JP2870896B2 - Magnetic resonance imaging equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a magnetic resonance (MR) method for a living body using magnetic resonance development.
The present invention relates to a magnetic resonance imaging apparatus that collects data and obtains a magnetic resonance tomographic image (hereinafter, referred to as an “MR image”).

(Prior art) A magnetic resonance imaging apparatus (hereinafter referred to as an "MRI apparatus") applies a uniform static magnetic field to a desired part of a living body and forms an RF magnetic field in a direction perpendicular to the static magnetic field by a transmitting RF coil. MR only for a specific slice to obtain an MR image
A phenomenon that causes the MR signal generated from the nucleus after the release of the RF magnetic field is detected by the RF coil. The static magnetic field is moved in the X'-axis direction (a coordinate system rotated by θ ° from the X-axis). Synthesized MR data is obtained, and this data is subjected to two-dimensional Fourier transform processing (hereinafter referred to as “2DFT processing”), and the X ′ axis of the slice portion is rotated in the XY plane, and An MR image can be formed by performing image reconstruction processing based on the projection information.

By the way, in such an MRI apparatus, various MR signals are collected by various pulse sequences. In general, pre-processing is performed for various purposes in the previous stage of the image reconstruction processing. Here, “pre-processing” is a broad concept including 2DFT processing as processing before obtaining a final image.

 Hereinafter, each preprocessing example will be described.

FIGS. 4 and 5 show a first preprocessing example. Fig. 4
FIG. 5 is a waveform diagram showing the collection of MR data, and FIG. 5 is a block diagram showing a conventional apparatus for executing the first preprocessing.

This first preprocessing is intended to reduce artifacts.

As shown in FIG. 4 (a), a gradient magnetic field Z is applied in the plus direction to collect, for example, 256 pieces of MR data M _F (M _F1 , M _F2 ... M _FN ) in the encoding direction, and as shown in FIG. , Disk D ₁
To memorize. Next, as shown in FIG. 4 (b), the polarity of the gradient magnetic field Z is reversed, and 256 pieces of MR data M _B (M _B1 , M _B2 ... M _BN ) are similarly collected in the encoding direction, and the disk D ₂ To memorize. Next, the data M _F in the disc D _1, D ₂ frequency spatial memory, the reconstituted image G _1, G ₂ in the real space is performed each 2DFT handle M _B, the further image G _1, G ₂ synthesized and so as to obtain the final image G _0. Simply MR data M _F
Requires twice as much storage capacity as when 2DFT processing is performed. Furthermore, after performing the 2DFT processing with the MR data once stored two-dimensionally as the pre-processing, the pre-processing time is required in addition to the synthesizing processing time to perform the synthesizing processing to obtain the final image. Is taking a long time.

FIG. 6 shows a second preprocessing example. This example is based on a pulse sequence and shows preprocessing in the echo planar method.

The AD-converted MR data is sequentially and two-dimensionally stored in the storage area according to the arrow in FIG. This data is
When trying to reconstruct with the reconstruction algorithm of 2DFT processing, the direction of the even-numbered row data (d2, d4, ...) and the odd-numbered row data (d1, d3, ...) are reversed, so Cannot be reconfigured. Therefore, the direction alignment of the even-numbered rows and the odd-numbered rows is performed as preprocessing. Since the pre-processing is performed after the MR data is collected two-dimensionally, the pre-processing takes time in addition to the reconstruction time, and it takes a long time to display an image.

FIG. 7 shows a third preprocessing example. Each waveform in the figure is
RF pulse P, slice positioning gradient magnetic field Zs,
The gradient magnetic field for encoding Ze, the gradient magnetic field for reading Zr, and the echo signal S are shown. This example uses SE method (spin echo method).
It shows pre-processing when collecting echoes.

Generally, the MR signal is represented by ∫∫f (u, v) e ^{j (xu + yv)} dudv (1).

Assuming that the _first echo E ₁ is ∫∫f ₁ (u, v) e ^{j (xu + yv)} dudv (2), the second echo E ₂ has ｖ−v and ∫∫f ₂ (u , v) is expressed as ^{e -j (-xu + yv) dudv} (3), the first echo E _1, phase encode information in the second echo E ₂ is positive or negative reversed. Therefore, if the reconstruction is performed as it is, the image is inverted in the phase encoding direction. In order to prevent this, preprocessing is performed on the collected data by the method described below.

That is, before the second complex conjugate of echo data E ₂ was calculated as the processing, by performing the process of arranging the reverse direction, the image has the same direction. But since the second echo data E ₂ is pretreated after being collected two-dimensionally, the time until image display as in the first and second pre-processing examples is long.

(Problems to be Solved by the Invention) As described above, after MR data is collected and stored two-dimensionally, image reconstruction processing is performed after preprocessing is performed based on the stored data. For this reason, in some cases, there is a problem that the image creation time is long.

Another problem is that the storage area is not used efficiently.

The present invention has been made in view of the above circumstances, and has as its object to provide a magnetic resonance imaging apparatus capable of improving the processing time or the use efficiency of the storage area and shortening the image creation time.

[Constitution of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a magnetic resonance imaging method for acquiring MR data two-dimensionally and then performing image reconstruction processing to obtain a magnetic resonance tomographic image. The apparatus comprises: two-dimensional storage means for storing the MR data two-dimensionally; and one-dimensional preprocessing means for performing one-dimensional operation preprocessing at a stage preceding the two-dimensional storage means. The means adds MR data collected when the gradient magnetic field direction is set to the forward direction and MR data obtained by rearranging the MR data obtained when the gradient magnetic field direction is set to the reverse direction in the time axis direction. To create one-dimensional data, and one-dimensional Fourier transform processing may be added. Further, it is preferable that the one-dimensional preprocessing means has a one-dimensional storage means for storing the MR data one-dimensionally.

(Operation) The operation of the device having the above configuration will be described below.

When the MR data is fetched, the one-dimensional preprocessing unit performs a rearrangement process on the data obtained according to the direction of the gradient magnetic field in the time axis direction, performs an average addition for each subsequent data, and then performs a one-dimensional preprocessing. Create data. The MR data preprocessed in this way is stored in the two-dimensional storage means.
It is stored dimensionally and subjected to image reconstruction processing to obtain a magnetic resonance tomographic image.

When one-dimensional Fourier transform processing is performed in addition to the one-dimensional operation pre-process, the one-dimensional pre-processing means performs one-dimensional Fourier transform processing on the acquired MR data and sends the data to the two-dimensional storage means. I do.

The MR data that has been sent a plurality of times after the one-dimensional Fourier transform processing is stored two-dimensionally by the two-dimensional storage means, and then the image including the other-dimensional Fourier transform processing of the one-dimensional Fourier transform processing Reconstruction processing is performed, and a magnetic resonance tomographic image is obtained.

If the one-dimensional preprocessing means is provided with a one-dimensional storage means, the one-dimensional storage means can read and write at a higher speed than the two-dimensional storage means and can be used as a storage area for preprocessing. Therefore, the processing time or the utilization efficiency of the storage area including the two-dimensional storage means is improved.

(Example) Hereinafter, an example of the present invention will be described in detail.

FIG. 1 shows a block diagram of an apparatus 1 according to one embodiment of the present invention.

The apparatus 1 includes a static magnetic field coil 7 for forming a main magnetic field of a constant strength inside, a gradient magnetic field coil 8 for forming a gradient magnetic field in the X, Y and Z directions, and a high frequency for exciting spins of biological nuclei. A magnet device 6 having a transmitting / receiving coil 9 for giving a pulse (RF pulse) and receiving an MR signal from a living body, and a gradient for controlling a gradient magnetic field by controlling a current to the gradient coil 8. A magnetic field control circuit 14,
A static magnetic field control circuit 15 for controlling a static magnetic field by controlling a current supplied to the static magnetic field coil 7, a high frequency oscillator 16 for oscillating a high frequency signal, and a timing signal for collecting an MR signal are generated. Controller 13 that controls the operation of the device and controls the gradient magnetic field, the generation sequence of the high-frequency pulse, and the like, and a gate circuit that modulates the high-frequency signal oscillated from the high-frequency oscillator 16 by a timing signal from the system controller 13 to generate a high-frequency pulse 17 and the high frequency pulse output from the gate circuit 17 is power amplified,
A power amplifier 18 for supplying to the transmitting and receiving coil 9 via the duplexer circuit 5 and a preamplifier for amplifying the MR signal taken in from the transmitting and receiving coil 9 via the duplexer circuit 5
19, and a phase detection circuit 20 including an AD converter 20a to be described later, which performs phase detection of the amplified MR signal and converts it into a digital signal.
A one-dimensional preprocessing means 21 for one-dimensionally preprocessing the MR data output from the circuit 20;
A waveform memory 22 connected to the subsequent stage of the memory 21 for two-dimensionally storing the MR data, and an MR image connected to the latter stage of the waveform memory 22 and performing 2DFT processing on the MR data stored two-dimensionally. And a display unit 24 for displaying an MR image.

As shown in FIG. 2, the one-dimensional pre-processing means 21 includes a programmable signal calculator 21a capable of performing pre-processing at a high speed which does not affect data collection, and MR data transmitted from the AD converter 20a. It has a buffer memory 21b as one-dimensional storage means for temporarily storing, and a program memory 21c for storing a program for executing predetermined preprocessing by the one-dimensional preprocessing means 21. The one-dimensional pre-processing means 21 performs pre-processing while collecting a plurality of (for example, 256) MR data periodically, for example, at 50 ms in the encoding direction. This pre-processing means 21
As a conventional example, similar to the first preprocessing example shown in FIG. 4, preprocessing for reducing artifacts is performed.

The operation of the present apparatus 1 will be described with reference to FIGS.

First, under the control of the static magnetic field control circuit 15, the static magnetic field coil 7
To form a uniform static magnetic field in the Z direction. The living body is arranged at the center of the magnet device 6.

Then, in accordance with a predetermined pulse sequence is subjected to selective excitation for the desired slice plane, from the slice plane 256 MR data _{M F (M F1, M F2} , ... M FN), M B (M B1, M B2, … M
_BN ) collection.

A programmable signal calculator 21a, when MR data M _F, is M _B is sent, perform preprocessing reads a program stored in the program memory 21c.

Under the control of the system controller 13, the gradient magnetic field control circuit 14 controls the current supplied to the gradient magnetic field coil 8 to make the direction of the gradient magnetic field (X, Y or Z direction) positive. The system controller 13 sends RF signals to the living body from the transmission / reception coil 9.
Apply a pulse. A magnetic resonance phenomenon occurs in the living body, and an MR signal is generated. This MR signal is detected by the transmission / reception coil 9, taken into the phase detection circuit 20 via the preamplifier 19, and subjected to phase detection.
_It is converted to _F1 and further temporarily stored in the buffer memory 21b.

Next, the gradient magnetic field control circuit 14
Under the control of, the direction of the gradient magnetic field (X, Y or Z direction) is reversed, and the MR data _MB1 is collected in the same manner.

The MR data _MB1 is captured by the phase detection circuit 20, phase-detected and digitally converted in the same manner as described above, and then captured by the programmable signal calculator 21a.

The programmable signal arithmetic unit 21a inverts the captured MR data M _B1 in the time axis direction and adds and averages the MR data M _F1 stored in the buffer memory 21b as data M _B1 ′ to obtain the MR data M ₀₁ . Then, it is sent to the waveform memory 22.

Similarly, all the 256 MR data M ₀ (M ₀₁ ,
When M ₀₂ ,... M _0N ) are stored in the waveform memory 22, the image creation unit 23 performs 2DFT processing to perform image reconstruction processing, and
Show MR image G ₁₀ which is processed in the image reconstruction.

According to the embodiment apparatus 1 configured as described above, not only can the processing time and the utilization efficiency of the storage area be improved,
Since the two MR data are added, the S / N ratio can be improved. Further, when the processing content of the preprocessing is changed in accordance with the progress of the MR technology, it can be changed only by rewriting the program, so that a magnetic resonance imaging apparatus excellent in applicability can be provided.

As mentioned above, although one Example was described, this invention is not limited to this, A various deformation | transformation implementation is possible in the range which does not change the summary.

For example, a case has been described where the one-dimensional preprocessing means performs preprocessing for removing artifacts, but one-dimensional Fourier transform processing may be performed, or another preprocessing may be performed. Although the first preprocessing example has been illustrated, it is needless to say that the same can be applied to other second and third preprocessing examples.

[Effects of the Invention] According to the present invention described in detail above, one-dimensional preprocessing means performs one-dimensional operation preprocessing of MR data in a stage preceding the two-dimensional storage means. It is possible to provide a magnetic resonance imaging apparatus capable of improving the use efficiency and shortening the image creation time.

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram of a one-dimensional preprocessing means of the apparatus, FIG. 3 is an explanatory view showing the operation of the apparatus, and FIG. , (B) are waveform diagrams showing a first example of preprocessing, and FIG.
FIG. 6 is an explanatory diagram showing a second preprocessing example, and FIG. 7 is an explanatory diagram showing a third preprocessing example. 1 ... magnetic resonance imaging apparatus, 21 ... 1-dimensional pre-processing means, 21b ... buffer memory (one-dimensional storage means), 22 ... waveform memory (two-dimensional storage means), G ₁₀ ... MR image, M _F, M _B ... MR
data.

Claims (3)

(57) [Claims] 1. A magnetic resonance imaging apparatus for obtaining a magnetic resonance tomographic image by performing image reconstruction processing after acquiring MR data two-dimensionally, a two-dimensional storage means for storing the MR data two-dimensionally, One-dimensional preprocessing means for performing one-dimensional operation preprocessing at a stage preceding the two-dimensional storage means, wherein the one-dimensional preprocessing means is collected when the gradient magnetic field direction is set to the forward direction.
A magnetic resonance imaging apparatus that creates one-dimensional data by adding MR data and MR data obtained when the gradient magnetic field direction is reversed to MR data obtained by performing a rearrangement process in the time axis direction. . 2. The magnetic resonance imaging apparatus according to claim 1, wherein said one-dimensional operation preprocessing means performs one-dimensional Fourier transform processing in addition to said preprocessing. 3. The magnetic resonance imaging apparatus according to claim 1, wherein said one-dimensional preprocessing means includes one-dimensional storage means for storing the MR data one-dimensionally.