JP3343385B2 - MRI equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to an MRI apparatus, and more particularly, to a method in which sampling data collected for each echo is k
The present invention relates to an MRI apparatus that stores data in the order of acquisition 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 the I method, a 90 ° pulse and 180
(4) After applying a pulse to form an image of the spin echo SE1, the read gradient RA is rapidly reversed so that a large number of echoes S
E2, SE3, SE4,... Are imaged. In the figure, PH is a phase encoding gradient. PP is the pre-phase gradient. Further, the pre-phase gradient PP and the read gradient R
The same hatched portion in A indicates that the gradient amounts are equal.

For example, as shown in FIG. 7, a k-space ksp has 128 (= N) views in the phase direction and 1 in the frequency direction.
It is assumed that the sample point is composed of 28 (= M) sample points. In this case, first, 128 echoes SE1, SE2, SE3,..., SE128 associated with each view are imaged using the pulse sequence A of the EPI method, and sampling numbers # 1 to # 12
Collect 8 sampled data. Then, the sampling data of # 1 to # 128 collected for each echo is
As shown in FIG. 8, the views are stored in the order of collection in the frequency direction of the associated view (that is, in the order of # 1 to # 128), and k
Distribute on 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 the negative polarity is collected as shown by a two-dot chain line with an arrow in FIG. The data is stored again in the reverse order, and the sampling points of the sampling data for each view are aligned. This is because, in the echoes SE2, SE4,..., The process of imaging the echo is opposite to the echoes SE1, SE3,. In FIG. 9, the direction of the arrow indicates the collection order. Thus, an 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 a multi-echo technique used for high-speed imaging. In the pulse sequence B of the FE method, one view scan VB for the repetition time TR is performed.
After the α ゜ pulse is applied to form an image of the field echo FE1, the read gradient RB is rapidly inverted to form a number of echoes FE2, FE3, FE4,. In the figure, PH is a phase encoding gradient. The same hatched portion in the read 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
.. Are imaged, and sampling data of # 1 to # 128 is collected for each echo by 28 view scans VB.

Then, # 1 to # 1 collected for each echo
As shown in FIG. 10B, each of the 28 sampling data is set to each k set for each echo FE1, FE2,.
Are stored in the order of collection in the frequency direction of the view associated with the space, and distributed on k-spaces ksp1, ksp2,. In FIG. 10B, the direction of the arrow indicates the collection order.

Next, the sampling data on the view corresponding to the echoes FE2, FE4,... Formed when the read gradient RB is negative, that is, k-space ksp
, Ksp4,... Are stored again in the order opposite to the collection order, as shown by the two-dot chain line with the arrow in FIG. In FIG. 10C, the direction of the arrow indicates the collection order. Thus, FIG.
K-spaces ksp1, ksp3, ksp3 as shown in FIG.
The images are respectively reconstructed based on the sampling data distributed above. 10 are reconstructed based on sampling data distributed on k-spaces ksp2, ksp4,... As shown in FIG.

[0010]

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

SUMMARY OF THE INVENTION It is an object of the present invention to provide an MRI apparatus capable of storing sampling data collected for each echo in a k-space properly by storing once.

[0012]

According to the MRI apparatus of the present invention, N echoes imaged by continuous inversion of a gradient magnetic field are associated with N views constituting a k-space, and M echoes are assigned to each echo. M which collects sampling data and stores them in the order of collection in the frequency direction of the associated view
In the RI apparatus, storage direction control means for reversing the correspondence between the collection order of the M sampling data collected from the echo and the frequency direction of storage in accordance with the polarity of the gradient magnetic field applied during the imaging of the echo is provided. It is characterized by having a configuration.

[0013]

In the MRI apparatus according to the present invention, the storage order control means stores the collection order of the M pieces of sampling data collected from the echo in accordance with the polarity of the gradient magnetic field applied when the echo is imaged. The correspondence in the frequency direction is reversed. Therefore, for example, M pieces of sampling data collected from the echo imaged when a negative gradient magnetic field is applied are stored once in the frequency direction of the associated view, and are stored in the opposite order from the collection order. , And it is not necessary to store the sampling data again as in the related art.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. It should be noted that the present invention is not limited by this. FIG. 1 is a block diagram of an MRI apparatus 1 according to one embodiment of the present invention. The computer 2 controls the overall operation based on instructions from the console 14. The sequence controller 3 operates the gradient magnetic field drive circuit 4 based on the stored sequence to generate a gradient magnetic field with the gradient magnetic field coil of the magnet assembly 5.
Further, it controls the gate modulation circuit 7, modulates the RF pulse generated by the RF oscillation circuit 6 into a predetermined waveform, and applies the RF pulse 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 a phase detector 10 via a preamplifier 9 and further input to a computer 2 via an 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. Then, the NM distributed on the 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 flowchart of FIG. After the user sets the subject on the magnet assembly 5, the console 1
When a scan instruction is given by using the computer 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 a pulse sequence A (see FIG. 4) of the EPI method are given by a user.

In step S1, as shown in FIG. 3, the computer 2 generates a k-space ksp composed of 128 (= N) views in the phase direction and 128 (= M) sample points in the frequency direction, It is set in the storage device 12.

In 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 is collected for each echo. . FIG.
90 ° is an RF pulse having a flip angle of 90 °. 1
80 ° is an RF pulse having a flip angle of 180 °. RA
Is the lead gradient. PH is the phase encoding gradient. PP is the pre-phase gradient. The same hatched portion in the pre-phase gradient PP and the read gradient RA indicates that the gradient amounts are equal.

Returning to FIG. 2, in step S3, the computer 2 instructs the sequence controller 3 to start scanning. The sequence controller 3 receives the scan start command from the computer 2 and checks the polarity of the read gradient RA to be applied next while performing the scan based on the adjusted pulse sequence A of the EPI method. The check result is transmitted to the computer 2.

If the content of the check result is positive, the computer 2 converts the echo data # 1 to # 128 input from the AD converter 11 into k-space ksp
Stored in the order of collection in the frequency direction of the above associated view. If the content of the check result is negative, the echoes # 1 to # 12 of the next echo input from the AD converter 11 are returned.
8 are stored in the frequency direction of the associated view on the k-space ksp in the order opposite to the collection order.

Thus, the k-space ksp in the storage device 12
On the top, as shown in FIG. 5, #
Sampling data 1 to # 128 are stored in the collection direction (solid line with arrow) or in the opposite order (dashed line with arrow) in the frequency direction of the associated view. In step S4, the computer 2 reconstructs an image based on the sampling data distributed on the k-space ksp and displays the image on the display device 13.

In the MRI apparatus 1 described above, the read gradient RA
Are stored in the order opposite to the collection order by storing once in the frequency direction of the associated view by storing once for each of the echoes SE2, SE4,. 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 related art, and the processing time can be reduced.

[0023]

According to the MRI apparatus of the present invention, the M pieces of sampling data collected for each echo are stored once in the frequency direction of the associated view by the storing order or the collecting order. They can be stored in the opposite order and stored properly in k-space. Therefore, there is no need to store the sampling data again, and the processing time can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a flowchart of an imaging operation by the apparatus of FIG. 1;

FIG. 3 is an explanatory diagram of a k-space related to imaging by the apparatus of FIG. 1;

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

FIG. 5 is an explanatory diagram of a data distribution on a k-space for imaging by the apparatus of FIG. 1;

FIG. 6 is an illustration of a pulse sequence of the EPI method.

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

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

FIG. 9 is an explanatory diagram of data distribution on 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 technique and a data distribution on k-space.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 MRI apparatus 2 Computer 3 Sequence controller 12 Storage device 14 Operation console A Pulse sequence of EPI method B Pulse sequence of FE method ksp k space M Number of sample points N Number of views RA Read gradient

──────────────────────────────────────────────────続 き Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61B 5/055 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A pulse sequence is executed to associate N views constituting a k-space with N echoes to be imaged by continuous inversion of a gradient magnetic field, and M samplings are performed for each echo. An MRI apparatus for collecting data, wherein when detecting that the polarity of a gradient magnetic field applied at the time of imaging of the echo is negative, the M pieces of sampling data are stored in the order of collection in the frequency direction of the k-space. The direction in which the M sampling data is stored in the order of acquisition when the polarity of the gradient magnetic field applied during the imaging of the echo is detected to be positive, is N × M An MRI apparatus comprising means for storing pieces of sampling data in the k-space. 2. The MRI apparatus according to claim 1, wherein said pulse sequence is a pulse sequence of an EPI method, and said gradient magnetic field is a gradient magnetic field of a read gradient.