JP4810432B2 - Magnetic resonance imaging device - Google Patents

Description

  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.

  The magnetic resonance imaging apparatus is a medical image diagnostic apparatus that causes nuclear magnetic resonance to occur in hydrogen nuclei 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.

  In MRI image diagnosis, a technique for shortening the imaging time by using a plurality of coils and image folding has been put into practical use (for example, see Non-Patent Document 1). Whereas the normal imaging method uses only the gradient magnetic field to provide position information in the phase encoding direction to the image, the imaging method of Non-Patent Document 1 uses the sensitivity distribution of the receiving coil in combination. The information is encoded in the image. Hereinafter, this encoding method is referred to as 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.

  The coil sensitivity combined encoding described above can be performed without phase encoding. In other words, by using a coil having the number of phase encodes or more, the number of phase encodes is 1, that is, it is not necessary to perform phase encode. The encoding in this case is called coil sensitivity encoding.

  Further, 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, it is not necessary to perform frequency encoding by measuring a nuclear magnetic resonance signal using coils having a frequency encoding number or more, 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 noise due to switching of the gradient magnetic field does not occur.

Japanese Patent Laid-Open No. 08-322814 Prussmann KP, Weiger M, Scheideger MB, Boesiger P. SENSE: sensibility encoding for fast MRI. Magn Reson Med, vol. 42, no. 5, 952-62, 1999

  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 image without folding. However, there is noise that cannot be ignored in actual photographing, and in order to obtain a stable solution even in the presence of noise, the primary independence between the sensitivity distributions of the subcoils needs to be high.

  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 lowers the primary independence between sensitivity distributions, so that gradient magnetic field encoding can be replaced with coil sensitivity encoding. It is difficult to increase the number of subcoils.

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

  Therefore, 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.

  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 generated from the inspection object Receiving means for receiving a nuclear magnetic resonance signal; image reconstructing means for reconstructing the image to be examined based on the received nuclear magnetic resonance signal; and sequence control means for controlling the operation of each means; In the magnetic resonance imaging apparatus for performing tomography of the inspection object by nuclear magnetic resonance, the receiving means receives the nuclear magnetic resonance signal in a spatially different sensitivity distribution state with respect to the inspection object. The image reconstructing means has a sensitivity distribution determined in advance and S of the nuclear magnetic resonance signal under a constraint on the magnetic moment in the inspection object. Using the ratio, and performs the arithmetic processing for determining the distribution of the magnetic moment of the region of interest in said object.

  (2) In the magnetic resonance imaging apparatus according to (1), the receiving unit includes a receiving coil including a plurality of subcoils that receive the nuclear magnetic resonance signal with spatially different sensitivity distributions. And

  (3) In the magnetic resonance imaging apparatus of (1), the inspection object is mounted and moved 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). 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, and the constraint condition is: It includes a condition that the distribution of the magnetic moment in the external 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.

  (5) In the magnetic resonance imaging apparatus, the acquisition using the gradient magnetic field is performed in advance at a resolution lower than the resolution of the image finally obtained (for example, the resolution of half or less of the resolution of the image finally obtained). The sensitivity distribution and the upper limit value and the lower limit value in the constraint condition are determined based on the distribution of the magnetic moment to be inspected.

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

  According to the present invention, by using the condition to be satisfied by the distribution of the magnetic moment, even when the primary independence of the sensitivity distribution of the receiving coil is low, the reconfiguration using the sensitivity distribution of the receiving coil can be performed stably. A resonance imaging apparatus can be realized.

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

(Example 1)
Hereinafter, a first embodiment of the magnetic resonance imaging apparatus according to the present invention will be described.

  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 target, and the inspection target 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. A nuclear magnetic resonance frequency (hereinafter referred to as a detection reference frequency) as a reference for detection is set by the sequencer 104. 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. The detected signal and measurement conditions can be stored in the storage medium 111 as necessary. When 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. When adjusting the uniformity of the static magnetic field, the sequencer 104 controls the current flowing through each shim coil. 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.

  The sequencer 104 normally performs control so that each device operates at a timing and intensity programmed in advance. Among the above programs, a program that describes the high-frequency magnetic field, the gradient magnetic field, and the timing and intensity of signal reception is called a pulse sequence.

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

  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.

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

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

  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, at time i (i = 1, 2, 3,..., L), only one subcoil ci is activated, and the nuclear magnetic resonance signal Si. Are measured sequentially.

  An example of a specific configuration of the receiving coil is shown in FIG. The receiving coil is composed of a plurality of subcoils 80, and FIG. 3 shows an example of a receiving coil including six subcoils (c1 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.

  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 obtained at a low resolution (for example, finally obtained) before imaging by the pulse sequence shown in FIG. The sensitivity distribution is created with the resolution of the image finally obtained by interpolation (for example, polynomial approximation).

The relationship between the sensitivity distribution of each subcoil obtained as described above and the inspection object is as shown in FIG. As shown in FIG. 4A, the sensitivity of the coil extends to the outside of 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 = 1, 2,..., N) -th section of the sensitivity distribution f _i (x) of the i-th subcoil is defined as f _ij . Further, as shown in FIG. 4B, the magnitude of the magnetic moment of the hydrogen nucleus existing in the j-th section is I _j . I _j is a value corresponding to the luminance information in the reconstructed image.

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

When the function f _i (x) indicating the sensitivity distribution is changed to i = 1, 2, 3,..., L by switching the subcoil, the nuclear magnetic resonance signal S _i (i = i = Each of 1, 2, 3,..., L) is expressed by the following equation (Equation 2).

Here, in this (Equation 2), f is a matrix having the sensitivity f _ij as an element, S is a vector having the nuclear magnetic resonance signal S _i as an element, and the magnitude of the magnetic moment (pixel value of the reconstructed image) ) Let I be a vector with I _j as an element.

An image can be reconstructed by obtaining I from (Equation 2). Unless the coil sensitivity distributions are completely the same, there is an inverse matrix f ⁻¹ of f, and therefore I can be easily obtained when no noise component is included in S. However, included actually no small noise, also due to low linear independence of each line spacing f from the shape of the f _i are similar to each other, right I is obtained in solution by f ^-1 Absent.

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

Here, e ′ is an objective function, which is 2 of the difference between the true value I of the magnitude of the magnetic moment and the estimated solution I ′.
Expected value of power. E {•} represents an expected value, and || • || represents the magnitude of the vector.

In (Equation 3), two constraint conditions are defined. That is, since there is no hydrogen nucleus outside the region of interest and the magnitude of the magnetic moment is 0, a condition that “I ′ _j = 0, j is outside the region of interest” is defined as the first constraint condition. Furthermore, I _'j is a positive value to represent the size, also, the imaging performed to determine the sensitivity distribution, I' because the apparent lower limit I _{inf j} and max I _{sup j} of _j, second Is defined as “I _{inf j} ≦ Ij ≦ I _{sup j} , jεregion of interest”.

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

In equation (4), sigma is the square of the reciprocal of SN ratio of the nuclear magnetic resonance signals, the second term sigma || I '|| ² is a section on noise. The second term is a term that makes the S / N ratio the maximum value.

  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. Each has its own convergence speed and stability. Which method is chosen depends on how reliable the computer performance and solution are required. Here, as an example, FIG. 5 shows a method of checking the range of the constraint condition every iteration and replacing the value of I ′ with the boundary value of the constraint condition when the range is exceeded, based on the Jacobi method as an example.

First, 0 is set as an initial value of I ′ _j (j = 1, 2, 3,..., N) (step 1). Next, determine the 'gradient vector ∂E / ∂I objective function e in the value of _j' set I (step 2). I ′ _j is changed by (the obtained gradient vector) × (1/2) (step 3). If the changed result I ′ _j does not satisfy the constraint condition, I ′ _j is further changed so as to satisfy the constraint condition and minimize the amount of change (step 4). The value of the objective function e is obtained from the changed I ′ _j (step 5). It is determined whether or not a convergence condition e <e0 (e0 = N · γ · ((average value of I _supj ) ² ) / 2) that the value of the obtained objective function e is sufficiently small (decreases to about the noise level) is satisfied. determination (step 6), the flow returns to step 2 does not satisfy, if they meet, to a solution of I _'j at this time. I ′ _j is determined by the above procedure, and a projection image in the x-axis direction is obtained.

The determined I ′ ₁ , I ′ ₂ , I ′ ₃ ,..., I ′ _N are stored in the memory 403. FIG. 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 at the time of nuclear magnetic resonance signal acquisition.

As described above, the operations for obtaining I ′ ₁ , I ′ ₂ , I ′ ₃ ,..., I ′ _N are performed for each change of the phase encoding gradient magnetic field, and by repeating this, all the magnetic resonance signals are stored in the memory 403. Will be stored.

  Thereafter, 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 two-dimensional corresponding to the tomographic image is obtained. Image information can be obtained.

  As is apparent from the above description, according to the magnetic resonance imaging apparatus of the present embodiment, it is understood that the position information in the x-axis direction is given and the image is obtained without particularly applying the readout gradient magnetic field. .

  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. However, the region outside the region of interest that cannot be obtained from the reconstructed image is also 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 axes indicating positions, and the scale is such that the pixel size is 1. The x-axis direction is a direction in which the sensitivity distribution changes in each subcoil and is a 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.

  As shown in FIG. 7, the used inspection object is a rectangle having a slit with a width of 4 pixels. In the upper diagram of FIG. 7, a region A indicated in white is a region where the inspection target exists, and has a region where there is no inspection target (a slit of 4 pixels) therebetween. The reconstruction in the x direction was performed with the number of sections N (see FIG. 4) 128. The region of interest 900 is a 64-pixel section from the center x = 32 to x = 95. The number L of coils used (see FIG. 4) is 64. The S / N ratio is 100.

  FIG. 8 shows a reconstructed image obtained by the present invention. In FIG. 8, the upper diagram shows a two-dimensional reconstructed image, 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 axes indicating positions, and the scale is equal to that in FIG. 7, but the range is the range of the region of interest 900 in FIG. The x-axis direction is a direction in which the sensitivity distribution changes in each subcoil and is a 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.

  As can be seen from the one-dimensional profile shown in the lower part of FIG. 8, a reconstructed image in which slits with a width of 4 pixels are separated is obtained by slightly dulling the edges of the outermost part to be inspected and the slit boundary part. It has been. That is, it can be seen that the present invention can capture images with a resolution of 4 pixels.

  FIG. 9 is a reconstructed image according to the conventional method. In FIG. 9, the upper diagram shows a two-dimensional reconstructed image, 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 positions indicating axes, the scale is the same as in FIGS. 7 and 8, but the range is the range of the region of interest 900 in FIG. The x-axis direction is a direction in which the sensitivity distribution changes in each subcoil and is a 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.

  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 above-described method of the present invention, and the x-axis direction is acquired. The region of interest is divided into 16 pixels to perform image reconstruction. That is, the pixel size in the x direction of the image shown in FIG. 9 is four times that in FIG. As can be seen from FIG. 9, no spatial resolution is obtained in the x direction, and image reconstruction has failed. It can also be seen that the luminance value of the image is 2000 times the original luminance value.

  In summary, in this embodiment, coil sensitivity encoding can be performed with a resolution that was impossible with the conventional method, and as a result, coil sensitivity encoding can be performed instead of frequency encoding, which is caused by switching of the gradient magnetic field. You can shoot without noise.

(Example 2)
As a second embodiment of the present invention, a method is described in which imaging is performed by changing the sensitivity distribution by moving a top plate on which an inspection object is placed in a desired direction. In this example, the top plate is configured to be movable in the body axis direction of the inspection target, but is not limited to this direction, and may be movable in a direction substantially perpendicular to the body axis direction, for example.

  FIG. 10 is a diagram illustrating a relationship among the inspection target 103, the top board 300, and the reception 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 the pulse sequence shown in FIG. In FIG. 11, RF is an excitation radio frequency pulse, Gs is a slice selective gradient magnetic field, Gr is a read gradient magnetic field, and the top plate positions p1, p2,... PL are top plates in a coordinate system x ′ based on a stationary receiving coil. The position of the coil and the coil sensitivity distribution indicate the coil sensitivity distribution in the coordinate system fixed to the top plate.

  First, the excitation high-frequency pulse 1 is applied to the inspection object simultaneously with the slice gradient magnetic field 2 to excite only a specific slice. As a result, only a specific slice generates the nuclear magnetic resonance signal 42.

  When the π pulse 41 is applied after a time τ after applying the excitation high-frequency pulse 1, the magnetic resonance signal once attenuated becomes large again, and begins to attenuate again after a certain time. When the application of the π pulse 43 is repeated after the time 2τ after the π pulse 41 is applied, the nuclear magnetic resonance signal repeatedly increases and decreases. In this case, the reading gradient magnetic field 5 is applied in the y direction in FIG. 10, thereby giving position information in the y direction.

Nuclear magnetic resonance signals are measured while moving the top plate. As shown in FIG. 11, the magnetic resonance signals (E ₁ (ky), E ₂ (ky), E ₃ (ky),... , E _L (ky)) are sequentially measured. Here, ky represents coordinates in the k space corresponding to the y direction. The nuclear magnetic resonance signal E _i (ky) is a value at a point ky in the k space of the nuclear magnetic resonance signal received at the top position Pi. The measured E _i is stored in the measurement memory 400 as shown in FIG. Hereinafter, the nuclear magnetic resonance signal S _i = E _i (ky) at a certain ky will be considered.

In top position Pi, inspected relationship between sensitivity distribution f _i of receiver coils at fixed coordinates in the top plate, like in Example 1, it becomes as shown in FIG. As shown in FIG. 4A, the sensitivity of the coil extends to the outside of the region of interest 900, and the region where the coil sensitivity exists is divided into N sections. In top position Pi, j of the sensitivity of the receiver coils at fixed coordinates in the top plate distribution _{f i (x) (j =} 1,2, ..., N) the average of th interval and _{f ij.} Further, as shown in FIG. 4B, the magnitude of the magnetic moment of the hydrogen nucleus existing in the j-th section is I _j . I _j is a value corresponding to the luminance information in the reconstructed image.

  In this way, it is possible to change the sensitivity distribution of the receiving coil with respect to the object to be inspected by moving the top plate as in the first embodiment, and the magnetic resonance signal Si observed at the i-th top plate position. Is represented by (Equation 1).

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

  Therefore, the magnitude I ′ of the magnetic moment can be obtained by (Expression 4) by exactly the same method as described in the first embodiment, and a projected image in the x-axis direction is obtained.

The determined I ′ ₁ , I ′ ₂ , I ′ ₃ ,..., I ′ _N are stored in the intermediate memory 401. FIG. 12B shows this storage state. Arranged along the x-axis direction at the corresponding ky. As described above, operations for obtaining I ′ ₁ , I ′ ₂ , I ′ ₃ ,..., I ′ _N and storing them in the intermediate memory 401 are sequentially performed for each ky.

  Thereafter, based on the information stored in the intermediate memory 401, as shown in FIG. 12 (c), the information obtained by Fourier transform in the y direction is stored in the image memory 402, thereby corresponding to the tomographic image. Image information can be obtained.

  As is apparent from the above description, according to the inspection apparatus using nuclear magnetic resonance according to the second embodiment, position information in the x-axis direction is given without applying a phase encoding gradient magnetic field, and an image is obtained. It is done. According to this method, it is not necessary to stop the top plate during encoding, encoding can be performed while continuously moving the top plate, and an image having no discontinuous area can be obtained efficiently.

  As described above in detail, according to the present invention, even when the primary independence between the sensitivity distributions of a plurality of receiving coils is low, reconstruction using the sensitivity distribution of the receiving coils can be performed stably, so that the primary independence is achieved. Encoding using the sensitivity distribution of the receiving coil can be performed without the restriction of maintaining As a result, it is possible to perform imaging using the sensitivity distribution of the receiving coil instead of applying the read gradient magnetic field, and to perform imaging with less noise.

  Also, in the imaging method that expands the field of view by moving the top plate, when the phase encoding direction is set to the moving direction, the top plate could not be moved continuously in the past. By using the reception coil sensitivity encoding, the top plate can be moved continuously, and a remarkable effect that an image without a discontinuous region can be efficiently obtained can be achieved.

  According to the present invention, by using the condition to be satisfied by the distribution of the magnetic moment, even when the primary independence of the sensitivity distribution of the receiving coil is low, the reconfiguration using the sensitivity distribution of the receiving coil can be performed stably. A resonance imaging apparatus can be realized, and its applicability is great in the medical field.

1 is a diagram illustrating a configuration example of a magnetic resonance imaging apparatus to which the present invention is applied. The figure explaining the pulse sequence which switches and image | photographs a subcoil in a 1st Example. The figure which shows the example of 1 structure of the receiving coil comprised with a some subcoil. The figure explaining the sensitivity distribution of each subcoil, and the relationship of test object. The figure explaining an example of the procedure of optimization. The figure explaining the state by which a nuclear magnetic resonance signal and image information are stored in memory. The figure which shows a test object. The figure which shows the reconstruction image by this invention. The figure which shows the reconstruction image by a conventional method. The figure explaining the relationship between the test object in the 2nd Example, a top plate, and a receiving coil. The figure explaining the pulse sequence which image | photographs, moving a top plate. The figure explaining the state by which a nuclear magnetic resonance signal and image information are stored in memory. The figure which shows the external appearance of an imaging device. The figure explaining the flow of imaging | photography until it acquires the image of the test object by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Excitation high frequency pulse, 2 ... Slice gradient magnetic field, 4 ... Phase encoding gradient magnetic field, 5 ... Reading gradient magnetic field, 41, 43, 44 ... Pi pulse, 42 ... Nuclear magnetic resonance signal, 45 ... Magnetic resonance signal, 46 ... Nuclear Magnetic resonance signal, 80 ... subcoil, 81 ... diode, 101 ... magnet for generating static magnetic field, 102 ... gradient magnetic field coil, 103 ... inspection object, 104 ... sequencer, 105 ... gradient magnetic field power supply, 106 ... high frequency magnetic field generator, 107 DESCRIPTION OF SYMBOLS ... Irradiation coil, 108 ... Receiver, 109 ... Computer, 110 ... Display, 111 ... Storage medium, 112 ... Shim coil, 113 ... Shim power source, 116 ... Reception coil, 300 ... Top plate, 301 ... Reception coil, 302 ... Top plate moving direction, 400 ... measurement memory, 401 ... intermediate memory, 402 ... image memory, 403 ... memory, 900 ... interest Pass.

Claims (9)

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 nuclear magnetic resonance generated from the inspection object Receiving means for receiving a signal, image reconstructing means for reconstructing an image reflecting the distribution of the magnetic moment of the region of interest to be inspected based on the received nuclear magnetic resonance signal, and the operation of each means In a magnetic resonance imaging apparatus for performing tomography of the examination object by nuclear magnetic resonance, comprising a sequence control means for controlling the display and a display means for displaying the reconstructed image,
Said receiving means includes a receiving coil for receiving the nuclear magnetic resonance signal in a different sensitivity distribution spatially relative said object, said image reconstruction means, said sensitivity distribution obtained in advance Using the S / N ratio of the magnetic resonance signal, the condition that the distribution of the magnetic moment in the outer region of the region of interest is known, and the upper and lower limits that the distribution of the magnetic moment in the region of interest can take are known. Under the constraint condition including the condition, the objective function including the term for maximizing the S / N ratio of the reconstructed image with respect to the region of interest and the external region is performed, A magnetic resonance imaging apparatus for performing a calculation process for obtaining a magnetic moment distribution in a region of interest. In the magnetic resonance imaging apparatus according to claim 1 , based on the distribution of the magnetic moment of the inspection object acquired in advance at a resolution lower than the resolution of the image finally obtained imaging 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. 2. The magnetic resonance imaging apparatus according to claim 1 , based on a distribution of magnetic moments of the inspection target obtained in advance at a resolution equal to or less than half the resolution of an image finally obtained by using the gradient magnetic field. A magnetic resonance imaging apparatus for determining the sensitivity distribution and the upper limit value and the lower limit value in the constraint condition. The magnetic resonance imaging apparatus according to claim 1, wherein the receiving unit includes a receiving coil including a plurality of subcoils that receive the nuclear magnetic resonance signals with spatially different sensitivity distributions, and the sequence control unit. magnetic but by controlling to receive nuclear magnetic resonance signals while switching the plurality of sub-coils, wherein said receiving means receives the nuclear magnetic resonance signal in a different sensitivity distribution in the spatial Resonance imaging device. 5. The magnetic resonance imaging apparatus according to claim 4, wherein the gradient magnetic field generating unit performs either one of phase encoding or frequency encoding in a direction perpendicular to an arrangement direction of the plurality of subcoils, and the image reconstruction unit includes: A magnetic resonance imaging apparatus characterized in that two-dimensional image information corresponding to the tomographic image to be examined is obtained by performing Fourier transform on a solution obtained by the objective function minimization process. 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 the inspection object are mounted and desired. And a receiving means for receiving a nuclear magnetic resonance signal generated from the inspection object, and a distribution of the magnetic moment of the region of interest of the inspection object based on the received nuclear magnetic resonance signal Image reconstructing means for reconstructing an image reflecting the image, sequence control means for controlling the operation of each means, and display means for displaying the reconstructed image. In a magnetic resonance imaging apparatus that performs tomography of an object,
  The sequence control means controls the receiving means so as to receive the nuclear magnetic resonance signal a plurality of times while the top plate is moving, and the image reconstruction means is configured to obtain the sensitivity distribution and the magnetic resonance obtained in advance. Using the signal-to-noise ratio of the signal, the condition that the distribution of the magnetic moment in the outer region of the region of interest is known and the condition that the upper and lower limits that the distribution of the magnetic moment in the region of interest can take are known are included. Under the constraint condition, the objective function including the term for maximizing the S / N ratio of the reconstructed image with respect to the region of interest and the external region is processed, and the region of interest in the inspection target is determined. A magnetic resonance imaging apparatus characterized by performing arithmetic processing for obtaining a magnetic moment distribution. In the magnetic resonance imaging apparatus according to claim 6 , based on the distribution of the magnetic moment of the inspection object acquired in advance at a resolution lower than the resolution of the image finally obtained imaging 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. The magnetic resonance imaging apparatus according to claim 6 , based on a distribution of magnetic moments of the inspection target obtained in advance with a resolution of half or less of the resolution of an image finally obtained by using the gradient magnetic field. A magnetic resonance imaging apparatus for determining the sensitivity distribution and the upper limit value and the lower limit value in the constraint condition. 7. The magnetic resonance imaging apparatus according to claim 6, wherein the gradient magnetic field generation unit performs either one of phase encoding or frequency encoding in a direction perpendicular to a moving direction of the top plate, and the image reconstruction unit includes: A magnetic resonance imaging apparatus characterized in that two-dimensional image information corresponding to a tomographic image to be examined is obtained by performing a Fourier transform on a solution obtained by objective function minimization processing.

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