WO2007122854A1

WO2007122854A1 - Magnetic resonance imaging device

Info

Publication number: WO2007122854A1
Application number: PCT/JP2007/053390
Authority: WO
Inventors: Shinji Kurokawa; Yo Taniguchi; Hisaaki Ochi
Original assignee: Hitachi Medical Corporation
Priority date: 2006-04-19
Filing date: 2007-02-23
Publication date: 2007-11-01
Also published as: JP4832510B2; JPWO2007122854A1

Abstract

A magnetic resonance imaging device is provided with features of image reconstructions that can be done in various sequences of a wider viewing field and high speed photographing method carries out photographing while continuously moving a table even in the case that a small moving direction is available for a signal acquisition region. When a magnetic resonance signal is received at a plurality of times while moving a table (moving means), a magnetic field is applied at a slant with respect to the moving direction and an application amount (strength and applying time) of the magnetic field at the slant with respect to the moving direction is changed at every data acquisition. Encoding in accordance with the slant magnetic field of the table moving direction, which is different from conventional phase encoding, is carried out for a series of phase encoding at different places of a test subject. When a magnetizing distribution of the test subject is obtained from a nuclear magnetic resonance signal, an imaginary part is independently sought by approximation, so that the magnetizing distribution of the test subject is stably determined in a viewing field that is wider than in a photographing space.

Description

Specification

Magnetic resonance imaging device

Technical field

[0001] The present invention uses a movable table in an inspection apparatus (MRI: Magnetic Resonance Imaging) using nuclear magnetic resonance, and uses a movable table to image a field of view larger than the imageable area limited in the apparatus. More particularly, the present invention relates to an image reconstruction method in the imaging technique.

Background art

[0002] An MRI system causes nuclear magnetic resonance to occur in hydrogen nuclei contained in a tissue to be examined placed in a static magnetic field space, and obtains a tomographic image of the examination object from the generated nuclear magnetic resonance signal. Device. In the MRI system, the area where signals can be acquired is limited to the static magnetic field space. Conventionally, only a relatively small area can be imaged, but in recent years it has become possible to perform whole-body imaging by moving the table. A new development of whole-body screening using is being started.

There are two types of whole body imaging: multi-station imaging (Non-Patent Document 1) and moving table imaging (Patent Document 1, Non-Patent Document 2). In both cases, a wider field (called total FOV) is taken with a limited field of view (called sub FOV) at the time of signal acquisition. Multi-station imaging is an imaging method in which the whole body is divided into sub FOVs and the whole images are created by joining these images. The shooting with each sub FOV is the same as the normal shooting method, so there is an advantage that it is easy to apply the conventional shooting technique, but the image is connected at the part where it is connected due to the static magnetic field inhomogeneity and the gradient magnetic field nonlinearity. Disadvantages are that the distortion and joints are not smooth, and that shooting is not possible while the table is moving. If the field of view in the table movement direction is narrow, the number of times that the table is moved after interruption is increased, and the shooting time becomes longer, which is a problem.

[0004] On the other hand, the moving table imaging method is an imaging method in which a signal is acquired while moving the table, and the lead-out direction must be the moving direction of the table. However, there is an advantage in that images can be acquired in a short time.

Patent Document 1: Japanese Patent Application Laid-Open No. 2003-135429

Non-Patent Document 1: Thomas K. F. Foo'Vincent B. Ho, Maureen N. Hood, Hani B. Marcos, Sandra L. Hess, and Peter L. Choyke, Radiology. 2001: 219: 835—841.

Patent Document 2: David G. Kruger, Stephen J. Riederer, Roger C. Grimmk, and Phillip J. Rossman, Magn. Reson. Med. 2002: 47: 224-231.

Disclosure of the invention

Problems to be solved by the invention

[0006] As described above, with the moving table imaging method, an image can be obtained in a short time without a seam, but the sub FOV moves in the moving direction due to the restriction that the lead-out direction must be the table moving direction. If it gets narrower, there is a problem that the shooting time increases.

[0007] That is, when the sub FOV becomes narrower in the table moving direction, the number of samples in the frequency encoding direction (lead-out direction) is reduced to obtain the same resolution image, and the phase encoding number does not change. ,. In general, the shooting time is almost proportional to the number of phase encodes, and is less affected by the number of samples in the frequency encode direction. Therefore, it takes the same time to acquire data for one sub FOV when the sub FOV is narrow or wide in the table movement direction, and when the sub FOV is narrow in the table movement direction, the shooting time of the enlarged field of view is long. become longer.

[0008] To solve this problem, it is possible to perform phase encoding in the direction of table movement. It was difficult to perform phase encoding in the direction of table movement with the conventional concept of using Fourier transform for reconstruction. . The reason is as follows. In the moving table imaging method, the excitation range always changes in the table moving direction. In the case of readout, all encoding is completed during one signal measurement, that is, in a time when the change in excitation range can be ignored. In the case of phase encoding, a different encoding is assigned for each signal measurement. Therefore, the excitation range will change greatly until the entire encoding is completed. Image reconstruction using Fourier transform is premised on receiving the target image range force S1 series encoding, and is not applicable in such cases. [0009] Therefore, the present invention obtains a signal by applying an encoding by a gradient magnetic field in the table moving direction, and calculates a magnetic distribution of an inspection object from a nuclear magnetic resonance signal measured by actual imaging using apparatus characteristic data. In order to obtain this, we provide a new imaging method that reconstructs an image by independently obtaining the imaginary part of the real part by approximation, so that even if the sub FOV in the table moving direction is narrow, the total FOV image can be obtained. The objective is to provide an MRI system that can capture images in a short time.

[0010] It is another object of the present invention to provide means for efficiently acquiring device characteristic data used for calculation of a hypothetical signal in the novel imaging method.

Means for solving the problem

[0011] The MRI apparatus of the present invention receives a nuclear magnetic resonance signal a plurality of times while moving a table (moving means), applies a gradient magnetic field in the direction of table movement before reception, and stores data every time data is acquired. Change the applied amount (strength and application time) of the gradient magnetic field in the bull movement direction. Encoding with this gradient magnetic field in the direction of table movement is a new encoding (referred to as sliding phase encoding (SPE)) in which one series of phase encoding is performed at different positions to be inspected, unlike conventional phase encoding. As with conventional encoding, it is impossible to apply the Fourier transform to image reconstruction. Thus, in the MRI apparatus of the present invention, the magnetization distribution of the total FOV in the inspection object is reconstructed by obtaining the magnetic field distribution by approximation independently of the real part imaginary part based on the relational expression between the received signal and the magnetization distribution. To do.

[0012] Device characteristic data such as gradient magnetic field nonlinearity, static magnetic field inhomogeneity, irradiation coil excitation distribution, and reception coil sensitivity distribution are used in the relational expression between the received signal and the magnetization distribution. The MRI apparatus of the present invention performs measurement of nuclear magnetic resonance signals (hereinafter referred to as apparatus characteristic measurement and! / ヽぅ) to obtain the apparatus characteristics, and the apparatus characteristics calculated from the measured nuclear magnetic resonance signal values. Image reconstruction is performed using the data. The measurement of the device characteristic data may be performed separately from the measurement of the nuclear magnetic resonance signal for obtaining the magnetization distribution of the inspection object (hereinafter referred to as main imaging), or may be performed simultaneously with the main imaging. In the former case, for example, device characteristics are measured by the multi-station imaging method. That is, the moving means is moved between a plurality of stations, and the apparatus characteristic measurement is executed at each station of the moving means. In the latter case, a part of the nuclear magnetic resonance signal measured in the main imaging can also be used as a signal for obtaining device characteristic data. . It is preferable that some of the combined nuclear magnetic resonance signals are low frequency region data.

The MRI apparatus of the present invention can be applied to both a vertical magnetic field type and a horizontal magnetic field type. Since sliding phase encoding can be performed independently of frequency encoding and phase encoding, it can be applied to 2D, 3D, and multi-slice imaging.

The invention's effect

[0014] According to the present invention, when the sub FOV in the table moving direction is reduced by performing the sliding phase encoding in the table moving direction, the sliding phase encoding for the sub FOV is reduced correspondingly. Can do. As a result, the time required to encode the unit distance in the table movement direction is almost constant, so that high-speed shooting can be performed regardless of the length of the sub FOV in the table movement direction.

[0015] Further, instead of Fourier transform as an image reconstruction method, the magnetic phase distribution is obtained by approximation based on the relational expression between the received signal and the magnetization distribution, and the real part imaginary part is obtained by approximation. Even if encoding is performed, the image including the phase can be reconstructed, and even when the phase of the magnetic field distribution is disturbed, the image quality equivalent to that of conventional moving table imaging can be obtained.

[0016] In addition, in the conventional moving table imaging method, a generally strong readout gradient magnetic field is applied in the table moving direction, so that FSE (first spin echo) is easily affected by the movement of the subject in the gradient magnetic field direction. In this invention, it is difficult to shoot without applying a readout gradient magnetic field in the direction of table movement. Shadows are also easy.

Furthermore, according to the present invention, approximate device characteristic data can be easily obtained in a relatively short time by measuring device characteristic data required for reconstruction by a multi-station imaging method. it can. Further, by performing the apparatus characteristic data simultaneously with the main photographing, it is possible to save time for acquiring the apparatus characteristic data and to perform the entire photographing at a high speed. BEST MODE FOR CARRYING OUT THE INVENTION

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

First, the configuration of an MRI apparatus to which the present invention is applied will be described. Figures 1 (a) and (b) Each is an overview of a horizontal magnetic field type MRI apparatus and a vertical magnetic field type MRI apparatus. The MRI apparatus of the present invention can also be applied to misaligned type MRI apparatuses. A horizontal magnetic field type MRI apparatus employs a solenoid type static magnetic field magnet 101 that generates a static magnetic field in the horizontal direction, and the object 103 is lying on the table 301 and placed in the bore of the magnet. Carry in and take a picture. In the vertical magnetic field type MRI apparatus, a pair of static magnetic field magnets 101 are arranged above and below the space in which the subject 103 is placed, and the subject 103 is carried into the static magnetic field space while being laid down on the table 301. . In the figure, the arrow r indicates the moving direction of the table. In the horizontal magnetic field type MRI apparatus shown in (a), it coincides with the static magnetic field direction force ^ direction. In the vertical magnetic field type MRI apparatus shown in (b), The moving direction of the table is a direction orthogonal to the static magnetic field direction.

FIG. 2 is a block diagram showing a schematic configuration of the MRI apparatus, and the same components as those in FIG. 1 are denoted by the same reference numerals. As shown in the figure, in a static magnetic field space (imaging space) generated by the static magnetic field magnet 101, a shim coil 112 for increasing the uniformity of the static magnetic field, a gradient magnetic field coil 102 for imparting a gradient to the static magnetic field, and an inspection object An irradiation coil 107 for generating a high-frequency magnetic field that excites an atomic nucleus (usually proton) that constitutes a (human) tissue, and a receiving coil 114 for detecting a nuclear magnetic resonance signal generated from an examination object Etc. are arranged. The table 301 that places the subject 103 on the bed is controlled by the table control device 302, and the subject 103 is carried into the imaging space and moved in the space. The table controller 302 can control and monitor the speed and position of the table.

[0020] The shim coil 112, the gradient magnetic field coil 102, the irradiation coil 107, and the reception coil 114 are connected to the shim power source 113, the gradient magnetic field power source 105, the high-frequency magnetic field generator 106, and the receiver 108, respectively. The operation is controlled by 104. The sequencer 104 performs control such that these devices operate at preprogrammed timing and intensity (pulse sequence), and performs control such as starting a pulse sequence in accordance with the drive of the table control device. The MRI apparatus includes a computer 109, a display 110, a storage medium 111, and the like as a signal processing system.

In such a configuration, the high frequency magnetic field generated by the high frequency magnetic field generator 106 is applied to the inspection object 103 through the irradiation coil 107. The nuclear magnetic resonance signal generated from the inspection object 103 is received by the receiving coil 114 and detected by the receiver 108. Base of detection The quasi nuclear magnetic resonance frequency is set by the sequencer 104. The detected signal is sent to the computer 109 where signal processing such as image reconstruction is performed. In the present invention, in addition to calculations such as normal correction calculation and Fourier transform, image reconstruction calculation unique to moving table shooting described later is performed. The processing result of the computer 109 is displayed on the display 110 and recorded on the storage medium 111. The storage medium 111 can store a detected signal and measurement conditions as necessary.

[0022] Next, a moving table photographing method employed in the present invention will be described in the first embodiment. Fig. 3 shows the relationship between the field of view (sub FOV) at the time of one signal acquisition and the wide field of view intended for imaging (in this case, the total FOV of the subject), and Fig. 4 shows the procedure for imaging and image reconstruction processing. Show.

In moving table imaging, imaging is performed while moving the table 301 (inspection object 103) in the direction of the arrow 303 as shown in FIG. As the receiving coil 114, a receiving coil fixed in the apparatus as shown in FIG. 3 is used. The field of view (sub FOV) 304 at the time of signal acquisition can be set arbitrarily, but optimally, it should be set to the same size as the area where a sufficiently large signal can be received. Although the field of view at the time of signal acquisition is limited, the field of view (total FOV) 305 such as the whole body is captured by moving while moving the table 301. Shooting is possible in both 2D and 3D, and the sliding phase encoding direction is set to the table moving direction. For example, in 2D, the cross section is not limited as long as the cross section includes an axis in the table moving direction that can be either a coronal plane or a sagittal plane. The lead-out direction is selected in a direction perpendicular to the table moving direction. In the following examples, the force described in 2D is increased by one encoding other than the sliding phase encoding.

[0024] As shown in FIG. 4 (a), the imaging is performed by step 601 (device characteristic measurement) for acquiring device characteristic data 604, step 602 (main imaging) for acquiring data 605 to be inspected, And step 603 for calculating the reconstructed image 606 to be inspected using the characteristic data and the inspection target data.

First, device characteristic measurement will be described.

Device characteristic data includes gradient magnetic field non-linearity, static magnetic field non-uniformity, excitation coil excitation distribution, reception It is useful for the sensitivity distribution of the coil. Of these, gradient magnetic field non-linearity hardly depends on the subject, so there is no need to acquire it every time, and data measured by other measurements such as imaging using a phantom is stored in a storage medium in advance.

Therefore, in apparatus characteristic measurement step 601, apparatus characteristic data relating to powerful signal intensity and phase such as signal intensity distribution due to non-uniform static magnetic field, excitation distribution of irradiation coil 107 and sensitivity distribution of reception coil 114 are obtained. Take a picture.

The details of the apparatus characteristic measurement step 601 are shown in FIG. 4 (b). As shown in the figure, this imaging is performed by multi-station imaging by moving the table between stations and repeating the steps of RF transmission and reception at each station to obtain image data of each station (step 63 Do in this case) A well-known 2D imaging method or 3D imaging method can be adopted for the device characteristics data generally changes smoothly, so low-resolution imaging is sufficient, and imaging time can be shortened.

[0028] The device characteristic data can be obtained by dividing by the uniform image of the image otal FOV obtained at each station. A uniform image is an image obtained when the coil sensitivity is uniform, and a uniform image of total FOV can be created by combining the images of each station (step 632, 633).

[0029] When photographing for device characteristic data, the sub FOV for obtaining device characteristic data is set sufficiently large so as to cover the entire range in which signal acquisition is possible as shown in FIG. . In addition, some sub FOVs are overlapped between stations. This makes it easy to synthesize uniform images and interpolate device characteristic data. In order to obtain accurate device characteristic data, it is preferable to overlap the sub FOV so that the total FOV can be covered only in the area that can be regarded as uniform in each station image. If priority is given to shortening the shooting time over accuracy, the overlap should be reduced. In order to create a more uniform total FOV image, it is possible to add shooting using another coil such as a body coil!

[0030] If image data is obtained by photographing at each station, a uniform image of total FOV is synthesized from the images obtained at each station. Next, the image obtained at each station is replaced with a uniform image of this total FOV, and the signal intensity distribution due to the static magnetic field inhomogeneity in the positional relationship between the subject and the coil at each station, the excitation distribution of the irradiation coil, Receive Obtain device characteristic data that matches the sensitivity distribution of the file. In this calculation, if necessary, a low-pass filter is applied to the obtained image, or an area without a subject is masked. This makes it possible to acquire device characteristic data stably against noise.

[0031] The device characteristic data acquired in this way is data for each station. In force image reconstruction, device characteristic data at each position of the subject that changes continuously in the main imaging is required. When reconstructing an image, the device characteristic data at the nearest station may be used, but it is preferably created by interpolating the device characteristic data between the stations.

Next, main imaging (acquisition of data to be inspected) will be described with reference to FIG. Fig. 6 (a) shows the procedure for the actual shooting, and Fig. 6 (b) shows the procedure for image reconstruction. In step 602, as shown in detail in FIG. 6 (a), the table is first moved (step 607). Next, R F is transmitted and received (step 608). RF transmission / reception is repeated until the table is moved to cover the total FOV (step 609). When the table is moved to cover the total FOV, the data acquisition is terminated (step 610).

[0033] In the case of whole body imaging shown in FIG. 3, the table movement range for covering the total FOV is the inspection object 103 and the table position 301 drawn with a solid line from the subject and table position drawn with a broken line. Up to is the movement range to cover the total FOV. Normally, the front force table is moved from the moving range as a run-up zone so that the table can be moved at a constant speed, and data is acquired at a position where one end of the total FOV is the center of the signal acquisition area. Acquisition starts, and data acquisition ends when the other end of the total FOV reaches the center of the signal acquisition area. The table position is detected by the table controller 302 and the information is sent to the sequencer.

FIG. 7 shows an example of a pulse sequence employed in step 608 for imaging. In FIG. 7, RF represents an excitation radio frequency pulse, Gs represents a slice selective gradient magnetic field, Gp represents a sliding phase encoding gradient magnetic field, and Gr represents a readout gradient magnetic field. This pulse sequence is similar in appearance to a general 2D gradient echo pulse sequence. The force Gp axis coincides with the table movement direction, and the acquisition position differs in the table movement direction. It differs in that the gradient magnetic field is applied by changing the applied amount (intensity and application time) for each data. In the present invention, such a Gp-axis gradient magnetic field is called a sliding phase encoding gradient magnetic field.

In imaging, first, a dephasing slice gradient magnetic field 203 is applied to an inspection target, and a gradient magnetic field applied by a subsequent slice gradient magnetic field 202 is prepared so as to be balanced. Next, an excitation high-frequency pulse 201 is applied simultaneously with the slice gradient magnetic field 202 to excite only a desired slice. As a result, only a specific slice generates the magnetic resonance signal 208. Immediately, the slice gradient magnetic field 204 for reference is applied, and the amount dephased by the slice gradient magnetic field 202 is restored. Next, a sliding phase encoding gradient magnetic field 205 is applied. At the same time, the read gradient magnetic field 206 for dephase is applied, and the gradient magnetic field applied by the subsequent read gradient magnetic field 207 is prepared so as to be balanced. Next, the read gradient magnetic field 207 is applied, and the signal is measured when the magnetic resonance signal 208 once attenuated by the dephase read gradient magnetic field 206 becomes large again. Finally, the sliding phase encoding gradient magnetic field 209 and the reference reading gradient magnetic field 210 are applied, the encoding at the time of acquisition of the magnetic resonance signal 208 is restored, and the next excitation high-frequency pulse 211 is prepared.

[0036] Excitation is performed with excitation high-frequency pulse 211 after time TR from excitation high-frequency pulse 201, and application of a gradient magnetic field and signal measurement are repeated in the same manner as described above. However, during this repetition, the sliding phase encoding gradient magnetic field 205 and the rephasing sliding phase encoding gradient magnetic field 209 are each changed to give position information in the sliding phase encoding direction.

[0037] The moving speed of the table may be constant or variable! The table controller can grasp the table position rtable (n) when the nth signal is acquired, so the sliding phase encoding amount changes from -π to π while the table position changes by sub FOV as shown in Fig. 9. Set the encoding amount k (n) when receiving each signal.

[0038] By applying the sliding phase encoding in this way, the signal S (n, ky) is obtained. In S (n, ky), ky represents a coordinate in the k space corresponding to the y direction (reading direction). S (n, ky) is the signal value at the point ky in the k space of the nth received magnetic resonance signal. Signal S (n, ky) is measured as image data for image reconstruction as shown in 08 (a). Stored in the RE 401. FIG. 8 is a diagram schematically showing a calculation added to the measurement data and a memory for storing the result.

In the calculation of the reconstructed image (FIG. 4: step 603), the image reconstruction calculation is performed using the measurement data 605 to be inspected and the device characteristic data 604 obtained in step 601. In the image reconstruction calculation, the magnetic moment distribution to be inspected is determined by obtaining the magnetization distribution independently of the real part and the imaginary part by approximation based on the relational expression between the received signal and the magnetization distribution. The details will be described below.

[0040] The measured signal S (n, ky) can be expressed by the following equation (1) using the position information of the table.

[Number 1]

(1)

S (n, k _v ) = fr, k _y ) exp (-ir ^f k (n) (l + d (r ^r ))) w _n (r ') dr

[0041] The signal S (n, ky) Fourier-transformed in the readout direction (y direction) can be expressed by the following equation (2).

[Equation 2]

(2) s (n, y) = (m (r, y) ex.p (-ir'k (n) (l + d (r ^f ))) w _n (r ^f ) dr These equations (1) In (2), i is the imaginary unit, r is the position in the moving direction of the table in the coordinate system fixed to the subject, _r 'is the position in the moving direction of the table in the stationary coordinate system fixed to the entire apparatus,

[0042] [Equation 3]

(3)

r ^f = r-r _tahle (n). Rtable (n) is the amount of table movement when the nth magnetic resonance signal is acquired. It is.

[0043] k (n) corresponds to the phase rotation by the sliding phase encoding gradient magnetic field G (n) received by the nth magnetic resonance signal, and is defined by the following equation (4). Figure 9 shows the relationship between the table movement amount rtable (n) and the graph.

[0044]

Where γ is the gyromagnetic ratio.

[0045] When there is a gradient magnetic field non-linearity and the gradient magnetic field force SG (n) (l + d (r ')) has a magnitude G (n), the phase rotation by the actual gradient magnetic field is

[Equation 5]

( Five )

= (1 + (r ')) (w)

It becomes. The terms of k (n) (l + d (r ')) in Eqs. (1) and (2) are terms that consider gradient magnetic field nonlinearity.

[0046] The function wn (r ') is a function representing the magnitude and phase of the signal obtained from the magnetization of magnitude 1 and phase 0 at position r' in the positional relationship between the subject and the coil at the time of obtaining the n-th signal. It is determined by the distribution of the static magnetic field, the excitation distribution of the RF coil, and the sensitivity distribution of the receiving coil. These are obtained by measuring device characteristic data in step 601. The static magnetic field distribution, RF coil excitation distribution, and receiver coil sensitivity distribution are uniform within the signal acquisition area (sub FOV, the length of the table movement direction is FOVsub), and the receiver coil has sensitivity outside the sub FOV. If not, wn (r ') is a step function as shown in Fig. 10.

[0047] m (r, y) is the magnetization at the position (r, y) of the subject, that is, the image of the object to be examined, and M (r, ky) is m (r, y) Is equivalent to the inverse Fourier transform of.

[0048] The signal s (n, y) obtained by Fourier-transforming the signal S (n, ky) in the readout direction is stored in the intermediate memory 402 as shown in Fig. 8 (b). Since this signal s (n, y) is phase-encoded from -π to π at a different position to be examined, m (r, y) Cannot be asked. S (n, y) and m (r, y) Since there is a relationship of equation (2) between them, in the present invention, m (r, y) is obtained by solving equation (2) in reverse. To solve equation (2) for m (r, y): : ,, k (n), (l + d (r ')), wn (r'), force that needs to know s (n, y) As mentioned above, r 'is obtained from equation (3) K (n) is defined by equation (4), and is set for the table position rtable (n) when the nth signal is acquired, that is, for n, as shown in FIG. (L + d (r ')) is data representing the nonlinearity of the gradient magnetic field and can be measured in advance, and wn (r') is obtained by the measurement in step 601. Therefore, if s (n, y) is measured, the unknown is only m (r, y), and solving this enables image reconstruction. However, since the solution becomes unstable if the equation is simply solved, the present invention enables stable image reconstruction by obtaining the magnetic flux distribution independently of the real part by approximation.

[0049] For image reconstruction, it is not necessary to obtain m (r, y) for continuous r. It is sufficient to obtain the magnetic distribution m (r, y) at the representative position r of each pixel of the image. is there. In addition, ignoring changes in the magnetic distribution within each pixel, Eq. (2) is discretized as follows.

[0050] Garden

(6) s (n,) =… m (rj, y) exp (((1 + d (r))) w _n (Α

(3)

[0051] In equation (6), r 'is represented by equation (3') similar to equation (3).

[0052] Ar is the size of the pixel in the r direction at each j.

J

The above discretized equation can be expressed as a matrix,

[0053] [Equation 7]

(7)

It becomes. Here, s and m are vectors represented by the following equations. [0054] [Equation 8]

[0055] [Equation 9]

(9)

[0056] Here, N is the number of signals, and J is the number of pixels in the r direction.

Also, matrix A has each element A (n, j)

[0057] [Equation 10]

(Ten)

A (n, j) = exp (−ir! K (n) (l + d (r ′))) w _n (ή) Αη

Furthermore, when formula (7) is expanded considering the real part imaginary part,

[0058] [Equation 11] (1 1)

Re (sy) + Im (sy) x i = (Re (A) + Im (A) i) (Re (my) + Im (my) xi)

[0059] [Equation 12]

(12)

e (s _y ) = Re (A) Re (m _y )-Im (A) Im (m _y )

Im (s _y ) = Im (A) Re (m _y ) + Re (A) Im (m _y ) To combine these two expressions into one, the vector s' and the matrices Ar and Ai are

y

Defined in

[0060] [Equation 13]

(13)

[0061] [Equation 14] (14)

ί Re (A),

V Im (A)

[0062] [Equation 15]

(15)

ί -Im (A),

Re (A) No By this definition, equation (12) becomes

[Equation 16]

(16)

It becomes.

By inverse matrix of Ar and Ai

[0064] [Equation 17]

(17)

One 1

_{Re (ni) = A-- rr s} ~ a _{_{'j - - A r A t}} Im (my) Im (ra y) = Aj s' r A "A r Re (m y).

[Equation 18]

It becomes. With this formula, the magnetic flux distribution can be obtained.

As will be described later,

Value.

The procedure for performing such image reconstruction is shown in FIG. 6 (b). First, since the values of the matrix elements defined by the device characteristic data force equations (14) and (15) are determined, the inverse matrix (703, 704) is obtained (steps 701, 702). Next, the inverse matrix (703,704) and the measured data force obtained are also used to obtain the real part imaginary part (707,708) of the magnetic flux distribution using equation (18) (steps 705,706). Finally, these real and imaginary parts are combined to obtain a reconstructed image (step 709). The m (r, y) thus obtained is stored in the image memory 403 as shown in FIG.

[0067] As described above, according to the present embodiment, imaging is performed in which sliding phase encoding is given in the moving direction of the table, and the magnetization distribution is approximated based on the relational expression between the received signal and the magnetization distribution. By reconstructing the image by calculating the real part and the imaginary part independently, the image quality equivalent to that of the conventional method is maintained even when the shootable area (sub FOV) in the direction of table movement is small, without increasing the shooting time. Shooting with an expanded field of view is possible.

In the above-described embodiment, the Knock sequence of FIG. 7 is illustrated as an imaging method. However, for example, phase encoding in the slice direction can be given to perform 3D imaging. In this case, image reconstruction can be similarly performed only by increasing the position dimension of the signal to be processed.

[0069] In the above embodiment, the case where image reconstruction is performed after all data has been acquired has been described. However, image reconstruction can also be performed in parallel with data acquisition. Hereinafter, as a modification of the first embodiment of the present invention, a method for performing image reconstruction in parallel with the main imaging will be described with reference to FIGS. 11a to 11c.

[0070] Also in the present embodiment, the configuration of the apparatus is the same as that of the first embodiment described above. . However, in the present embodiment, as shown in FIG. 11a, in the present embodiment, device characteristic data is acquired in the first step (601), and in the next step, an inverse matrix necessary for image reconstruction is calculated. (720) In the last step, a reconstructed image of the inspection object is calculated using the apparatus characteristic data and the inspection object data in parallel with the main photographing (722).

[0071] The method for acquiring the device characteristic data is the same as in the first embodiment. After obtaining the device characteristic data, the inverse matrix of the matrix defined by equations (14) and (15) is obtained. This inverse matrix is required for image reconstruction according to Equation (18).

[0072] Parallel processing of the main photographing and image reconstruction is realized by performing an element force that can calculate the calculation of Expression (18). For example, as shown in FIG. 1 ib, the main imaging is performed while moving the table in the same manner as the main imaging of the first embodiment, and the reconstructed image is updated as necessary after RF transmission / reception.

[0073] As shown in FIG. 11c, the reconstructed image is updated by obtaining the magnetization distribution (updated) from the newly acquired data and adding it to the magnetization distribution before the update. . Specifically, the update of the magnetic distribution is obtained by setting the S'y element in Eq. (18) to 0 except for the newly acquired data element. Re (m) and Im (m) obtained in this way are

y y

Become.

In the above-described embodiment, the case has been described in which shooting is performed separately from the main shooting when acquiring the device characteristic data. However, the device characteristic data can be acquired simultaneously with the main shooting. Hereinafter, as a second embodiment of the present invention, a method for acquiring apparatus characteristic data at the same time as main imaging will be described with reference to FIGS. 12 and 13. FIG.

Also in the present embodiment, the configuration of the apparatus is the same as that of the first embodiment described above. However, in the present embodiment, as shown in FIG. 12 (a), in the present embodiment, the device characteristic data acquisition and the main photographing are simultaneously performed in the first step (625), and the device characteristic data is obtained in the next step. The reconstructed image of the inspection object is calculated using the inspection object data (626).

[0076] Simultaneous acquisition of device characteristic data is realized by using only low-frequency data in the frequency domain in actual imaging. In other words, only the low-frequency region is cut out from the SPE data acquired in this shooting, and a low-pass image for device data is acquired by Fourier transform. At this time, if the area where the signal can be acquired does not fit within the sub FOV, the low-frequency data is taken densely and the FO Extend V. For example, as shown in FIG. 12 (b), the main shooting is performed while moving the table in the same manner as the main shooting in the first embodiment (627, 628), and the sliding phase encoding step is performed only in the low frequency range. Increase by 0.5 (629).

FIG. 13 shows an example of the relationship between the sliding phase encoding and the table position and the processing of the obtained data in photographing according to the present embodiment. First, densely measured low-frequency data is extracted from the SPE data obtained by such imaging, and the origin is first corrected (Fig. 13, step 641). Since the main shooting is performed while moving the table position, the origin position differs in each signal acquisition. Different origin positions mean that the offset value of the gradient magnetic field is shifted. The correction of the origin position is a correction that corrects such a deviation of the offset value of the gradient magnetic field, and exp (-ir (n) k (n) (l + d (r '))) is applied to the signal.

table

Correction can be made. That is, the processing of the following equation (19) is performed.

[0078] [Equation 19]

(1 9)) w _n (r ') dr

The above equation (19) includes a nonlinear term of the gradient magnetic field, but if the nonlinearity of the gradient magnetic field is negligible, exp (-ir (n) k (n)) may be applied to the signal. . Processing in that case

table

Is represented by the following equation (20).

[0079] [Equation 20]

(2 0)

S (n _t k _y ) x exp (-/ r _toWe (n) k (n))

M (r, k) cxp (~~ irk (n)) w _n (r ^r ) dr

[0080] After correcting the origin position, as shown in Fig. 13, zero-filling the high-frequency data is performed to fill the k-space and create k-space data for one low-pass image (step 642). A low-pass image at one table position can be acquired by Fourier transforming this k-space data (step 643). In sliding phase encoding that performs phase encoding in the table movement direction, the FOV differs for each data acquisition, so image reconstruction by Fourier transform is usually not possible. However, if only low-frequency data is used, the table Since the FOV does not change much with little change in position, it is possible to reconstruct the image by Fourier transform approximately if the origin position of each data is corrected.

This low-pass image can be obtained for each loop of sliding phase encoding, and device characteristic data can be created using the low-pass image data at each position in the same manner as in the first embodiment. That is, device characteristic data can be obtained by dividing each low-pass image data by the total FOV uniform image data. Overall device characteristic data is created by interpolation from the device characteristic data obtained at each position (644).

It should be noted that the interval between positions where the device characteristic data can be acquired is determined by the number of sliding phase encoding loops. The narrower the interval, that is, the denser the acquisition position of each image for acquiring device characteristic data, the more accurate the creation of a uniform image and the interpolation of device characteristic data. In this embodiment, the interval between the acquisition positions can be narrowed by increasing the sliding phase encoding loop as shown in 014 (a) by sparse the force sliding phase encoding step that slows the table moving speed.

In addition, although the case where the low-frequency sliding phase encoding step is increased by 0.5 has been described, in this case, the number of signal acquisition times increases, and thus the imaging time of the main imaging increases. In order to suppress the increase in the shooting time of the main shooting, as shown in FIG. 15, the number of signal acquisitions may be reduced by increasing the sliding phase encoding step, for example, by 2 each in the high frequency range. In the flow shown in Fig. 15, the frequency domain is divided into three, and the sliding phase encoding step is increased by 0.5 in the low frequency range and increased by 2 in the high frequency range. This change in the amount of sliding phase encoding is shown in Fig. 14 (b). Figure 16 shows the SPE data obtained by shooting using such a sliding phase encoding step.

The calculation method for reconstructing an image using the device characteristic data acquired in this way and the image data acquired at the same time is the same as that in the first embodiment.

According to the present embodiment, shooting for acquiring device characteristic data is performed separately from main shooting. Since it is not necessary to do so, the overall shooting time can be shortened.

In the above-described embodiment, the case where the receiving coil is fixed to the apparatus has been described. The present invention can also be applied to the case where the receiving coil is fixed to the subject.

First, as a third embodiment, a method will be described in which device characteristics data is acquired in advance using a coil fixed to a subject, and main imaging is performed by force.

In the present embodiment, the apparatus characteristic measurement 601 is performed prior to the main photographing 602, and the image reconstruction 603 is performed using the apparatus characteristic data in the first embodiment shown in FIG. 4 (a). Is the same. However, in the present embodiment, as shown in FIG. 17, since the coil 114 is fixed to the subject 103, the coil 114 moves with the movement of the subject (table 301), and a plurality of images are taken to capture the total FOV. Switch the coil for use. When switching multiple coils, you can use multiple coils at the same time to receive.

[0088] In the signal obtained by such imaging, a dimension corresponding to the coil number is added to distinguish the signal obtained by each coil force, and image reconstruction applying Formula (8) is executed. . For example, the signal S (n, ky, c) obtained by the c-th coil force is expressed by the following equation (21).

[0089] [Equation 21]

( twenty one )

S (n. K _v , c)-(r, k _y ) ep (-ir'k (n) (l + d (r '))) w _nc (r') dr

= 0

[0090] The signal S (n, ky, c) that is Fourier-transformed in the readout direction (y direction) can be expressed by the following equation (22).

[0091] [Equation 22]

(2 2) s (n,, c) = ((r,) cxp (-ir'k (n) (l + ')), _c (r ^r ) dr

Jr-0

[0092] For image reconstruction, it is not necessary to obtain m (r, y) for continuous r. It is sufficient to obtain the magnetic distribution m (r, y) at the representative position r of each pixel of the image. is there. In addition, ignoring changes in the magnetic distribution in each pixel, Eq. (22) is discretized as follows.

[0093] [Equation 23] s (n,, c) = ^ ^J m (r., y) exp (— / '+ (r'))) w „ _c (rj) Ar. where r 'is the same as in equation (3) It is expressed by the following formula.

[0094] [Equation 24]

(24) '=--(

ΔΓ is the size of the pixel in the r direction at each j.

The above discretized equation can be expressed as a matrix,

[0095] the [number _{_{25] s y = A m y}} . Here, s "m is a vector represented by the following equation.

y y

[0096] [Equation 26]

(26)

(s (hy) ヽ

5 (2,, 1) [0097] [Numerical 27]

(27)

(r)

Where N is the number of signals, C is the number of coils, and J is the number of pixels in the r direction.

The matrix A "has each element A" ((n-1) X C + c, j)

[0098] [Equation 28]

(28)

A (n ~ 1) XC + C, J) = exp (~ ^ («) (l + (r '))) A matrix represented by _{> c} () Δ.

Furthermore, when formula (25) is expanded considering the real part imaginary part,

[0099] [Equation 29]

(29)

Re (s "y) + Im (s" y) Xi = (Re (A ^ff ) + Im (A ") Xi) (Re (my) + Im (my) Xi). When divided into

[0100] [Equation 30]

(30)

Re «)-Re (A") Re (m _y ) ― Im (A ") Im (m _y )

Im (s) = Ira (A ") Re (m _y ) + Re (A ^ff ) Im (m _y )

[0101] To combine these two expressions into one, the vector s "'and the matrix A" r, A "i are

y

Define as follows. [0102] [Equation 31]

1)

Re (^ (2 _? J)) tlf

^S y ― Im ((l,))

im (S "(2,))

[0103] [Equation 32]

(32)

A _r ―

V Im (A ")

[0104] [Equation 33]

(33)

,-Im (A '),

A

Re (A ^ff ) No By this definition, equation (30) becomes

[0105] [Numerical 34]

(34) s: = A: Re (m _y ) + A im (m _v ) It becomes.

By the inverse matrix of A "r, A" i,

[0106] [Equation 35]

(3 5)

It becomes. As in Equation (17), the terms Ar—i and Af Ar can be ignored,

[0107] [Equation 36]

(3 6)

Jim ML. I ^A i _y . With this formula, the magnetic flux distribution can be obtained.

On the other hand, for the device characteristic data acquisition 601, the device characteristic data w (r ′) shown in Expression (21) is obtained for each coil. First, with respect to the c-th coil, a case where apparatus characteristic data relating to a signal received from the coil is acquired will be described with reference to FIG. FIG. 18 is a diagram showing the coil position with respect to the center of the static magnetic field at the time of signal acquisition.

[0109] Optimally, as shown in Fig. 18, both the static magnetic field distribution and the excitation coil excitation distribution have a uniform regional force. The station should be covered so that the sensitivity area of the receiving coil is covered by one or more imaging. Set. By cutting out and joining areas with uniform imaging results, it is possible to create an image of the entire sensitivity area of the receiving coil when the static magnetic field and irradiation are uniform. In the example shown in FIG. 18, in the image 1601 of the first station, the image 1601b of the region where the static magnetic field and the irradiation are uniform and in the image 1602 of the second station, the magnetostatic field and the irradiation are uniform. By combining the image 1602a of the area, an image 1603 of the entire sensitivity area of the receiving coil is obtained. An image representing this sensitivity distribution is represented by a uniform image 1600 created by using the usual multi-station imaging method. The sensitivity distribution of the coil can be obtained.

[0110] Next, the image 1603 shows the image obtained with the c-th coil, so that the remaining device characteristics, that is, the static magnetic field inhomogeneity and the irradiation coil excitation distribution, can be obtained.

In the example of FIG. 18, by dividing the image 1601 obtained at station 1 and the 1602 obtained at station 2 in the composite image 1603, device characteristic data other than the sensitivity distribution at station 1 and station 2, respectively. Is obtained.

[0112] <Image 1601> ÷ <Image 1603> = <Device characteristics of station 1>

The device characteristic data w (r ′) of the c-th coil can be obtained by multiplying the receiving coil sensitivity distribution, the static magnetic field non-uniformity, and the irradiation coil excitation distribution.

[0113] By performing the same process for other coils, device characteristic data w (r ') including sensitivity distribution is obtained for all coils.

[0114] After the apparatus characteristic data is acquired, the steps of acquiring the inspection object data 605 and calculating the inspection object reconstructed image 606 using the apparatus characteristic data and the inspection object data are as follows:

As described above, this can be performed in the same manner as in the first embodiment.

[0115] Next, as a fourth embodiment, a method of acquiring apparatus characteristic data simultaneously with main imaging using a coil fixed to a subject will be described. In this case, the same shooting as in the second embodiment is performed! To acquire the device characteristic data! As in the third embodiment, the c-th coil force is obtained as S (n , ky, c), each coil is considered separately.

[0116] First, also in the present embodiment, the configuration of the apparatus is the same as that of the third embodiment described above. As shown in FIG. 12 of the second embodiment, the imaging procedure is to simultaneously acquire the apparatus characteristic data and the main imaging in step 625, and in step 626, use the apparatus characteristic data 604 and the inspection object data 605. A reconstructed image 606 to be inspected is calculated.

[0117] For simultaneous acquisition of device characteristic data, only the low frequency data in the frequency domain is used in this embodiment, the origin position of each data is corrected, and image reconstruction is performed approximately by Fourier transform. This is the same as in the second embodiment. However, in this embodiment The device characteristic data is acquired for each coil as in the third embodiment.

[0118] First, pay attention to the c-th coil, and consider the case where device characteristic data relating to the received signal is received.

[0119] Optimally, as shown in Fig. 18, the area where both the static magnetic field distribution and the excitation coil excitation distribution are uniform covers the sensitivity area of the receiving coil by one or more imaging. Set the data acquisition position. In other words, Fig. 18 shows the force indicating the coil position in the multi-station. As shown in Fig. 13, when the sliding phase encoding step is set, the center position of the first loop (from π force to π) of the sliding phase encoding (low) The position when the frequency component is acquired) is the first shooting position in FIG. 18, and the center position of the second loop (the position when acquiring the low frequency component) is the second shooting position in FIG. Perform a sliding phase encoding step while moving the table (ie coil). The method of cutting out low-frequency data and reconstructing one image, such as SPE data, is the same as in the second embodiment. Here, the images obtained by executing the first and second loops are used. The low frequency data is cut out from each of the images, the origin is corrected, the high frequency data is zero-filled, and the image is reconstructed by the Fourier transform.

Next, a uniform image is created from each image reconstructed in this way. A uniform image may be obtained by adding the images together, cutting out only the uniform part, or by using multi-station shooting.

Device characteristic data is obtained from the images of the coils thus obtained and the created uniform image in the same manner as in the third embodiment. That is, first, the sensitivity distribution of the c-th coil is obtained by dividing the image obtained by combining the images at the respective acquisition positions with respect to the c-th coil by the uniform distribution image. Next, device characteristics other than the sensitivity distribution at each acquisition position can be obtained by dividing the image at each acquisition position with the image obtained by combining the images at the acquisition positions for the c-th coil.

[0122] <image 1603> ÷ <uniform image 1600> = <sensitivity distribution of c-th coil>

By multiplying the sensitivity distribution, static magnetic field inhomogeneity, and excitation coil excitation distribution obtained in this way, the entire device characteristic data can be obtained. In this case as well, the device characteristic data obtained at each acquisition position may be interpolated, or the device characteristic data at the nearest acquisition position may be used for image reconstruction.

[0123] As in the first to third embodiments, an image is reconstructed from a signal obtained by actual imaging and a signal calculated using device characteristic data.

Example

[0124] In order to confirm the effect of the present invention, a moving table photographing simulation experiment according to the first embodiment was performed using an inspection object as shown in FIG. The area shown in white in Fig. 19 is the area where the inspection object exists.

[0125] The shooting parameters are sub FOV = 320mm x 320mm (256 pixels x 128 pixels), total F

OV = 320 mm X 960 mm (256 pixels X 384 pixels).

[0126] In the shooting according to the first embodiment, the r-axis direction is the direction of table movement, sliding phase encoding is performed in this direction, and the y-axis direction perpendicular to the table movement direction is the readout direction. .

FIG. 20 (a) shows a reconstructed image obtained by the first embodiment. In addition, Fig. 20 (b) shows a reconstructed image obtained by the reconstruction method that obtains only the magnitude of the magnetic flux distribution without using the approximation divided into reality. In the reconstruction method for obtaining only the magnitude of the magnetization distribution, a large signal is missing in a striped pattern, but it is certain that the lack of signal is improved by the reconstruction method of the present invention.

Also, Fig. 21 (a) shows an image reconstructed by the present invention in Fig. 21 (a), and Fig. 21 (b) shows an FSE sequence that is difficult to shoot with a conventional table moving imaging method that performs frequency encoding in the table moving direction. An image reconstructed by the method described in Non-Patent Document 2 is shown. As shown in these, it was confirmed that the FSE sequence can be reconstructed in the present invention. Similar results were obtained for other examples.

On the other hand, as shown in FIG. 22, the shooting time 501 of the conventional moving table shooting method is set to 1 when sub FOV = 40 cm in the table moving direction. Then, the time becomes longer as the sub FOV becomes narrower, whereas in the present embodiment, the number of sliding phase encodings for the sub FOV decreases corresponding to the reduction of the sub FOV, so the shooting time 502 remains unchanged.

[0129] When the device characteristic data is separately acquired, the imaging time is extended by that amount. However, the imaging that requires a high-resolution image for acquiring the device characteristic data is completed in a short time. Furthermore, the device characteristic data can be acquired in a shorter time by interpolating. Also, if device characteristic data is acquired simultaneously, the shooting time will not increase.

Industrial applicability

[0130] According to the present invention, it is possible to perform moving table imaging without increasing the imaging time even when the signal acquisition area is narrow in the table movement direction. Even a device with a narrow imageable area in the direction of table movement is useful because it enables full-body imaging at high speed.

Brief Description of Drawings

[0131] [FIG. 1] A view showing an overview of an MRI apparatus to which the present invention is applied, in which (a) shows a horizontal magnetic field type apparatus and (b) shows a vertical magnetic field type apparatus.

FIG. 2 is a diagram showing a configuration example of an MRI apparatus to which the present invention is applied.

FIG. 3 is a diagram showing the relationship between the total FOV to be examined and the signal acquisition area.

FIG. 4 is a diagram showing a procedure for shooting a moving table according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a sub FOV for acquiring device characteristic data and a sub FOV for actual photographing.

FIG. 6 is a diagram showing a procedure of main photographing according to the first embodiment.

FIG. 7 is a diagram showing an example of a pulse sequence used for moving table imaging.

FIG. 8 is a diagram showing signals and processing results used for image reconstruction in 2D imaging.

FIG. 9 is a diagram showing the relationship between table position and sliding phase encoding.

FIG. 10 is a diagram showing device characteristics in a signal acquisition region.

FIG. 11a is a diagram showing a modification example of the photographing procedure according to the first embodiment.

[Fig. Lib] A diagram showing an example of a change in imaging procedure according to the first embodiment.

FIG. 11c is a diagram showing a modification example of the photographing procedure according to the first embodiment.

FIG. 12 is a diagram showing an example of a moving table photographing procedure according to the second embodiment of the present invention. FIG. 13 is a diagram showing an apparatus characteristic data acquisition procedure according to the second embodiment of the present invention.

[FIG. 14] (a) and (b) are diagrams each showing a relationship between a sliding phase encoding and a table position in a modification of the second embodiment.

FIG. 15 is a diagram showing a modified example of the procedure of the second embodiment.

FIG. 16 is a diagram showing SPE data obtained by a modified example of the procedure of the second embodiment.

FIG. 17 is a diagram showing a relationship between an inspection object and a coil in the third and fourth embodiments.

FIG. 18 is a diagram for explaining a coil position in apparatus characteristic measurement according to the third and fourth embodiments.

FIG. 19 is a diagram showing an inspection object in the example.

20 is a diagram showing a reconstructed image of the inspection object in FIG. 17 according to the first embodiment.

FIG. 21 is a diagram showing a reconstructed image of the inspection object in FIG. 17 according to the first embodiment.

[Fig. 22] Comparison of shooting time between the conventional method and the present invention.

Explanation of symbols

101 'Magnet that generates static magnetic field, 102 ...' Gradient magnetic field coil, 103 ... 'Inspection object, 10 4 ·' Sequencer, 105 · 'Gradient magnetic field power supply, 106 · · High frequency magnetic field generator, · · · Coil for irradiation, 108 · · 'Receiver, 109 · ·' Calculator, 110 · · 'Display, 111 · ·' Storage medium, 112 · • 'Shim coil, 113 · ·' Sim power supply, 114 · · 'Receiving coil, 301 ··' Table, 302 ·· 'Table control device.

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 an imaging space where a static magnetic field is generated, a gradient magnetic field generating means for generating a gradient magnetic field to be applied to the inspection object, Based on the received nuclear magnetic resonance signal, the image of the inspection object is reproduced again based on the movable moving means for mounting the inspection object, the receiving means for receiving the nuclear magnetic resonance signal generated from the inspection object. A magnetic resonance imaging apparatus comprising: an image reconstructing unit that configures; a control unit that controls the operation of each of the units; and a display unit that displays the reconstructed image.

The control means performs measurement of a nuclear magnetic resonance signal for obtaining device characteristic data as device characteristic measurement, and measurement of a nuclear magnetic resonance signal for obtaining the magnetization distribution of the inspection object as main imaging. The gradient magnetic field generating means and the reception means are configured to receive the nuclear magnetic resonance signal a plurality of times during the movement of the movement means and to change the amount of gradient magnetic field applied in the movement direction of the movement means for each reception. Control

The image reconstruction means calculates a device characteristic using the nuclear magnetic resonance signal measured in the device characteristic measurement, and the nuclear magnetic resonance signal force measured in the main imaging using the device characteristic is also the magnetic field of the inspection object. A magnetic resonance imaging apparatus characterized in that, in order to obtain a wrinkle distribution, a real part imaginary part is obtained by approximation, and a magnetization distribution of the inspection object in a field of view wider than the imaging space is determined.

[2] A high-frequency magnetic field generating means for generating a high-frequency magnetic field to be applied to an inspection object placed in an imaging space where a static magnetic field is generated, a gradient magnetic field generating means for generating a gradient magnetic field to be applied to the inspection object, Based on the received nuclear magnetic resonance signal, the image of the inspection object is reproduced again based on the movable moving means for mounting the inspection object, the receiving means for receiving the nuclear magnetic resonance signal generated from the inspection object. A magnetic resonance imaging apparatus comprising: an image reconstructing unit that configures; a control unit that controls the operation of each of the units; and a display unit that displays the reconstructed image.

The control means performs measurement of a nuclear magnetic resonance signal for obtaining device characteristic data as device characteristic measurement, and measurement of a nuclear magnetic resonance signal for obtaining the magnetization distribution of the inspection object as main imaging. The magnetic means during movement of the moving means Receiving the resonance signal a plurality of times, controlling the gradient magnetic field generating means and the receiving means so as to change the application amount of the gradient magnetic field in the moving direction of the moving means for each reception;

The image reconstruction means calculates a device characteristic using the nuclear magnetic resonance signal measured in the device characteristic measurement, and uses the device characteristic to measure the nuclear magnetic resonance signal measured in the main imaging. In order to obtain the magnetic distribution, the number of variables to be obtained at the same time in order to represent the magnetization distribution is reduced by approximation, and the magnetization distribution of the inspection object in the field of view that is wider than the imaging space is determined. Magnetic resonance imaging device.

[3] In the magnetic resonance imaging apparatus according to claim 1 or 2,

The magnetic resonance imaging apparatus characterized in that the control means controls the movement means to move between a plurality of stations and performs the apparatus characteristic measurement at each station of the movement means.

[4] In the magnetic resonance imaging apparatus according to claim 1 or 2,

The magnetic resonance imaging apparatus characterized in that the control means performs the apparatus characteristic measurement simultaneously with the main imaging.

[5] The magnetic resonance imaging apparatus according to claim 4,

The magnetic resonance imaging apparatus characterized in that the image reconstruction means uses a part of the nuclear magnetic resonance signal measured in the main imaging as a nuclear magnetic resonance signal for obtaining the device characteristics.

[6] The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance imaging apparatus according to claim 1 is

The receiving means comprises a receiving coil fixed to the device;

The image reconstructing means calculates device characteristics at each moving means position when measuring a nuclear magnetic resonance signal in the main imaging, using a signal received by a receiving coil fixed to the apparatus. Magnetic resonance imaging device.

[7] The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance imaging apparatus according to claim 1 is

The receiving means includes a receiving coil fixed to an inspection object,

The image reconstruction means uses the signal received by the receiving coil fixed to the inspection object to calculate the apparatus characteristics at each moving means position when measuring the nuclear magnetic resonance signal for the main imaging. A magnetic resonance imaging apparatus.

[8] In the magnetic resonance imaging apparatus according to claim 1 or 2,

The image reconstruction means approximates the correspondence from the real part of the magnetization distribution to the nuclear magnetic resonance signal and the correspondence from the imaginary part of the magnetic distribution to the nuclear magnetic resonance signal as linearly independent. A magnetic resonance imaging apparatus for obtaining a real part and an imaginary part of a wrinkle distribution.

[9] In the magnetic resonance imaging apparatus according to claim 6 or 7,

The receiving unit includes a plurality of the receiving coils, and the image reconstruction unit uses the signals received by the plurality of receiving coils to measure a nuclear magnetic resonance signal during the main imaging. A magnetic resonance imaging apparatus characterized in that the apparatus characteristics at each moving means position are calculated.

[10] In the magnetic resonance imaging apparatus according to claim 7,

The magnetic resonance imaging apparatus, wherein the receiving means includes a plurality of the receiving coils that are used by switching.