JPH06261886A - Mri device - Google Patents

Abstract

PURPOSE:To provide the MRI device by which sampling data collected at every echo can be stored properly on a (k) space by storing it once each. CONSTITUTION:A sequence controller 3 checks polarity of a lead gradient applied in the next time, while executing a scan, based on a pulse sequence, and transmits a result of its check to a computer 2 at any time. When the contents of the result of check are positive, the computer 2 stores sampling data of an echo collected in the next time in order of collection in the frequency direction on a (k) space set in a storage device 12. When the contents of the result of check are negative, its data is stored in order being opposite to the order of collection. In such a manner, the processing time can be curtailed.

Description

Detailed Description of the Invention

[0001] The present invention relates to an MRI apparatus, and more specifically to k sampling data collected for each echo.
The present invention relates to an MRI apparatus that stores data in the order of collection in the frequency direction in space.

[0002]

[Industrial applications]

[0003]

2. Description of the Related Art FIG. 6 is a view showing an example of a pulse sequence of the EPI method used for high speed imaging. This EP
In the pulse sequence A of method I, 90 ° pulse and 180
After the spin echo SE1 is imaged by applying a ° pulse, a large number of echoes S are obtained by rapidly inverting the read gradient RA.
Image E2, SE3, SE4, ... In the figure, PH is the phase encode gradient. PP is the pre-phase gradient. Also, the pre-phase gradient PP and the lead gradient R
The same shaded area in A indicates that the gradient amounts are equal.

For example, as shown in FIG. 7, the k-space ksp has 128 (= N) views in the phase direction and 1 in the frequency direction.
It is assumed that it is composed of 28 (= M) sample points. In this case, first, using the pulse sequence A of the EPI method, 128 echos SE1, SE2, SE3, ..., SE128 associated with each view are imaged, and sampling numbers # 1 to # are assigned to each echo. 12
Collect 8 sampling data. Then, the sampling data of # 1 to # 128 collected for each echo is
As shown in FIG. 8, k is stored in the order of collection (that is, the order of # 1 to # 128) in the frequency direction of the associated view, and k
It is distributed on the space ksp. In FIG. 8, the direction of the arrow indicates the collection order.

Next, the sampling data on the view associated with the echoes SE2, SE4, ... Formed when the read gradient RA is negative is collected as shown by the chain double-dashed line with an arrow in FIG. Store them in the reverse order, and align the sample points of the sampling data for each view. This is because, in the echoes SE2, SE4, ..., The echo imaging process is opposite to the echoes SE1, SE3, ... Imaged when the read gradient RA is positive. In addition, in FIG. 9, the direction of the arrow indicates the collection order. Thus, the image is reconstructed based on the sampling data distributed on the k-space ksp.

FIG. 10A is a view showing an example of a pulse sequence of the FE method using the multi-echo method used for high speed imaging. In the pulse sequence B of the FE method, one view scan VB with the repetition time TR
Then, after the field echo FE1 is imaged by applying the α ° pulse, the lead gradient RB is rapidly inverted to image a large number of echoes FE2, FE3, FE4, .... In the figure, PH is the phase encode gradient. Further, the same shaded portion in the lead gradient RB indicates that the gradient amounts are equal.

In the case where the k-space ksp is as shown in FIG. 7, first, the pulse sequence B of the FE method is used to
128 echoes FE1, FE2, FE3, ... Corresponding to each view are imaged by 28 times of view scan VB, and sampling data of # 1 to # 128 is collected for each echo.

# 1 to # 1 collected for each echo
As shown in (b) of FIG. 10, the sampling data of 28 is set for each of the echoes FE1, FE2, ...
The views are stored in the order of collection in the frequency direction of the views associated with the space, and are distributed on the k spaces ksp1, ksp2, .... In FIG. 10B, the direction of the arrow indicates the collection order.

Next, the sampling data on the view associated with the echoes FE2, FE4, ... Formed when the read gradient RB is negative, that is, k space ksp
Sampling data on all views of 2, ksp4, ... Are stored again in the order opposite to the collection order, as indicated by the chain double-dashed line with an arrow in (c) of FIG. In FIG. 10C, the direction of the arrow indicates the collection order. Thus, Figure 1
K spaces ksp1, ksp3, as shown in (b) of 0.
... Each image is reconstructed based on the sampling data distributed above. Further, each image is reconstructed based on the sampling data distributed on the k spaces ksp2, ksp4, ... As shown in (c) of FIG.

[0010]

In the conventional MRI apparatus that performs imaging by using the pulse sequence A of the EPI method, the pulse sequence B of the FE method, etc., the sampling data collected for each echo is stored in the k space. Since it is necessary to store the sampling data in the frequency direction once in the collection order and then to store the sampling data on a predetermined view again in the order opposite to the collection order, it is a troublesome work twice.

Therefore, an object of the present invention is to provide an MRI apparatus capable of properly storing sampling data collected for each echo in the k space by storing the sampling data once.

[0012]

According to the MRI apparatus of the present invention, N views forming a k-space are associated with N echoes imaged by continuous inversion of a gradient magnetic field or the like, and M echoes are generated for each echo. M sampling data are collected and stored in the order of collection in the frequency direction of the associated view M
In the RI apparatus, storage direction control means for reversing the correspondence between the collection order of the M pieces of sampling data collected from the echo and the frequency direction to be stored according to the polarity of the gradient magnetic field applied during the imaging of the echo. The feature is that it is provided.

[0013]

In the MRI apparatus of the present invention, the storage order control means stores the collection order of M sampling data collected from the echo in accordance with the polarity of the gradient magnetic field applied during the imaging of the echo. The correspondence in the frequency direction is reversed. Therefore, for example, M pieces of sampling data collected from echoes imaged when a negative gradient magnetic field is applied are stored once in the frequency direction of the associated view, and the sampling order is opposite to the order of collection. It becomes possible to store in the order of, and there is no need to store the sampling data again as in the conventional case.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail based on the embodiments shown in the drawings. The present invention is not limited to this. FIG. 1 is a block diagram of an MRI apparatus 1 according to an embodiment of the present invention. The computer 2 controls the overall operation based on the instruction from the console 14. The sequence controller 3 operates the gradient magnetic field driving circuit 4 based on the stored sequence, and causes the gradient magnetic field coil of the magnet assembly 5 to generate a gradient magnetic field.
Further, the gate modulation circuit 7 is controlled to modulate the RF pulse generated by the RF oscillation circuit 6 into a predetermined waveform, and the RF pulse is applied from the RF power amplifier 8 to the transmission coil of the magnet assembly 5.

The NMR signal obtained by the receiving coil of the magnet assembly 5 is input to the phase detector 10 via the preamplifier 9 and further to the computer 2 via the AD converter 11. The computer 2 assigns the data of the NMR signal obtained from the AD converter 11 to the storage device 12 k
Store in space. And the NMs distributed in k-space
An image is reconstructed based on the data of the R signal and displayed on the display device 13.

Next, the imaging operation will be described with reference to the flow chart of FIG. After the user sets the subject on the magnet assembly 5, the console 1
When a scan instruction is given using 4, the computer 2 and the sequence controller 3 execute the following processing. As a specific example, the number of views constituting the k space is 128.
(= N), the number of sampling points 128 (= M), and a scan instruction such as the pulse sequence A of the EPI method (see FIG. 4) are assumed to be given by the user.

In step S1, the computer 2 computes a k-space ksp composed of 128 (= N) views in the phase direction and 128 (= M) sample points in the frequency direction, as shown in FIG. It is set in the storage device 12.

At step S2, the computer 2 stores the EP stored in the sequence controller 3 as shown in FIG.
The pulse sequence A of the I method is adjusted so that 128 echoes SE1, SE2, ..., SE128 corresponding to 128 views are imaged and sampling data of sample numbers # 1 to # 128 are collected for each echo. . Figure 4
90 ° is an RF pulse with a flip angle of 90 °. 1
80 ° is an RF pulse with a flip angle of 180 °. RA
Is the lead slope. PH is the phase encode gradient. PP is the pre-phase gradient. Further, in the pre-phase gradient PP and the read gradient RA, the same shaded area indicates that the gradient amounts are equal.

Returning to FIG. 2, in step S3, the computer 2 commands the sequence controller 3 to start scanning. In response to a scan start command from the computer 2, the sequence controller 3 executes a scan based on the adjusted pulse sequence A of the EPI method and checks the polarity of the read gradient RA to be applied next, and at any time. The check result is transmitted to the computer 2.

If the content of the check result is positive, the computer 2 calculates the sampling data of echoes # 1 to # 128 next input from the AD converter 11 as the k-space ksp.
Store in the acquisition order in the frequency direction of the above associated view. If the content of the check result is negative, the echoes # 1 to # 12 input from the AD converter 11 next time.
The sampling data of 8 is stored in the order opposite to the collection order in the frequency direction of the associated view on the k-space ksp.

Thus, the k space ksp in the storage device 12
Above, # collected per echo, as shown in Figure 5
The sampling data of 1 to # 128 are stored in the frequency direction of the associated view in the collection order (solid line with arrow) or the opposite order (broken line with arrow). In step S4, the computer 2 reconstructs an image based on the sampling data distributed on the k space ksp and displays it on the display device 13.

In the MRI apparatus 1 described above, the read gradient RA
Sampling data of # 1 to # 128 for each echo SE2, SE4, ... Formed when N is a negative electrode is stored once in the frequency direction of the associated view in the order opposite to the collection order. It can be stored and properly stored on the k space ksp. Therefore, it is not necessary to store the sampling data again as in the conventional case, and the processing time can be shortened.

[0023]

According to the MRI apparatus of the present invention, the M sampling data collected for each echo is stored once in the frequency direction of the associated view. It can be stored in the opposite order and properly stored on k-space. Therefore, it is not necessary to store the sampling data again, and the processing time can be shortened.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an MRI apparatus of the present invention.

FIG. 2 is a flow chart of an imaging operation by the apparatus of FIG.

3 is an explanatory diagram of a k-space related to imaging by the apparatus of FIG.

4 is an exemplary diagram of a pulse sequence used for imaging by the apparatus of FIG. 1. FIG.

5 is an explanatory diagram of data distribution on a k-space related to imaging by the apparatus of FIG.

FIG. 6 is a view showing an example of a pulse sequence of the EPI method.

FIG. 7 is an explanatory diagram of k-space.

FIG. 8 is an explanatory diagram of data distribution on a k-space by a conventional MRI apparatus.

FIG. 9 is an explanatory diagram of data distribution on a k-space by a conventional MRI apparatus.

FIG. 10 is an explanatory diagram of a pulse sequence of the FE method using the multi-echo method and a data distribution on the k space.

[Explanation of symbols]

 1 MRI device 2 computer 3 sequence controller 12 storage device 14 operator console A pulse sequence of EPI method B pulse sequence of FE method ksp k space M sample points number N views number RA read gradient

Claims (2)

[Claims] 1. N views forming a k-space are associated with N echoes imaged by continuous inversion of a gradient magnetic field, and M sampling data are collected for each echo and are associated with each other. In an MRI apparatus that stores the data in the order of collection in the frequency direction of the view, the M pieces of sampling data collected from the echo are stored in the order of collection according to the polarity of the gradient magnetic field applied at the time of imaging the echo. An MRI apparatus comprising storage direction control means for reversing the correspondence in the frequency direction. 2. N views forming a k-space are associated with N echoes imaged by a desired pulse sequence, and M sampling data are collected for each echo,
In an MRI apparatus that stores the associated views in the acquisition direction in the frequency direction, a storage direction changing means capable of changing the correspondence between the acquisition order of M sampling data collected for each echo and the frequency direction to be stored. An MRI apparatus characterized by being provided.