JPWO2017013801A1 - Magnetic resonance imaging system - Google Patents

Abstract

In the MRI apparatus, a magnetization transfer image is obtained without prolonging the imaging time and without increasing the SAR. A magnetization transfer image is obtained without using a dedicated pre-pulse for acquiring the magnetization transfer image. In other words, the image acquisition sequence is executed by changing the value of the imaging parameter that affects the magnetization transfer effect, and two or more images having different magnetization transfer effects are acquired. Then, an index for evaluating the magnetization transfer effect is calculated from the pixel value of each image and displayed as a magnetization transfer image.

Description

  The present invention relates to a magnetic resonance imaging (MRI) technique, and more particularly to a magnetization transfer image generation technique.

  The MRI apparatus is a medical diagnostic imaging apparatus that mainly uses proton nuclear magnetic resonance. The MRI apparatus can non-invasively capture an image of an arbitrary cross section, and can acquire information related to biological functions such as blood flow and metabolic functions in addition to morphological information.

  In an MRI apparatus, an enhanced image highlighting relative differences in physical properties of biological tissues (for example, T1: longitudinal relaxation time, T2: transverse relaxation time, PD: proton density, D: diffusion coefficient, MT: magnetization transfer, etc.) Can be obtained. These emphasized images (for example, T1-weighted image, T2-weighted image, FLAIR (Fluid Attenuated IR), diffusion-weighted image, MRA, magnetization movement-weighted image) have a sequence (pulse sequence) and parameters (imaging parameters) used for imaging. Obtained by changing and performing imaging.

  Protons to be subjected to MRI include protons of bound water constituting polymers such as proteins and phospholipids in addition to protons of free water. The magnetization transfer (MT) effect is a phenomenon in which the relaxation or saturation of one proton affects the relaxation or saturation of the other proton. This magnetization transfer enhanced image in which the magnetization transfer effect is emphasized (hereinafter, simply referred to as a magnetization transfer image or MTR (Magnetization Transfer Rate) image) can detect the degree of myelination and the degree of demyelination in the white matter of the brain. Therefore, it is considered useful for the diagnosis of multiple sclerosis.

  An RF pulse irradiated for the purpose of saturating only the protons of the bound water is called an MTC (Magnetization Transfer Contrast) pulse. As a technique for acquiring a magnetization transfer image, a technique for calculating a ratio between an image obtained by applying this MTC pulse as a pre-pulse and an image obtained without applying an MTC pulse is known (for example, non-patent literature). 1). Since the MTC pulse is applied to a frequency band that is distant from the resonance frequency band of free water, this method is generally called an off-resonance method.

  On the other hand, there is a method called an on-resonance method in which a binary pulse having a resonance frequency of free water is irradiated as an RF pulse to saturate the magnetization of only the bound water (for example, see Non-Patent Document 2). This method uses the fact that the T2 decrease is faster as the resonance frequency band is wider, and the signal is lost only for protons in the bound water having a short T2.

Hirohiko Kimura, Robert I. Grossman, Robert E. et al. Lenkinski, Francisco Gonzalez-Scarano al., "Proton MR spectroscopy magnetization transfer ratio in multiple sclerosis: correlative findings of active versus irreversible plaque disease" American Journal of Neuroradiology 1996 17 p1539-1547 Christian T. Stoeck, Peng Hu, Dana C. et al. Peters, Kraig V. Kissinger, Beth Goddu, Lois Goepfert, Long Ngo, Warren J. et al. Manning, Sebastian Kozerke, Reza Nezafat, “Optimization of on-resonant Magnetization Transfer Contrast in Coronary Vein MRI” 27, Mand Reson 18

  As described above, the methods described in Non-Patent Document 1 and Non-Patent Document 2 require a dedicated pre-pulse (MTC pulse) for observing the magnetization transfer effect. The prepulse is added to the image acquisition pulse sequence, and the imaging time is extended as compared with the case where the prepulse is not used.

  Further, the MTC pulse has a large energy, and particularly in a high magnetic field device of 3T (Tesla) or more, the SAR (specific absorption rate) is increased, and imaging is restricted.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique for obtaining a magnetization transfer image in an MRI apparatus without prolonging the imaging time and without increasing the SAR.

  The present invention obtains a magnetization transfer image without using a dedicated pre-pulse for acquiring the magnetization transfer image. In other words, the image acquisition sequence is executed by changing the value of the imaging parameter that affects the magnetization transfer effect, and two or more images having different magnetization transfer effects are acquired. Then, an index for evaluating the magnetization transfer effect is calculated from the pixel value of each image and displayed as a magnetization transfer image.

  Specifically, using the first image data imaged using the first imaging parameter set and the second imaging parameter set having a value of at least one imaging parameter different from the first imaging parameter set. A magnetization movement index calculation unit that calculates a magnetization movement index that is an index for evaluating the magnetization movement effect from the second image data captured in this manner, and the first image data and the second image data are The magnetic resonance imaging apparatus is characterized in that the magnetization transfer effects are different.

  According to the present invention, in the MRI apparatus, a magnetization transfer image can be obtained without prolonging the imaging time and without increasing the SAR.

It is a block diagram which shows the typical structure of the MRI apparatus of 1st embodiment. It is a functional block diagram of the computer of a first embodiment. (A) And (b) is explanatory drawing for demonstrating the magnetization transfer effect. It is a flowchart of the magnetization movement image generation process of 1st embodiment. It is explanatory drawing for demonstrating the example of a parameter setting screen of 1st embodiment. (A) And (b) is explanatory drawing for demonstrating the example of image data of 1st embodiment, (c) shows the change of the pixel value of the image data of (a) and (b). It is a graph. It is explanatory drawing for demonstrating the example of the magnetization movement image of 1st embodiment. It is explanatory drawing for demonstrating the modification of the magnetization movement calculation method of 1st embodiment. It is a functional block diagram of the computer of a second embodiment. It is a flowchart of the magnetization movement image generation process of 2nd embodiment. (A)-(h) is explanatory drawing for demonstrating the example of the magnetic resonance parameter image of 2nd embodiment. (A)-(d) is explanatory drawing for demonstrating the example of the magnetization movement image of 2nd embodiment.

<< First Embodiment >>
Hereinafter, a first embodiment to which the present invention is applied will be described. In all the drawings for explaining the embodiments of the present invention, the same reference numerals are given to components having the same function unless otherwise specified, and the repeated description thereof is omitted.

  First, the magnetic resonance imaging (MRI) apparatus of this embodiment will be described.

  In general, an MRI apparatus applies a slice gradient magnetic field to a subject placed in a static magnetic field and simultaneously applies a radio frequency magnetic field (RF) pulse having a specific frequency to excite nuclear magnetization in a cross section to be imaged. By applying a phase encoding gradient magnetic field and a readout gradient magnetic field to the excited nuclear magnetization, plane position information is given, and an NMR signal (echo signal) at which nuclear magnetization is generated is measured. The measurement of the NMR signal is repeated until a measurement space called k-space is filled. The signal filled in the k space is imaged by inverse Fourier transform.

  The RF pulse for generating the echo signal and each gradient magnetic field are applied based on a preset pulse sequence and imaging parameters. Various pulse sequences are known depending on the purpose. For example, in the gradient echo (GrE) type high-speed imaging method, the number of NMR necessary for obtaining one tomographic image by sequentially changing the phase encoding gradient magnetic field for each repetition time (hereinafter referred to as TR) of the pulse sequence. This is a method of measuring signals.

  The imaging parameters control each pulse applied in the pulse sequence and the gradient magnetic field. The repetition time TR, the echo time TE, the flip angle α that determines the intensity of the RF pulse, the phase θ of irradiation of the RF pulse, etc. is there.

  In a general MR examination, an imaging region to be diagnosed is set using an image acquired by imaging for positioning, a pulse sequence or an imaging parameter is changed, and a plurality of image types (for example, T1-weighted image, T2-weighted image) are set. , FLAIR, diffusion weighted image, MRA). The user adjusts the window level (WL) and window width (WW) of the acquired image by manual operation, and creates a diagnostic image by clipping a signal that hinders diagnosis as necessary.

  As described above, the MRI apparatus 100 of the present embodiment applies a high-frequency magnetic field to the subject 103 placed in a static magnetic field to excite nuclear magnetization in the subject 103 and generate a nuclear magnetic resonance signal (NMR). Signal, echo signal). At this time, position information is given to a magnetic resonance signal measured by applying a gradient magnetic field, and imaging (imaging) is performed.

  FIG. 1 is a block diagram showing a typical configuration of an MRI apparatus 100 according to the present embodiment for realizing this. The MRI apparatus 100 of the present embodiment includes a magnet 101 that generates a static magnetic field, a gradient magnetic field coil 102 that generates a gradient magnetic field, and an RF coil that irradiates a subject (living body) 103 with a high-frequency magnetic field pulse (hereinafter referred to as an RF pulse). 107, an RF probe 108 for detecting an echo signal generated from the subject 103, and a bed (table) 115 on which the subject (for example, a living body) 103 is placed in a static magnetic field space generated by the magnet 101. .

  Furthermore, the MRI apparatus 100 of the present embodiment includes a gradient magnetic field power source 105 that drives the gradient magnetic field coil 102, a high-frequency magnetic field generator 106 that drives the RF coil 107, and a receiver that receives echo signals detected by the RF probe 108. 109, a sequencer 104 that sends commands to the gradient magnetic field power source 105 and the high frequency magnetic field generator 106 to generate a gradient magnetic field and a high frequency magnetic field, respectively, and sets a nuclear magnetic resonance frequency as a reference for detection in the receiver 109; A computer 110 that performs signal processing on the detected signal, a display device 111 that displays a processing result in the computer 110, a storage device 112 that stores the processing result, and an input device 116 that receives an instruction from a user . The storage device 112 holds various data necessary for processing in the computer 110.

  The MRI apparatus 100 may further include a shim coil 113 and a shim power source 114 that drives the shim coil 113 when the static magnetic field uniformity needs to be adjusted. The shim coil 113 includes a plurality of channels, and generates an additional magnetic field that corrects the static magnetic field nonuniformity by the current supplied from the shim power supply 114. The sequencer 104 controls the current that flows through each channel that forms the shim coil 113 when adjusting the static magnetic field uniformity.

  In the MRI apparatus 100 having the above configuration, an RF pulse is applied to the subject 103 through the RF coil 107 under the control of the sequencer 104, and a gradient magnetic field for providing position information such as slice selection and phase encoding to the echo signal. A pulse is applied by the gradient coil 102. Further, a signal generated from the subject 103 is received by the RF probe 108, and the detected signal is sent to the computer 110, where signal processing such as image reconstruction is performed. The storage device 112 may store not only the signal processing result but also the detected signal itself, imaging conditions, and the like as necessary.

  The computer 110 includes a CPU and a memory, and performs not only signal processing for processing a received signal but also control of operations of the entire MRI apparatus 100. For example, the sequencer 104 is instructed to operate each unit at a preprogrammed timing and intensity, and the operation of each unit constituting the MRI apparatus 100 is controlled to perform measurement. The pulse sequence describes the high frequency magnetic field, gradient magnetic field, signal reception timing and intensity, among other programs. As described above, the measurement is performed according to the pulse sequence and imaging parameters necessary for controlling the pulse sequence. The pulse sequence is created in advance and stored in the storage device 112, and the imaging parameters are input from the user via the user interface.

  The magnet 101 is a static magnetic field generator, the gradient magnetic field coil 102 and the gradient magnetic field power source 105 are gradient magnetic field generators, the RF coil 107 and the high frequency magnetic field generator 106 are high frequency transmitters, the RF probe 108 and the receiver 109 are The detection unit for detecting the NMR signal generated from the subject 103, the sequencer 104 and the computer 110 function as a control unit, and the computer 110 further functions as an image reconstruction unit.

  In such an MRI apparatus 100, by controlling the timing and intensity of the high-frequency magnetic field and gradient magnetic field set in the pulse sequence, it is possible to image an arbitrary imaging cross section of the imaging target subject. In general, the position of the imaging section relative to the subject to be imaged is determined and reflected in the pulse sequence, thereby imaging a desired imaging section.

  At this time, the computer 110 controls user interfaces such as the input device 116 and the display device 111, and performs user interface processing such as presenting processing results to the user and receiving input from the user. Further, the echo signal acquired by the MRI apparatus 100 is processed to reconstruct an image. Alternatively, the echo signal is processed, control values necessary for imaging such as the center frequency and the RF irradiation intensity are calculated and transmitted to the sequencer 104.

  Furthermore, the computer 110 according to the present embodiment executes a predetermined pulse sequence, obtains an index (hereinafter referred to as a magnetization transfer index) that can evaluate the magnetization transfer effect by calculation, and outputs it as a magnetization transfer image and diagnostic information. .

  In order to realize this, as shown in FIG. 2, the computer 110 according to the present embodiment receives and sets imaging parameter values including imaging parameters that affect the magnetization transfer effect (hereinafter referred to as magnetization transfer parameters). An imaging parameter setting unit 210, an imaging unit 220, a magnetization movement index calculation unit 230 that calculates a magnetization movement index, a display processing unit 250 that generates a display image from the obtained pixel values and displays the display image on the display device 111. .

  Each function realized by the computer 110 is realized by the CPU loading and executing software (program) stored in the storage device 112 in advance in the memory. Note that it is not necessary to realize all of the above functions by software, and a part or all of the functions may be realized by hardware such as ASIC (Application Specific Integrated Circuit).

  Further, information necessary for execution of processing realized by each function, information in the middle of processing, and finally obtained information are stored in the storage device 112.

[Magnetic transfer effect]
Prior to the description of each part, the magnetization transfer effect will be described. FIG. 3A and FIG. 3B are explanatory diagrams for explaining the magnetization transfer effect.

In general, in a biological tissue in which free water protons (hereinafter referred to as free water protons) and protons such as polymers (hereinafter referred to as bonded water protons) coexist, free water protons (H _f ) Cross relaxation is performed with bound water protons (H _r ) with limited motion in contact with the polymer surface via chemical exchange or through dipole-dipole interactions through space. That is, one relaxation or saturation affects the other relaxation. This phenomenon is called a magnetization transfer effect.

  FIG. 3A shows frequency spectra 910 and 920 of free water and combined water. In general, free water has a long T2 relaxation (lateral relaxation) time, and bound water has a short T2 relaxation time. Since the signal value of free water protons has a long T2 relaxation time, the signal value after Fourier transform shows a sharp peak with a narrow half-value width, as shown in FIG. On the other hand, since the signal value of the bound water proton has a short T2 relaxation time, the signal value after Fourier transform has a wide half-value width.

  Of the conventional methods using MTC pulses, in the off-resonance method, an RF pulse is irradiated to a frequency band 931 several kHz away from the resonance frequency band 911 of free water protons, and a saturation phenomenon occurs only in the bound water protons. To get. Here, the resonance frequency band 921 of the bound water proton is wide and the resonance frequency band 911 of the free water proton is narrow.

  As shown in FIG. 3 (b), the signal intensity of the combined water ptron decreases (from 920 to 923) due to the saturation phenomenon. At this time, the saturation of the bound water proton affects the free water proton by the magnetization transfer effect 932, and the signal intensity of the free water proton also decreases (from 910 to 913).

  Due to the magnetization transfer effect, a difference in signal value occurs between a portion where chemical exchange and / or cross relaxation between free water and bound water is reflected, and a portion where it is not, and a different contrast image is obtained. This contrast image is a magnetization transfer image, and can be used for distinguishing a lesion from a living body and normal tissue.

  Conventionally, as described above, this magnetization transfer image is obtained by taking a ratio between an image acquired by applying an MTC pulse as a pre-pulse and causing a magnetization transfer effect and an image acquired without applying an MTC pulse, Is generated. In the present embodiment, the magnetization transfer image is calculated without applying this MTC pulse. That is, in the present embodiment, among the imaging parameters that are essential at the time of imaging, the imaging parameters that affect the magnetization transfer effect are changed to acquire images, the magnetization transfer index is calculated using each pixel value, and the magnetization A moving image is used.

[Flow of magnetization transfer image generation processing]
The flow of the magnetization transfer image generation process of this embodiment by each function realized by the computer 110 of this embodiment will be described. FIG. 4 is a process flow of the magnetization transfer image generation process of the present embodiment.

  First, the imaging parameter setting unit 210 sets an imaging parameter set for acquiring data for calculating the magnetization movement index according to an instruction from the operator via the input device 116 (step S1101). Here, a pulse sequence corresponding to the target imaging is also set.

  Details of the setting method will be described later. In the present embodiment, two or more sets of imaging parameter sets are set. It should be noted that between two or more imaging parameter sets to be set, at least one of the magnetization transfer parameters has different values.

  Next, the imaging unit 220 performs imaging according to an imaging start instruction via the operator's input device 116 (step S1102). In the present embodiment, the imaging unit 220 instructs the sequencer 104 according to the imaging parameter set and pulse sequence set by the imaging parameter setting unit 210, and measures an echo signal. Then, an image is reconstructed from the obtained echo signal. Since two or more sets of imaging parameter sets are set as described above, the set number of images is obtained here. Each image is acquired according to the same pulse sequence.

  Next, the magnetization transfer index calculation unit 230 calculates a magnetization transfer index from the obtained image (step S1103).

  Finally, the display processing unit 250 generates an image using the calculated magnetization movement index as a pixel value, and displays it on the display device 111 (step S1104).

  Details of each process will be described below.

[Imaging parameter set setting process]
First, the magnetization movement parameter setting process by the imaging parameter setting unit 210 will be described.

  The imaging parameter setting unit 210 accepts input of imaging parameters by the operator via the input device 116 and sets the accepted imaging parameters. In accepting, for example, the imaging parameter setting unit 210 displays a parameter setting screen 300 on the display device 111 and accepts an input via the screen. Note that each data constituting the parameter setting screen 300 is stored in the storage device 112 in advance.

  An example of the parameter setting screen 300 displayed at this time is shown in FIG. Here, a case where an RF pulse irradiation band (RF irradiation band) is used as a magnetization transfer parameter is illustrated.

  As shown in the figure, the parameter setting screen 300 includes a protocol instruction receiving area 310, an imaging parameter setting area 320, and a protocol saving instruction receiving area 330.

[Protocol Instruction Reception Area]
The protocol instruction reception area 310 is an area for receiving an instruction for a protocol used for imaging via the area. Here, one or more imaging protocols prepared in advance are displayed so that they can be selected. In the present embodiment, the operator selects a protocol for imaging magnetization transfer images from selectable imaging protocols.

  Note that selectable imaging protocols are stored in the storage device 112 in advance. Each imaging protocol includes a pulse sequence used for the imaging protocol, an imaging parameter type to be set when the pulse sequence is executed, and information for specifying a setting condition of each imaging parameter type. It is stored in association. Also, recommended values for each imaging parameter type to be set may be held together.

  For example, a pulse sequence of a 3D gradient echo method is held in association with a magnetization transfer effect imaging protocol. Also, as the imaging parameter type to be set, imaging field of view (FOV), repetition time (TR), echo time (TE), flip angle (FA), and other magnetization transfer parameters are registered.

  As the imaging parameter type setting conditions, for example, a settable range of values of each imaging parameter type is stored. The settable range is determined in advance by hardware restrictions, imaging type restrictions, or imaging parameters related to SAR (Specific Absorption Rate) due to restrictions by the upper limit value of the SAR.

  Further, as described above, when imaging a magnetization movement image, it is necessary to set a plurality of different imaging parameter values for one or more magnetization movement parameters. Therefore, for the magnetization transfer parameter, not only the settable range of each parameter value but also constraint information between values of the same imaging parameter is previously stored as information for specifying the setting condition.

  For example, when the magnetization transfer parameter is the RF irradiation band, the constraint information between the same imaging parameter values may be different. In addition, since the RF irradiation time is determined by the value of the RF irradiation band, there are restrictions due to the timing of SAR application and the timing of gradient magnetic field application and echo acquisition determined by other imaging parameters.

[Imaging parameter setting area]
In the imaging parameter setting area 320, an imaging parameter name is displayed as information for specifying an imaging parameter type to be set. The displayed imaging parameter name is held in association with the protocol selected in the protocol instruction reception area 310. In addition, the imaging parameter setting area 320 includes a value receiving area 321 that receives input of values used for imaging for each imaging parameter type. If the recommended value is stored in advance, the recommended value is displayed in this value receiving area 321.

  Further, the imaging parameter setting area 320 may include a setting area specific to each protocol for each imaging protocol. For example, when a magnetization transfer effect imaging protocol is selected as in the present embodiment, two or more values are set for one or more magnetization transfer parameters among imaging parameters essential for imaging. For this reason, in the present embodiment, the imaging parameter setting area 320 includes a magnetization movement parameter setting area 340 that receives values of two or more magnetization movement parameters.

  FIG. 5 illustrates a case where the RF irradiation band is displayed as the magnetization transfer parameter.

  Similarly, the magnetization movement parameter setting area 340 includes an area for displaying an imaging parameter name set as a magnetization movement parameter, and a value reception area 341 for receiving an input of a set value. If the recommended value is stored in advance, the recommended value is displayed in the value receiving area 341.

  The operator can input a value within the settable range via the value reception areas 321 and 341. Similarly, when the recommended value is displayed, the value can be changed within the settable range.

  That is, when the recommended value is held, the imaging parameter setting unit 210 of the present embodiment displays the recommended value together with information for specifying the imaging parameter in the imaging parameter setting area 320 when receiving the designation of the imaging protocol. . In addition, the imaging parameter setting unit 210 receives values input from the operator via the value reception areas 321 and 341.

  At this time, when an input of a value outside the settable range or a value that does not satisfy the constraint condition is received, the imaging parameter setting unit 210 may be configured to notify the operator to that effect. When the imaging parameter setting unit 210 accepts an input of a value outside the settable range, the imaging parameter setting unit 210 sets a value within the settable range that is closest to the accepted value, and accepts an input of a value that does not satisfy the constraint condition Alternatively, a value satisfying the constraint condition closest to the accepted value may be set.

[Protocol save instruction reception area]
The protocol storage instruction reception area 330 receives an instruction to confirm the imaging parameter input via the imaging parameter setting area 320.

  When the imaging parameter setting unit 210 receives an instruction from the operator via the protocol storage instruction reception area 330, the imaging parameter displayed in the imaging parameter setting area 320 at that time is displayed together with the pulse sequence in the protocol instruction reception area. The data is stored in the storage device 112 in association with the protocol received in 310.

[Magnetic transfer index calculation processing]
Next, the magnetization movement index calculation process by the magnetization movement index calculation unit 230 will be described.

  In the present embodiment, the magnetization movement index calculation unit 230 has a first image data imaged using the first imaging parameter set, and a second image data value different from that of the first imaging parameter set. A magnetization transfer index that is an index for evaluating the magnetization transfer effect is calculated from the second image data captured using the imaging parameter set.

  At this time, the first and second imaging parameter sets are set so that the first image data and the second image data have different magnetization transfer effects. For this reason, in the present embodiment, imaging parameters having different values between the first imaging parameter set and the second imaging parameter set are magnetization transfer parameters that are imaging parameters that affect the magnetization transfer effect. The magnetization transfer parameter whose value is changed is selected from imaging parameters that must be set during imaging.

  And the magnetization movement parameter | index calculation part 230 of this embodiment calculates the difference between 1st image data and 2nd image data as a magnetization movement parameter | index. At this time, the magnetization movement index calculation unit 230 of the present embodiment calculates any one of a difference, a ratio, and a difference ratio as the difference.

  As an example of the imaging parameter related to the magnetization transfer, there is an RF pulse irradiation band (RF irradiation band) as described above. Hereinafter, a case where the magnetization transfer parameter whose value is changed between the first imaging parameter set and the second imaging parameter set is the RF irradiation band will be described as an example, and specifically, the magnetization transfer index calculation process of the present embodiment will be described. Will be explained.

  FIGS. 6A and 6B show images 401 and 402 obtained by performing imaging while changing the value of the RF irradiation band. The image 401 that is the first image data has an RF irradiation band of ± 556 kHz, and the image 402 that is the second image data has an RF irradiation band of ± 278 kHz, each acquired by a 3D gradient echo method. Is. The imaging parameters (imaging conditions) other than the RF irradiation band are all acquired with the same value. That is, the difference in the imaging parameters between the image 401 and the image 402 is only the RF irradiation band.

  FIG. 6C is graphs 411 and 412 in which the pixel values in the lines 403 of the image 401 and the image 402 are plotted. As shown in this figure, it can be confirmed that there is a difference in pixel value even when only the RF irradiation band is changed.

  As shown in this figure, in the region of the subject 103, it can be seen that the signal value 412 of the image 402 obtained by setting the RF irradiation band to ± 278 kHz is higher. This is a phenomenon that occurs because the resonance frequency band of polymer protons (bonded water protons) is wide and the magnetization transfer phenomenon is further promoted by widening the on-resonance RF irradiation band.

なお、Ａ（ｒ）は、画像４０１の画素ｒの画素値、Ｂ（ｒ）は、画像４０２の画素ｒの画素値、Ｒ（ｒ）は、画素ｒの差分比である。As described above, the magnetization transfer index calculation unit 230 calculates a magnetization transfer index for each pixel (voxel) using the pixel values (voxel values) of the two images 401 and 402 acquired by changing only the magnetization transfer parameter. To do. In the present embodiment, as the magnetization movement index, for example, a difference ratio represented by the following expression (1) is calculated.

A (r) is the pixel value of the pixel r of the image 401, B (r) is the pixel value of the pixel r of the image 402, and R (r) is the difference ratio of the pixel r.

  The magnetization transfer index is not limited to this. It is only necessary to reflect a difference (difference) in pixel values between images acquired by changing the magnetization transfer parameter. For example, only the difference or only the ratio may be used.

  FIG. 7 shows an image (magnetization movement image) 501 having a magnetization movement index as a pixel value. As described above, since the image 401 and the image 402 have different RF irradiation bands, the influence of the magnetization transfer effect included in the pixel is different. Each pixel of the image 501 whose pixel value is the difference ratio between these images indicates the magnitude of the magnetization transfer effect. That is, in the image 501, the larger the pixel value, the more actively the magnetization transfer phenomenon, suggesting that there is much polymer.

  As described above, the MRI apparatus 100 according to the present embodiment includes the first image data imaged using the first imaging parameter set, the first imaging parameter set, and the value of at least one imaging parameter. A magnetization movement index calculation unit 230 is provided that calculates a magnetization movement index that is an index for evaluating the magnetization movement effect from second image data captured using a different second imaging parameter set. At this time, the first image data and the second image data have different magnetization transfer effects. For example, the imaging parameter having a different value between the first imaging parameter set and the second imaging parameter set is a magnetization transfer parameter that is an imaging parameter that affects the magnetization transfer effect. The first image data and the second image data are acquired according to the same pulse sequence.

  In the MRI apparatus 100 of the present embodiment, the magnetization movement index calculation unit 230 calculates the difference between the first image data and the second image data as the magnetization movement index. The difference calculated here is one of a difference, a ratio, and a difference ratio.

  As described above, according to the present embodiment, the magnetization movement index is obtained from two or more image data obtained by imaging while changing the value of the magnetization movement parameter that affects the magnetization movement effect among the imaging parameters essential for imaging. calculate.

  Therefore, according to the present embodiment, an index reflecting the magnetization transfer effect can be calculated only by changing a parameter essential at the time of imaging without using a pre-pulse dedicated to the magnetization transfer effect such as an MTC pulse. Therefore, the imaging time can be shortened by the pre-pulse application time. Further, SAR can be expected to be reduced by the amount that the prepulse is not applied.

<Other examples of magnetization transfer parameters>
In the above-described embodiment, the case where the RF irradiation band is used as the magnetization transfer parameter is described as an example of the magnetization transfer parameter. However, the magnetization transfer parameter is not limited to this. Any imaging parameter whose magnetization saturation changes by changing the value may be used. For example, a flip angle (FA), a repetition time (TR), or the like may be used.

  Since the degree of saturation of each of these imaging parameters is changed by changing the value, it is possible to perform imaging with the influence of the magnetization transfer effect included in the pixel value changed as in the RF irradiation band. Therefore, using the result, as in the present embodiment, it is possible to calculate an index related to the magnetization transfer effect without using a pre-pulse.

<Other examples of magnetization transfer indices>
Moreover, in the said embodiment, the example which calculates the difference of each pixel value (voxel value) of the acquired image according to said Formula (1) as a magnetization movement parameter | index is shown. However, the calculation of the magnetization transfer index is not limited to this.

  For example, three or more values may be set for the magnetization transfer parameter whose value is to be changed, and the magnetization transfer index may be calculated from the obtained image by the following method.

  That is, the magnetization movement index calculation unit 230 uses the third image data captured using a third imaging parameter set having a value of at least one imaging parameter different from the first imaging parameter set and the second imaging parameter set. Then, the coefficient of the approximate expression obtained by fitting the first image data and the second image data is calculated as a magnetization movement index. At this time, the magnetization transfer parameter is set so that the third image data, the first image data, and the second image data have different magnetization transfer effects.

  Hereinafter, this method will be described by taking as an example a case where three values are set using the RF irradiation band as the magnetization transfer parameter.

  In this example as well, three different values of imaging parameters are accepted via the imaging parameter setting unit 210, and the MRI apparatus 100 acquires three images in accordance with instructions from the imaging unit 220.

  As shown in FIG. 8, the magnetization transfer index calculation unit 230 sets the voxel values 441, 442, and 443 for the voxels 430 of the acquired images 421, 422, and 423, and the horizontal axis (x-axis) for the RF irradiation band. (RF BW [kHz]), and the vertical axis (y-axis) is plotted on the coordinates with the signal intensity (Signal Intensity).

Then, the plot result is fitted with a polynomial 450. Here, for example, the following equation (2) is used as a polynomial.
y = ax ² + bx + c (2)

  The magnetization movement index calculation unit 230 calculates the coefficients a, b, and c of each term as the magnetization movement index. Each coefficient is calculated by, for example, the least square method. If the number of images is equal to or greater than the number of coefficients, it may be calculated analytically. And the image which uses each obtained coefficient as a pixel value is output as a magnetization movement image.

  Thus, by using the coefficient of the approximate expression of the pixel value for each value of the magnetization transfer parameter as the magnetization transfer index, the relationship between the irradiation band of the RF pulse and the influence of the magnetization transfer effect is expressed, and a specific frequency It is considered possible to analyze macromolecules present in the belt.

<Other examples of parameter setting screen>
Moreover, when the recommended value of the imaging parameter is prepared in advance as an imaging parameter set, the approximate influence degree of the magnetization transfer effect for each recommended value may be held together. In this case, the parameter setting screen 300 may be configured to present an approximate degree of influence of the magnetization transfer effect between the prepared imaging parameter sets.

  In other words, the imaging parameter setting unit 210 holds a plurality of recommended values of imaging parameters for each imaging protocol and information indicating the degree of change in the magnetization transfer effect for each recommended value. Then, when the imaging parameter setting unit 210 accepts the designation of the imaging protocol, the imaging parameter setting unit 210 displays a recommended value in a manner that can be selected together with information for specifying the imaging parameter in the imaging parameter setting area 320. The degree of change in the magnetization transfer effect held in association with the recommended value is displayed.

  By configuring in this way, setting of the value of the magnetization transfer parameter having a higher magnetization transfer effect can be supported. Therefore, even an operator without specialized knowledge can easily set the optimum magnetization transfer parameter.

<Other variations>
Further, in the above embodiment, when setting the imaging parameter set, when a protocol specification is accepted, the imaging parameter to be used is displayed accordingly, received correction from the operator, and the instruction is accepted. However, it is not limited to this.

  For example, when the recommended value can be held in advance, when the protocol designation is accepted from the operator, the imaging is performed using the recommended value held in advance without presenting the value of each imaging parameter to the operator. You may comprise. In other words, the configuration may be such that the process from the parameter call to the calculation of the index related to the magnetization transfer effect is executed seamlessly with a single instruction from the operator. Thereby, it can be expected to further reduce the inspection time.

<< Second Embodiment >>
Next, a second embodiment to which the present invention is applied will be described. In the first embodiment, an index (magnetization transfer index) that can evaluate the magnetization transfer effect is calculated using pixel values (voxel values) of images acquired by changing the value of the magnetization transfer parameter. On the other hand, in this embodiment, a more quantitative magnetization transfer index is calculated.

  The MRI apparatus of the present embodiment has basically the same configuration as the MRI apparatus 100 of the first embodiment. However, as described above, since the calculation method of the magnetization transfer index is different, the function realized by the computer 110 is different. Hereinafter, a description will be given focusing on the configuration different from the first embodiment.

  In the present embodiment, in addition to the magnetization movement index, the magnetic resonance parameter is calculated for each image data group having different magnetization movement. That is, magnetic resonance parameters having different magnetization transfer effects are calculated with the same magnetic resonance parameter. Then, a magnetization transfer index is calculated using magnetic resonance parameters having different magnetization transfer effects. The magnetic resonance parameter is a physical property value of the subject 103, such as T1, T2, or PD.

  In order to realize this, as shown in FIG. 9, the computer 110 according to the present embodiment includes the configuration of the first embodiment shown in FIG. 2 (an imaging parameter setting unit 210, an imaging unit 220, and a magnetization movement index calculation unit). 230). The magnetization transfer index calculation unit 230 of this embodiment further includes a magnetic resonance parameter calculation unit 231.

  The magnetic resonance parameter calculation unit 231 calculates a magnetic resonance parameter from the pixel value (voxel value) of an image captured in accordance with an instruction from the imaging unit 220. The magnetic resonance parameter is a physical property value of the subject 103 such as a T1 value, a T2 value, or a PD.

  Moreover, in this embodiment, the process of the magnetization movement parameter | index calculation part 230 differs. In the first embodiment, the magnetization transfer index is calculated using the pixel values (voxel values) of the respective image data having different magnetization transfer effects. In this embodiment, the magnetic resonance parameter calculation unit 231 calculates A magnetization transfer index is calculated from magnetic resonance parameters having different magnetization transfer effects.

[Flow of magnetization transfer image generation processing]
The flow of the magnetization transfer image generation process of this embodiment by each function realized by the computer 110 of this embodiment will be described. FIG. 10 is a process flow of the magnetization transfer image generation process of the present embodiment.

  First, as in the first embodiment, the imaging parameter setting unit 210 sets an imaging parameter set for acquiring data for calculating the magnetization movement index in accordance with an instruction from the operator via the input device 116 (step S2101). . Note that in this embodiment as well, two or more sets of imaging parameter sets are set as in the first embodiment. It is assumed that at least one or more magnetization transfer parameter values among the magnetization transfer parameters are different between two or more imaging parameter sets to be set.

  Next, the imaging unit 220 performs imaging in accordance with an imaging start instruction via the operator's input device 116 (step S2102). This process is also the same as in the first embodiment.

  Next, in the present embodiment, the magnetic resonance parameter calculation unit 231 calculates the magnetic resonance parameter from each of the image data with different magnetization transfer effects acquired according to the pulse sequence executed according to the instruction of the imaging unit 220 (step S2103). Details of this magnetic resonance parameter calculation processing will be described later.

  Then, the magnetization transfer index calculating unit 230 calculates a magnetization transfer index from the magnetic resonance parameter (step S2104). In this embodiment, the magnetization transfer index is calculated for each magnetic resonance parameter. Details of this magnetization movement index calculation processing will also be described later.

  Finally, the display processing unit 250 generates an image using the magnetization transfer index as a pixel value and displays the image on the display device 111 (step S2105). At this time, in this embodiment, since the magnetization transfer index is calculated for each magnetic resonance parameter, the magnetic resonance parameter name is also displayed.

  Hereinafter, details of the magnetic resonance parameter calculation process and the magnetization transfer index calculation process, which are processes different from the first embodiment, will be described.

[Magnetic resonance parameter calculation processing]
The magnetic resonance parameter calculation unit 231 according to the present embodiment calculates the same type of magnetic resonance parameter for each image data group having different magnetization transfer effects. That is, one or more magnetic resonance parameters, which are physical property values of the subject 103, are calculated from the first image data and the second image data. Note that the first image data is captured using the first imaging parameter set, and the second image data is a second image in which the value of at least one imaging parameter is different from that of the first imaging parameter set. Are captured using the imaging parameter set. These first image data and second image data have different magnetization transfer effects.

  The method for calculating the magnetic resonance parameters is not limited. Various existing techniques can be used. For example, when a sequence in which the signal intensity is formulated, such as a spin echo sequence, is used for imaging, the calculation is performed from the pixel value of the obtained image using the formulated signal intensity function.

  Hereinafter, a magnetic resonance parameter calculation process when imaging is performed using a sequence (for example, an RF-soiled Grass sequence) in which a signal intensity function is not formulated as a pulse sequence will be described.

  In this case, the signal function fs is created in advance by simulation or the like. Then, the magnetic resonance parameter calculation unit 231 fits the signal value (pixel value) for each pixel of each image acquired with different imaging parameters to the signal function fs created in advance, and estimates the magnetic resonance parameter.

[Signal function]
First, a method for creating the signal function fs will be described. This signal function fs is created in advance by numerical simulation.

  The signal function fs is a function generated for each imaging sequence, and is a parameter (subject parameter; magnetic resonance parameter) that depends on the subject 103 and is a physical property value of a living tissue and a parameter (device parameter) that depends on the device. This is a function that returns the signal intensity of each pixel with at least one of them and an imaging condition (imaging parameter) set when the user executes a pulse sequence.

  Imaging parameters that can be changed in the RF-soiled Grass sequence are a flip angle FA, a repetition time TR, an echo time TE, and an RF phase increment value θ. Of these, the RF phase increment value θ is generally fixed at 117 degrees so that an image contrast with less T2 dependency equivalent to FLASH, which is one of high-speed imaging methods, can be obtained. This is because when the RF phase increment value θ is changed, the T2 dependence of the image contrast changes greatly.

  The subject parameters include a longitudinal relaxation time T1, a lateral relaxation time T2, a chemical shift Cs, and a spin density PD. The apparatus parameters include magnetic field intensity B0, transmission coil irradiation intensity B1, and reception coil sensitivity Sc.

なお、送信コイルの照射強度Ｂ１は撮像時にはフリップ角ＦＡの係数となるため、ＦＡとの積の形にしておく。The signal function fs of the RF-soiled Grass sequence is expressed by the following equation (3) using the above parameters.

It should be noted that the irradiation intensity B1 of the transmission coil is a coefficient of the flip angle FA at the time of imaging, and is thus in the form of a product with FA.

  The signal function fs is created by interpolation by creating a signal by numerical simulation by comprehensively changing the imaging parameters for arbitrary values of the subject parameters T1, T2, and Cs. At this time, PD, B1, and Sc to be imaged are set constant (for example, 1). Further, B0 is set to be the same as the magnetic field intensity (for example, 3T) of the apparatus used for imaging.

  Numerical simulation uses an object model in which spins are placed on lattice points, receives imaging sequence, imaging parameters, and device parameters as input, solves Bloch's equation, which is the basic equation of magnetic resonance, and outputs a nuclear magnetic resonance signal It shall be.

  The object model is given as a spatial distribution of spins (γ, M0, T1, T2, Cs). Here, γ is a magnetic rotation ratio, M0 is thermal equilibrium magnetization (spin density), and an image is reconstructed from a nuclear magnetic resonance signal, whereby an image under a given condition can be obtained.

ここで、（ｘ，ｙ，ｚ）は３次元の直交座標系を表し、ｚは静磁場（強度がＢ０）の向きに等しい。また、（Ｍｘ，Ｍｙ，Ｍｚ）はスピン、Ｇ_ｘ，Ｇ_ｙ，Ｇ_ｚはそれぞれ添字方向の傾斜磁場強度、Ｈ１は高周波磁場強度、ｆ０は回転座標系の周波数である。The Bloch equation is a first-order linear ordinary differential equation and is represented by the following equation (4).

Here, (x, y, z) represents a three-dimensional orthogonal coordinate system, and z is equal to the direction of the static magnetic field (intensity is B0). (Mx, My, Mz) is spin, G _x , G _y , G _z are gradient magnetic field strengths in the subscript direction, H 1 is high-frequency magnetic field strength, and f 0 is the frequency of the rotating coordinate system.

[Method of estimating magnetic resonance parameters]
Next, a method for estimating a physical property value using the signal function fs will be described. In this case, the magnetic resonance parameters are estimated by changing the imaging parameters FA, TR, TE, and θ to capture a plurality of images and fitting the signal value I for each pixel to the signal function fs.

Note that parameters that can be estimated by this fitting include apparatus parameters that depend on the MRI apparatus 100. It is difficult to freely control the apparatus parameters at the time of imaging, and it is impossible to separate the apparatus parameters other than B1 simply by changing the imaging parameters. For this reason, the signal function fs is fitted to the function f obtained by variable conversion as in the following equation (5). For the function fitting, for example, a least square method is used.

  When the pulse sequence used at the time of imaging is a sequence in which the signal intensity function is not formulated, the magnetic resonance parameter calculation unit 231 of the present embodiment uses the function f and calculates the magnetic resonance parameter from the pixel value of the obtained image. (For example, physical property values of the subject 103 such as T1 value, T2 value, and PD) are estimated.

  In this case, the imaging parameter setting unit 210 sets different imaging parameters (for example, FA, TR, TE, θ) for each value of the magnetization movement parameter. That is, in this case, a value of 2 or more is set for the magnetization transfer parameter as in the first embodiment. Further, different values are set for a plurality of imaging parameter types for each value of each magnetization transfer parameter. For this reason, for example, when n different values are set for the magnetization transfer parameter and m different values are set for magnetic resonance parameter calculation, a total of n × m imaging parameter sets are set. Note that n and m are integers of 2 or more.

  The imaging parameter is set through the parameter setting screen 300, for example, as in the first embodiment. Also in the present embodiment, as in the first embodiment, recommended values, setting conditions, and the like may be stored in advance. The processing when a value outside the settable range and not satisfying the constraint is input is the same as in the first embodiment.

[Magnetic transfer index calculation processing]
The magnetization transfer index calculating unit 230 according to the present embodiment calculates the magnetization transfer index using the same kind of magnetic resonance parameters obtained for each image data group having different magnetization transfer effects. That is, the magnetization transfer index is calculated using the first magnetic resonance parameter estimated from the first image data and the second magnetic resonance parameter estimated from the second image data.

  The magnetization transfer index calculation unit 230 calculates the difference between the first magnetic resonance parameter and the second magnetic resonance parameter as the magnetization transfer index for each magnetic resonance parameter. Here, the difference to be calculated is, for example, any one of a difference, a ratio, and a difference ratio.

  For example, when three types of values T1, T2, and PD are estimated as magnetic resonance parameters, each is used to calculate a magnetization transfer index. Therefore, at least three magnetization transfer indices are calculated.

  In addition, when multiple types of magnetic resonance parameters are calculated, the magnetization transfer index may be calculated by combining them.

For example, M _f that is the proton density PD when the magnetization transfer effect is suppressed, M _s that is the PD when the magnetization transfer decrease occurs and saturation occurs, and the T1 value when the magnetization transfer effect is suppressed The exchange rate constant K may be calculated according to the following equation (6) using T1 _f that is a magnetization transfer index.

<Example>
Below, the specific example of this embodiment is shown.

本実施例では、磁化移動パラメータのＲＦ照射帯域の値を、±２７８ｋＨｚおよび５５６ｋＨｚの２通り設定した。そして、それぞれの帯域について、撮像パラメータのＴＲ、ＦＡ、θについて、６通りの組み合わせの値を設定し、計１２の撮像パラメータセットを設定した。Here, it is assumed that 12 sets shown in Table 1 below are set as the imaging parameter set. The imaging parameter set is received by the imaging parameter setting unit 210 via the parameter setting screen 300.

In this example, the value of the RF irradiation band of the magnetization transfer parameter was set in two ways: ± 278 kHz and 556 kHz. Then, for each band, six combinations of values for imaging parameters TR, FA, and θ were set, and a total of 12 imaging parameter sets were set.

  11A to 11 (A) to 11 (A) to 11 (A) to 11 (A) to 11 (A) to 11 (A) to 11 (A) to 11 (A) to 11 (B), the images having the magnetic resonance parameters calculated by the magnetic resonance parameter calculation unit 231 as pixel values from the twelve image data obtained by imaging performed using these imaging parameter sets. h).

  11 (a) to 11 (d) are images (a image) 611 having a pixel value a (calculated from an image acquired in an RF irradiation band ± 278 kHz, and images having a pixel value B1 (B1 image). 612, an image (T1 image) 613 having T1 as a pixel value, and an image (T2 image) 614 having T2 as a pixel value. 11E to 11F are an a image 621, a B1 image 622, a T1 image 623, and a T2 image 624 calculated from images acquired in the RF irradiation band ± 556 kHz.

  The magnetic resonance parameter calculation unit 231 calculates (estimates) the values of a, B1, T1, and T2 from the image data of the imaging result using the above signal function and function fitting. At this time, these values (a, B1, T1, T2) were calculated (estimated) for each RF irradiation band.

  In addition, FIGS. 12A to 12D show images in which the magnetization transfer index calculation unit 230 uses the calculation result of the magnetic resonance parameter calculation unit 231 and uses the calculated magnetization transfer index as a pixel value. Here, FIGS. 12A to 12C are images (magnetization transfer images) 631 having a difference ratio of a as pixel values (magnetization transfer images) 631 and images (magnetization transfer images) having a difference ratio of T1 as pixel values, respectively. 633 is an image (magnetization transfer image) 634 in which the difference ratio of T2 is a pixel value. FIG. 12D shows an image (magnetization transfer image) 635 having the above-described exchange rate constant K as a pixel value.

  As described above, the MRI apparatus 100 according to the present embodiment, as in the first embodiment, includes at least the first image data captured using the first imaging parameter set, the first imaging parameter set, and the first imaging parameter set. A magnetization movement index calculation unit 230 that calculates a magnetization movement index that is an index for evaluating the magnetization movement effect from second image data captured using a second imaging parameter set having different values of one imaging parameter. Prepare. At this time, the first image data and the second image data have different magnetization transfer effects. For example, the imaging parameter having a different value between the first imaging parameter set and the second imaging parameter set is a magnetization transfer parameter that is an imaging parameter that affects the magnetization transfer effect. The first image data and the second image data are acquired according to the same pulse sequence.

  The magnetization movement index calculation unit 230 according to the present embodiment calculates one or more magnetic resonance parameters, which are physical property values of the subject, from the first image data and the second image data, respectively. Part 231. And the magnetization movement parameter | index calculation part 230 of this embodiment uses the 1st magnetic resonance parameter estimated from said 1st image data, and the 2nd magnetic resonance parameter estimated from said 2nd image data. The magnetization transfer index is calculated. At this time, for example, the magnetization movement index calculation unit calculates a difference between the first magnetic resonance parameter and the second magnetic resonance parameter as the magnetization movement index for each magnetic resonance parameter. The difference may be any of a difference, a ratio, and a difference ratio.

  As described above, according to the present embodiment, as in the first embodiment, an index that reflects the magnetization transfer effect can be obtained by changing only the essential parameters at the time of imaging without using a pre-pulse dedicated to the magnetization transfer effect such as an MTC pulse. (Magnetization transfer index) can be calculated. Therefore, the imaging time can be shortened by the pre-pulse application time. Further, SAR can be expected to be reduced by the amount that the prepulse is not applied.

  Furthermore, according to this embodiment, a more quantitative index can be obtained by associating this magnetization transfer index with a physical property value.

<Modification>
At least two values of the magnetization transfer parameter are necessary. When the pulse sequence used at the time of imaging is a sequence in which the signal intensity function is not formulated, and the above estimation method is used, the number of magnetic resonance parameters to be calculated is m (4 in the above example). The number of data (imaging parameter set number) is required to be at least 2 × m. However, it is not necessarily limited to this.

  The first imaging parameter set and the second imaging parameter set have different values of the plurality of imaging parameters, and the plurality of imaging parameters having different values can be combined to combine the first image and the second imaging parameter set. It is not particularly necessary to obtain image data by changing the value of the magnetization transfer parameter as long as it is an imaging parameter that causes a magnetization transfer effect different from that of the image.

  For example, a magnetic resonance parameter with a short TR and a high FA has a high magnetization transfer effect, and a magnetic resonance parameter with a long TR and a small FA has a low magnetization transfer effect. Using this, as a set of imaging parameters, parameters are set without changing the value of the magnetization transfer parameter (in the above example, the value of the RF pulse band), and the magnetism is relatively short and the FA is high. The image data group measured with the resonance parameter and the image data group measured with the magnetic resonance parameter having a long TR and a small FA are obtained, and the magnetic resonance parameter is obtained for each. The magnetization transfer index may be calculated from

For example, the RF irradiation band is ± 556, and (TR, FA, θ) = {(20, 30, 2), (20, 30, 22), (40, 10, 2), (40, 30, 2) , (40, 10, 8), (40, 10, 5), (10, 40, 2), (10, 40, 22)}, (TR, FA, θ) = {(20, 30, 2), (20, 30, 22), (40, 10, 2), (40, 30, 2), (40, 10, 8), (40, 10, 5)} T1 _A , T2 _A and PD _A are estimated from the first data group. Next, (TR, FA, θ) = {(40, 10, 2), (40, 30, 2), (40, 10, 8), (40, 10, 5), (10, 40, 2 ), (10, 40, 22)} T1 _B , T2 _B and PD _B are estimated from the second data group. Thus, by changing the combination of data when calculating the magnetic resonance parameters, the magnetic resonance parameters having different magnetization transfer effects are calculated, and the magnetization transfer index is calculated.

  Further, for example, when there are imaging parameter sets having five different values, four imaging parameter sets are selected in order from an imaging parameter set having a high magnetization transfer effect, and a magnetic resonance parameter having a high magnetization transfer effect is calculated from the result, Also, four parameters are sequentially selected from the imaging parameter set having a low magnetization transfer effect, and a magnetic resonance parameter having a low magnetization transfer effect is calculated. And you may comprise so that a magnetization movement parameter | index may be calculated from both magnetic resonance parameters.

  Thereby, it is possible to calculate magnetic resonance parameters having different magnetization transfer effects without changing the magnetization transfer parameters. Therefore, it is possible to calculate the magnetization transfer index for each physical property value in a shorter time.

  Also in this embodiment, when calculating the magnetization transfer index for each physical property value, three or more image data having different magnetization transfer effects are used, an approximate expression is determined, and the coefficient of the approximate expression is used as the magnetization transfer index. You may comprise.

  DESCRIPTION OF SYMBOLS 100 ... MRI apparatus, 101 ... Magnet, 102 ... Gradient magnetic field coil, 103 ... Subject, 104 ... Sequencer, 105 ... Gradient magnetic field power supply, 106 ... High frequency magnetic field generator, 107 ... RF coil, 108 ... RF probe, 109 ... Reception 110, calculator, 111, display device, 112, storage device, 113, shim coil, 114, shim power source, 116, input device, 210, imaging parameter setting unit, 220, imaging unit, 230, magnetization transfer index calculation unit, 231 ... Magnetic resonance parameter calculation unit, 250 ... Display processing unit, 300 ... Parameter setting screen, 310 ... Protocol instruction reception area, 320 ... Imaging parameter setting area, 321 ... Value reception area, 330 ... Protocol storage instruction reception area, 340 ... Magnetization transfer parameter setting area, 341 ... value receiving area, 401 ... RF irradiation band Image when narrow, 402 ... Image when RF irradiation band is wide, 403 ... Line, 411 ... Graph of signal value of image 401, 412 ... Graph of signal value of image 402, 421 ... Image, 422: Image, 423: Image, 430 ... Voxel, 441 ... Voxel value, 442: Voxel value, 443: Voxel value, 450 ... Polynomial, 501 ... Magnetic transfer image, 611 ... a image, 612 ... B1 image, 613 ... T1 image, 614 ... T2 image 621 ... a image, 622 ... B1 image, 623 ... T1 image, 624 ... T2 image, 631 ... a magnetization transfer image, 633 ... T1 magnetization transfer image, 634 ... T2 magnetization transfer image, 635 ... exchange rate constant. Magnetization transfer image of K, 910 ... free water frequency spectrum, 911 ... free water proton resonance frequency band, 912 ... bound water proton resonance Frequency band, 920 ... bound water of the frequency spectrum, 931 ... frequency band, 932 ... magnetization transfer effect

Claims (15)

First image data imaged using the first imaging parameter set, and second imaged using the second imaging parameter set having a value of at least one imaging parameter different from that of the first imaging parameter set A magnetization transfer index calculation unit that calculates a magnetization transfer index that is an index for evaluating the magnetization transfer effect from the image data of
The first image data and the second image data have different magnetization transfer effects,
The magnetic resonance imaging apparatus, wherein the first image data and the second image data are acquired according to the same pulse sequence. The magnetic resonance imaging apparatus according to claim 1,
The magnetic resonance imaging apparatus, wherein the magnetization transfer index calculating unit calculates a difference between the first image data and the second image data as the magnetization transfer index. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the magnetization transfer index calculation unit sets a magnetic resonance parameter that is a physical property value of a subject to 1 from the first image data and the second image data, respectively. A magnetic resonance parameter calculation unit for calculating above is provided,
The magnetization transfer index is calculated using a first magnetic resonance parameter estimated from the first image data and a second magnetic resonance parameter estimated from the second image data. Resonance imaging device. The magnetic resonance imaging apparatus according to claim 3,
The magnetization transfer index calculation unit calculates a difference between the first magnetic resonance parameter and the second magnetic resonance parameter as the magnetization transfer index for each magnetic resonance parameter. . The magnetic resonance imaging apparatus according to claim 1,
The magnetic resonance imaging characterized in that the imaging parameters having different values between the first imaging parameter set and the second imaging parameter set are magnetization transfer parameters that are imaging parameters that affect the magnetization transfer effect. apparatus. The magnetic resonance imaging apparatus according to claim 3,
In the first imaging parameter set and the second imaging parameter set, the values of the plurality of imaging parameters are different,
The magnetic resonance imaging apparatus, wherein the plurality of imaging parameters having different values are imaging parameters that, when combined, cause different magnetization transfer effects in the first image and the second image. The magnetic resonance imaging apparatus according to claim 2,
The magnetic resonance imaging apparatus, wherein the difference is any one of a difference, a ratio, and a difference ratio. The magnetic resonance imaging apparatus according to claim 1,
The magnetization movement index calculation unit includes third image data captured using a third imaging parameter set having a value of at least one imaging parameter different from the first imaging parameter set and the second imaging parameter set. , Calculating the coefficient of the approximate expression obtained by fitting the first image data and the second image data as the magnetization movement index,
The magnetic resonance imaging apparatus, wherein the third image data, the first image data, and the second image data have different magnetization transfer effects. The magnetic resonance imaging apparatus according to claim 1,
A magnetic resonance imaging apparatus, further comprising: an imaging parameter setting unit that receives and sets a value of the imaging parameter. The magnetic resonance imaging apparatus according to claim 9,
The imaging parameters having different values between the first imaging parameter set and the second imaging parameter set are magnetization transfer parameters that are imaging parameters that affect the magnetization transfer effect;
The imaging parameter setting unit accepts the setting of the value of the imaging parameter via a parameter setting screen,
The parameter setting screen includes an imaging parameter setting area for receiving a value of the imaging parameter,
The magnetic resonance imaging apparatus, wherein the imaging parameter setting region includes a magnetization transfer parameter setting region that receives values of two or more magnetization transfer parameters. The magnetic resonance imaging apparatus according to claim 10,
The imaging parameter setting unit holds a recommended value of the imaging parameter for each imaging protocol,
When the imaging parameter setting unit receives designation of the imaging protocol, the imaging parameter setting unit displays the recommended value together with information for specifying the imaging parameter in the imaging parameter setting area. The magnetic resonance imaging apparatus according to claim 10,
The imaging parameter setting unit holds information for specifying a settable range of each imaging parameter and information for specifying a constraint between two or more magnetization movement parameters,
The imaging parameter setting unit notifies an operator when an input of a value outside the settable range or a value that does not satisfy the constraint condition is received. The magnetic resonance imaging apparatus according to claim 10,
The imaging parameter setting unit holds information for specifying a settable range of each imaging parameter and information for specifying a constraint between two or more magnetization movement parameters,
When receiving an input of a value outside the settable range, the imaging parameter setting unit sets a value within the settable range that is closest to the received value, and receives an input of a value that does not satisfy the constraint condition And a value that satisfies the constraint condition closest to the accepted value is set. The magnetic resonance imaging apparatus according to claim 10,
The imaging parameter setting unit holds a plurality of recommended values of the imaging parameter for each imaging protocol, and holds information indicating the degree of change in the magnetization transfer effect for each recommended value,
When the imaging parameter setting unit receives the specification of the imaging protocol, the imaging parameter setting unit displays the recommended value in a mode that can be selected together with information for specifying the imaging parameter in the imaging parameter setting area. A magnetic resonance imaging apparatus that displays a degree of change in the magnetization transfer effect held in association with a recommended value. The magnetic resonance imaging apparatus according to claim 5,
The magnetic resonance imaging apparatus, wherein the magnetization transfer parameter is one of an irradiation band of a high-frequency magnetic field pulse, a flip angle, and a repetition time.

Images