WO2007122854A1 - Dispositif d'imagerie à résonance magnétique - Google Patents

Dispositif d'imagerie à résonance magnétique Download PDF

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Publication number
WO2007122854A1
WO2007122854A1 PCT/JP2007/053390 JP2007053390W WO2007122854A1 WO 2007122854 A1 WO2007122854 A1 WO 2007122854A1 JP 2007053390 W JP2007053390 W JP 2007053390W WO 2007122854 A1 WO2007122854 A1 WO 2007122854A1
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Prior art keywords
magnetic resonance
magnetic field
image
inspection object
imaging apparatus
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PCT/JP2007/053390
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English (en)
Japanese (ja)
Inventor
Shinji Kurokawa
Yo Taniguchi
Hisaaki Ochi
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Hitachi Medical Corporation
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Priority to JP2008511985A priority Critical patent/JP4832510B2/ja
Publication of WO2007122854A1 publication Critical patent/WO2007122854A1/fr

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging

Definitions

  • 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.
  • MRI Magnetic Resonance Imaging
  • 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.
  • Non-Patent Document 1 multi-station imaging
  • Patent Document 1 moving table imaging
  • sub FOV limited field of view
  • 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.
  • 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.
  • the lead-out direction must be the moving direction of the table.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • SPE sliding phase encoding
  • 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.
  • 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! / ⁇ ⁇ ) 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.
  • 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.
  • 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.
  • 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 sliding phase encoding for the sub FOV is reduced correspondingly. Can do.
  • 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.
  • 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.
  • 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.
  • FIG. 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.
  • 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.
  • the arrow r indicates the moving direction of the table.
  • the horizontal magnetic field type MRI apparatus shown in (a) it coincides with the static magnetic field direction force ⁇ direction.
  • 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.
  • 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
  • An irradiation coil 107 for generating a high-frequency magnetic field that excites an atomic nucleus (usually proton) that constitutes a (human) tissue
  • a receiving coil 114 for detecting a nuclear magnetic resonance signal generated from an examination object Etc.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the force described in 2D is increased by one encoding other than the sliding phase encoding.
  • 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.
  • step 601 device characteristic measurement
  • step 602 main imaging
  • step 603 for calculating the reconstructed image 606 to be inspected using the characteristic data and the inspection target data.
  • 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.
  • 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.
  • 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.
  • FIG. 4 (b) 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.
  • 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).
  • 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. .
  • some sub FOVs are overlapped between stations. This makes it easy to synthesize uniform images and interpolate device characteristic data.
  • another coil such as a body coil!
  • 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.
  • the device characteristic data acquired in this way is data for each station.
  • device characteristic data at each position of the subject that changes continuously in the main imaging is required.
  • 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.
  • step 602 shows the procedure for the actual shooting
  • Fig. 6 (b) shows the procedure for image reconstruction.
  • step 602 as shown in detail in FIG. 6 (a), the table is first moved (step 607).
  • 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).
  • the data acquisition is terminated (step 610).
  • 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.
  • 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.
  • RF represents an excitation radio frequency pulse
  • Gs represents a slice selective gradient magnetic field
  • Gp represents a sliding phase encoding gradient magnetic field
  • 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.
  • such a Gp-axis gradient magnetic field is called a sliding phase encoding gradient magnetic field.
  • 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.
  • 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.
  • the slice gradient magnetic field 204 for reference is applied, and the amount dephased by the slice gradient magnetic field 202 is restored.
  • a sliding phase encoding gradient magnetic field 205 is applied.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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 - ⁇ to ⁇ while the table position changes by sub FOV as shown in Fig. 9. Set the encoding amount k (n) when receiving each signal.
  • the signal S (n, ky) is obtained.
  • 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).
  • FIG. 8 is a diagram schematically showing a calculation added to the measurement data and a memory for storing the result.
  • the image reconstruction calculation is performed using the measurement data 605 to be inspected and the device characteristic data 604 obtained in step 601.
  • 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.
  • the measured signal S (n, ky) can be expressed by the following equation (1) using the position information of the table.
  • Rtable (n) is the amount of table movement when the nth magnetic resonance signal is acquired. It is.
  • 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.
  • ⁇ is the gyromagnetic ratio
  • 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.
  • 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.
  • 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 - ⁇ to ⁇ 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.
  • 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.
  • the present invention enables stable image reconstruction by obtaining the magnetic flux distribution independently of the real part by approximation.
  • Equation (6) r 'is represented by equation (3') similar to equation (3).
  • Ar is the size of the pixel in the r direction at each j.
  • N is the number of signals
  • J is the number of pixels in the r direction.
  • matrix A has each element A (n, j)
  • the procedure for performing such image reconstruction is shown in FIG. 6 (b).
  • the inverse matrix (703, 704) is obtained (steps 701, 702).
  • 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).
  • 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.
  • 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.
  • the Knock sequence of FIG. 7 is illustrated as an imaging method.
  • phase encoding in the slice direction can be given to perform 3D imaging.
  • image reconstruction can be similarly performed only by increasing the position dimension of the signal to be processed.
  • the configuration of the apparatus is the same as that of the first embodiment described above.
  • device characteristic data is acquired in the first step (601), and in the next step, an inverse matrix necessary for image reconstruction is calculated.
  • 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).
  • 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).
  • 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.
  • 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. .
  • 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
  • FIG. 12 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. 12 a method for acquiring apparatus characteristic data at the same time as main imaging will be described with reference to FIGS. 12 and 13.
  • the configuration of the apparatus is the same as that of the first embodiment described above.
  • 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).
  • 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.
  • 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.
  • 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
  • step 642 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).
  • the FOV 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).
  • the interval between positions where the device characteristic data can be acquired is determined by the number of sliding phase encoding loops.
  • 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.
  • the number of signal acquisition times increases, and thus the imaging time of the main imaging increases.
  • 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.
  • 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.
  • 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.
  • 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.
  • the coil 114 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.
  • the signal S (n, ky, c) that is Fourier-transformed in the readout direction (y direction) can be expressed by the following equation (22).
  • ⁇ is the size of the pixel in the r direction at each j.
  • N is the number of signals
  • C is the number of coils
  • J is the number of pixels in the r direction.
  • the matrix A has each element A" ((n-1) X C + c, j)
  • 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.
  • 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.
  • the image 1601b of the region where the static magnetic field and the irradiation are uniform in the image 1602 of the second station, the magnetostatic field and the irradiation are uniform.
  • 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.
  • 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.
  • 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.
  • 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:
  • the configuration of the apparatus is the same as that of the third embodiment described above.
  • 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.
  • Fig. 18 shows the force indicating the coil position in the multi-station.
  • the center position of the first loop (from ⁇ force to ⁇ ) 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.
  • the method of cutting out low-frequency data and reconstructing one image, such as SPE data is the same as in the second embodiment.
  • 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.
  • 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.
  • the entire device characteristic data can be obtained.
  • 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.
  • an image is reconstructed from a signal obtained by actual imaging and a signal calculated using device characteristic data.
  • OV 320 mm X 960 mm (256 pixels X 384 pixels).
  • 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.
  • 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.
  • 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.
  • Fig. 21 (a) shows an image reconstructed by the present invention in Fig. 21 (a)
  • 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.
  • the imaging time is extended by that amount.
  • the imaging that requires a high-resolution image for acquiring the device characteristic data is completed in a short time.
  • 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.
  • 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.
  • FIG. 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.
  • 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.

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Abstract

L'invention concerne un dispositif d'imagerie à résonance magnétique pourvu de caractéristiques de reconstitutions d'image faisant appel à diverses séquences d'un champ de visualisation plus large et un procédé de photographie à grande vitesse permettant de photographier tout en déplaçant une table de façon continue même avec une faible direction de déplacement pour une région d'acquisition de signal donnée. Lorsqu'un signal de résonance magnétique est reçu à plusieurs reprises tout en déplaçant une table (moyens mobiles), un champ magnétique est appliqué en oblique par rapport au sens de déplacement et une quantité d'application (force et temps d'application) du champ magnétique en oblique par rapport au sens de déplacement est modifiée pour chaque acquisition de données. Un codage conforme au champ magnétique oblique du sens de déplacement de la table, qui est différent du codage de phase conventionnel, est réalisé pour une série de codage de phase en différents endroits d'un sujet test. Si une distribution de magnétisation du sujet test s'obtient à partir d'un signal de résonance magnétique nucléaire, une partie imaginaire est recherchée de manière indépendante par approximation, de telle sorte que la distribution de magnétisation du sujet test est déterminée de manière stable dans un champ de visualisation plus large qu'un espace de photographie.
PCT/JP2007/053390 2006-04-19 2007-02-23 Dispositif d'imagerie à résonance magnétique WO2007122854A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009142522A (ja) * 2007-12-17 2009-07-02 Hitachi Medical Corp 磁気共鳴イメージング装置

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Publication number Priority date Publication date Assignee Title
JP2000229073A (ja) * 1998-12-24 2000-08-22 Marconi Electronic Syst Ltd 磁気共鳴画像装置
JP2002248089A (ja) * 2001-02-23 2002-09-03 Hitachi Medical Corp 磁気共鳴イメージング装置および方法
JP2004097826A (ja) * 2002-09-12 2004-04-02 General Electric Co <Ge> 並行受信を用いたｍｒｉによって大きなボリュームを撮像する方法及びシステム
US20040207401A1 (en) * 2003-01-16 2004-10-21 Rainer Kirsch Magnetic resonance imaging (MRI) with continuous table motion
WO2006117922A1 (fr) * 2005-04-28 2006-11-09 Hitachi Medical Corporation Appareil d’imagerie à résonance magnétique

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Publication number Priority date Publication date Assignee Title
JP2000229073A (ja) * 1998-12-24 2000-08-22 Marconi Electronic Syst Ltd 磁気共鳴画像装置
JP2002248089A (ja) * 2001-02-23 2002-09-03 Hitachi Medical Corp 磁気共鳴イメージング装置および方法
JP2004097826A (ja) * 2002-09-12 2004-04-02 General Electric Co <Ge> 並行受信を用いたｍｒｉによって大きなボリュームを撮像する方法及びシステム
US20040207401A1 (en) * 2003-01-16 2004-10-21 Rainer Kirsch Magnetic resonance imaging (MRI) with continuous table motion
WO2006117922A1 (fr) * 2005-04-28 2006-11-09 Hitachi Medical Corporation Appareil d’imagerie à résonance magnétique

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009142522A (ja) * 2007-12-17 2009-07-02 Hitachi Medical Corp 磁気共鳴イメージング装置

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