI apparatus 100 according to the third embodiment will be described.

  The operation in the third embodiment is similar to the first and second embodiments in many respects. The operation in the third embodiment is different from that in the first and second embodiments in the method of changing the allowable range.

  In the third embodiment, the main control unit 10g changes the width of the allowable range according to the obtained index size. Specifically, as shown in FIGS. 16 and 17, the width of the allowable range when the respiratory variation is large is made smaller than the allowable range when the respiratory variation is small.

  According to the third embodiment, it is possible to prevent the data collection in each of the states in which the breathing levels are significantly different when the breathing fluctuation becomes large.

  The third embodiment is useful when the image quality is more important than the inspection efficiency.

(Fourth embodiment)
In the fourth embodiment, the main control unit 10g has the following functions. The plurality of functions can be realized by causing a processor included in the main control unit 10g to execute a program.

  One of the functions is to control each related unit so that the data acquisition unit 10b acquires the NMR signal for monitoring. One of the functions described above detects the respiratory level of the subject 200 based on the monitoring NMR signal acquired by the data collection unit 10b. One of the functions is to control each related unit so that the data collecting unit 10b collects the reconstruction NMR signal when the detected respiration level change rate is equal to or lower than a predetermined value.

  Next, the operation of the MRI apparatus 100 of the fourth embodiment will be described.

  In the fourth embodiment, for example, the sequence shown in FIG. 2 is applied as in the first embodiment.

  Then, the main control unit 10g executes the process shown in FIG. 18 every time the MPP is acquired.

In step Sb1, the main controller 10g measures the velocity of the diaphragm. Specifically, the current respiration level is first detected based on the newly acquired MPP. Then, the main control unit 10g measures the current diaphragm speed based on the state of the change of the respiratory level detected here from the previously detected respiratory level. Specifically, the two respiration levels detected in succession are represented as L _i and L _{i + 1} , and the time difference between the timings at which these two respiration levels L _i and L _{i + 1} are detected is represented as Δt. In this case, the velocity V of the diaphragm can be calculated by the following equation.

V = (L _{i + 1} −L _i ) / Δt
In the case where the sequence shown in FIG. 2 is adopted, Δt corresponds to the RR interval in the electrocardiogram.

  In step Sb2, the main control unit 10g confirms whether or not the speed measured in step Sb1 is equal to or less than a specified speed. The prescribed speed is predetermined with an arbitrary value sufficiently smaller than the maximum speed of the diaphragm.

  If the diaphragm speed is equal to or less than the specified speed, the main control unit 10g proceeds from step Sb2 to step Sb3. In step Sb3, the main control unit 10g controls each related unit so that the data collection unit 10b collects the reconstruction NMR signal.

  However, if the diaphragm speed is not less than the specified speed, the main control unit 10g ends the process of FIG. 18 without collecting the reconstruction NMR signal.

  Thus, only when the current diaphragm velocity obtained from the MPP is sufficiently small, data collection is performed in the immediately subsequent data collection period. Here, the velocity of the diaphragm becomes zero when the respiration level reaches a peak. Therefore, data collection is performed only when the respiration level is near the peak. Such an operation is equivalent to the fact that, as shown in FIG. 19, the threshold value SL is changed according to the change in the breathing level, and data collection is performed only when the breathing level exceeds the threshold value SL.

  As described above, according to the fourth embodiment, it is possible to continue imaging even if the respiratory level changes.

  This embodiment can be variously modified as follows.

  The respiration level may be detected by another means. For example, a respiratory synchronization sensor or an expiration meter can be used. However, the respiratory synchronization sensor is attached to the abdomen of the subject 200 and detects a respiratory level based on the physical movement of the abdomen.

  In step Sa3 in the first embodiment, a range different from the allowable range may be determined, and it may be confirmed whether or not the average peak value is included in this range.

  Step Sa3 in the first embodiment may be omitted. That is, regardless of the newly obtained average peak value, the allowable range may be reset based on the average peak value.

  In the first to third embodiments, an image that allows the subject 200 to recognize the change in the allowable range may be displayed on the display system 12. In this way, the subject 200 can adjust the respiration so that the peak of the respiration level is matched with the allowable range after the change. If such display is not performed, the video transmission system 11 and the display system 12 may not be provided.

  The second or third embodiment can be implemented in combination with the first embodiment.

  If the second and third embodiments are selectively performed according to the user's wishes, it is possible to use an operation that emphasizes inspection efficiency and an operation that emphasizes image quality according to user needs, which is convenient.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 1 ... Static magnetic field magnet, 2 ... Gradient magnetic field coil unit, 3 ... Gradient magnetic field power supply, 4 ... Bed, 5 ... Bed control part, 6 ... Transmission RF coil, 7 ... Transmission part, 8 ... Reception RF coil, 9 ... Reception part DESCRIPTION OF SYMBOLS 10a ... Interface part, 10b ... Data collection part, 10d ... Memory | storage part, 10 ... Computer system, 10c ... Reconstruction part, 10g ... Main control part, 10f ... Input part, 10e ... Display part, 11 ... Video transmission system, DESCRIPTION OF SYMBOLS 12 ... Display system, 100 ... Magnetic resonance imaging device (MRI apparatus), 200 ... Subject.

Claims (6)

A collecting means for applying a uniform static magnetic field to the subject and applying a high-frequency magnetic field and a gradient magnetic field to the subject according to a predetermined pulse sequence to collect magnetic resonance signals from the subject;
Imaging means for imaging the subject based on the magnetic resonance signals collected by the collecting means;
Detecting means for detecting a respiration level of the subject;
Control means for controlling the imaging means to image the subject based on the magnetic resonance signal for imaging collected by the collecting means in a state where the detected respiration level is within an allowable range. When,
Means for obtaining a peak value of respiration of the subject from the detected respiration level;
A magnetic resonance imaging apparatus comprising: changing means for changing an allowable range based on the peak value.   The magnetic resonance imaging apparatus according to claim 1, wherein the changing unit shifts a center level of the allowable range.   The magnetic resonance imaging apparatus according to claim 1, wherein the changing unit changes a width of the allowable range. The detection means repeatedly detects the respiratory level,
The changing means calculates an average value of the peak values of the respiration levels based on the N respiration levels detected by the detecting means, and changes the allowable range based on the average values. The magnetic resonance imaging apparatus according to claim 1.   The change means is characterized in that a value obtained by adding a specified value to the average value is an upper limit value of the allowable range, and a value obtained by subtracting the specified value from the average value is a lower limit value of the allowable range. Item 5. The magnetic resonance imaging apparatus according to Item 4.   The changing means sets a value obtained by adding a first specified value to the average value as an upper limit value of the allowable range, and subtracting a second specified value different from the first specified value from the average value. The magnetic resonance imaging apparatus according to claim 4, wherein the lower limit value of the allowable range is set.

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