JP6579908B2 - Magnetic resonance imaging apparatus and diffusion weighted image calculation method - Google Patents

Description

  The present invention relates to a magnetic resonance imaging (hereinafter referred to as `` MRI '') apparatus, and in particular, diffusion enhancement of an arbitrary b value using a plurality of diffusion weighted images respectively acquired using a plurality (two or more) of b values. The present invention relates to a technique for obtaining an image.

  The MRI device measures NMR signals generated by the spins of the subject, especially the tissues of the human body, and visualizes the form and function of the head, abdomen, limbs, etc. in two or three dimensions Device. In imaging, the NMR signal is given different phase encoding depending on the gradient magnetic field and is frequency-encoded and measured as time-series data. The measured NMR signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.

  As a method for calculating a diffusion-weighted image having an arbitrary b value using a diffusion-weighted image obtained by an MRI apparatus, there is a method disclosed in Patent Document 1. Here, the b value is a parameter representing the strength of MPG (Motion Probing Gradient) added to the diffusion enhancement sequence, and the diffusion enhancement image with enhanced diffusion as the b value increases. Note that b value = 0 means that no MPG is added to the diffusion weighted image capturing sequence (that is, the amplitude of the MPG is zero).

  The method described in Patent Document 1 obtains two or more original images by imaging each imaging region using b values of two or more, and calculates an apparent diffusion coefficient (ADC) from the two or more original images. Then, a diffusion-weighted image having an arbitrary b value is calculated based on the apparent diffusion coefficient (ADC). By this method, it is possible to calculate a diffusion weighted image without a decrease in SNR or an increase in artifacts. Hereinafter, an apparent diffusion coefficient (ADC) is simply referred to as a diffusion coefficient (ADC) unless misunderstanding occurs.

JP 2013-255854 A

  However, in Patent Document 1, no consideration is given to the difference in the calculated values depending on the static magnetic field strength of the MRI apparatus to be imaged. In the diffusion-weighted image calculated by the method of Patent Document 1, since the signal value of the original diffusion-weighted image obtained by the static magnetic field strength of the MRI apparatus used for imaging differs, the calculated diffusion coefficient (ADC) is also the static magnetic field strength. Will depend on.

  Therefore, an object of the present invention is to provide an MRI apparatus and a diffusion weighted image calculation method capable of calculating an apparent diffusion coefficient (ADC) and calculating a diffusion weighted image with an arbitrary b value without depending on the static magnetic field strength. Is to provide.

In order to achieve the above object, the MRI apparatus and the diffusion weighted image calculation method of the present invention calculate a measurement diffusion coefficient (ADC _mrs ) from each diffusion weighted image acquired with a plurality of b values including b value = 0. . Then, by correcting using the measured diffusion coefficient for each tissue (ADC _mrs) the reference diffusion coefficient (ADC _RFR) to give the correction diffusion coefficient (ADC _crt), any by using the correction diffusion coefficient (ADC _crt) b-value diffusion weighted image is calculated. Alternatively, to obtain a measurement diffusion coefficient information measurement diffusion coefficient based on the order to correct the (ADC _mrs) (ADC _mrs) correction diffusion coefficient corrected (ADC _crt), using the correction diffusion coefficient (ADC _crt) A diffusion weighted image having an arbitrary b value is calculated.

  According to the MRI apparatus and the diffusion weighted image calculation method of the present invention, an apparent diffusion coefficient (ADC) can be calculated without depending on the static magnetic field strength, and a diffusion weighted image can be calculated with an arbitrary b value. .

The figure which shows an example of the whole structure of the MRI apparatus which concerns on this invention The flowchart which shows the processing flow of Example 1 of this invention. GUI diagram used in Example 1 of the present invention The figure which shows the diffusion coefficient of Example 1 of this invention The flowchart which shows the processing flow of Example 2 of this invention. GUI diagram used in Embodiment 2 of the present invention The figure which shows the diffusion coefficient of Example 2 of this invention The flowchart which shows the processing flow of Example 3 of this invention. GUI diagram used in Example 3 of the present invention The figure which shows the example which images and displays the correction value for every pixel

  Hereinafter, preferred embodiments of the MRI apparatus of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments of the invention, and the repetitive description thereof is omitted.

  First, an overall outline of an example of an MRI apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the overall configuration of an embodiment of an MRI apparatus according to the present invention. This MRI apparatus uses a NMR phenomenon to obtain a tomographic image of a subject.As shown in FIG. 1, the MRI apparatus includes a static magnetic field generation system 2, a gradient magnetic field generation system 3, a transmission system 5, A reception system 6, a signal processing system 7, a sequencer 4, and an arithmetic processing unit (CPU) 8 are provided.

  The static magnetic field generation system 2 generates a uniform static magnetic field in the direction perpendicular to the body axis of the subject 1 in the case of the vertical magnetic field method and in the direction of the body axis of the subject 1 in the case of the horizontal magnetic field method. A permanent magnet type, normal conduction type or superconducting type static magnetic field generation source is arranged around the specimen 1.

  The gradient magnetic field generation system 3 includes a gradient magnetic field coil 9 that applies a gradient magnetic field in the three-axis directions of X, Y, and Z, which is a coordinate system (stationary coordinate system) of the MRI apparatus, and a gradient magnetic field that drives each gradient magnetic field coil. Gradient magnetic fields Gx, Gy, and Gz are applied in the X, Y, and Z axis directions by driving the gradient magnetic field power supply 10 of each coil according to a command from the sequencer 4 described later. . At the time of imaging, a slice selection gradient magnetic field pulse (Gs) is applied in a direction orthogonal to the slice plane (imaging cross section) to set a slice plane for the subject 1, and the remaining two orthogonal to the slice plane and orthogonal to each other A phase encode gradient magnetic field pulse (Gp) and a frequency encode gradient magnetic field pulse (Gf) are applied in one direction, and position information in each direction is encoded in the echo signal.

  The sequencer 4 is a control means that repeatedly applies a high-frequency magnetic field pulse (hereinafter referred to as an “RF pulse”) and a gradient magnetic field pulse in a predetermined pulse sequence, and operates under the control of the arithmetic processing unit 8 to obtain a tomographic image of the subject 1. Various commands necessary for data collection are sent to the transmission system 5, the gradient magnetic field generation system 3, and the reception system 6.

  The transmission system 5 irradiates the subject 1 with RF pulses in order to cause nuclear magnetic resonance to occur in the nuclear spins of the atoms constituting the living tissue of the subject 1, and includes a high frequency oscillator 11, a modulator 12, and a high frequency amplifier. 13 and a high frequency coil (transmission coil) 14a on the transmission side. The RF pulse output from the high-frequency oscillator 11 is amplitude-modulated by the modulator 12 at the timing according to the command from the sequencer 4, and the amplitude-modulated RF pulse is amplified by the high-frequency amplifier 13 and then placed close to the subject 1. By supplying to the high frequency coil 14a, the subject 1 is irradiated with the RF pulse.

  The receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the biological tissue of the subject 1, and receives a high-frequency coil (receiving coil) 14b on the receiving side and a signal amplifier 15 And a quadrature phase detector 16 and an A / D converter 17. After the NMR signal of the response of the subject 1 induced by the electromagnetic wave irradiated from the high frequency coil 14a on the transmission side is detected by the high frequency coil 14b arranged close to the subject 1 and amplified by the signal amplifier 15, The quadrature phase detector 16 divides the signal into two orthogonal signals at the timing according to the command from the sequencer 4, and each signal is converted into a digital quantity by the A / D converter 17 and sent to the signal processing system 7.

The signal processing system 7 performs various data processing and display and storage of processing results, and includes an external storage device such as an optical disk 19 and a magnetic disk 18, and a display 20 including a CRT or the like. When data from the reception system 6 is input to the arithmetic processing unit (CPU) 8, the arithmetic processing unit 8 executes processing such as signal processing and image reconstruction, and displays the tomographic image of the subject 1 as a result of the processing. 20 and recorded on the magnetic disk 18 of the external storage device.

  The operation unit 25 inputs various control information of the MRI apparatus and control information of processing performed in the signal processing system 7, and includes a trackball or mouse 23 and a keyboard 24. The operation unit 25 is disposed close to the display 20, and the operator controls various processes of the MRI apparatus interactively through the operation unit 25 while looking at the display 20.

  In FIG. 1, the high-frequency coil 14a and the gradient magnetic field coil 9 on the transmission side face the subject 1 in the static magnetic field space of the static magnetic field generation system 2 into which the subject 1 is inserted, in the case of the vertical magnetic field method. If the horizontal magnetic field method is used, the subject 1 is installed so as to surround it. On the other hand, the high-frequency coil 14b on the reception side is disposed so as to face or surround the subject 1. The gradient magnetic field generation system 3, the transmission system 5, the reception system 6, and the sequencer 4 are collectively referred to as a measurement control unit.

  At present, the radionuclide to be imaged by the MRI apparatus is a hydrogen nucleus (proton) which is a main constituent material of the subject as being widely used clinically. By imaging information on the spatial distribution of proton density and the spatial distribution of relaxation time in the excited state, the form or function of the human head, abdomen, limbs, etc. is imaged two-dimensionally or three-dimensionally.

Embodiments of the MRI apparatus and the diffusion weighted image calculation method of the present invention will be described below.
In the present invention, a measured diffusion coefficient (ADC _mrs ) is calculated from diffusion-weighted images acquired with a plurality of b values including b value = 0.

Then, by correcting using the measured diffusion coefficient for each tissue (ADC _mrs) the reference diffusion coefficient (ADC _RFR) to give the correction diffusion coefficient (ADC _crt), any by using the correction diffusion coefficient (ADC _crt) b-value diffusion weighted image is calculated.

Alternatively, to obtain a measurement diffusion coefficient information measurement diffusion coefficient based on the order to correct the (ADC _mrs) (ADC _mrs) correction diffusion coefficient corrected (ADC _crt), using the correction diffusion coefficient (ADC _crt) A diffusion weighted image having an arbitrary b value is calculated.

Example 1 according to the MRI apparatus and the diffusion weighted image calculation method of the present invention will be described. In Example 1, a diffusion coefficient (ADC) is calculated from diffusion weighted images acquired using a plurality of (two or more) b values including b value = 0, and the calculated diffusion coefficient (ADC) is more correct. Correction is performed using the diffusion coefficient (ADC), and a diffusion-weighted image having an arbitrary b value is calculated and displayed using the corrected diffusion coefficient (ADC). Hereinafter, the diffusion coefficient (ADC) calculated from the diffusion weighted image is referred to as a measured diffusion coefficient (ADC _mrs ), and the corrected measured diffusion coefficient (ADC _mrs ) is referred to as a corrected diffusion coefficient (ADC _crt ).

  The first embodiment will be described in detail based on the flowchart showing the processing flow of the first embodiment shown in FIG. This processing flow is stored in advance on the magnetic disk 18 as a program, and is executed by the arithmetic processing unit 8 reading the program from the magnetic disk 18 and executing it.

(Step S201)
The operator sets up the subject in the static magnetic field generation system 2. Then, the imaging condition of the diffusion weighted image capturing sequence for capturing each of the diffusion weighted images having a plurality of b values including b value = 0 and the T1 weighted image and the T2 weighted image is set via the operation unit 25. .

(Step S202)
The MRI apparatus acquires and acquires each of the diffusion-weighted images having a plurality of b values including b value = 0, the T1-weighted images, and the T2-weighted images on the same cross section of the subject under the imaging conditions set in step S201. Each image data is stored in the magnetic disk 18.

(Step S203)
The operator inputs an arbitrary b value used for calculation of the diffusion weighted image via the operation unit 25. FIG. 3 shows an example of a GUI displayed on the display 20 for accepting input of an arbitrary b value. The operator directly inputs the b value (bfactor) into the input area 301 on the GUI shown in FIG. 3 or inputs the b value (bfactor) by operating the slider bar 302.

(Step S204)
The arithmetic processing unit 8 uses the diffusion-weighted image S ₀ with b value = 0 acquired in step S202 and the diffusion-weighted image S with one b value among a plurality of b values, to measure a diffusion coefficient (ADC). _mrs ). The measurement diffusion coefficient (ADC _mrs ) is calculated according to the following equation.

here,
ADC _mrs : Measured apparent diffusion coefficient (measured diffusion coefficient)
S: b value diffusion weighted image
S ₀ : diffusion weighted image with b value = 0
b: Arbitrary b value The measurement diffusion coefficient (ADC _mrs ) is also calculated based on the above formula for the diffusion weighted image (S) of other b values. FIG. 4 shows an example 401 of the measured diffusion coefficient (ADC _mrs ) calculated with a plurality of b values.

When calculating ADC using multiple b values, substituting each set of values (b _i , S _i ) into the above equation to create the following group of equations and solving them using the least squares method, calculate.
1n (S _l ) = 1n (S ₀ ) −ADCXb ₁
1n (S ₂ ) = 1n (S ₀ ) −ADCXb ₂
...

(Step S205)
The arithmetic processing unit 8 corrects the measured diffusion coefficient (ADC _mrs ) calculated in step S204 using a reference diffusion coefficient (ADC _rfr ) prepared in advance as a more correct diffusion coefficient (ADC), and corrects diffusion. Get the coefficient (ADC _crt ). In this way, by correcting the measurement diffusion coefficient (ADC _mrs ) based on the reference diffusion coefficient (ADC _rfr ), the measurement diffusion coefficient (ADC _mrs ) does not depend on the static magnetic field strength of the MRI apparatus from which the measurement diffusion coefficient (ADC _mrs ) was obtained. A corrected diffusion coefficient (ADC _crt ) can be obtained.

  Specifically, the arithmetic processing unit 8 obtains a pixel value ratio for each pixel of the T1-weighted image, the T2-weighted image, and the diffusion-weighted image acquired in step S202. Then, the obtained ratio is compared with the ratio of the pixel value for each tissue stored in advance on the magnetic disk 18, and the tissue having the closest ratio value is determined for each pixel.

Then, the average value of the measured diffusion coefficient (ADC _mrs ) calculated in step S204 is calculated for each determined tissue, and the difference from the reference diffusion coefficient (ADC _rfr ) for each tissue prepared in advance is calculated. Finally, the difference of the calculated diffusion coefficient (ADC) corresponding to the organization of the pixel is added to the measured diffusion coefficient (ADC _mrs ) for each pixel. In this way, the arithmetic processing unit 8 _corrects the measured diffusion coefficient (ADC _mrs ) using the reference diffusion coefficient (ADC _rfr ) for each tissue to obtain a corrected diffusion coefficient (ADC _crt ). The difference in diffusion coefficient (ADC) for each pixel may be displayed on the display 20 as a diffusion coefficient (ADC) correction value image 1001, as shown in FIG.

The ratio of pixel values for each tissue and the reference diffusion coefficient (ADC _rfr ) stored in advance on the magnetic disk 18 as described above will be described later.

(Step S206)
The arithmetic processing unit 8 uses the corrected diffusion coefficient (ADC _crt ) acquired in step S205 and the arbitrary b value (bfactor) input in step S203 to generate a diffusion weighted image (S _bfactor ) of an arbitrary b value. Calculate using the following formula:

here,
ADC _crt : Corrected diffusion coefficient
S ₀ : diffusion weighted image with b value = 0
S _bfactor : diffusion-weighted image with an arbitrary b value
bfactor: any b value

(Step S207)
The arithmetic processing unit 8 displays the diffusion weighted image of the arbitrary b value calculated in step 206 on the display 20.

  The above is the description of the processing flow of the first embodiment.

Next, the ratio of pixel values for each tissue of the T1-weighted image, the T2-weighted image, and the diffusion-weighted image and the reference diffusion coefficient (ADC _rfr ), which are required to be stored in the magnetic disk 18 in advance in step S205. Will be described. In Example 1, a measurement diffusion coefficient (ADC _mrs ) calculated from a diffusion-weighted image captured by a high magnetic field (for example, any of 1.2 Tesla, 1.5 Tesla, 3 Tesla, 7 Tesla, etc.) MRI apparatus is used as a reference diffusion coefficient ( ADC _rfr ). FIG. 4 shows an example 402 of a reference diffusion coefficient (ADC _rfr ) prepared in advance.

Specifically, it is calculated as follows. A tissue is discriminated for each pixel using a T1-weighted image and a T2-weighted image captured by a high magnetic field MRI apparatus. The discrimination of the tissue for each pixel may be visually specified by the operator, or may be performed by the arithmetic processing unit 8 using a known algorithm. Then, the arithmetic processing unit 8 determines the ratio of the average value of the pixel values of the T1-weighted image and the T2-weighted image obtained by determining the tissue for each pixel and the diffusion-weighted image captured by the same high magnetic field MRI apparatus for each tissue. Calculated and stored in the magnetic disk 18. In addition, the arithmetic processing unit 8 obtains an average value for each tissue of the diffusion coefficient (ADC) calculated from the diffusion weighted image captured by the high magnetic field MRI apparatus, and uses the magnetic field as a reference diffusion coefficient (ADC _rfr ) for each tissue. Save to disk 18.

As described above, in the first embodiment of the present invention, the arithmetic processing unit 8 calculates a measured diffusion coefficient (ADC _mrs ) from a plurality of (two or more) b-value diffusion weighted images including b value = 0, the measured diffusion coefficient for each tissue (ADC _mrs) corrected using the reference diffusion coefficient (ADC _RFR) to give the correction diffusion coefficient (ADC _crt) with any b value using the correction diffusion coefficient (ADC _crt) Is calculated. As a result, a more accurate diffusion-weighted image having an arbitrary b value can be calculated without depending on the static magnetic field strength. In particular, it is possible to obtain a diffusion-weighted image equivalent to that of a high-field MRI device even when it is difficult to capture a diffusion-weighted image with a high b value with a low-field MRI device that does not have a high-output gradient magnetic field power supply .

A second embodiment according to the MRI apparatus and the diffusion weighted image calculation method of the present invention will be described. In Example 2, a measurement diffusion coefficient (ADC _mrs ) is calculated from a diffusion weighted image acquired using a b value of 2 or more, a reference diffusion coefficient (ADC _rfr ) as a correction reference is selected, and the selected reference diffusion The measurement diffusion coefficient (ADC _mrs ) is corrected using the coefficient (ADC _rfr ), and a diffusion weighted image is calculated using the corrected diffusion coefficient (ADC _crc ) obtained by the correction and an arbitrary b value.

  FIG. 5 is a flowchart showing the processing flow of the embodiment 2 of the present invention. This processing flow is stored in advance on the magnetic disk 18 as a program, and is executed by the arithmetic processing unit 8 reading the program from the magnetic disk 18 and executing it. Hereinafter, each step of FIG. 5 will be described in detail. The same steps as those in the first embodiment are denoted by the same step symbols, and the description thereof is omitted.

(Steps S201 to S204)
Same as Example 1.

(Step S301)
Processing unit 8, a plurality of reference spreading factor which had been prepared beforehand by selecting a reference spreading factor of interest from the _{(ADC rfr) (ADC rfr)} , the selected criteria diffusion coefficient (ADC _RFR) Based on the above, the measured diffusion coefficient (ADC _mrs ) calculated in step S204 is corrected to obtain a corrected expansion coefficient (ADC _crc ).

FIG. 6 shows an example of a GUI used for selecting the reference diffusion coefficient (ADC _rfr ). The operator can input an arbitrary b value by dragging the horizontal axis 601 of the two orthogonal axes displayed on the cDWI image with the trackball or the mouse 23, and the vertical axis 602 with the trackball or the mouse 23. An arbitrary reference selection coefficient (ADC _rfr ) can be selected by _dragging .

As the reference selection coefficient (ADC _rfr ), for example, the diffusion coefficient (ADC) acquired with an MRI apparatus having a static magnetic field strength such as 1.2 Tesla, 1.5 Tesla, 3 Tesla, and 7 Tesla can be used. The coefficient (ADC _rfr ) is stored in advance on the magnetic disk 18. FIG. 7 shows an example of each diffusion coefficient. A dotted line 701 indicates the diffusion coefficient (ADC) acquired by the 1.5 Tesla MRI apparatus, and a dashed line 702 indicates the diffusion coefficient (ADC) acquired by the 3 Tesla MRI apparatus.

Then, when the target reference diffusion coefficient (ADC _rfr ) is selected from a plurality of reference diffusion coefficients (ADC _rfr ) by the operator via the GUI as shown in FIG. 6, the arithmetic processing unit 8 _Corrects the measured diffusion coefficient (ADC _mrs ) based on the selected reference diffusion coefficient (ADC _rfr ) to obtain a corrected diffusion coefficient (ADC _crt ). The correction method is the same as in the first embodiment.

In Example 2, as described in Step S205 of Example 1 above, the difference in diffusion coefficient (ADC) for each pixel determined based on the reference diffusion number (ADC _rfr ) selected as described above. 11 may be displayed on the display 20 as a diffusion coefficient (ADC) correction value image 1101 as shown in FIG.

(Step S302)
The arithmetic processing unit 8 calculates a diffusion weighted image using the corrected diffusion coefficient (ADC _crt ) calculated in step S301 and the arbitrary b value set in step S203. The calculation method is the same as in Example 1.

(Step S206)
Same as Example 1.

  The above is the description of the processing flow of the second embodiment.

As described above, in the second embodiment of the present invention, the arithmetic processing unit 8 calculates a measurement diffusion coefficient (ADC _mrs ) using a plurality of (two or more) b-value diffusion weighted images including b value = 0. _{Correcting the} measured diffusion coefficient (ADC _mrs ) using a reference diffusion coefficient (ADC _rfr ) selected from among a plurality of reference diffusion coefficients (ADC _rfr ) to obtain a corrected diffusion coefficient (ADC _crt ) A diffusion-weighted image having an arbitrary b value is calculated using the diffusion coefficient (ADC _crt ). As a result, as in the first embodiment, a more accurate diffusion-weighted image having an arbitrary b value can be calculated without depending on the static magnetic field strength. In particular, since the reference diffusion coefficient (ADC _rfr ) used for correction is selected, a diffusion-weighted image equivalent to a high magnetic field MRI apparatus having an arbitrary static magnetic field strength can be obtained.

A third embodiment according to the MRI apparatus and the diffusion weighted image calculation method of the present invention will be described. In Example 3, 2 or more to calculate a measured diffusion coefficient from the diffusion-weighted images of the b value (ADC _mrs), the correction diffusion coefficient by correcting the measured diffusion coefficient (ADC _mrs) by the operator's input (ADC _crt) A diffusion weighted image is calculated using the corrected diffusion coefficient (ADC _crc ) obtained by the correction and an arbitrary b value.

  FIG. 8 is a flowchart showing a process flow of the third embodiment of the present invention. This processing flow is stored in advance on the magnetic disk 18 as a program, and is executed by the arithmetic processing unit 8 reading the program from the magnetic disk 18 and executing it. Hereinafter, each step of FIG. 8 will be described in detail.

(Steps S201 to S204)
Same as Example 1.

(Step S401)
The operator inputs information for correcting the measured diffusion coefficient (ADC _mrs ) calculated in S204 via the operation unit 25. Then, the arithmetic processing unit 8 corrects the measured diffusion coefficient (ADC _mrs ) based on the input information to obtain a corrected diffusion coefficient (ADC _crt ). An example of a GUI for this purpose is shown in FIG. The arithmetic processing unit 8 displays a graph 901 of the measured diffusion coefficient (ADC _mrs ) on the display 20. Then, the operator corrects the shape of the graph 901 of the measured diffusion coefficient (ADC _mrs ) via the operation unit 25, and the arithmetic processing unit 8 corrects the corrected diffusion coefficient (ADC _crt ) based on the corrected graph shape 902. Ask for.

(Step S402)
The arithmetic processing unit 8 calculates a diffusion weighted image using the corrected diffusion coefficient (ADC _crt ) calculated in step S401 and the arbitrary b value set in step S203. The calculation method is the same as in Example 1.

(Step S206)
Same as Example 1.

  The above is the description of the processing flow of the third embodiment.

As described above, in the third embodiment of the present invention, the GUI for receiving information for correcting the measurement diffusion coefficient (ADC _mrs ) is displayed, and the arithmetic processing unit 8 is based on the information input via the GUI. correcting the measured diffusion coefficient (ADC _mrs) to give the correction diffusion coefficient (ADC _crt) and to calculate the diffusion weighted image of any b value using the correction diffusion coefficient (ADC _crt). As a result, as in the first and second embodiments, the degree of diffusion in the diffusion weighted image can be enhanced without depending on the static magnetic field strength, and diagnosis can be facilitated.

  As mentioned above, although the Example of this invention was described, it cannot be overemphasized that this invention is not limited to these.

  1 subject, 2 static magnetic field generation system, 3 gradient magnetic field generation system, 4 sequencer, 5 transmission system, 6 reception system, 7 signal processing system, 8 arithmetic processing unit (CPU), 9 gradient magnetic field coil, 10 gradient magnetic field power supply, 11 High-frequency oscillator, 12 modulator, 13 high-frequency amplifier, 14a high-frequency coil (transmitting coil), 14b high-frequency coil (receiving coil), 15 signal amplifier, 16 quadrature detector, 17 A / D converter, 18 magnetic disk, 19 Optical disc, 20 display, 23 trackball or mouse, 24 keyboard

Claims (10)

A static magnetic field generator for generating a uniform static magnetic field in a space for accommodating a subject;
In accordance with a diffusion weighted sequence, a measurement control unit that detects an NMR signal generated from the subject by applying an MPG having an arbitrary b value including b value = 0 to the subject;
An arithmetic processing unit for acquiring a diffusion weighted image for each b value from the detected NMR signal;
A magnetic resonance imaging apparatus comprising:
The arithmetic processing unit, the calculated measurement diffusion coefficient _{(ADC mrs)} from the diffusion weighted image, correction diffusion coefficient is corrected using the measured diffusion coefficient for each tissue _{(ADC mrs)} the reference diffusion coefficient _{(ADC RFR)} A magnetic resonance imaging apparatus characterized in that (ADC _crt ) is obtained, and a diffusion weighted image having an arbitrary b value is calculated using the corrected diffusion coefficient (ADC _crt ). The magnetic resonance imaging apparatus according to claim 1.
The reference diffusion coefficient (ADC _rfr ) is obtained from a diffusion weighted image obtained with a static magnetic field strength of 1.2 Tesla, 1.5 Tesla, 3 Tesla, or 7 Tesla. Magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 1 or 2,
The arithmetic processing unit _obtains a difference between an average value of the measured diffusion coefficient (ADC _mrs ) for each tissue and the reference diffusion coefficient (ADC _rfr ) for each tissue, and the difference corresponding to the tissue of the pixel for each pixel. _Is added to the measured diffusion coefficient (ADC _mrs ) to obtain the corrected diffusion coefficient (ADC _crt ). The magnetic resonance imaging apparatus according to claim 3.
A magnetic resonance imaging apparatus, wherein a difference between an average value of measured diffusion coefficients (ADC _mrs ) for each tissue and a reference diffusion coefficient (ADC _rfr ) for each tissue is displayed as an image. The magnetic resonance imaging apparatus according to any one of claims 1 to 4,
The arithmetic processing unit obtains the corrected diffusion coefficient (ADC _crt ) using a reference diffusion coefficient (ADC _rfr ) selected from among the plurality of reference diffusion coefficients (ADC _rfr ) obtained with different static magnetic field strengths. A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 5.
A magnetic resonance imaging apparatus for displaying a GUI for _receiving selection of one reference diffusion coefficient (ADC _rfr ) from among the plurality of reference diffusion coefficients (ADC _rfr ). The magnetic resonance imaging apparatus according to any one of claims 1 to 6,
A magnetic resonance imaging apparatus comprising storage means for storing the reference diffusion coefficient (ADC _rfr ) for each tissue. The magnetic resonance imaging apparatus according to any one of claims 1 to 7 ,
A magnetic resonance imaging apparatus for displaying a GUI for receiving an input of the arbitrary b value. A static magnetic field generator for generating a uniform static magnetic field in a space for accommodating a subject;
In accordance with a diffusion weighted sequence, a measurement control unit that detects an NMR signal generated from the subject by applying an MPG having an arbitrary b value including b value = 0 to the subject;
An arithmetic processing unit for acquiring a diffusion weighted image for each b value from the detected NMR signal;
A diffusion-weighted image calculation method in a magnetic resonance imaging apparatus comprising:
Calculating a measured diffusion coefficient (ADC _mrs ) from the diffusion weighted image;
Correcting the measured diffusion coefficient (ADC _mrs ) for each tissue using a reference diffusion coefficient (ADC _rfr ) to obtain a corrected diffusion coefficient (ADC _crt );
And calculating a diffusion-weighted image having an arbitrary b value using the corrected diffusion coefficient (ADC _crt ). 10. The diffusion weighted image calculation method according to claim 9 , wherein the step of obtaining the corrected diffusion coefficient (ADC _crt ) includes:
_Obtaining an average value of the measured diffusion coefficient (ADC _mrs ) for each tissue of the diffusion weighted image;
_Determining a difference between an average value of the measured diffusion coefficient (ADC _mrs ) for each tissue and the reference diffusion coefficient (ADC _rfr ) for each tissue;
_{Adding the} difference to the measured diffusion coefficient (ADC _mrs ) for each tissue to obtain the corrected diffusion coefficient (ADC _crt ).

Images