WO2006038371A1

WO2006038371A1 - Magnetic resonance imaging device

Info

Publication number: WO2006038371A1
Application number: PCT/JP2005/014202
Authority: WO
Inventors: Shinji Kurokawa; Yo Taniguchi; Hisaaki Ochi
Original assignee: Hitachi Medical Corporation
Priority date: 2004-09-30
Filing date: 2005-08-03
Publication date: 2006-04-13
Also published as: JPWO2006038371A1; JP4810432B2

Abstract

There is provided a magnetic resonance imaging device capable of performing stable reconfiguration by using a coil sensitivity distribution even when the primary independence of the sensitivity distribution is low. The magnetic resonance imaging device includes: high-frequency magnetic field generation means for generating a high-frequency magnetic field to be applied to an examinee placed in a static magnetic field; gradient magnetic field generation means for generating a gradient magnetic field to be applied to the examinee; reception means for receiving the nuclear magnetic resonance signal generated from the examinee; image reconfiguration means for reconfiguring an image of the examinee according to the received magnetic resonance signal; and sequence control means for controlling operations of the respective means. The reception means has a reception coil for receiving the nuclear magnetic resonance signal by the spatially different sensitivity distributions for the examinee in a plurality of times of reception. Under the restrictive condition to set a range of the magnetic moment in the examinee, the image reconfiguration means uses the SN ratio of the sensitivity distribution and the magnetic resonance signal calculated in advance so as to perform calculation to acquire the distribution of the magnetic moment of the concerned region in the examinee by optimization to maximize the SN ratio of the reconfigured image.

Description

Specification

Magnetic resonance imaging device

Technical field

The present invention relates to an inspection apparatus (MRI: Magnetic Resonance Imaging) using nuclear magnetic resonance, and more particularly, to a magnetic resonance imaging technique using coil sensitivity.

Background art

[0002] A magnetic resonance imaging apparatus is a medical diagnostic imaging apparatus that causes nuclear magnetic resonance to occur in a hydrogen nucleus in an arbitrary cross section that crosses an examination target, and obtains a tomographic image in the cross section from the generated nuclear magnetic resonance signal. .

[0003] In MRI image diagnosis, a technique for reducing imaging time by utilizing a plurality of coils and image folding has been put into practical use (for example, see Non-Patent Document 1). In contrast to the normal imaging method, which uses only a gradient magnetic field to add position information in the phase encoding direction to an image, the imaging method of Non-Patent Document 1 uses the sensitivity distribution of the receiving coil in combination. The information is encoded into the image. Hereinafter, this encoding method is referred to as a coil sensitivity combined encoding, and encoding using only a normal gradient magnetic field that does not use sensitivity distribution is referred to as gradient magnetic field encoding.

[0004] The coil sensitivity combined encoding described above can be performed without phase encoding. In other words, by using a coil with more than the number of phase encodes, the number of phase encodes

1, that is, there is no need to perform phase encoding. This encoding is called coil sensitivity encoding.

[0005] In addition, the coil sensitivity encoding can be used not only in the phase encoding direction but also in the frequency encoding direction (reading direction) (see, for example, Patent Document 1). That is, by measuring a nuclear magnetic resonance signal using a coil having a frequency encoding number or more, it is not necessary to perform frequency encoding, and therefore it is not necessary to apply a gradient magnetic field for reading. When the gradient magnetic field for reading is not applied, there is an advantage that no noise is generated by switching the gradient magnetic field.

[0006] Patent Document 1: Japanese Patent Laid-Open No. 08-322814 Non-Patent Literature l: Pruessmann KP, Weiger M, Scheidegger MB, Boesiger P. SENSE: sensitivity encoding for fast MRI. Magn Reson Med, vol. 42, no. 5, 952-62, 1999

Disclosure of the invention

Problems to be solved by the invention

If there is no noise generated from the inspection object, the coil sensitivity encoding described in Non-Patent Document 1 or Patent Document 1 described above can be performed to obtain an unfolded image. However, there is noise that cannot be ignored in actual shooting, and in order to obtain a stable solution even in the presence of noise, the first-order independence between the sensitivity distributions of each subcoil must be high.

[0008] In order to increase the number of coil sensitivity encodings, it is necessary to increase the number of subcoils. However, increasing the number of subcoils generally reduces the primary independence between the sensitivity distributions. It is difficult to increase the number of subcoils as the sensitivity encoding is replaced.

[0009] When primary independence between sensitivity distributions decreases, reconstruction becomes unstable. That is, an image different from the object to be photographed is reconstructed.

Accordingly, an object of the present invention is to provide a magnetic resonance imaging apparatus that can stably perform reconstruction using the sensitivity distribution of the coil even when the primary independence of the sensitivity distribution is low. Means for solving the problem

In order to achieve the above object, the magnetic resonance imaging apparatus of the present invention has the following characteristics.

(1) High-frequency magnetic field generating means for generating a high-frequency magnetic field to be applied to an inspection object placed in a static magnetic field space, gradient magnetic field generating means for generating a gradient magnetic field to be applied to the inspection object, and the inspection object Receiving means for receiving a nuclear magnetic resonance signal generated from the image, an image reconstruction means for reconstructing the image to be inspected based on the received nuclear magnetic resonance signal, and operations of the respective means. And a sequence control means for controlling the tomography of the examination object by nuclear magnetic resonance. In the magnetic resonance imaging apparatus, the receiving means has a spatially different sensitivity distribution state with respect to the examination object. The nuclear magnetic resonance signal The image reconstruction means uses the sensitivity distribution obtained in advance and the S / N ratio of the nuclear magnetic resonance signal under the constraint on the magnetic moment in the inspection object, An arithmetic processing for obtaining a magnetic moment distribution of a region of interest in the inspection object is performed.

[0013] (2) In the magnetic resonance imaging apparatus of (1), the receiving means includes a receiving coil configured by a plurality of sub-coil members that receive the nuclear magnetic resonance signals with spatially different sensitivity distributions. It is characterized by comprising.

[0014] (3) In the magnetic resonance imaging apparatus of (1), the inspection object is mounted and in a desired direction (for example, in the body axis direction of the inspection object or in a direction substantially perpendicular to the body axis direction) And b) a movable top plate, wherein the pulse sequence control means controls the receiving means so as to receive the magnetic resonance signal a plurality of times during the movement of the top board.

(4) In the magnetic resonance imaging apparatus, the image reconstruction unit performs processing for maximizing an SN ratio of the reconstructed image with respect to the region of interest and an external region of the region of interest, The constraint condition includes a condition that the distribution of the magnetic moment in the outer region is known, and a condition that an upper limit value and a lower limit value that can be taken by the distribution of the magnetic moment in the region of interest are known. Features.

[0016] (5) In the magnetic resonance imaging apparatus, a resolution lower than the resolution of an image finally obtained by imaging using the gradient magnetic field (for example, less than half the resolution of the finally obtained image) The sensitivity distribution and the upper limit value and the lower limit value in the constraint conditions are determined based on the magnetic moment distribution of the inspection object obtained in advance at a resolution of (5).

[0017] (6) The magnetic resonance imaging apparatus includes a display means for displaying the reconstructed image.

The invention's effect

[0018] According to the present invention, by using the condition to be satisfied by the distribution of the magnetic moment, the reconstruction using the sensitivity distribution of the receiving coil can be performed even when the primary independence of the sensitivity distribution of the receiving coil is low. A magnetic resonance imaging apparatus capable of performing stably can be realized. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0020] (Example 1)

A first embodiment of the magnetic resonance imaging apparatus according to the present invention will be described below.

FIG. 13 is a schematic view of a magnetic resonance imaging apparatus, and FIG. 1 is a block diagram showing a schematic configuration of the nuclear magnetic resonance imaging apparatus. In FIG. 13, 101 is a magnet that generates a static magnetic field, 103 is an inspection object, and 300 is a top plate. In FIG. 1, 101 is a magnet that generates a static magnetic field, 102 is a coil that generates a gradient magnetic field, 103 is an inspection object, and the inspection object 103 is installed in a static magnetic field space generated by the magnet 101. The sequencer 104 sends commands to the gradient magnetic field power source 105 and the high-frequency magnetic field generator 106 to generate a gradient magnetic field and a high-frequency magnetic field, respectively. The high frequency magnetic field is applied to the inspection object 103 through the irradiation coil 107. A signal generated from the inspection object 103 is received by the receiving coil 116 and detected by the receiver 108. The sequencer 104 sets a nuclear magnetic resonance frequency (hereinafter referred to as a detection reference frequency) as a reference for detection. The detected signal is sent to the computer 109, where signal processing such as image reconstruction is performed.

The result is displayed on the display 110. If necessary, the detected signal and measurement conditions can be stored in the storage medium 111. If it is necessary to adjust the static magnetic field uniformity, the shim coil 112 is used. The shim coil 112 includes a plurality of channels, and current is supplied from the shim power supply 113. The sequencer 104 controls the current flowing through each shim coil during static magnetic field uniformity adjustment. The sequencer 104 sends a command to the shim power supply 113 to generate an additional magnetic field from the shim coil 112 so as to correct the static magnetic field inhomogeneity.

[0023] Note that the sequencer 104 normally performs control so that each device operates at a preprogrammed timing and intensity. Among the above programs, those that describe the timing and intensity of the high-frequency magnetic field, gradient magnetic field, and signal reception are called pulse sequences.

FIG. 14 shows the flow of photographing according to the present invention using this apparatus. The shooting is performed for the main shooting by switching the coil sensitivity and the preliminary shooting at a low resolution using a normal gradient magnetic field. Preliminary shooting can be performed in a short time because of its low resolution (Step 1), and the sensitivity distribution of each coil is acquired by preliminary shooting (Step 2). From the same preliminary shooting Determine the existence range to be inspected and the upper and lower limits of the pixel value of each pixel in the reconstructed image (step 3). In the actual shooting, shooting is performed while switching the coil (step 4). The image to be inspected is reconstructed by optimization from the data obtained in the main imaging, the sensitivity distribution obtained in the preliminary imaging, and the conditions of the inspection object (Step 5).

The imaging in this embodiment is performed using the pulse sequence shown in FIG. In FIG. 2, RF represents an excitation radio frequency pulse, Gs represents a slice selective gradient magnetic field, and Ge represents a phase encoding gradient magnetic field.

[0026] First, the excitation high-frequency pulse 1 is applied simultaneously with the slice gradient magnetic field 2 to the inspection object, and only a desired slice is excited.

[0027] After time τ after applying the excitation high-frequency pulse 1, when the π pulse 41 is applied, the nuclear magnetic resonance signal (echo signal) 45 gradually increases, and starts to attenuate again after a certain time. When π pulses 43 and 44 are applied again after π pulse 41 is applied for 2 hours, magnetic resonance signals 46 and 47 repeatedly increase and decrease. During this repetition, phase encode gradient magnetic fields 4an and 4bn are applied, respectively, to thereby provide position information in the y direction.

[0028] The nuclear magnetic resonance signal is measured while switching the L sub-coils constituting the receiving coil. As shown in Fig. 2, at each time between two π pulses, only one subcoil ci is active at time i (i = l, 2, 3, ..., L), and the nuclear magnetic resonance signal Si Are measured sequentially.

FIG. 3 shows an example of a specific configuration of the receiving coil. The receiving coil is composed of a plurality of sub-coils 80. FIG. 3 shows an example of a receiving coil composed of six sub-coils (cl to c6). A diode 81 is connected to each subcoil, and each diode can be individually turned ON / OFF by a signal from the sequencer 104.

[0030] In order to obtain the sensitivity distribution of each sub-coil, imaging using a gradient magnetic field generally performed in a magnetic resonance imaging apparatus is performed at a low resolution (for example, before imaging with the pulse sequence shown in FIG. 2). , Half of the resolution of the finally obtained image), and a sensitivity distribution is created with the resolution of the finally obtained image by interpolation (for example, polynomial approximation).

[0031] The relationship between the sensitivity distribution of each sub-coil obtained as described above and the inspection object is as shown in FIG. As shown in Figure 4 (a), the sensitivity of the coil also extends outside the region of interest 900. The area where the coil sensitivity exists is divided into N sections. Let f be the average value of the sensitivity distribution f (X) of the i-th sub-coil; j (j = l, 2, ..., N) -th interval. In addition, as shown in Fig. 4 (b), the magnitude of the magnetic moment of the hydrogen nucleus in the jth section is I. I is a value corresponding to the luminance information in the reconstructed image.

Here, the nuclear magnetic resonance signal S observed through the i-th subcoil is expressed by the following (Equation 1).

[0033] [Equation 1]

N

D

[0034] When the function f (X) indicating the sensitivity distribution by changing the subcoil is changed to i = l, 2, 3,..., L, the nuclear magnetic resonance signal ( Each of i = l, 2, 3, ..., L) is expressed by the following equation (Equation 2).

[0035] [Equation 2],

(Equation 2)

j

[0036] Here, in this (Equation 2), f is a matrix whose element is sensitivity f, s is a vector whose element is a nuclear magnetic resonance signal S, and the magnitude of the magnetic moment (reconstructed) I represents a vector with I as the element).

[0037] An image can be reconstructed by obtaining I from (Expression 2). Unless the coil sensitivity distributions are exactly the same, the inverse matrix Γ ^{1 of} f exists, so if S does not contain noise components, I can be easily obtained. However, in practice, noise is included with little force, and since the shapes of f are similar to each other, the primary independence between each row of f is low, so the solution by Γ ¹ is correct. I can't get 1!

Therefore, in this embodiment, correct I is obtained by the following solution. That is, magnetic For example, Ij (j E region of interest) within the region of interest is determined based on the MMSE (Minimum Mean Square Error) criterion with constraints shown in (Equation 3).

[0039] [Equation 3]

Minimize e = Ε {\\ 1-Γ \\ ~}

'/ ;.

Subject to <j

ί IR

Here, e ′ is an objective function, which is an expected value of the square of the difference between the true value I of the magnitude of the magnetic moment and the estimated solution I ′. Ε {·} is the expected value, and | 卜 II is the size of the vector.

[0041] (Equation 3) defines two constraint conditions. In other words, since there are no hydrogen nuclei outside the region of interest and the magnitude of the magnetic moment is 0, the first constraint condition is “= 0, j is outside the region of interest”. Furthermore, I 'is a positive value to represent the magnitude, and from the image taken to determine the sensitivity distribution,

] Lower limit I I

to know inf j and upper limit sup j

The second constraint is “I ≤ Ij ≤ I; region of interest”.

lnr j sup j

[0042] Since the nuclear magnetic resonance signal acquired by the receiving coil and the noise generated by the test object are considered to follow a mutually independent stochastic process, (Equation 3) is replaced by (Equation 4).

[0043] [Equation 4]

Minimize e = \\ S-fV || ² + σ \\ 尸¹¹²

{r J _f = 0, Z

Subject to i

In (Equation 4), σ is the square of the reciprocal of the SN ratio of the nuclear magnetic resonance signal, and the second term σ || lf is a term related to noise. The second term is a term that maximizes the S / N ratio.

[0045] Although the solution of (Equation 4) is uniquely determined, there are various methods such as a method based on the Jacobi method and a gradient projection method as specific methods for optimization. For convergence speed and stability Which method is selected depends on how reliable the computer performance and solution are required. Here, as an example, the Jacobi method is used as a basic example. Figure 5 shows a method for checking the range of the constraint condition at each iteration and replacing the value with the boundary value of the constraint condition if the range is exceeded.

First, 0 is set as an initial value of (j = 1, 2, 3,..., N) (step 1). Next, the gradient vector d el d I 'of the objective function e at the set value is obtained (step 2). (Calculated gradient vector) Change only X (1/2) (Step 3). If the result of the change does not satisfy the restriction condition, change to further satisfy the constraint condition and minimize the amount of change (step 4). The value of the objective function e is obtained from the change (Step 5). It is determined whether or not the convergence condition e = eO (eO = N 'γ · ((average value of 1) ² ) / 2) is satisfied that the value of the objective function e obtained is sufficiently small (decreases to about the noise level). Size sup]

(Step 6) If not satisfied, go back to Step 2, and if it is satisfied, let I ′ at that time be the solution. By the above procedure, is determined, and a projected image in the X-axis direction is obtained.

[0047] determined,,,

1 2 3 ... is the memory

Stored in N403. Figure 6 shows this storage state. Each is arranged and stored along the X-axis direction at a position on the ky axis in the figure corresponding to the phase encoding gradient magnetic field applied when acquiring the nuclear magnetic resonance signal.

[0048] As described above, the operation for obtaining,,, ..., I 'is performed for each change of the phase encoding gradient magnetic field.

1 2 3 N

By repeating this, all the magnetic resonance signals are stored in the memory 403 by repeating this process.

[0049] After that, based on the information stored in the memory 403, as shown in the lower diagram of FIG. 6, information obtained by Fourier transform in the ky direction is stored in the image memory 402, so that the tomographic image can be handled. 2D image information will be obtained.

As is apparent from the above description, according to the magnetic resonance imaging apparatus of the present embodiment, the position information in the X-axis direction is given without particularly applying the read-out gradient magnetic field, and the image force S is obtained. IJ is halfway to be done.

[0051] Hereinafter, in order to show the effect of the present embodiment, a comparison with an image obtained by a conventional method is performed.

FIG. 7 is an image to be obtained by photographing the inspection object, and shows the shape of the inspection object. The However, even outside the region of interest that cannot be obtained with the reconstructed image, it can be displayed.

In FIG. 7, the upper diagram shows a two-dimensional image to be inspected, and the lower diagram shows a one-dimensional profile obtained by projecting the image on the X axis. The X-axis and y-axis in the figure are the position axes, and the scale is set so that the pixel size is 1. The X-axis direction is the direction in which the sensitivity distribution changes in each subcoil, and is the direction in which coil sensitivity encoding is performed. The y-axis direction is the direction in which the sensitivity distribution does not change in each sub-coil, and is the direction in which frequency encoding is performed. The vertical axis of the lower profile indicates the pixel value.

[0054] As shown in FIG. 7, the inspection object used is a rectangle having a slit with a width of 4 pixels. In the upper diagram of FIG. 7, the area A shown in white is an area where the inspection object exists, and there is an area where there is no inspection object (a 4-pixel slit) between them. The reconstruction in the X direction was performed with 128 sections (see Fig. 4) 128. The region of interest 900 is a 64-pixel section from the center x = 32 to x = 95. The number of coils L used (see Fig. 4) is 64. The SN ratio is 100.

[0055] FIG. 8 shows a reconstructed image obtained by the present invention. In Fig. 8, the upper diagram shows the two-dimensional reconstructed image, and the lower diagram shows the one-dimensional profile that is projected onto the X axis. The X and y axes in the figure are axes indicating the position, the scale is the same as in FIG. 7, but the range is the range of the region of interest 900 in FIG. The X-axis direction is the direction in which the sensitivity distribution changes in each subcoil, and is the direction in which coil sensitivity encoding is performed. The y-axis direction is a direction in which the sensitivity distribution does not change in each sub-coil, and is a direction in which frequency encoding is performed. The vertical axis of the lower profile indicates the pixel value.

[0056] As shown in the lower part of the one-dimensional profile shown in the lower part of Fig. 8, the outermost part to be inspected and the edge of the slit boundary part are slightly dull, and a slit with a width of 4 pixels is separated. A reconstructed image is obtained. In other words, it can be seen that the present invention allows photographing with a resolution of 4 pixels.

FIG. 9 is a reconstructed image according to the conventional method. In Fig. 9, the upper diagram shows the two-dimensional reconstructed image, and the lower diagram shows the one-dimensional profile that is projected onto the X axis. The X-axis and y-axis in the figure are axes indicating position, and the scale is the same as in FIGS. In the X-axis direction, the sensitivity distribution changes in each subcoil. This is the direction in which coil sensitivity encoding is performed. The y-axis direction is a direction in which the sensitivity distribution does not change in each subcoil, and is a direction in which frequency encoding is performed. The vertical axis of the lower profile indicates the pixel value.

[0058] An image is acquired using 16 subcoils that cover the region where the inspection target exists so that the spatial resolution in the X direction is the same as the spatial resolution achieved by the method of the present invention described above. The region of interest in the X-axis direction is divided into 16 pixels and image reconstruction is performed. In other words, the pixel size in the X direction of the image shown in Fig. 9 is four times that of Fig. 8. As can be seen from Fig. 9, spatial resolution is not obtained in the X direction, and image reconstruction fails. It can also be seen that the luminance value of the image is 2000 times the original luminance value.

[0059] In summary, in this embodiment, coil sensitivity encoding can be performed with resolution that was not possible with the conventional method. As a result, coil sensitivity encoding can be performed instead of frequency encoding, and the gradient magnetic field can be encoded. It is possible to shoot without noise caused by switching.

[0060] (Example 2)

As a second embodiment of the present invention, a method will be described in which imaging is performed by changing the sensitivity distribution by moving the top plate on which the inspection object is placed in a desired direction. In this example, the top plate is

The force configured to be movable in the body axis direction of the inspection object

Further, it may be movable in a direction substantially perpendicular to the body axis direction.

FIG. 10 is a diagram showing a relationship among the inspection target 103, the top plate 300, and the receiving coil 301. The inspection object is placed on a movable top plate, and the receiving coil is composed of a single coil and is stationary.

Imaging is performed using a pulse sequence shown in FIG. In Fig. 11, RF is the excitation high-frequency pulse, Gs is the slice selective gradient magnetic field, Gr is the read gradient magnetic field, and the top plate positions pl, p2, and -pL are the celestial coordinates in the coordinate system x 'with reference to the stationary receiver coil. The plate position and coil sensitivity distribution show the coil sensitivity distribution in the coordinate system fixed to the top plate.

[0063] First, the excitation high-frequency pulse 1 is applied to the inspection object simultaneously with the slice gradient magnetic field 2, and only a specific slice is excited. As a result, only a specific slice generates the nuclear magnetic resonance signal 42. [0064] A time after applying the excitation high-frequency pulse 1, when the π pulse 41 is applied, the magnetic resonance signal once attenuated becomes large again, and begins to attenuate again after a certain time. When the π pulse 43 is applied again after 2 hours and the π pulse 43 is applied again, the nuclear magnetic resonance signal repeatedly increases and decreases. During this repetition, a read gradient magnetic field 5 is applied in the y direction in FIG. 10 to give position information in the y direction.

[0065] The nuclear magnetic resonance signal is measured while moving the top board. As shown in Fig. 11, the magnetic resonance signals (E (ky), E (ky), E (ky), ... ゝ are applied by the receiving coil while applying the reading gradient magnetic field in each of two π pulses. E (ky)) is measured sequentially. here

1 2 3 L

And ky represents the coordinate in k space corresponding to the y direction. The nuclear magnetic resonance signal E (ky) is a value at a point ky in the k space of the nuclear magnetic resonance signal received at the top plate position Pi. The measured E is stored in the measurement memory 400 as shown in FIG. Below we consider the nuclear magnetic resonance signal S = E (ky) at a certain ky.

[0066] The relationship between the sensitivity distribution f of the receiving coil and the inspection target at the coordinates fixed to the top plate at the top plate position Pi is as shown in FIG. As shown in FIG. 4 (a), the sensitivity of the coil extends outside the region of interest 900, and the region where the coil sensitivity exists is divided into N sections. The average value of the j (j = l, 2, ..., N) -th section of the sensitivity distribution f (X) of the receiving coil at coordinates fixed to the top board at the top board position Pi is assumed to be f . Also, as shown in Fig. 4 (b), the magnitude of the magnetic moment of the hydrogen nucleus existing in the j-th section is I and j. I is a value corresponding to the luminance information in the reconstructed image.

[0067] In this way, it is possible to change the sensitivity distribution of the receiving coil with respect to the inspection object by moving the top plate and to take an image, and the magnetic field observed at the i-th top plate position. The resonance signal Si is expressed by (Equation 1).

[0068] When the function f (X) indicating the sensitivity distribution is changed to i = l, 2, 3, ..., L by the movement of the top position, the nuclear magnetic resonance signal S (1 = 1 , 2, 3,..., L) are also expressed by (Equation 2) as in Example 1. In the second embodiment, the sensitivity distribution is obtained for the position of each of the plurality of coils. A specific method is as described in Example 1.

[0069] Therefore, the magnitude of the magnetic moment can be obtained by (Equation 4) by exactly the same method as described in Example 1, and a projected image in the X-axis direction can be obtained. [0070] determined,,,... Is an intermediate memory

格納 Stored in 401. Indicates this storage state

one two Three

This is shown in Fig. 12 (b). Arranged along the X-axis in the corresponding ky. As described above, I ′,, 1 ′,... Are sequentially obtained for each operation force ky stored in the intermediate memory 401.

1 2 3 N

[0071] After that, based on the information stored in the intermediate memory 401, as shown in FIG. 12 (c), information obtained by Fourier transform in the y direction is stored in the image memory 402 to store the tomographic image. 2D image information corresponding to is obtained.

As is clear from the above description, according to the inspection apparatus using nuclear magnetic resonance according to Example 2, position information in the X-axis direction is given without particularly applying a phase encoding gradient magnetic field. An image is obtained. According to this method, encoding can be performed while continuously moving the top plate that does not require the top plate to be stopped during encoding, and V ヽ images without discontinuous regions can be obtained efficiently.

[0073] As described in detail above, according to the present invention, it is possible to stably perform reconfiguration using the sensitivity distribution of the receiving coil even when the primary independence between the sensitivity distributions of the plurality of receiving coils is low. Thus, encoding using the sensitivity distribution of the receiving coil can be performed without restriction of maintaining primary independence. As a result, a reading gradient magnetic field is not applied, and instead, imaging using the sensitivity distribution of the receiving coil can be performed, and imaging with less noise can be performed.

[0074] In addition, in the imaging method in which the field of view is enlarged by moving the top plate, if the phase encoding direction is set to the moving direction, the force that has conventionally been unable to move the top plate continuously is used. Therefore, if the receiver coil sensitivity encoding is used instead of the phase encoding, the top plate can be moved continuously, and images without discontinuous areas can be obtained efficiently. Can be achieved.

Industrial applicability

[0075] According to the present invention, reconfiguration using the sensitivity distribution of the receiving coil can be performed even when the primary independence of the sensitivity distribution of the receiving coil is low by using the condition to be satisfied by the distribution of the magnetic moment. A stable magnetic resonance imaging system can be realized in the medical field! The possibility of its use is great.

Brief Description of Drawings

FIG. 1 is a diagram showing a configuration example of a magnetic resonance imaging apparatus to which the present invention is applied. FIG. 2 is a diagram for explaining a pulse sequence for performing imaging by switching sub-coils in the first embodiment.

FIG. 3 is a diagram showing a configuration example of a receiving coil including a plurality of subcoils.

FIG. 4 is a diagram for explaining the relationship between the sensitivity distribution of each subcoil and the inspection object.

FIG. 5 is a diagram for explaining an example of an optimization procedure.

FIG. 6 is a diagram for explaining a state in which nuclear magnetic resonance signals and image information are stored in a memory.

FIG. 7 is a diagram showing the inspection target.

FIG. 8 shows a reconstructed image according to the present invention.

FIG. 9 is a diagram showing a reconstructed image obtained by a conventional method.

FIG. 10 is a diagram for explaining the relationship among the inspection object, the top plate, and the receiving coil in the second embodiment.

FIG. 11 is a diagram for explaining a pulse sequence for performing imaging while moving the top board.

FIG. 12 is a diagram for explaining a state in which nuclear magnetic resonance signals and image information are stored in a memory.

FIG. 13 is a diagram showing an overview of a photographing apparatus.

FIG. 14 is a diagram for explaining a flow of photographing until an image to be inspected according to the present invention is acquired. Explanation of symbols

1 ... excitation high-frequency pulse, 2 ... slice gradient magnetic field, 4 ... phase encoding gradient magnetic field, 5 ... read gradient magnetic field, 41, 43, 4Φ ... pi pulse, 42 ... nuclear magnetic resonance signal, 45 ... Magnetic resonance signal, 46 ... Nuclear magnetic resonance signal, 80 ... subcoil, 81 ... diode, 101 ... magnet that generates static magnetic field, 102 ... gradient magnetic field coil, 103 ... test object, 104 "sequencer, 10" 5 ... Gradient magnetic field power source, 106 ... High frequency magnetic field generator, 107 ... Irradiation coil, 108 ... Receiver, 109 ... Computer, 110 ... Display, 111 ... Storage medium, 112 ... Shim coil, 113 ··· Shim power supply, 116… Receiving coil, 300 ··· Top plate, 301 ··· Receiving coil, 302 ··· Direction of moving the top plate, 400 ··· Measurement memory, 401 ··· Intermediate memory, 402 ·· · Image memory, 403 · · · Memory, 900 · · · Interest area.

Claims

The scope of the claims

[1] A high-frequency magnetic field generating means for generating a high-frequency magnetic field to be applied to an inspection object placed in a static magnetic field space, a gradient magnetic field generating means for generating a gradient magnetic field to be applied to the inspection object, and generated from the inspection object A receiving means for receiving a nuclear magnetic resonance signal, an image reconstruction means for reconstructing the image to be inspected based on the received nuclear magnetic resonance signal, and the operation of each means. In a magnetic resonance imaging apparatus comprising a sequence control means for controlling and a display means for displaying the reconstructed image, and performing tomography of the examination object by nuclear magnetic resonance, the receiving means comprises: A receiving coil that receives the nuclear magnetic resonance signal in a spatially different sensitivity distribution state, and the image reconstructing means is configured in advance under a constraint on the magnetic moment in the inspection object. Used because was the sensitivity distribution and the SN ratio of the magnetic resonance signals, the magnetic resonance imaging apparatus you and performs the arithmetic processing for determining the distribution of the magnetic moment of the region of interest in said object.

[2] The magnetic resonance imaging apparatus according to claim 1! Then, the image reconstruction means performs processing for maximizing the SN ratio of the reconstructed image with respect to the region of interest and the region outside the region of interest, and the constraint condition is the magnetic field in the region outside the region. 2. A magnetic resonance imaging apparatus comprising: a condition that a moment distribution is known; and a condition that an upper limit value and a lower limit value that can be taken by the magnetic moment distribution in the region of interest are known.

[3] In the magnetic resonance imaging apparatus according to claim 2, the magnetic moment of the inspection object obtained by performing in advance at a resolution lower than the resolution of the image finally obtained by using the gradient magnetic field. The magnetic resonance imaging apparatus, wherein the sensitivity distribution and the upper limit value and the lower limit value in the constraint condition are determined based on the distribution of

[4] In the magnetic resonance imaging apparatus according to claim 2, the magnetic field of the object to be inspected acquired in advance with a resolution equal to or less than half the resolution of the image finally obtained using the gradient magnetic field. A magnetic resonance imaging apparatus that determines the sensitivity distribution and the upper limit value and the lower limit value in the constraint condition based on a moment distribution.

[5] In the magnetic resonance imaging apparatus according to claim 1, the receiving means are spatially connected to each other. A plurality of sub-coil receivers for receiving the nuclear magnetic resonance signals with different sensitivity distributions, and the sequence control means receives the nuclear magnetic resonance signals while switching the plurality of sub-coils. A magnetic resonance imaging apparatus.

[6] The magnetic resonance imaging apparatus according to claim 1, further comprising a top plate on which the inspection object is mounted and movable in a desired direction, and the pulse sequence control means includes the top plate A magnetic resonance imaging apparatus for controlling the receiving means so as to receive the nuclear magnetic resonance signal a plurality of times during movement.

[7] The magnetic resonance imaging apparatus according to [6], wherein the image reconstruction unit performs a process of maximizing an SN ratio of the reconstructed image with respect to the region of interest and an external region of the region of interest. The constraint condition includes a condition that the distribution of the magnetic moment in the outer region is known, and a condition that the upper limit value and the lower limit value that can be taken by the distribution of the magnetic moment in the region of interest are known. Magnetic resonation imaging device characterized by

[8] In the magnetic resonance imaging apparatus according to claim 7, the magnetic moment of the inspection object obtained by performing in advance at a resolution lower than the resolution of the image finally obtained by using the gradient magnetic field. And determining the sensitivity distribution and the upper limit value and the lower limit value in the constraint condition.

[9] In the magnetic resonance imaging apparatus according to claim 7, the magnetic field of the object to be inspected acquired in advance with a resolution equal to or less than half of the resolution of the image finally obtained using the gradient magnetic field. A magnetic resonance imaging apparatus that determines the sensitivity distribution and the upper limit value and the lower limit value in the constraint condition based on a moment distribution.

10. The magnetic resonance imaging apparatus according to claim 6, wherein the top plate is movable in the body axis direction of the inspection object.

[11] A high-frequency magnetic field generating means for generating a high-frequency magnetic field to be applied to an inspection object placed in a static magnetic field space, a gradient magnetic field generating means for generating a gradient magnetic field to be applied to the inspection object, and generated from the inspection object Based on the receiving means for receiving the nuclear magnetic resonance signal using a receiving coil comprising a plurality of subcoils, and the received nuclear magnetic resonance signal, Image reconstructing means for reconstructing an image to be inspected, sequence control means for controlling the operation of each means, and display means for displaying the reconstructed image, wherein the sequence control means The image reconstructing means performs control to receive a nuclear magnetic resonance signal while switching the plurality of subcoils, and the image reconstructing means sets the plurality of the plurality of subcoils under a constraint condition for setting a range of the magnitude of the magnetic moment in the inspection target. Using the sensitivity distribution of the receiving coil obtained by switching the subcoil and the S / N ratio of the nuclear magnetic resonance signal, an arithmetic process for obtaining the distribution of the magnetic moment of the region of interest in the inspection object is performed. A magnetic resonance imaging apparatus.

[12] A high-frequency magnetic field generating means for generating a high-frequency magnetic field to be applied to an inspection object mounted on a top plate, which is placed in a static magnetic field space, and a gradient magnetic field generating means for generating a gradient magnetic field to be applied to the inspection object; Receiving means for receiving a nuclear magnetic resonance signal generated by the inspection object using a single receiving coil, and an image for reconstructing the image of the inspection object based on the received nuclear magnetic resonance signal Reconstructing means, sequence control means for controlling the operation of each means, and display means for displaying the reconstructed image, wherein the top plate moves in the body axis direction of the inspection object The image reconstruction means is configured to receive the nuclear magnetic resonance signal during the movement of the top board under a constraint condition that sets a range of the magnitude of the magnetic moment in the inspection object. Requested reception Using the SN ratio of the sensitivity distribution of yl and said nuclear magnetic resonance signals, the magnetic resonance imaging apparatus and performs arithmetic processing for obtaining the distribution of the magnetic moment of put that region of interest to the test object.

[13] The magnetic resonance imaging apparatus according to claim 11, wherein the gradient magnetic field generating means performs either phase encoding or frequency encoding in a direction perpendicular to a body axis direction of the inspection object. A magnetic resonance imaging apparatus.

[14] The magnetic resonance imaging apparatus according to [12], wherein the gradient magnetic field generating means performs either phase encoding or frequency encoding in a direction perpendicular to a body axis direction of the inspection object. A magnetic resonance imaging apparatus.