JP5993861B2 - Magnetic resonance imaging apparatus and data acquisition rate determination optimization method - Google Patents

Description

  The present invention relates to a magnetic resonance imaging (hereinafter referred to as MRI) technique, and more particularly to an imaging technique using a partial echo method (half echo method) for collecting data of only a part of an echo signal.

  When performing MRI imaging of a fluid such as blood, a technique for suppressing blood outside the imaging surface is used to improve image quality. For example, the suppression is performed by applying an RF pulse called a pre-saturation pulse (hereinafter, pre-saturation) to the outside of the imaging surface prior to the execution of the pulse sequence of the main imaging. However, when presachi is used, longitudinal magnetization recovers with time, so that it cannot be sufficiently suppressed when the blood flow velocity is slow, the imaging slab is thick, and the presachi position is separated from the imaging position.

  As a solution to this, there is a technique for suppressing blood by applying a bipolar crusher gradient magnetic field according to the blood flow rate or a crusher gradient magnetic field according to the blood flow rate before and after the 180 ° pulse. For example, a bipolar crusher gradient magnetic field is shown in Non-Patent Document 1, and a method of applying before and after a 180 ° pulse is shown in Patent Document 1.

  The crusher gradient magnetic field is applied within TE (echo time: time from the 90 ° RF pulse (excitation RF pulse) until the signal intensity of the echo signal becomes maximum). However, because the crusher gradient magnetic field requires a larger amount of application as the blood flow velocity is slower, if the TE is short, such as when acquiring a T1-weighted image, it overlaps with the application timing of the readout gradient magnetic field and cannot be applied sufficiently There is.

  In general, the contrast of an image is strongly influenced by TE. Therefore, TE needs to be maintained in order to obtain a desired contrast. There is a partial echo (half echo) method as a method of delaying the timing of applying a readout gradient magnetic field without extending TE (see, for example, Non-Patent Document 1).

  In contrast to the crusher gradient magnetic field, there is a technique for improving the blood rendering ability by applying a gradient magnetic field in order to correct the dephasing of nuclear magnetization caused by the movement of blood flow etc. 2). The gradient magnetic field applied at this time is called a Gradient Moment Nulling (hereinafter, GMN) pulse. This GMN pulse is also applied in TE.

Japanese Patent No. 3434816

Ray H. Hashemi et al., “MRI: The Basics Second Edition. Philadelphia”, Lippincott Williams & Wilkins. '') (2004) pp286 Ray H. Hashemi et al., “MRI: The Basics Second Edition. Philadelphia”, Lippincott Williams & Wilkins. ]) (2004) pp325-328, pp317

  The combination with the half-echo method is effective for applying the crusher gradient magnetic field and GMN pulse sufficiently. Even when no gradient magnetic field is applied in the TE, the half-echo method is useful when imaging with a pulse sequence with a short TE. In the half-echo method, the readout gradient magnetic field application timing is delayed by not acquiring data in the high frequency region of the k space when acquiring a signal. The high-frequency data in this k-space contributes to the sharpness of the image, so depending on the ratio of the band that is not acquired to the entire band (hereinafter referred to as AMI), the ability to draw fine structures and the overall image are reduced. Blurring occurs.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress deterioration in image quality in a short TE sequence.

  The present invention obtains the gradient magnetic field application time required to achieve the object, and determines the optimum acquisition rate of the echo signal (k-space data) accordingly.

  Specifically, a magnetic resonance imaging apparatus including a control unit that controls measurement of an echo signal according to a pulse sequence, wherein the control unit determines a data acquisition rate in k-space based on an imaging condition A magnetic resonance imaging apparatus comprising: a pulse generation unit configured to generate a pulse sequence according to the imaging unit and the data acquisition rate determined by the data acquisition rate determination unit.

  The k-space data acquisition rate determination method in the magnetic resonance imaging apparatus includes a data acquisition rate determination step for determining the data acquisition rate according to the amount of gradient magnetic field applied in the TE. Provided is a data acquisition rate determination method.

  According to the present invention, it is possible to suppress deterioration in image quality in a sequence with a short TE.

Functional block diagram of the MRI apparatus of the first embodiment (a) is explanatory drawing for demonstrating the pulse sequence of 1st embodiment, (b) is explanatory drawing for demonstrating the pulse sequence of the modification of 1st embodiment. (a) And (b) is explanatory drawing for demonstrating the data acquisition rate determination process of 1st embodiment. Functional block diagram of the control unit of the first embodiment Flow chart of imaging processing of the first embodiment Flow chart of data acquisition rate determination processing of the first embodiment (a) is the k-space data arrangement acquired by the conventional half-echo method, and (b) is an explanatory diagram for explaining the k-space data arrangement acquired by the half-echo method of the present embodiment. (a) is explanatory drawing for demonstrating the pulse sequence of 2nd embodiment, (b) is explanatory drawing for demonstrating the modification of the pulse sequence of 2nd embodiment. Functional block diagram of the control unit of the second embodiment Explanatory diagram for explaining the flow velocity image acquired in the flow velocity measurement sequence Flow chart of imaging processing of the second embodiment Flow chart of data acquisition rate determination processing of the second embodiment (a) is a graph showing the relationship between the blood flow velocity v and the blood signal value SI _A, (b) is a graph showing the relationship between the crusher gradient magnetic field application amount S and the suppression rate α Pulse sequence diagram for explaining the data acquisition rate determination process of the second embodiment (a)-(d) is explanatory drawing for demonstrating the relationship between the data abandonment rate AMI and frequency band in k space. Explanatory drawing for explaining the change of the fine structure in the real space when the weight is changed Explanatory drawing for demonstrating the weighting calculation method of the data abandonment rate AMI in k space of 2nd embodiment Graph showing line profile slope δ and β Explanatory diagram for explaining the weighting calculation method of the data abandonment rate AMI in k-space during 3D measurement Schematic diagram of blood vessel wall Explanatory drawing for demonstrating the profile in k space of the blood vessel wall (a)-(d) is explanatory drawing for demonstrating the data acquisition area | region of the modification of 2nd embodiment.

<< First Embodiment >>
Hereinafter, a first embodiment to which the present invention is applied will be described. Hereinafter, in all the drawings for explaining the embodiments of the present invention, those having the same function are denoted by the same reference numerals, and repeated explanation thereof is omitted.

  In this embodiment, in imaging (GMN method) to improve blood visualization by applying a GMN pulse that corrects the dephasing of nuclear magnetization caused by movement such as blood flow, the acquisition ratio of echo signals is determined, Improve image quality.

  First, the configuration of the MRI apparatus of this embodiment will be described. FIG. 1 is a functional block diagram of the MRI apparatus 100 of the present embodiment. The MRI apparatus 100 of the present embodiment includes a magnet 102, a gradient magnetic field coil 103, a radio frequency magnetic field (RF) coil 104, an RF probe 105, a gradient magnetic field power source 106, an RF transmission unit 107, and a signal detection unit 108. A signal processing unit 109, a control unit 110, a display unit 111, an operation unit 112, and a bed 113.

  The magnet 102 generates a static magnetic field in a region (examination space) around the subject 101. The gradient magnetic field coil 103 is composed of coils in three directions of X, Y, and Z, and each applies a gradient magnetic field pulse to the examination space in accordance with a signal from the gradient magnetic field power supply 106. The RF coil 104 applies (irradiates) an RF pulse to the examination space in accordance with a signal from the RF transmission unit 107. The RF probe 105 detects an MR signal (echo signal) generated by the subject 101. The echo signal received by the RF probe 105 is detected by the signal detection unit 108, subjected to signal processing by the signal processing unit 109, and input to the control unit 110. The control unit 110 controls the operation of each unit, reconstructs an image from the input signal, and displays the image on the display unit 111. The bed 113 is for a subject to lie down.

  Note that the MRI apparatus 100 may further include a shim coil that corrects the static magnetic field inhomogeneity in the examination space, and a shim power source that supplies current to the shim coil.

  Currently, the imaging target of MRI is the main constituent substance of the subject 101, proton. By imaging the spatial distribution of proton density and the relaxation phenomenon of excited protons, the shape or function of the human head, abdomen, limbs, etc. is imaged two-dimensionally or three-dimensionally.

  At the time of imaging, different phase encoding is given depending on the gradient magnetic field, and an echo signal obtained by each phase encoding is detected. As the number of phase encodings, values such as 128, 256, and 512 are usually selected per image. Each echo signal is usually obtained as a time-series signal composed of 128, 256, 512, and 1024 sampling data. These data are subjected to Fourier transform (hereinafter referred to as FT) to create one MR image which is a two-dimensional or three-dimensional image.

  The imaging is realized by the control unit 110 controlling the operation of each unit according to a predetermined control time chart (pulse sequence). The control unit 110 controls operations of the gradient magnetic field power source 106, the RF transmission unit 107, and the signal detection unit 108 according to the pulse sequence, applies RF pulses and gradient magnetic field pulses, and collects echo signals. At this time, the application amount of the RF pulse, the gradient magnetic field pulse, and the like are determined by scan parameters set by the user via the operation unit 112.

  In the present embodiment, imaging is performed by the GMN method as described above. An example of a GMN method pulse sequence used in this embodiment is shown in FIG. In this figure, RF / SI, Gs, Gp, and Gr indicate the axes of the RF pulse and echo signal, slice selection gradient magnetic field, phase encoding gradient magnetic field, and readout gradient magnetic field, respectively.

  As shown in this figure, in the GMN method, an RF pulse 301, a slice selection gradient magnetic field 311 to be applied together with the RF pulse 301, a phase encoding gradient magnetic field 321 and a readout gradient magnetic field 331 to be applied when the echo signal 341 is acquired. , GMN pulse 322. FIG. 2 (a) illustrates a case where the GMN pulse 322 is inserted in the phase encoding direction.

  As described above, the GMN pulse 322 is a pulse applied in the TE to correct the dephasing of the nuclear magnetization caused by the movement of blood flow or the like, and the phase shift of the spin moving in the phase encoding direction is Applied to zero at the echo center. Therefore, the application amount (here, application time) of the GMN pulse 322 in the phase encoding direction is proportional to the application amount (here, application time) of the applied phase encode gradient magnetic field 321.

  In the GMN method, echo signals 341 to be arranged in each frequency region of k space are collected by changing the application amount of the phase encoding gradient magnetic field 321 during one TR. At this time, when collecting the echo signal 341 in the low frequency region of the k space, the application amount of the phase encoding gradient magnetic field 321 is small and the application time can be shortened as shown in FIG. The application amount is also small, and the application time is shortened. On the other hand, when the echo signal 341 in the high frequency region of the k space is collected, the application amount of the phase encoding gradient magnetic field 321 is increased as shown in FIG. 3B, so that the application amount of the GMN pulse 322 is also increased. Therefore, in the case of a pulse sequence with a short TE, the application time of the phase encoding gradient magnetic field 321 and the GMN pulse 322 becomes long, and these application times may overlap with the application time of the readout gradient magnetic field 331.

In such a case, a half echo method is used in which the application start time of the readout gradient magnetic field 331 is _delayed from t _rs0 which is a predetermined time to t _pf which is the application end time of the GMN pulse 322.

  At this time, in this embodiment, the application start time of the readout gradient magnetic field 331 is changed according to the total application time of the phase encoding gradient magnetic field 321 and the GMN pulse 322. In the half echo method, since the application end time of the readout gradient magnetic field 331 is not changed, the application start time of the readout gradient magnetic field 331 changes. Since the echo signal (k space data) is acquired during the application period of the readout gradient magnetic field 331, the data acquisition rate in the readout direction of the k space changes according to the application period. Here, the data acquisition rate is the ratio of the bandwidth for acquiring data in the lead-out direction to the entire bandwidth.

Note that the data acquisition rate may be specified using an AMI that is a ratio of the band in the lead-out direction where data is not acquired to the entire band. The AMI can be calculated by the following equation (1) using a predetermined readout gradient magnetic field application time T ₀ and a time ΔT obtained by delaying the readout gradient magnetic field application start time.

AMI = ΔT / T0 (1)
That is, AMI is a data abandonment rate.

  In this embodiment, the data acquisition rate is increased as much as possible for each application period of the phase encoding gradient magnetic field 321 and the GMN pulse 322, in other words, the AMI that is the data abandonment rate is increased by the phase encoding gradient magnetic field 321 and the GMN pulse. The image quality is improved by adjusting it to be as small as possible every 322 total application times.

  In order to realize this, the control unit 110 of the present embodiment includes a data acquisition rate determination unit 210, a sequence creation unit 220, and an imaging unit 230, as shown in FIG. Each of these units is realized by the CPU provided in the control unit 110 loading a program previously stored in the storage device into the memory and executing it.

The data acquisition rate determination unit 210 determines the k space data acquisition rate for each total application time of the phase encoding gradient magnetic field 321 and the GMN pulse 322. As described above, the application amount of the GMN pulse 322 changes according to the application amount of the phase encoding gradient magnetic field 321. Therefore, the data acquisition rate determination unit 210 of the present embodiment determines the k space data acquisition rate for each phase encoding. In the present embodiment, the data acquisition rate is determined by determining the readout gradient magnetic field application start time _trs corresponding to the data acquisition start time. The portion where the total application time of the gradient magnetic field of the phase encode axis (in this embodiment, the phase encode gradient magnetic field 321 and the GMN pulse 322) and the application time of the readout gradient magnetic field 331 overlap is the application time of the readout gradient magnetic field 331. Cut from. The cutting ratio is set to the minimum value at which a GMN pulse can be applied in each phase encoding.

Specifically, the data acquisition rate determination unit 210 calculates the application amount (application time) of the entire gradient magnetic field applied in the phase encoding direction for each phase encoding from the imaging conditions and imaging parameters, and the application end time t Determine _pf . Then, based on the determined application end time t _pf , the readout gradient magnetic field application start time _trs is determined.

For example, as shown in FIG. 3 (a), the data acquisition rate determination unit 210 determines the application end time t _{pf as} it is if it is before the predetermined readout gradient magnetic field application start time _trs0 . the readout gradient magnetic field application start time t _rs0, the readout gradient magnetic field application start time t _rs. On the other hand, as shown in FIG. 3 (b), when the application end time t _pf exceeds the predetermined readout gradient magnetic field application start time t _rs0 , the application end time t _{pf is set} to the readout gradient magnetic field application start time t. _rs . The predetermined readout gradient magnetic field application start time _trs0 is determined from TE, BW, the number of frequency encodings, and the like set as imaging conditions (imaging parameters).

The sequence creation unit 220 creates a pulse sequence used for imaging, reflecting the set imaging conditions and the readout gradient magnetic field application start time _trs determined by the data acquisition rate determination unit 210.

  The imaging unit 230 performs imaging in accordance with the pulse sequence created by the sequence creation unit 220, and obtains an image.

The flow of the imaging process of the present embodiment by the above units will be described with reference to FIG.
First, the data acquisition rate determination unit 210 receives settings of imaging conditions such as an imaging method and imaging parameters (step S1101). In the present embodiment, the setting of the application amount of each pulse constituting the pulse sequence 300 of the present embodiment shown in FIG.

Next, the data acquisition rate determination unit 510 performs data acquisition rate determination processing for determining the data acquisition rate for each phase encoding amount n (step S1102). The output of the data acquisition rate determination process of this embodiment is the application start time t _rsn of the _readout gradient magnetic field 331 for each phase encode n (n is a natural number). Details of the data acquisition rate determination process of this embodiment will be described later.

After that, the sequence creation unit 220 creates a pulse sequence using the set imaging conditions and the readout gradient magnetic field application start time t _rsn of each phase encode n determined by the data acquisition rate determination unit 210 in step S1102 ( Step S1103).

  Then, the imaging unit 230 executes the created pulse sequence and acquires an image (step S1104). Specifically, an echo signal is measured according to the created pulse sequence, arranged in k-space, and an image is reconstructed.

  Next, details of the data acquisition rate determination process by the data acquisition rate determination unit 210 of the present embodiment will be described. FIG. 6 is a processing flow of the data acquisition rate determination processing of the present embodiment. Here, the total number of steps of phase encoding is N (N is a natural number).

The data acquisition rate determination unit 210 of this embodiment calculates the application end time t _pfn of the phase encoding gradient magnetic field 321 and the GMN pulse 322 for each phase encoding amount n (step S1201) (step S1202).

Then, the application start time t _rsn of the _readout gradient magnetic field 331 is determined according to the result. Here, the data acquisition rate determination unit 210 _compares the application end time t _pfn of the phase encoding gradient magnetic field 321 and the GMN pulse 322 with a predetermined readout gradient magnetic field 331 application start time _trs0 (step S1203), If the end time t _pfn is before the application start time t _rs0 (t _pfn ≦ t _rs0 ), the application start time t _rsn of the _readout gradient magnetic field 331 having the phase encoding amount n is _set to t _rs0 (step S1204). .

On the other hand, if the end time t _pfn is after the application start time t _rs0 (t _pfn > t _rs0 ), the application start time t _rsn of the _readout gradient magnetic field 331 with the phase encoding amount n is _set to t _pfn ( Step S1205).

  The data acquisition rate determination unit 210 repeats the above process for the total number of phase encoding steps N (steps S1206 and S1207).

Note that the application end time t _pfn may be calculated in advance for all phase encoding amounts, and then each may be compared with the application start time _trs0 .

  As shown in FIG. 3 (a), since the application amount of the phase encoding gradient magnetic field 321 is close to 0 near the center (low frequency region) of the k space, the application amount of the GMN pulse 322 becomes 0 accordingly. Therefore, it is not necessary to cut the readout gradient magnetic field application time T0.

  On the other hand, as shown in FIG. 3 (b), the application amount of the phase encoding gradient magnetic field 321 is increased at the end portion (high frequency region) of the k space, and accordingly, the application amount of the GMN pulse 322 is also increased. Therefore, the total application time of the phase encoding gradient magnetic field 321 and the GMN pulse 322 also becomes long, and accordingly, the application time of the readout gradient magnetic field 331 needs to be shortened. The amount of data acquisition is reduced by the shortening. That is, increase the value of AMI. At this time, the reduction is performed from data in a high frequency band.

  Here, the k-space echo signal arrangement obtained by the conventional half-echo method is shown in FIG. 7 (a), and the k-space echo signal arrangement obtained according to the pulse sequence created in step S1103 is shown in FIG. 7 (b). . As shown in these figures, the AMI is conventionally constant regardless of the phase encoding amount. That is, the application start time of the readout gradient magnetic field 331 is determined based on the maximum application time of the phase encoding gradient magnetic field 321 and the GMN pulse 322. Accordingly, as shown in FIG. 7 (a), only the same amount of data can be obtained in the entire frequency region of the k space.

  On the other hand, according to the method of the present embodiment, the application start time of the readout gradient magnetic field 331 is set early in the low frequency region of the k space. That is, the AMI is set small. Therefore, as shown in FIG. 7 (b), the data acquisition rate in the low frequency region 610 in the phase encoding direction in the k space can be made higher than in FIG. 7 (a). The data acquisition rate in the high frequency region 620 of the k space is the same. Thus, since data in the low frequency region of the k space can be increased, contrast can be improved and image quality can be improved.

  In the above embodiment, two-dimensional imaging has been described as an example, and a case where a GMN pulse or the like is applied in the phase encoding direction has been described as an example. However, the present invention is not limited to this. The same applies to the case where a GMN pulse is applied in the slice direction in addition to the phase encoding direction in three-dimensional imaging. It can be applied to all pulse sequences in which a gradient magnetic field such as a GMN pulse is applied in one or two directions orthogonal to the readout direction. At this time, the total of the gradient magnetic field application times in all directions orthogonal to the readout direction may be calculated, and the readout gradient magnetic field application start time may be determined accordingly by the same method as in the above embodiment.

  As described above, the magnetic resonance imaging apparatus of the present embodiment is a magnetic resonance imaging apparatus including a control unit that controls measurement of echo signals according to a pulse sequence, and the control unit includes a gradient magnetic field applied in TE. A pulse sequence is created according to the data acquisition rate determination unit that determines the data acquisition rate of the k space, the set imaging conditions, and the data acquisition rate determined by the data acquisition rate determination unit in accordance with the applied amount of A sequence creation unit. The pulse sequence includes a gradient magnetic field to be applied in the TE, and a gradient magnetic field in the TE that changes in accordance with at least one of a phase encode gradient magnetic field and a slice encode gradient magnetic field, and the data The acquisition rate determining unit determines a data acquisition start time according to a total application amount of the slice encode gradient magnetic field, the phase encode gradient magnetic field, and the TE gradient magnetic field, and determines the data acquisition rate. To do.

  At this time, the data acquisition rate determination unit calculates the application end time of the slice encode gradient magnetic field, the phase encode gradient magnetic field, and the gradient magnetic field in TE for each slice encode and phase encode, and according to the calculation result The data acquisition rate may be determined by determining the data acquisition start time.

  The data acquisition rate determination unit may use the application end time as the data acquisition start time when the calculated application end time is later than the predetermined data acquisition start time.

  For example, the data acquisition rate determination unit can make the data acquisition rate in the high frequency region of the k space lower than the data acquisition rate in the low frequency region.

  Therefore, according to the present embodiment, the application start time of the readout gradient magnetic field 331 is determined according to the application amounts of the phase encoding gradient magnetic field 321 and the GMN pulse 322. Therefore, the acquisition time of the GMN pulse 322 can be reliably ensured. That is, even for a short TE sequence, the required GMN pulse 322 can be applied for each phase encoding. Therefore, the blood rendering ability can be sufficiently improved.

  In this embodiment, since the application start time of the readout gradient magnetic field 331 is determined according to the application amount of the phase encoding gradient magnetic field 321 and the GMN pulse 322, the application amount of the phase encoding gradient magnetic field 321 and the GMN pulse 322 is If it is small, the application time of the readout gradient magnetic field 331, that is, the data acquisition time can be sufficiently secured even with a short TE sequence. Therefore, even with a short TE sequence, a sufficient GMN pulse can be applied, and more data in the low frequency region of k-space can be obtained than in the conventional method.

  Therefore, according to the present embodiment, in the imaging using the half echo method and applying the desired gradient magnetic field in the TE, the object can be sufficiently achieved, and the data sampling amount in the low frequency region can be increased. Therefore, sufficient contrast can be obtained.

  In addition, although the case where a predetermined target gradient magnetic field is applied in addition to the gradient magnetic field for encoding in one or two directions orthogonal to the readout direction has been described as an example, the present invention is not limited thereto. For example, as shown in FIG. 2 (b), the present invention may be applied to a pulse sequence 350 in which there is no gradient magnetic field to be applied in TE other than a phase encoding gradient magnetic field and a slice encoding gradient magnetic field.

When TE is short, the gradient magnetic field application amount (application end time t _fn ) in the direction perpendicular to the readout direction is compared with the _readout gradient magnetic field application start time t _rs0 determined according to TE, and t _fn is t _rs0 In the following cases, the readout gradient magnetic field application start time is set to t _fn .

  By configuring the pulse sequence used for imaging in this way, even in the case of imaging with a short TE, data in the low frequency region can be sufficiently acquired. Therefore, an image with high contrast can be obtained with a desired TE.

<< Second Embodiment >>
Next, a second embodiment to which the present invention is applied will be described. In the first embodiment, the gradient magnetic field applied in the TE changes according to the application amount of the phase encode gradient magnetic field and the slice encode gradient magnetic field. Therefore, the data acquisition rate, that is, the readout gradient magnetic field application start time is determined from the imaging conditions in accordance with the application amount of these encode gradient magnetic fields. On the other hand, in this embodiment, the gradient magnetic field applied in the TE is not affected by the application amount of the phase encode gradient magnetic field and the slice encode gradient magnetic field. In this embodiment, in such a case, an optimum data acquisition rate is determined in order to improve the image quality.

  In the present embodiment, a crusher gradient magnetic field will be described as an example of the gradient magnetic field applied in the TE. The crusher gradient magnetic field is applied in order to suppress blood from outside the imaging surface when imaging fluid such as blood. The applied amount of the crusher gradient magnetic field varies depending on the blood flow rate.

  The high frequency region of k-space greatly contributes to image sharpness. On the other hand, the low frequency region greatly contributes to the rough contrast of the image. Therefore, in this embodiment, the necessary crusher gradient magnetic field application amount is obtained from the blood flow velocity, the slab thickness, etc., and the data acquisition rate (AMI) in the readout direction and the crusher gradient magnetic field in accordance with the frequency region of the k space. The applied amount is determined. The blood flow rate that determines the application amount of the crusher gradient magnetic field is obtained by pre-measurement or pre-scan.

  The MRI apparatus used in this embodiment is the same as that in the first embodiment. Hereinafter, the present embodiment will be described focusing on the configuration different from the first embodiment.

  First, the pulse sequence of this embodiment will be described. As described above, in this embodiment, by applying a crusher gradient magnetic field according to the blood flow velocity, blood outside the imaging surface is suppressed and image quality is improved.

  FIG. 8 (a) is an example of the pulse sequence 400 of the present embodiment. Here, a case where the SE (spin echo) method is used is illustrated. The crusher gradient magnetic field is applied before and after the 180 ° pulse. In the SE method, the crusher gradient magnetic field pulse may be inserted in at least one axial direction of the three axial directions. Here, as an example, a case of applying in the slice encode gradient magnetic field axis direction (slice direction) is illustrated. In this figure, RF / SI, Gs, and Gr are axes of an RF pulse and an echo signal, a slice selection gradient magnetic field, and a readout gradient magnetic field, respectively. Here, the phase encoding axis is not shown.

  As shown in the figure, the pulse sequence of the present embodiment includes a 90 ° pulse 401, a 180 ° pulse 402, a slice selection gradient magnetic field 411 to be applied together with the 90 ° pulse, a slice refocus gradient magnetic field 412, and a 180 ° A slice selection gradient magnetic field 414 to be applied together with the pulse, crusher gradient magnetic fields 413 and 415 to be applied before and after the slice selection gradient magnetic field 414, and a readout gradient magnetic field 431 to be applied when the echo signal 441 is acquired.

  Note that the crusher gradient magnetic field 413 applied before the 180 ° pulse 402 may be superposed with the slice refocus gradient magnetic field 412 as 416 as shown in the pulse sequence 450 of FIG.

  In the present embodiment, the blood flow rate is determined by pre-measurement or pre-scanning, and based on the blood flow rate, the maximum application amount of the necessary crusher gradient magnetic fields 413 and 415 is determined. Then, the application amount of the crusher gradient magnetic fields 413 and 415 and the application time of the readout gradient magnetic field 431, that is, the data acquisition rate and AMI are changed according to the frequency region of the k space. Here, the maximum application amount of the necessary crusher gradient magnetic fields 413 and 415 is referred to as a reference application amount of the crusher gradient magnetic fields 413 and 415.

  It is an echo signal arranged in the low frequency region of k-space that affects the contrast of the reconstructed image. Therefore, in this embodiment, when acquiring an echo signal arranged in the low frequency region of k-space, the necessary maximum amount (reference application amount) of the crusher gradient magnetic fields 413 and 415 is applied to sufficiently suppress blood outside the imaging surface. And maintain the contrast of the image. On the other hand, the echo signal arranged in the high frequency region does not affect the contrast of the image as much as the low frequency region. However, it affects the sharpness of the image. Therefore, at the time of acquiring the echo signal arranged in the high frequency region, the application of the crusher gradient magnetic fields 413 and 415 is reduced, the data acquisition rate is increased correspondingly, and the sharpness of the image is maintained.

  In order to realize this, the control unit 110 of the present embodiment, as shown in FIG. 9, in addition to the data acquisition rate determination unit 510, the sequence creation unit 520, the imaging unit 530, the flow rate determination unit 540, Is provided. Each of these units is realized by the CPU provided in the control unit 110 loading a program previously stored in the storage device into the memory and executing it.

The flow rate determination unit 540 determines the flow rate of the blood flow in the target blood vessel. Specifically, the same position as the imaging position of the main imaging is imaged by a flow velocity measurement sequence (typically a Phase Contrast sequence), and a flow velocity image 701 representing the flow velocity distribution is acquired. An example of the flow velocity image 701 acquired here is shown in FIG. Then, the flow velocity determination unit 540 identifies the flow velocity V ₁ of the target blood vessel 702 in the acquired flow velocity image 701. It should be noted that the flow velocity image 701 may be configured so that the operator inputs from the experience value as a parameter. Further, the MRI apparatus 100 may be configured to hold it as a fixed value.

As in the first embodiment, the data acquisition rate determination unit 510 of this embodiment determines the data acquisition rate for each phase encoding. Also in this embodiment, since the application end time of the readout gradient magnetic field 331 is fixed as in the first embodiment, the readout gradient magnetic field application start time _trs is determined.

As in the first embodiment, the sequence creation unit 520 creates a pulse sequence used for imaging, reflecting the set imaging conditions and the readout gradient magnetic field application start time _trs determined by the data acquisition rate determination unit 510. To do.

  The imaging unit 530 performs imaging in accordance with the pulse sequence created by the sequence creation unit 220 to obtain an image.

  Next, the flow of the imaging process of this embodiment by these units will be described with reference to FIG.

  First, the control unit 110 accepts setting of imaging conditions such as an imaging method and imaging parameters (step S2101). In the present embodiment, setting of the application amount of each pulse constituting the pulse sequences 400 and 450 of the present embodiment shown in FIG. 8 (a) or FIG. 8 (b) excluding the crusher gradient magnetic field pulse is accepted.

Then, the flow rate determining unit 540 performs the imaging of the imaging position of the imaging at a flow rate measurement sequence, and calculates the flow velocity V ₁ of the target vessel 702 (step S2102).

Next, the data acquisition rate determination unit 510 performs a data acquisition rate determination process for determining the data acquisition rate for each phase encoding based on the blood flow velocity V ₁ (step S2103). The output of the data acquisition rate determination process of the present embodiment is the application start time t _rsn of the _readout gradient magnetic field 431 for each phase encode n. Details of the data acquisition rate determination process of this embodiment will be described later.

After that, the sequence creation unit 520 creates a pulse sequence using the set imaging conditions and the readout gradient magnetic field application start time _trsn of each phase encode n determined by the data acquisition rate determination unit 510 in step S2103 ( Step S2104).

  Then, the imaging unit 530 executes the created pulse sequence and acquires an image (step S2105). Specifically, an echo signal is measured according to the created pulse sequence, arranged in k-space, and an image is reconstructed.

  Next, details of the data acquisition rate determination process by the data acquisition rate determination unit 510 of the present embodiment will be described. FIG. 12 is a processing flow of the data acquisition rate determination processing of the present embodiment.

  First, the data acquisition rate determination unit 510 uses the blood flow rate determined by the flow rate determination unit 540 to determine a reference application amount that is a necessary crusher gradient magnetic field application amount (step S2201). From the determined reference application amount and TE, the application start time of the readout gradient magnetic field 431 when applying the reference application amount of the crusher gradient magnetic field is determined. Then, the AMI at this time is calculated (step S2202). The application start time of the readout gradient magnetic field 431 when applying the reference application amount of the crusher gradient magnetic field is referred to as a reference application start time, and AMI is referred to as a reference AMI.

Then, the data acquisition rate determination unit 510 uses the reference AMI and a predetermined edge rendering capability coefficient Q to determine how to change the AMI for each phase encoding (hereinafter referred to as a weight) (step S2203). ). Then, the data acquisition rate determination unit 510 performs a crusher gradient magnetic field application amount (actual application amount) that is actually applied for each phase encoding n according to the determined weight, and a readout gradient magnetic field application start time that can realize the actual application amount. t _rsn is determined (step S2204).

Specific examples of obtaining the reference application amount S, which is the required crusher gradient magnetic field application amount, from the blood flow velocity V ₁ in the reference application amount determination process in step S2201 above are shown in FIGS. 13 (a) and 13 (b). I will explain.

And blood flow velocity V [cm / s], and the signal value SI _A blood, the case of fixing the imaging conditions such as the TE and slab thickness, is inversely proportional, as shown in FIG. 13 (a). Further, the applied amount S [sec * T / m] of the crusher gradient magnetic field and the blood suppression rate α [%] are in an inversely proportional relationship as shown in FIG. The suppression rate α is a ratio of the blood signal value when the crusher gradient magnetic field is applied to the blood signal value when the crusher gradient magnetic field is not applied. Usually, it may be suppressed to about 10%.

First, the data acquisition rate determination unit 510, the relationship between the blood flow velocity V and the signal value SI _A showing a graph of FIG. 13 (a), by substituting the calculated blood flow velocity V _1, the predicted signal value of the blood Calculate SI _A (V ₁ ).

Next, the data acquisition rate determination unit 510 calculates a crusher gradient magnetic field application area (application amount) S ₁ necessary for suppressing blood. Specifically, the desired suppression rate α ₁ is substituted into the relational expression between the application amount S and the suppression rate α shown in the graph of FIG. 13 (b), and the necessary gradient magnetic field application area S (α ₁ ) is calculated. calculate. For the suppression rate α _{1 to be} substituted, for example, the above value of 10% is used. Note that α ₁ may hold an experience value internally, or may be input as a parameter by the operator. The calculated application amount S ₁ and the reference application amount.

  Next, determination of the reference application start time of the readout gradient magnetic field 431 and the reference AMI by the data acquisition rate determination unit 510 in step S2202 will be described.

Data acquisition rate determination unit 510, based on the reference application amount S _1, to determine these criteria the application start time and the reference AMI. FIG. 14 shows an extracted portion related to the pulse sequence shown in FIG. The time (Duration) required for the MRI apparatus 100 to apply the reference application amount S ₁ of the crusher gradient magnetic field 415 applied after the 180 ° pulse 402 is 451. The band 452 where the crusher gradient magnetic field 415 overlaps the readout gradient magnetic field 431 is cut. That is, the application end time of the crusher gradient magnetic field 415 is set as the reference application start time _trs . When the overlapping time interval is Ta and the application time of the readout gradient magnetic field 431 is TGr, the reference AMI is expressed by Ta / TGr.

Next, an AMI weight determination method in step S2203 will be described. Upon determining a reference application start time t _rs and reference AMI, data acquisition rate determination unit 510 includes a reference application amount S _1, using the factor Q of a predetermined edge depiction performance, to determine the weight of AMI.

First, the relationship between the frequency band and the AMI weight in the k space will be described with reference to FIGS. 15 (a) to 15 (d) and FIG. FIG. 15 (a) shows the state of k-space when all signals in k-space are acquired, that is, when AMI = 0 [%] (case 1). At this time, the readout gradient magnetic field application start time t _rs is a readout gradient magnetic field application start time t _rs0 a predetermined.

  FIG. 15 (b) shows the state of the k space when the half-echo method is used and the signal in the high frequency region is uniformly cut by A%, that is, when AMI = A [%] (case 2).

  Fig. 15 (c) shows the state of k space when echo signals are acquired (case 3) so that AMI is A% when the phase encoding amount is 0 and AMI decreases toward the high frequency region. .

  Fig. 15 (d) shows the state of k-space when echo signals are acquired (case 4) so that the AMI when the phase encoding amount is 0 is A% and the AMI increases toward the high frequency region. It is. FIG. 16 shows a change in the line profile of the edge portion of the fine structure on the image (real space) reconstructed from the respective k-space data in each of these cases. 15 (b) to 15 (d) show a case where A% = 25%.

  As shown in FIG. 16, the line profile of case 2 is broader than that of case 1. On the other hand, in Case 3 where the AMI in the high frequency region is reduced, the profile improves. Conversely, in case 4 where the AMI in the high frequency region is increased, the profile deteriorates. In other words, it can be seen that, when improving the ability to draw a fine structure, it is better to reduce the AMI in the high frequency region as in Case 3 shown in FIG. 15 (c).

  In the present embodiment, in view of this, AMI weighting as in Case 3 is realized. In other words, when the phase encoding amount is 0, the application of the readout gradient magnetic field 431 is started at a time when all the necessary crusher gradient magnetic field application amount can be applied (the AMI as the reference AMI at this time), and the other In the region, the crusher gradient magnetic field application amount is reduced and the AMI is also reduced at the higher frequency region.

  Next, a method for determining the weighting in case 3 will be described. Here, a case where the area to be cut in the k space is a semi-ellipse circumscribing the k space as shown in FIG.

  When the radius of the ellipse in the kr direction is Φr, Φr is the minimum value to which the reference application amount S of the crusher gradient magnetic field can be applied, that is, 502 (Ta) in FIG. When expressed using the value AMI of AMI, Φr = A × Wkr where the total bandwidth of kr is Wkr.

  On the other hand, the radius in the kp direction is Φp. When the total bandwidth is Wkp, the radius is expressed as Φp = β × Wkp. At this time, when β is infinite or close to infinity, the radius Φp is also infinite, and there is no weight ((FIG. 15 (b)) as in case 2. Also, when β = 1, the radius Φp is Wkp, which is the same weight as case 3 (FIG. 15 (c)).

  Here, assuming that the slope of the line profile at the edge portion in FIG. 16 is δ, there is a relationship shown in FIG. 18 between β and δ. That is, δ changes according to β.

Here, the slope when AMI = 0 [%] is δ ₀ , and the slope when AMI = A [%] and no weight (case 2) in FIG. 15B is δ _C. When AMI is A [%], the image quality can be improved between δ ₀ and δ _C. Here, δ ₀ / δ (β) is defined as an image quality improvement coefficient (edge rendering ability coefficient) Q. The data acquisition rate determination unit 510 of the present embodiment determines δ (β) according to a preset edge rendering ability coefficient Q, and specifies the weighting from the relationship between β and δ _C shown in FIG. To decide. Note that Q may be held as a recommended value by the system, or may be input by an operator.

The data acquisition rate determination unit 510 of this embodiment calculates Φp = β × Wkp according to the determined β, determines the AMI for each phase encoding amount n, and determines the readout gradient magnetic field application start time t _rsn . Further, the actual application amount G _crn of the crusher gradient magnetic field for each phase encoding amount n is determined from TE and the readout gradient magnetic field application start time _trsn .

  In this embodiment, the case of 2D imaging has been described as an example, but the same applies to 3D imaging. That is, when the phase encoding and slice encoding are 0, the reference application amount is calculated, and based on that, the reference AMI is determined, weighted so as to satisfy the predetermined edge rendering capability coefficient Q, and for each phase encoding and slice encoding. Determine the AMI. As shown in FIG. 19, the weighting is determined in the same manner as in 2D imaging.

  As described above, the magnetic resonance imaging apparatus of the present embodiment is a magnetic resonance imaging apparatus including a control unit that controls measurement of echo signals according to a pulse sequence, and the control unit includes a gradient magnetic field applied in TE. Creation of a pulse sequence according to the data acquisition rate determining unit that determines the data acquisition rate of k-space according to the applied amount, the imaging conditions, and the data acquisition rate determined by the data acquisition rate determining unit A section.

  The imaging target is a fluid, and the pulse sequence includes a crusher gradient magnetic field whose application amount changes according to the flow rate of the fluid, and the control unit determines a flow rate of the fluid of the imaging target. A data acquisition rate determination unit that calculates a data acquisition rate according to an application amount of the crusher gradient magnetic field determined according to the flow velocity, and then calculates a desired value for each of at least one of phase encoding and slice encoding. The data acquisition rate is weighted according to image quality, and the data acquisition rate is determined.

  The reference application amount may be determined so as to achieve a desired suppression rate based on a signal value of the fluid determined according to the flow velocity.

  The reference data acquisition rate is defined as a predetermined data acquisition time TGr, and a time when the application time when the crusher gradient magnetic field is applied by the reference application amount overlaps the predetermined data acquisition time TGr is Ta. Then, it may be calculated as a value obtained by dividing Ta by TGr.

  The weight may be determined such that the applied amount of the crusher gradient magnetic field is reduced as the frequency goes to a high frequency region, using a preset index for specifying the image quality.

  For example, the data acquisition rate determination unit can make the data acquisition rate in the high frequency region of the k space higher than the data acquisition rate in the low frequency region.

  The high frequency region of k-space greatly contributes to the sharpness of the image. On the other hand, the low frequency region greatly contributes to the rough contrast of the image. According to the present embodiment, a sufficient crusher gradient magnetic field is applied in a low frequency region that contributes to contrast, and AMI is reduced and acquired data is increased in a high frequency region that contributes to image sharpness. Therefore, it is possible to obtain an image with sufficient blood suppression effect and reduced reduction in the ability to draw a fine structure and overall image blur.

  According to the present embodiment, the imaging efficiency can be improved from the flow velocity of the fluid to be imaged and the frequency characteristics of the k space, and even when the TE is short and the half-echo method is used, the deterioration of the image quality can be reduced.

  In the above embodiment, the reference application amount of the crusher gradient magnetic field when the application amount of the phase encoding gradient magnetic field is 0 is determined using the suppression rate α. However, the method for determining the reference application amount is not limited to this. For example, the reference application amount may be calculated by converting into a signal value.

In general, when analyzing using the signal value of the acquired image, it is desirable that the blood signal value be equal to or less than a certain value SI ₁ in order to facilitate discrimination between blood and other tissues. Therefore, when calculating the reference application amount in terms of signal value, since α (S) × SI _A (V ₁ ) is the blood signal value predicted when the crusher gradient magnetic field is applied, SI ₁ = α S satisfying (S) × SI _A (V ₁ ) is calculated and set as a crusher gradient magnetic field application area S ₁ .

  In the above embodiment, the weighting is determined regardless of the position of the region of interest in the imaging range. However, the AMI weighting may be determined in consideration of a specific tissue in the imaging range. Good.

  For example, in blood vessel diagnosis, it may be important to clearly depict a specific tissue such as a blood vessel lumen or a blood vessel wall. An organization to be clearly drawn may be specified in advance, and in consideration thereof, the weight of the AMI may be determined in step S2203.

When improving the blur of a fine structure, the weight of k space can be determined more suitably by designating a fine structure. Hereinafter, a case where a blood vessel wall is designated as a fine structure will be described.
The designation of the structure may be a value held by the system, or may be designated by the operator using the size or name of the structure.

  FIG. 20 is a view schematically showing the blood vessel wall 710. Here, the blood vessel wall 710 has a structure with a thickness of Wx. As shown in FIG. 21, the structure having such a structure is a signal having 0 intersections for every 1 / Wx in the kx space. If such a signal is cut at the peak of the signal as shown at 711 in FIG. 21, an artifact called ripple is likely to appear in the reconstructed image (real space), resulting in poor visibility of the fine structure. . Conversely, if the signal is cut at a zero crossing such as 712, ripples are unlikely to appear in the reconstructed image (real space).

  Therefore, in determining the weight in step S2203, if Φr and Φp are limited to an integral multiple of 1 / Wx, a result image with less ripple can be acquired.

The average vessel wall thickness Wx depends on the site, but is about 1.5 mm at the neck. In this case, Φr and Φp may be limited to integer multiples of 667 [m ⁻¹ ].

  In this way, when changing the applied amount of the crusher gradient magnetic field so as to decrease toward the high frequency region, this change is specified by a coefficient according to the thickness of the structure to be imaged. As a result, a resulting image can be obtained.

  Further, when the size of the imaging field of view is FOVx, the pixel size in the k space is 1 / FOVx. Therefore, the restriction of Φr and Φp in the k space may be specified by the number of pixels.

  In the methods of the above embodiments, the direction in which image blur occurs and the direction in which the blur can be improved are limited to the lead-out direction. In this case, the result image is an image having anisotropy in which the image is blurred only in the readout direction. In order to improve this, for example, when signals are acquired a plurality of times and integrated, a region where the data acquisition ratio in the k space is reduced may be changed for each integration. Details of this method are shown in FIG.

  Here, every time a signal is acquired, the area where the signal is cut is changed. For example, when signals are acquired twice and integrated, the first time, as shown in FIG. 22 (a), the one end side in the lead-out direction is cut and signals are acquired as in the above embodiments. Then, in the second time, as shown in FIG. 22 (b), the area where the signal is not acquired (the area to be cut) is changed to the end opposite to that in FIG. 22 (a) in the lead-out direction. Note that the signal acquisition as shown in FIG. 22B can be realized by inverting the polarity of the readout gradient magnetic field Gr in the pulse sequence that realizes the signal acquisition shown in FIG.

  Furthermore, the application axis of the readout gradient magnetic field Gr221 may be changed. Regions obtained by changing are shown in FIG. 22 (c) and FIG. 22 (d). These can be realized by changing the application axes of the readout gradient magnetic field Gr and the phase encoding gradient magnetic field in the pulse sequence for realizing the signal acquisition in FIGS. 22 (a) and 22 (b).

  For example, when acquiring and integrating signals four times, signals are acquired as shown in FIGS. 22 (a), 22 (b), 22 (c), and 22 (d), respectively. To reconstruct the image.

  In this way, the pulse sequence is configured to change the readout gradient magnetic field so that the signal acquisition region changes with each repetition, the obtained k-space data is integrated, and the image is reconstructed to cut each. Can be complemented, and blurring of the image can be reduced. In addition, since the different cut areas are integrated, the cut area as a whole is isotropic, and the blur of the obtained image is isotropic.

  As described above, according to each embodiment of the present invention, in accordance with the application amount of the gradient magnetic field applied in the TE, the acquisition ratio of the partial echo is determined so that a desired image quality can be realized, Determine the data acquisition rate in k-space. Accordingly, a sufficient suppression effect can be obtained in fluid imaging, and a reduction in the ability to draw a fine structure caused by a half-echo and an overall image blur can be reduced. In addition, when integrating a plurality, it is possible to make the direction in which the rendering ability decreases isotropic.

  In addition, each unit in each of the above embodiments may be realized by a unit other than the control unit 110 included in the MRI apparatus 100. For example, the control unit 110 of the MRI apparatus 100 and the MRI apparatus 110 capable of transmitting and receiving data may be constructed on an information processing apparatus that is independent.

  100 MRI system, 101 Subject, 102 Magnet, 103 Gradient magnetic field coil, 104 RF coil, 105 RF probe, 106 Gradient magnetic field power supply, 107 RF transmitter, 108 Signal detector, 109 Signal processor, 110 Controller, 111 Display Unit, 112 operation unit, 113 bed, 210 data acquisition rate determination unit, 220 sequence creation unit, 230 imaging unit, 300 pulse sequence, 301 RF pulse, 311 slice selection gradient magnetic field, 321 phase encoding gradient magnetic field, 322 GMN pulse, 331 Readout gradient magnetic field, 341 echo signal, 350 pulse sequence, 400 pulse sequence, 401 90 ° pulse, 402 180 ° pulse, 411 slice selective gradient magnetic field, 412 slice refocus gradient magnetic field, 413 crusher gradient magnetic field, 414 slice selective gradient magnetic field , 415 crusher gradient field, 431 readout gradient field, 441 echo signal, 450 pulse sequence, 451 Duration, 452 band , 510 Data acquisition rate determination unit, 520 sequence creation unit, 530 imaging unit, 540 flow velocity determination unit, 610 low frequency region, 620 high frequency region, 701 flow velocity image, 702 vessel of interest, 710 blood vessel wall, 711 signal peak, 712 0 intersection

Claims (16)

A magnetic resonance imaging apparatus including a control unit that controls measurement of an echo signal according to a pulse sequence,
The control unit is a data acquisition rate determination unit that determines the data acquisition rate of k-space according to the application amount of the gradient magnetic field applied within the echo time (TE),
A magnetic resonance imaging apparatus, comprising: a sequence creation unit that creates a pulse sequence according to a set imaging condition and a data acquisition rate determined by the data acquisition rate determination unit. The magnetic resonance imaging apparatus according to claim 1,
The pulse sequence is a gradient magnetic field to be applied in the TE, and includes a gradient magnetic field in TE whose application amount changes according to the application amount of at least one of a phase encode gradient magnetic field and a slice encode gradient magnetic field,
The data acquisition rate determination unit determines a data acquisition start time according to a total application amount of the slice encode gradient magnetic field, the phase encode gradient magnetic field, and the gradient magnetic field in TE, and determines the data acquisition rate. A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 2,
The data acquisition rate determination unit calculates an application end time of the slice encode gradient magnetic field, the phase encode gradient magnetic field, and the gradient magnetic field in TE for each slice encode and phase encode, and acquires the data according to the calculation result A magnetic resonance imaging apparatus, wherein the data acquisition rate is determined by determining a start time. The magnetic resonance imaging apparatus according to claim 3,
The data acquisition rate determination unit, when the calculated application end time is later than the predetermined data acquisition start time, sets the application end time as the data acquisition start time. . The magnetic resonance imaging apparatus according to claim 2,
The magnetic resonance imaging apparatus, wherein the gradient magnetic field in TE is a GMN pulse. The magnetic resonance imaging apparatus according to any one of claims 1 to 5,
The magnetic resonance imaging apparatus, wherein the data acquisition rate determination unit makes the data acquisition rate in a high frequency region of k space lower than the data acquisition rate in a low frequency region. The magnetic resonance imaging apparatus according to claim 1,
The imaging object is a fluid,
The pulse sequence includes a crusher gradient magnetic field whose applied amount changes according to the flow velocity of the fluid,
The control unit further includes a flow rate determination unit that determines a flow rate of the fluid to be imaged,
The data acquisition rate determination unit calculates a data acquisition rate according to a reference application amount that is an application amount of the crusher gradient magnetic field determined according to the flow velocity as a reference data acquisition rate, and then at least in a phase encoding direction and a slice encoding direction On the other hand, a magnetic resonance imaging apparatus, wherein the data acquisition rate is determined by weighting the data acquisition rate according to a desired image quality. The magnetic resonance imaging apparatus according to claim 7 ,
The crusher gradient magnetic field suppresses the fluid from outside the imaging surface,
The magnetic resonance imaging apparatus characterized in that the reference application amount is determined based on a signal value of the fluid determined according to the flow velocity so as to realize a desired suppression rate. The magnetic resonance imaging apparatus according to claim 7,
The magnetic resonance imaging apparatus characterized in that the reference application amount is determined such that a signal value of the fluid determined according to the flow velocity is equal to or less than a predetermined value. The magnetic resonance imaging apparatus according to claim 7,
The reference data acquisition rate is defined as TGr as a predetermined data acquisition time, and Ta as an application time when the crusher gradient magnetic field is applied by the reference application amount and the predetermined data acquisition time TGr. The magnetic resonance imaging apparatus is calculated as a value obtained by dividing Ta by TGr. The magnetic resonance imaging apparatus according to claim 7,
The magnetic resonance imaging apparatus according to claim 1, wherein the weight is determined so as to reduce an application amount of the crusher gradient magnetic field as the frequency goes to a high frequency region, using a preset index for specifying the image quality. The magnetic resonance imaging apparatus according to claim 7,
The magnetic resonance imaging apparatus, wherein the weight is determined in consideration of a structure of an imaging target. The magnetic resonance imaging apparatus according to claim 11,
The change in the applied amount of the crusher gradient magnetic field is specified by a coefficient corresponding to the thickness of the structure to be imaged. The magnetic resonance imaging apparatus according to any one of claims 7 to 13,
The magnetic resonance imaging apparatus, wherein the data acquisition rate determination unit makes the data acquisition rate in a high frequency region of k space higher than the data acquisition rate in a low frequency region. The magnetic resonance imaging apparatus according to any one of claims 1 to 14 ,
The controller is configured to repeat the measurement of the echo signal according to the pulse sequence a plurality of times for each repetition time of the pulse sequence, and to integrate the obtained results,
The sequence creation unit changes the readout gradient magnetic field so that the data acquisition region changes at every repetition. A method for determining a data acquisition rate of k-space in a magnetic resonance imaging apparatus,
Data acquisition rate determination method characterized by comprising a data acquisition rate determining step of determining a data acquisition rate according to the application amount of the gradient magnetic field to be applied to the echo time in (TE).

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