JP2015066085A - Magnetic resonance apparatus and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic resonance apparatus which can suppress degradation of image quality to the minimum and can increase the number of slices to be photographed during 1TR.SOLUTION: A magnetic resonance apparatus has: scanning means which performs sequences B1, B2, and B3 for collecting an echo of a central ky view, echos of 32 positive views, and echos of 5 negative views out of 31 negative views from a slice; view number setting means which sets a value of a number x of negative ky views for collecting echos; pulse width setting means which sets a pulse width δ of an MPG on the basis of the value of x; and amplitude setting means which sets an amplitude g of the MPG on the basis of the pulse width δ.

Description

  The present invention relates to a magnetic resonance apparatus that executes a sequence including MPG for performing diffusion weighting, and a program applied to the magnetic resonance apparatus.

MPG (Motion
A method of acquiring a diffusion weighted image using Probing Gradient) is known (see Patent Document 1).

JP 2012-157687 A

  A DWEPI (Diffusion Weighted EPI) method using EPI is also known as a method for acquiring a diffusion weighted image. In DWEPI, in order to make the effective TE (Echo Time) as short as possible, the MPG amplitude is set to the maximum value of the MPG amplitude that can be set by the magnetic resonance apparatus. In DWEPI, echoes are generally collected by the fractional ky method. In the fractional ky method, echoes of ky views that are approximately half of the k space are collected by single shot EPI, but the echoes of the remaining ky views are not collected, so that the scan time can be shortened. However, in DWEPI, as described above, the MPG amplitude is set to the maximum value in order to shorten the effective TE, so that the amount of heat generated by the gradient magnetic field power supply increases. In general, the amount of heat generated by the gradient magnetic field power source is proportional to the square integral of the area of the gradient pulse waveform. Therefore, if the MPG amplitude is set to the maximum value, the amount of heat generated by the gradient magnetic field power source becomes considerably large. Therefore, in order to reduce the load of the gradient magnetic field power source, it is necessary to increase the waiting time between sequences. For this reason, when performing multi-slice scanning, there is a problem that it is difficult to increase the number of slices to be imaged during 1TR.

  Therefore, as a method of reducing the heat generation amount of the gradient magnetic field power source, it is conceivable to increase the MPG pulse width. Since the MPG amplitude can be reduced by widening the MPG pulse width, the amount of heat generated by the gradient magnetic field power supply can be reduced. However, if the MPG pulse width is too wide, there is a problem that the effective TE is extended. As a method for preventing the extension of the effective TE, it is conceivable to reduce the number of echo trains collected in one single shot EPI. However, if the number of echo trains is too small, the SN ratio is lowered and the image quality is greatly deteriorated. There is a problem of doing.

  Therefore, a technique for minimizing the deterioration of image quality and increasing the number of slices to be photographed during 1TR is desired.

The first aspect of the present invention includes k negative views with view numbers −n to −1, a central view with view number 0, and m positive views with view numbers 1 to m. A magnetic resonance apparatus that performs a sequence for collecting echoes arranged in space and collects echoes from a plurality of slices during 1TR,
A sequence including MPG for performing diffusion weighting, wherein, from the slice, the echo of the central view, the echoes of the m positive views, and x of the n negative views (< n) a scanning means for executing a sequence for collecting the echoes of the negative view of the book;
View number setting means for setting the value of x;
Pulse width setting means for setting the pulse width of the MPG based on the value of x;
Amplitude setting means for setting the amplitude of the MPG based on the pulse width;
This is a magnetic resonance apparatus.

The second aspect of the present invention includes k negative views with view numbers −n to −1, a central view with view number 0, and m positive views with view numbers 1 to m. A magnetic resonance apparatus that performs a sequence for collecting echoes arranged in space and collects echoes from a plurality of slices during 1TR,
A sequence including MPG for performing diffusion weighting, wherein from the slice, echoes of the central view, echoes of the n negative views, and x (<< of the m positive views) m) a scanning means for executing a sequence for collecting the echoes of the negative view of the book;
View number setting means for setting the value of x;
Pulse width setting means for setting the pulse width of the MPG based on the value of x;
Amplitude setting means for setting the amplitude of the MPG based on the pulse width;
This is a magnetic resonance apparatus.

A third aspect of the present invention includes k negative views with view numbers −n to −1, a central view with view number 0, and m positive views with view numbers 1 to m. A magnetic resonance apparatus that executes a sequence for collecting echoes arranged in space and collects echoes from a plurality of slices during 1TR, and includes a MPG for performing diffusion weighting. Collect the echoes of the central view, the echoes of the m positive views, and the echoes of x (<n) negative views out of the n negative views from the slice. A program applied to a magnetic resonance apparatus for executing a sequence for
A view number setting process for setting the value of x;
A pulse width setting process for setting the MPG pulse width based on the value of x;
An amplitude setting process for setting the amplitude of the MPG based on the pulse width;
Is a program for causing a computer to execute.

The fourth aspect of the present invention includes k negative views with view numbers −n to −1, a central view with view number 0, and m positive views with view numbers 1 to m. A magnetic resonance apparatus that executes a sequence for collecting echoes arranged in space and collects echoes from a plurality of slices during 1TR, and includes a MPG for performing diffusion weighting. Collect from the slice the echoes of the central view, the echoes of the n negative views, and the echoes of x (<m) negative views of the m positive views. A program applied to a magnetic resonance apparatus for executing a sequence for
A view number setting process for setting the value of x;
A pulse width setting process for setting the MPG pulse width based on the value of x;
An amplitude setting process for setting the amplitude of the MPG based on the pulse width;
Is a program for causing a computer to execute.

  Since the value of the number x of views from which echoes are collected is set before setting the MPG pulse width, it is possible to ensure the minimum necessary SN ratio. In addition, since the MPG amplitude is set based on the MPG pulse width, the MPG amplitude can be set to the smallest possible value. Therefore, since the amount of heat generated by the gradient magnetic field power supply of the MR apparatus can be reduced, the waiting time between sequences can be shortened, and as a result, the number of slices to be imaged during 1TR can be increased.

It is the schematic of the magnetic resonance apparatus of one form of this invention. It is a figure which shows schematically the imaging | photography site | part of this form. It is explanatory drawing when the image of slice SL1 is acquired. It is a figure which shows an example of sequence A1. It is a figure which shows an example of sequence A2. It is a figure which shows an example of sequence A3. It is a figure which shows the example in which sequence A1, A2, and A3 for acquiring the image of slice SL2 is performed during idle time t _id . It is explanatory drawing when acquiring the image of slice SL3. It is explanatory drawing of another scan. It is explanatory drawing of sequence B1. It is a figure which compares and shows the sequence A1 and the sequence B1. It is a figure which shows sequence B2 concretely. It is a figure which shows sequence B3 concretely. It is a figure which shows the flow in this form. It is a figure which shows an example of the method of making an operator select SN ratio priority mode or slice number priority mode.

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

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

  The magnet 2 has a bore 21 in which the subject 11 is accommodated. The magnet 2 includes a gradient coil 22 and an RF coil (not shown).

  The table 3 has a cradle 3 a that supports the subject 11. The cradle 3a is configured to be able to move into the bore 21. The subject 11 is transported to the bore 21 by the cradle 3a.

  The reception coil 4 is attached to the subject 11. The receiving coil 4 receives a magnetic resonance signal from the subject 11.

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

  The transmitter 5 supplies current to the RF coil, and the gradient magnetic field power supply 6 supplies current to the gradient coil 22. The receiver 7 performs signal processing such as detection on the signal received from the receiving coil 4. A combination of the magnet 2, the receiving coil 4, the transmitter 5, the gradient magnetic field power source 6, and the receiver 7 corresponds to the scanning means.

  The control unit 8 transmits necessary information to the display unit 9 and reconstructs an image based on data received from the receiving coil 4 so as to realize various operations of the MR device 100. Control the operation of each part. The control unit 8 includes a view number setting unit 81, a pulse width setting unit 82, an amplitude setting unit 83, and the like.

The view number setting means 81 sets the number x of negative ky views from which echoes are collected.
The pulse width setting means 82 sets the MPG pulse width δ.
The amplitude setting means 83 sets the MPg amplitude g.

  The control unit 8 is an example of a view number setting unit 81, a pulse width setting unit 82, and an amplitude setting unit 83, and functions as these units by executing a predetermined program.

The operation unit 9 is operated by an operator and inputs various information to the control unit 8. The display unit 10 displays various information.
The MR apparatus 100 is configured as described above.
The subject 11 is imaged using the MRI apparatus 100 configured as described above.

FIG. 2 is a diagram schematically showing an imaging region of this embodiment.
In this embodiment, the head is photographed. The operator sets a plurality of slices on the head. Here, for convenience of explanation, it is assumed that three slices SL1 to SL3 are set. Below, the method to acquire the image of slice SL1-SL3 is demonstrated.

3 to 8 are explanatory diagrams for acquiring images of the slices SL1 to SL3.
First, a method for acquiring an image of the slice SL1 will be described.

FIG. 3 is an explanatory diagram when an image of the slice SL1 is acquired.
When acquiring an image of slice SL1, sequences A1, A2, and A3 are executed at each repetition time TR.

  The sequences A1, A2, and A3 are sequences for acquiring a diffusion weighted image. Hereinafter, the sequences A1, A2, and A3 will be described (see FIGS. 4 to 6).

4 to 6 are diagrams showing an example of the sequences A1, A2, and A3.
The sequences A1, A2, and A3 are sequences for acquiring the following diffusion weighted images.
Sequence A1: Diffusion-weighted image when MPG is applied in the slice selection direction Sequence A2: Diffusion-weighted image when MPG is applied in the frequency encoding direction (lead-out direction) Sequence A3: When MPG is applied in the phase encoding direction Diffusion weighted image

Hereinafter, sequences A1, A2, and A3 will be described in detail.
FIG. 4 is a diagram illustrating an example of the sequence A1.
The sequence A1 has the following pulses (1) to (4).

(1) RF pulse (1a) Excitation pulse α1 for exciting the slice
(1b) Refocus pulse α2 for refocusing spin

図４では、ＭＰＧの振幅ｇ、パルス幅δ、およびパルス間隔Δは、それぞれ、ｇ＝ｇ１、δ＝δ１、およびΔ＝Δ１に設定されている。尚、ＭＰＧの振幅ｇ１は、ＭＲ装置１００で設定可能なＭＰＧの振幅の最大値を表しており、ｇ１の値は、ＭＲ装置１００で使用される勾配磁場電源の性能などによって事前に決まっている。
ここで、ＭＰＧのパルス間隔Δは以下の式で表すことができる。

式（２）を式（１）に代入すると、以下の式が得られる。

式（３）より、ｂ値は、γ、ｇ、δ、およびｄによって決まる値であることが分かる。 (2) Gradient pulse in the slice selection direction (2a) Slice selection gradient pulses G _s1 and G _s2 for selecting a slice
(2b) MPG for performing diffusion weighting
The b value of MPG is expressed by the following equation.

In FIG. 4, the amplitude g, the pulse width δ, and the pulse interval Δ of the MPG are set to g = g1, δ = δ1, and Δ = Δ1, respectively. The MPG amplitude g1 represents the maximum value of the MPG amplitude that can be set by the MR apparatus 100, and the value of g1 is determined in advance depending on the performance of the gradient magnetic field power source used in the MR apparatus 100 and the like. .
The MPG pulse interval Δ can be expressed by the following equation.

Substituting equation (2) into equation (1) yields the following equation:

From equation (3), it can be seen that the b value is a value determined by γ, g, δ, and d.

(3) Gradient pulse in frequency encoding direction (3a) Gradient pulse G _fs for correction
(3b) Read gradient pulses G- _{5 to} G- ₁ for collecting echoes of negative ky views (view numbers -5 to _-1 ) in k space
(3c) Read gradient pulse G ₀ for collecting echoes of the central view (view number 0) in k-space
(3d) Read gradient pulses G ₁ -G ₃₂ for collecting echoes of positive ky views (view numbers 1-32) in k-space
The pulse width of each of the readout gradient pulses G _{−5 to} G ₃₂ is indicated by “ta”.

(4) Gradient pulse in phase encoding direction (4a) Gradient pulse G _ps for correction
(4b) Phase encoding gradient pulse Gp

Next, echoes collected by the sequence A1 will be described.
In the sequence A1, echoes are collected by the fractional ky method. The fractional ky method is a data collection method that collects echoes of views slightly more than half of the ky direction, but does not collect echoes of the remaining views. FIG. 4 shows how echoes are arranged in k-space having 64 ky views. The k-space includes 32 positive ky views, a central ky view, and 31 negative ky views. In Figure 4, the echo _E -5 _{to E -1} negative ky view of five (view number -5-1), and echo _{E 0} of the center ky view (view number 0), 32 positive The echoes E _{1 to} E ₃₂ of the ky views (view numbers _{1 to 32} ) are collected, and the echoes of the remaining 26 negative ky views (view numbers −31 to -6) are not collected. Has been. Therefore, of the 31 negative ky views (view numbers −31 to −1), only five negative ky views (view numbers −5 to −1) are collected.

Of the 31 negative ky views, the number x of negative ky views from which echoes are collected can be determined by the following equation.

For example, when Ta = 5 msec and ta = 1 msec, x has the following value.

Therefore, it can be seen that when Ta = 5 msec and ta = 1 msec, echoes of five ky views can be collected during the time Ta. Note that the value of x may have a value less than or equal to the first decimal place depending on the value of Ta or ta. For example, when Ta = 5.1 msec and ta = 1 sec, the following values are obtained by substituting these values into equation (4).

As shown in Expression (6), when x has a value of the first decimal place, the value of the first decimal place may be rounded down. Therefore, x = 5. In FIG. 4, an example of x = 5 is shown.
The sequence A1 is configured as described above.

  Sequences A2 and A3 are shown in FIGS. 5 and 6, respectively. The sequences A2 and A3 are the same as the sequence A1 except for the direction in which MPG is applied.

  Therefore, three diffusion weighted images of the slice SL1 can be acquired by executing the sequences A1, A2, and A3.

Returning to FIG. 3, the description will be continued.
The time t _seq during which the sequences A1, A2, and A3 are actually executed is sufficiently shorter than the repetition time TR. Therefore, there is a free time t _id between the sequences. Therefore, the sequences A1, A2, and A3 for collecting echoes from the slice SL2 during the idle time t _id are executed (see FIG. 7).

FIG. 7 is a diagram illustrating an example in which sequences A1, A2, and A3 for collecting echoes from the slice SL2 are executed during the idle time t _id .

  When an echo is acquired from the slice SL2, the sequences A1, A2, and A3 are executed at each repetition time TR as in the case of acquiring the echo from the slice SL1. The sequences A1, A2, and A3 when collecting data from the slice SL2 are the same as the sequences shown in FIGS. 4 to 6 except for the excitation frequencies of the excitation pulse α1 and the refocus pulse α2.

  In FIG. 7, a waiting time Tw for reducing the load of the gradient magnetic field power supply is provided between the sequence of slice SL1 and the sequence of slice SL2. In particular, in this embodiment, the MPG included in the sequences A1, A2, and A3 has a larger amplitude than other gradient pulses (see FIGS. 4 to 6), so that when the MPG is applied, the amount of heat generated by the gradient magnetic field power supply is large. Therefore, a large load is applied to the gradient magnetic field power source. Therefore, as shown in FIG. 7, a waiting time Tw for reducing the load is provided between the sequence of slice SL1 and the sequence of slice SL2.

By executing the sequence of the slice SL2 during the idle time t _id of the slice SL1, diffusion-weighted images of the two slices SL1 and SL2 can be acquired during 1TR.

  In this embodiment, as shown in FIG. 2, in addition to the slices SL1 and SL2, it is necessary to acquire a diffusion weighted image of the slice SL3. However, if a diffusion-weighted image of three slices SL1, SL2, and SL3 is acquired during 1TR, a sufficient waiting time Tw cannot be secured. Therefore, when acquiring the image of the slice SL3, the sequence is executed as follows (see FIG. 8).

FIG. 8 is an explanatory diagram when the sequence of the slice SL3 is executed.
After the sequence of slices SL1 and SL2 is executed (after 3TR has elapsed), a period Q for executing the sequence of slice SL3 is provided. In the period Q, sequences A1 to A3 for collecting echoes from the slice SL3 are executed every repetition time TR.

  In FIG. 8, a multi-slice scan is executed in order to acquire diffusion-weighted images of three slices SL1 to SL3. However, since only the diffusion-weighted images of the two slices SL1 and SL2 can be acquired in 1TR, only the diffusion-weighted images of the two slices SL1 and SL2 can be acquired in the first 3TR. Therefore, after acquiring the diffusion-weighted images of the slices SL1 and SL2, 3TR is further required to acquire the diffusion-weighted image of the slice SL3, so that the scan time becomes long. Therefore, in this embodiment, in addition to the scan shown in FIG. 8, another scan that can shorten the scan time is prepared. Hereinafter, another scan will be described.

FIG. 9 is an explanatory diagram of another scan.
In another scan, sequences B1, B2, and B3 are executed every repetition time TR. The sequences B1, B2, and B3 are configured so that echoes of three slices SL1, SL2, and SL3 can be collected during 1TR. Below, sequence B1, B2, and B3 are demonstrated in order.

FIG. 10 is an explanatory diagram of the sequence B1.
In FIG. 10, only the sequences B1, B2, and B3 of the slice SL1 are shown for the sake of space, and the sequences of the slices SL2 and SL3 are not shown.

The sequence B1 has an MPG in the slice selection direction, like the sequence A1 (see FIG. 4). However, the sequence B1 is configured such that the number of negative ky views from which echoes are collected is reduced compared to the sequence A1. Specifically, in sequence A1, five negative ky view echoes E- _{5 to} E- ₁ (view numbers -5 to _-1 ) are collected, but in sequence B1, three negative ky view echoes are collected. E- _{3 to} E- ₁ (view numbers -3 to _-1 ) are collected. Therefore, in sequence A1, it is necessary to apply five gradient pulses G- _{5 to} G- ₁ during the effective TE, but in sequence B1, three gradient pulses G- _{3 to} G- ₁ are effective during the effective TE. _What is necessary is _just to apply _-1 . FIG. 11 shows a comparison between the sequence A1 and the sequence B1. In sequence A1, gradient pulses G- ₅ and G- ₄ are applied, so it is necessary to secure time t1 for applying two gradient pulses G- ₅ and G- ₄ . However, since the gradient pulses G- ₅ and G- ₄ are not applied in the sequence B1, it is not necessary to secure the time t1 for applying the two gradient pulses G- ₅ and G- ₄ . Therefore, compared with the sequence A1, the sequence B1 can increase the MPG pulse width δ by t1. That is, the MPG pulse width δ in the sequence B1 can be expressed by the following equation.

As described above, the sequence B1 can expand the MPG pulse width by t1 compared to the sequence A1. Therefore, the amplitude g of the MPG of the sequence B1 is set to be Δg more than the amplitude g (= g1) of the MPG of the sequence A1, while keeping the b value of the MPG of the sequence B1 at the same value as the b value of the MPG of the sequence A1. Can only be lowered. That is, the MPG amplitude g in the sequence B1 can be expressed by the following equation.

  As shown in Formula (8), the sequence B1 can make the amplitude g of MPG lower than the sequence A1. Therefore, the sequence B1 can reduce the amount of heat generated by the gradient magnetic field power supply compared to the sequence A1, and thus the load on the gradient magnetic field power supply can be reduced.

  In the above description, the sequence B1 is taken up, but the sequences B2 and B3 can also be described in the same manner as the sequence B1. FIG. 12 specifically shows the sequence B2, and FIG. 13 specifically shows the sequence B3.

  The sequences B2 and B3 are the same as the sequence B1 except that the application direction of the MPG is different. Accordingly, in the sequences B2 and B3, similarly to the sequence B1, the MPG amplitude g can be set to g = g2 = g1−Δg, so that the load of the gradient magnetic field power supply can be reduced.

  As described above, in the sequences B1 to B3, the amplitude g of the MPG can be made lower than in the sequences A1 to A3, so that the load on the gradient magnetic field power source can be reduced. Therefore, by using the sequences B1 to B3, the waiting time Tw (see FIG. 9) for reducing the load of the gradient magnetic field power supply can be shortened. By shortening the waiting time Tw, the time interval between sequences can be narrowed, so that the number of slices to be imaged during 1TR can be increased. Therefore, in the scan of FIG. 9, since the image of three slices can be acquired in 1TR, the scan time can be shortened.

The scan of FIG. 8 can acquire only two slices of echo in 1TR, so the scan time becomes longer. On the other hand, the number of negative ky views in which echoes are collected is two more than the scan of FIG. Therefore, the SN ratio can be improved. Therefore, when it is desired to improve the SN ratio of the image, the sequences A1, A2, and A3 may be executed. On the other hand, when it is desired to increase the number of slices captured during 1TR, the sequences B1, B2, and B3 are performed. It can be seen that
Next, a flow when executing the scan shown in FIGS. 8 and 9 will be described.

FIG. 14 is a diagram showing a flow in this embodiment.
The flow of this embodiment is roughly divided into two steps ST10 and ST20. In step ST10, values of various parameters of the sequence are set. In step ST20, the sequence is executed in accordance with the parameter value set in step ST10.

  Of steps ST10 and ST20, step ST10 is particularly important, so step ST10 will be specifically described below.

  First, in step ST11, the operator sets the b value of MPG. After setting the b value, the process proceeds to step ST12.

  In step ST12, the operator is allowed to select which of the SN ratio priority mode and the slice number priority mode is to be executed. The SN ratio priority mode is a mode for executing sequences A1, A2, and A3 for improving the SN ratio of an image. On the other hand, the slice number priority mode is a mode in which sequences B1, B2, and B3 for increasing the number of slices to be shot during 1TR are executed. As a method for causing the operator to select a mode, as shown in FIG. 15, a method of displaying selection columns C1 and C2 for selecting the SN ratio priority mode or the slice number priority mode on the display unit 10 (see FIG. 1). There is. For example, when the operator wants to select the SN ratio priority mode, the operator operates the operation unit (for example, a mouse) and selects the selection column C1 of the SN ratio priority mode. On the other hand, when the operator wants to select the slice number priority mode, the operator operates the operation unit (for example, a mouse) to select the selection field C2 for the slice number priority mode. If the S / N ratio priority mode selection field C1 is selected, the process proceeds to step ST13. If the slice number priority mode selection field C2 is selected, the process proceeds to step ST14. Here, it is assumed that the SN ratio priority mode is selected. Accordingly, the process proceeds to step ST13.

In step ST13, parameter values of sequences A1, A2, and A3 executed in the SN ratio priority mode are set. Hereinafter, a method for setting the parameter values of the sequences A1, A2, and A3 will be described with reference to FIGS.
Since step ST13 includes steps ST13a, ST13b, and ST13c, each step will be described in turn.

  In step ST13a, the operator sets the effective TE (see FIGS. 4 to 6) of the sequences A1, A2, and A3. After setting the effective TE, the process proceeds to step ST13b.

  In step ST13b, the MPG amplitude g and pulse width δ are set. Hereinafter, a method for setting the amplitude g and the pulse width δ of the MPG will be described.

  First, the amplitude setting means 83 (see FIG. 1) sets the MPG amplitude g value to the maximum MPG amplitude value g1 that can be set by the MR apparatus 100. The value of g1 is determined in advance according to the performance of the gradient magnetic field power source used in the MR apparatus 100. Therefore, the amplitude setting means 83 sets g = g1.

Next, the pulse width setting means 82 (see FIG. 1) sets δ using equation (3). Formula (3) includes five parameters b, γ, g, δ, and d. Of the five parameters, γ is a known value because it is the gyromagnetic ratio. Since d is a fixed value (time interval determined by the pulse width of the slice selection gradient pulse G _s2 ), d is also a known value. Since b is set by the operator in step ST11, b is also a known value. Furthermore, g is set to g = g1. Accordingly, since the remaining four parameters excluding δ are known among the five parameters, δ can be calculated from Equation (3). Here, it is assumed that the calculated δ is δ = δ1.

  Therefore, the MPG amplitude g (= g1) and pulse width δ (= δ1) can be set. After setting the MPG amplitude g (= g1) and pulse width δ (= δ1), the process proceeds to step ST13c.

In step ST13c, the view number setting means 81 (see FIG. 1) sets the number x of negative ky views from which echoes are collected among the 31 negative ky views using the equation (4). . Equation (4) includes three parameters x, Ta, and ta. Ta in the formula (4) can be expressed by the following formula.

Therefore, substituting equation (9) into equation (4) yields the following equation:

Expression (10) includes five parameters x, TE, d, δ, and ta. Of the five parameters, d is a fixed value (time interval determined by the pulse width of the slice selection gradient pulse G _s2 ), so d is a known value. Further, since ta is a fixed value (pulse width of the read gradient pulse), ta is also a known value. Since TE is set by the operator in step ST13a, TE is also a known value. Furthermore, since δ is set in step ST13b, δ is also a known value. Therefore, since the remaining four parameters excluding xa are known among the five parameters, x can be obtained from Expression (10). Here, it is assumed that x = 5. Since x = 5, during the time Ta, readout gradient pulses G _{−5 to} G for collecting echoes of five ky views with ky = −5, −4, −3, −2, and −1. _-1 is set.
Therefore, the parameter values of the sequences A1 to A3 can be set.

  When step ST13c ends, the process proceeds to step ST20, and sequences A1 to A3 are executed according to the parameter values set in step ST13, and the flow ends.

  When the S / N ratio priority mode is selected, the MPG amplitude g is set to the maximum value g1 of the MPG amplitude that can be set by the MR apparatus 100, so that the MPG pulse width δ can be reduced. Therefore, since the time Ta can be lengthened, the number x of negative ky views from which data is collected can be increased, and the SN ratio can be improved.

  In the above description, the example in which the SN ratio priority mode is selected in step ST12 has been described. Next, an example in which the slice number priority mode is selected in step ST12 will be described.

  When the slice number priority mode is selected in step ST12, the process proceeds to step ST14.

In step ST14, parameter values of the sequences B1, B2, and B3 executed in the slice number priority mode are set. Hereinafter, a method for setting the parameter values of the sequences B1, B2, and B3 will be described with reference to FIGS.
Since step ST14 includes steps ST14a, ST14b, and ST14c, each step will be described in order.

  In step ST14a, the operator sets the effective TE (see FIGS. 10 to 13) of the sequences B1, B2, and B3. After setting the effective TE, the process proceeds to step ST14b.

In step ST14b, the view number setting means 81 sets the number x of negative ky views from which echoes are collected among the 31 negative ky views. In the slice number priority mode, the value of x necessary to ensure the minimum SN ratio is set as the default value of x. Here, x = 3. Therefore, since the view number setting means 81 sets x = 3, as shown in FIG. 10, the readout gradient pulse G for collecting data of three ky views of ky = −3, −2, −1. _{-3 to} G- ₁ are set. After setting x, the process proceeds to step ST14c.

  In step ST14c, the MPG amplitude g and pulse width δ are set. Hereinafter, a method for setting the amplitude g and the pulse width δ of the MPG will be described.

First, the pulse width setting means 82 sets the MPG pulse width δ. In the slice number priority mode, the MPG pulse width δ can be expressed by the following equation.

Further, the time Tb in the equation (11) can be expressed by the following equation.

Therefore, when the formula (12) is substituted into the formula (11), the following formula is obtained.

Formula (13) includes five parameters δ, TE, d, x, and ta. Of the five parameters, d is a fixed value (time interval determined by the pulse width of the slice selection gradient pulse G _s2 ), so d is a known value. Further, since ta is a fixed value (pulse width of the read gradient pulse), ta is also a known value. Since TE is set by the operator in step ST14a, TE is also a known value. Further, since x is x = 3 set in step ST14b, x is also a known value. Therefore, since the remaining four parameters excluding δ are known among the five parameters, δ can be calculated from Equation (13). Here, it is assumed that the calculated δ is δ = δ2. Therefore, the pulse width setting means 82 sets δ = δ2.

Next, the amplitude setting means 83 sets the MPG amplitude g using equation (3). Formula (3) includes five parameters b, γ, g, δ, and d. Among the five parameters, γ is a known value because it is a magnetorotation ratio, and d is a known value because d is a fixed value (time interval determined by the pulse width of the slice selection gradient pulse G _s2 ). . Since b is set by the operator in step ST11, b is also a known value. Furthermore, δ is set to δ = δ2. Accordingly, since the remaining four parameters excluding g among the five parameters are known, g can be calculated from Equation (3). Here, the calculated g is g = g2.

  Therefore, the MPG amplitude g (= g2) and pulse width δ (= δ2) in the sequences B1 to B3 can be set.

  When step ST14c ends, the process proceeds to step ST20, and sequences B1 to B3 are executed according to the parameter values set in step ST14, and the flow ends.

  When the slice number priority mode is selected, the number x of negative ky views from which data is collected is set to a value (x = 3 in this embodiment) necessary to ensure a minimum SN ratio. Therefore, the MPG pulse width δ can be made longer than in the SN ratio priority mode. Since the MPg amplitude g can be lowered by increasing the MPG pulse width δ, the sequence waiting time Tw (see FIG. 9) provided for reducing the load such as the gradient magnetic field power source is shortened. Can do. As a result, the number of slices taken during 1TR can be increased, so that the scan time can be shortened.

  In the present embodiment, an example in which echoes are arranged in k-space including 64 views has been described. However, the present invention is not limited to 64 views in k-space. It may be.

  In this embodiment, an example is described in which echoes of all ky views are collected in a positive region of k space, and echoes of some ky views are collected in a negative region. However, the present invention is not limited to this example, and an example of collecting echoes of all ky views in the negative region of k-space and collecting echoes of some ky views in the positive region is also possible. Can be applied.

2 Magnet 3 Table 3a Cradle 4 Receiving coil 5 Transmitter 6 Gradient magnetic field power supply 7 Receiver 8 Control unit 81 View number setting unit 82 Pulse width setting unit 83 Amplitude setting unit 9 Operation unit 10 Display unit 11 Subject 21 Bore 100 MR apparatus

Claims (12)

Collect echoes placed in k-space, including n negative views with view numbers -n to -1, a central view with view number 0, and m positive views with view numbers 1 to m. A magnetic resonance apparatus that collects echoes from a plurality of slices during 1TR,
A sequence including MPG for performing diffusion weighting, wherein, from the slice, the echo of the central view, the echoes of the m positive views, and x of the n negative views (< n) a scanning means for executing a sequence for collecting the echoes of the negative view of the book;
View number setting means for setting the value of x;
Pulse width setting means for setting the pulse width of the MPG based on the value of x;
Amplitude setting means for setting the amplitude of the MPG based on the pulse width;
A magnetic resonance apparatus. Collect echoes placed in k-space, including n negative views with view numbers -n to -1, a central view with view number 0, and m positive views with view numbers 1 to m. A magnetic resonance apparatus that collects echoes from a plurality of slices during 1TR,
A sequence including MPG for performing diffusion weighting, wherein from the slice, echoes of the central view, echoes of the n negative views, and x (<< of the m positive views) m) a scanning means for executing a sequence for collecting the echoes of the negative view of the book;
View number setting means for setting the value of x;
Pulse width setting means for setting the pulse width of the MPG based on the value of x;
Amplitude setting means for setting the amplitude of the MPG based on the pulse width;
A magnetic resonance apparatus. The scanning means includes
A first mode including a first sequence including MPG for performing the diffusion weighting, the first sequence for increasing the number of slices in which echoes are collected during 1TR;
A second mode including an MPG for performing the diffusion weighting, the second mode executing the second sequence for improving the SN ratio of the image;
The magnetic resonance apparatus according to claim 1, comprising:   The magnetic resonance apparatus according to claim 3, further comprising an operation unit that is operated by an operator to select one of the first mode and the second mode. The view number setting means includes:
5. The magnetic resonance apparatus according to claim 4, wherein when the first mode is selected, the value of x is set to a value necessary for ensuring a minimum S / N ratio. The pulse width setting means includes
6. The magnetic resonance apparatus according to claim 5, wherein a pulse width of the MPG of the first sequence is set based on an effective TE of the first sequence and the value of x. The amplitude setting means includes
The magnetic resonance apparatus according to claim 6, wherein an amplitude of the MPG of the first sequence is set based on a b value of the MPG of the first sequence and a pulse width of the MPG of the first sequence. The amplitude setting means includes
When the second mode is selected, the MPG amplitude of the second sequence is set to a maximum value of the MPG amplitude that can be set by the magnetic resonance apparatus. The magnetic resonance apparatus according to item. The pulse width setting means includes
9. The magnetic resonance apparatus according to claim 8, wherein a pulse width of the MPG of the second sequence is set based on a b value of the MPG of the second sequence and an amplitude of the MPG of the second sequence. The view number setting means includes:
The magnetic resonance apparatus according to claim 9, wherein the value of x is set based on an effective TE of the second sequence and a pulse width of the MPG of the second sequence. Collect echoes placed in k-space, including n negative views with view numbers -n to -1, a central view with view number 0, and m positive views with view numbers 1 to m. And a sequence including an MPG for performing diffusion weighting, wherein the center view includes the MPG for performing diffusion weighting, and collects echoes from a plurality of slices during 1TR. Resonance apparatus for executing a sequence for collecting echoes of m, echoes of the m positive views, and echoes of x (<n) negative views of the n negative views A program that applies to
A view number setting process for setting the value of x;
A pulse width setting process for setting the MPG pulse width based on the value of x;
An amplitude setting process for setting the amplitude of the MPG based on the pulse width;
A program to make a computer execute. Collect echoes placed in k-space, including n negative views with view numbers -n to -1, a central view with view number 0, and m positive views with view numbers 1 to m. And a sequence including an MPG for performing diffusion weighting, wherein the center view includes the MPG for performing diffusion weighting, and collects echoes from a plurality of slices during 1TR. Resonance apparatus for performing a sequence to collect echoes of n negative views, echoes of x (<m) negative views out of the m positive views A program that applies to
A view number setting process for setting the value of x;
A pulse width setting process for setting the MPG pulse width based on the value of x;
An amplitude setting process for setting the amplitude of the MPG based on the pulse width;
A program to make a computer execute.

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