JP6230882B2 - Magnetic resonance imaging apparatus and echo time setting method - Google Patents

Description

  The present invention measures nuclear magnetic resonance (hereinafter referred to as `` NMR '') signals from hydrogen, phosphorus, etc. in a subject and images nuclear density distribution, relaxation time distribution, etc. In particular, the present invention relates to gradient magnetic field pulse application control.

  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, 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.

  The specimen includes water tissue and adipose tissue. The NMR signal from the hydrogen proton of the water tissue (hereinafter abbreviated as water signal) and the NMR signal from the hydrogen proton of the adipose tissue (hereinafter abbreviated as fat signal). ) Nuclear magnetic resonance frequencies differ by 3.5 ppm.

  Therefore, in clinical practice, an image in which an NMR signal from a fat tissue is suppressed is often required, and various methods for obtaining an image in which an fat signal is suppressed have been put into practical use. As an example, there is a method in which a plurality of images having different echo times (TE) are acquired and a water / fat separated image is obtained by calculation between NMR signals or images.

  This is generally called the Dixon method, and two measurements are made as one set by the SE (spin echo) method or GrE (gradient echo) method, and the phase of the water signal and fat signal is the same (below) , Referred to as `` In-Phase ''), and the other time, the phase of both signals is a difference of π (180 °) (hereinafter referred to as `` Out-of-Phase '') Set to echo time (TE) and measure each. By performing these two sets of measurements as many times as the number of phase encoding necessary for image creation, and adding or subtracting two acquired measurement data or two images respectively obtained from each measurement data A water image that is an image mainly including a water signal and a fat image that is an image mainly including a fat signal are obtained.

  The time τ when the phase difference between the water signal and the fat signal is π is inversely proportional to the static magnetic field strength, and the shorter the stronger the static magnetic field strength is. For example, 1.5T is about 2.24 msec, and 3.0T is about 1.12 msec.

  On the other hand, in the case of water / fat separation measurement using a GrE sequence, the echo time (TE) setting is generally controlled so that a value deviating from the optimum value for water / fat separation measurement is not set. It is. For example, the echo time (TE) is fixed at a value such that the water signal and fat signal are in-phase and out-of-phase, so that selection by the operator is impossible, or it is automatically performed according to the imaging conditions. Set the echo time (TE) on the device side to be In-Phase or Out-of-Phase.

  Alternatively, instead of being able to set a value other than the optimum value, a method (Patent Document 1) that enables water / fat separation measurement by calculating a phase-corrected image from the obtained image by complex calculation Proposed.

International Publication No. 2011/108314

  However, in the conventional GrE-based water / fat separation measurement based on the Dixon method, if the echo time (TE) cannot be input, it may not be possible to obtain an image having the contrast desired by the operator. Alternatively, even if the echo time (TE) can be input, the operator must calculate and set the echo time (TE) in advance so as to be in-phase and out-of-phase.

  In addition, even if measurement is possible with an echo time (TE) other than the optimal values for In-Phase and Out-of-Phase, in order to perform water / fat separation stably, as in (Patent Document 1) Therefore, it is necessary to reconstruct by performing a complicated operation between images.

  Therefore, the present invention has been made in view of the above problems, and the problem to be solved is that a pulse sequence is obtained in order to obtain an image of a target contrast in separation measurement of a plurality of tissues based on the Dixon method in an MRI apparatus. It is possible to input echo time (TE), and easily obtain separated images of multiple tissues without reconstructing with complicated calculation by using signals deviated from In-Phase and Out-of-Phase. .

  In order to solve the above problems, the present invention accepts an input of an echo time of a pulse sequence by an operator, and based on the input echo time by the operator, an intermediate value between the Out-of-Phase time and the In-Phase time. An intermediate value closest to the input echo time is obtained as a corrected echo time from a plurality of possible intermediate values, and the corrected echo time is set as an echo time of the pulse sequence.

  If the echo time of the pulse sequence is set in this way, the echo time should be an intermediate value between the Out-of-Phase time and the In-Phase time, so the Out time is set based on the set echo time. -of-Phase time and In-Phase time are calculated, Out-of-Phase echo signal is measured at Out-of-Phase time, and In-Phase echo signal is measured at In-Phase time. Become.

  According to the MRI apparatus and gradient magnetic field application control method of the present invention, in the separation measurement of a plurality of tissues based on the Dixon method in the MRI apparatus, the operator inputs an echo time (TE) of a pulse sequence to obtain a target contrast. Therefore, it is possible to easily obtain a separated image of a plurality of tissues without reconstructing with complicated calculation by using a signal shifted from In-Phase or Out-of-Phase.

The block diagram which shows the whole structure of one Example of the MRI apparatus which concerns on this invention An RF pulse (RF) and an echo signal (Echo) which is an echo signal from the subject based on the application of the RF pulse to the subject and is measured by reversal of the gradient magnetic field are displayed along the time axis. Figure Functional block diagram showing each function of the arithmetic processing unit 114 Flowchart showing the processing flow of the first embodiment Flowchart showing the processing flow of the second embodiment Figure showing an example of the echo time (TE) setting GUI

  Hereinafter, preferred embodiments of the MRI apparatus of the present invention will be described in detail with reference to the accompanying drawings. In all the drawings for explaining the embodiments of the invention, those having the same function are given the same reference numerals, and their repeated explanation is omitted.

  First, 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 101. As shown in FIG. 1, a static magnetic field generating magnet 102, a gradient magnetic field coil 103, a gradient magnetic field power supply 109, and an RF transmission coil 104 and RF transmitter 110, RF receiver coil 105 and signal processor 107, measurement control unit 111, overall control unit 112, display / operation unit 118, and top plate on which the subject 101 is mounted generates a static magnetic field. And a bed 106 to be taken in and out of the magnet 102.

  The static magnetic field generating magnet 102 generates a uniform static magnetic field in the direction perpendicular to the body axis of the subject 101 in the vertical magnetic field method and in the body axis direction in the horizontal magnetic field method. A permanent magnet type, normal conducting type or superconducting type static magnetic field generating source is arranged around the.

  The gradient magnetic field coil 103 is a coil wound in the three-axis directions of X, Y, and Z that are the real space coordinate system (stationary coordinate system) of the MRI apparatus, and each gradient magnetic field coil is a gradient magnetic field that drives it. A current is supplied to the power source 109. Specifically, the gradient magnetic field power supply 109 of each gradient coil is driven according to a command from the measurement control unit 111 described later, and supplies a current to each gradient coil. Thereby, gradient magnetic fields Gx, Gy, and Gz are generated in the three-axis directions of X, Y, and Z.

  When imaging a two-dimensional slice plane, a slice 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 101, orthogonal to the slice plane and orthogonal to each other. Phase encoding gradient magnetic field pulse (Gp) and frequency encoding (reading) gradient magnetic field pulse (Gf) are applied in the remaining two directions, and position information in each direction is encoded in the nuclear magnetic resonance signal (echo signal). The

  The RF transmission coil 104 is a coil that irradiates the subject 101 with an RF pulse, and is connected to the RF transmission unit 110 and supplied with a high-frequency pulse current. As a result, an NMR phenomenon is induced in the nuclear spin constituting the biological tissue of the subject 101. Specifically, the RF transmission unit 110 is driven in accordance with a command from the measurement control unit 111 (to be described later), amplitude-modulates and amplifies the high-frequency pulse, and then the RF transmission unit 104 is placed near the subject 101 after being amplified. By supplying, the subject 101 is irradiated with the RF pulse.

  The RF receiving coil 105 is a coil that receives an echo signal emitted by the NMR phenomenon of spin that constitutes the living tissue of the subject 101, and is connected to the signal processing unit 107 so that the received echo signal is sent to the signal processing unit 107. Sent.

  The signal processing unit 107 performs detection processing of the echo signal received by the RF receiving coil 105. Specifically, in accordance with a command from the measurement control unit 111 described later, the signal processing unit 107 amplifies the received echo signal and divides it into two orthogonal signals by quadrature detection, For example, 128, 256, 512, etc.) are sampled, and each sampling signal is A / D converted into a digital quantity. Therefore, the echo signal is obtained as time-series digital data (hereinafter referred to as echo data) composed of a predetermined number of sampling data. Then, the signal processing unit 107 performs various processes on the echo data, and sends the processed echo data to the measurement control unit 111.

  The measurement control unit 111 mainly transmits various commands for collecting echo data necessary for reconstruction of the tomographic image of the subject 101 to the gradient magnetic field power source 109, the RF transmission unit 110, and the signal processing unit 107. And a control unit for controlling them. Specifically, the measurement control unit 111 operates under the control of the overall control unit 112 described later, and the gradient magnetic field power source 109, the RF transmission unit 110, and the signal processing unit 107 are controlled based on control data of a predetermined pulse sequence. Control to repeatedly perform the irradiation of the RF pulse and the application of the gradient magnetic field pulse to the subject 101 and the detection of the echo signal from the subject 101 to reconstruct an image of the imaging region of the subject 101 Control the collection of required echo data. In the repetition, the application amount of the phase encoding gradient magnetic field is changed in the case of two-dimensional imaging, and the application amount of the slice encoding gradient magnetic field is further changed in the case of three-dimensional imaging. Values such as 128, 256, and 512 are normally selected as the number of phase encodings, and values such as 16, 32, and 64 are normally selected as the number of slice encodings. With these controls, echo data from the signal processing unit 107 is output to the overall control unit 112.

  The overall control unit 112 controls the measurement control unit 111 and controls various data processing and processing result display and storage, and includes an arithmetic processing unit (CPU) 114, a memory 113, and a magnetic disk. And the like, and a network IF 116 that interfaces with an external network. Further, an external storage unit 117 such as an optical disk may be connected to the overall control unit 112.

  Specifically, when the measurement control unit 111 collects echo data by executing an imaging sequence and the echo data is input from the measurement control unit 111, the arithmetic processing unit 114 converts the encoded information applied to the echo data. Based on this, it is stored in an area corresponding to the k space in the memory 113. Hereinafter, the statement that the echo data is arranged in the k space means that the echo data is stored in an area corresponding to the k space in the memory 113. A group of echo data stored in an area corresponding to the k space in the memory 113 is also referred to as k space data.

  Then, the arithmetic processing unit 114 performs processing such as signal processing and image reconstruction by Fourier transform on the k-space data, and displays the resulting image of the subject 101 on the display / operation unit 118 described later. The data is recorded in the internal storage unit 115 or the external storage unit 117, or transferred to an external device via the network IF 116.

  The display / operation unit 118 includes a display unit for displaying the reconstructed image of the subject 101, a trackball or a mouse and a keyboard for inputting various control information of the MRI apparatus and control information for processing performed by the overall control unit 112. Etc., and an operation unit. The operation unit is disposed in the vicinity of the display unit, and an operator interactively controls various processes of the MRI apparatus through the operation unit while looking at the display 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.

  The present invention relates to separation measurement of a plurality of tissues based on the Dixon method in an MRI apparatus. More specifically, the present invention relates to a pulse sequence echo time (TE) setting method based on the Dixon method. Therefore, in the following description, water / fat separation measurement will be described as an example. However, the present invention is not limited to water / fat separation measurement, and can be similarly applied when obtaining an image in which a plurality of tissues having different nuclear magnetic resonance frequencies are mixed, and separating them. it can.

<Outline of water / fat separation measurement>
The water / fat separation measurement using the GrE sequence based on the Dixon method according to the present invention will be described.

  In water / fat separation measurement using the GrE system sequence based on the Dixon method, the phase of the water signal and fat signal generated after the water tissue and fat tissue are simultaneously excited by the RF pulse is the elapsed time from the application of the RF pulse. Depending on. In order to acquire a water image and a fat image, an In-Phase image is obtained based on an echo signal measured at an elapsed time when the phase difference between the water signal and the fat signal becomes zero (hereinafter abbreviated as In-Phase time). Are acquired on the basis of echo signals measured at different elapsed times (hereinafter, abbreviated as Out-of-Phase times). Then, a water image mainly including a water signal and a fat image mainly including a fat signal are obtained by calculation between the In-Phase image and the Out-of-Phase image. These In-Phase time and Out-of-Phase time differ depending on the strength of the static magnetic field, and are discontinuous values that are an integral multiple of the initial (minimum) Out-of-Phase time.

  Next, an outline of a GrE water / fat separation sequence based on the Dixon method according to the present invention will be described with reference to FIG. FIG. 2 shows an RF pulse (RF) and an echo signal (Echo) which is an echo signal from the subject based on application of the RF pulse to the subject and is measured by reversal of the gradient magnetic field on the time axis. It is the figure displayed collectively. In FIG. 2, the gradient magnetic field pulse is not shown.

  From the application of the RF pulse 201, the echo signal 202 that appears in the Out-of-Phase time in which the water signal and the fat signal are out of phase (Out-of-Phase), and the water signal and the fat signal are in phase (In -Echo signal 203 appearing at the In-Phase time of (Phase) and alternately appear at every first (minimum) Out-of-Phase time τ204. Each echo signal 202, 203 is a gradient echo obtained by reversing the polarity of the gradient magnetic field.

In the present invention, among the adjacent intermediate values 205 of Out-of-Phase time and In-Phase time, the intermediate value 205 nearest to the input echo time (input TE) input by the operator is corrected echo time. (Correction TE) is obtained, and the correction TE is set to the echo time (TE) of the pulse sequence. Thereby, the operator can set the optimal echo time (TE) for realizing the contrast expected with the input TE with the water / fat separated image.
Hereinafter, each example about the calculation method of correction TE is described in detail.

<< Example 1 >>
Next, a first embodiment of the MRI apparatus and the echo time setting method of the present invention will be described. In the first embodiment, a correction TE closest to the input TE input by the operator is obtained based on a predetermined calculation formula, and the obtained correction TE is set as an echo time (TE) of the pulse sequence.

<Outline of Echo Time Setting Method of Example 1>
First, an outline of the echo time setting method according to the first embodiment will be described.

  The operator tries to set the echo time (TE) of the pulse sequence to a desired value in order to obtain an image with a desired contrast. In the case of water / fat separation measurement, this echo time (TE) should be set to an intermediate value (average value) between the In-Phase time and the Out-of-Phase time. However, as described above, since the In-Phase time and Out-of-Phase time can only take discontinuous values, the echo time in the case of water / fat separation measurement using a GrE system sequence based on the Dixon method ( TE) cannot be set arbitrarily. As a result, an image having a contrast desired by the operator may not be obtained.

  Therefore, in the first embodiment, the echo time (TE) of the pulse sequence is set as close as possible to the echo time desired by the operator under the constraints of the In-Phase time and the Out-of-Phase time. Specifically, among the adjacent In-Phase time and Out-of-Phase time and their intermediate value (average value), the intermediate value nearest to the input TE input by the operator is obtained as a corrected TE, The obtained correction TE is set as an echo time (TE) of the pulse sequence.

The above will be described in detail using mathematical expressions as follows. That is, the minimum value of the Out-of-Phase time in which the phase of the water signal and the phase of the fat signal are different by τ, and the correction as described above is performed according to the input TE input by the operator using the equation (1). Ask for TE. That means
y = 1.5 × τ + 2.0 × τ × n (n: integer greater than or equal to 0) (1)
Among the values y obtained in step (1), y closest to the input TE is obtained as a corrected TE.

For this purpose, first, when x is determined in equation (1) and x is obtained, equation (2) is obtained.

Next, assuming that y is an input TE, the following equation (3) is obtained.

(x: integer greater than or equal to 0. rounded off after decimal point)
The value obtained by rounding off the decimal part of x obtained from equation (3) to an integer is defined as [x]. The value of y obtained by substituting the obtained [x] into the equation (1) is set as a corrected TE.
Modified TE = 1.5 × τ + 2.0 × τ × [x] (4)
By obtaining a corrected TE close to the input TE as described above and using the echo time (TE) of the pulse sequence, a water image, a fat image, or a composite image thereof having a contrast close to that expected by the input TE is obtained. Can be obtained.

<Each function of Example 1>
Next, each function of the arithmetic processing unit 114 for realizing the MRI apparatus and the echo time setting method of the first embodiment will be described based on the functional block diagram shown in FIG. The arithmetic processing unit 114 according to the first embodiment includes an imaging parameter setting unit 301, an echo time candidate calculation unit 302, a modified echo time setting unit 303, and a measurement timing setting unit 304.

  The imaging parameter setting unit 301 displays an imaging parameter setting GUI (Graphical User Interface) on the display unit 118, and accepts input settings of imaging parameter values by the operator. This imaging parameter includes an echo time (TE). The imaging parameter setting unit 301 notifies the echo time candidate calculation unit 302 of the echo time (TE) input by the operator via the setting GUI as the input TE described above. When a corrected TE is notified from a corrected echo time setting unit 303 described later, the corrected TE is set as the echo time (TE) instead of the input TE. Then, an out-of-phase time for measuring the out-of-phase echo signal and an in-phase time for measuring the in-phase echo signal are notified from the measurement timing setting unit 304 described later. Then, the imaging parameters of the GrE system sequence are set so that echo signals are measured at the Out-of-Phase time and the In-Phase time, respectively.

  The echo time candidate calculation unit 302 obtains the value of the minimum Out-of-Phase time τ at which the phase difference between the water signal and the fat signal is π each time, or calculates the value in advance, or calculates the internal storage unit 115 in advance. Get the value stored in.

In any case, the minimum Out-of-Phase time τ can be obtained from a predetermined static magnetic field strength (B ₀ ) and a chemical shift (σ = 3.5 ppm) between water tissue and adipose tissue. it can. Specifically, the minimum time τ can be calculated by the following equation (5).
τ = 1 / (2γB ₀ σ) (5)
Here, γ is a magnetic rotation ratio. Then, the echo time candidate calculation unit 302 is based on the minimum Out-of-Phase time τ obtained based on the equation (5) and the input TE notified from the imaging parameter setting unit 301, as described above ( Using the equations (1) to (4), the correction TE is calculated and notified to the correction echo time setting unit 303.

  The correction echo time setting unit 303 notifies the imaging parameter setting unit 301 and the measurement timing setting unit 304 of the correction TE notified from the echo time candidate calculation unit 302, and inputs it to the imaging parameter setting GUI of the display unit 118. Replace the displayed input TE with the modified TE.

The measurement timing setting unit 304 obtains the Out-of-Phase time immediately before the correction TE and the In-Phase time immediately after the correction TE based on the correction TE notified from the correction echo time setting unit 303. In particular,
Out-of-Phase time immediately before the corrected TE = corrected TE-τ / 2
In-Phase time immediately after correction TE = Correction TE + τ / 2 (6)
And

  The Out-of-Phase time immediately before the modified TE is the Out-of-Phase time for measuring the Out-of-Phase echo signal, and the In-Phase time immediately after the modified TE is the In-Phase echo signal. This is the In-Phase time for measurement.

<Processing flow of Example 1>
Next, a processing flow performed by the above-described functional units in cooperation with each other for realizing the MRI apparatus and the echo time setting method of the first embodiment will be described based on the flowchart shown in FIG. This processing flow is stored in advance in the internal storage unit 115 as a program, and is executed by the arithmetic processing unit 114 reading the program from the internal storage unit 115 and executing it. Hereinafter, the processing contents of each processing step will be described in detail.

  In step 401, the imaging parameter setting unit 301 displays an imaging parameter setting GUI (Graphical User Interface) on the display unit 118, and accepts input settings of imaging parameter values by the operator. In particular, the input of the echo time (TE) of the pulse sequence is accepted, and the input echo time (TE) is set as the input TE.

  Alternatively, when the input TE input / displayed in the imaging parameter setting GUI is replaced with the corrected TE in step 404 described later, and the operator further changes the replaced corrected TE, the input after the change is made. Let the value be the new input TE.

  In step 402, the echo time candidate calculation unit 302 obtains the value of the minimum Out-of-Phase time τ at which the phase difference between the water signal and the fat signal becomes π, or obtains the internal storage unit 115. Get the value stored in.

  In step 403, the echo time candidate calculation unit 302 determines whether the input TE input in step 401 or the input TE corrected in step 405 and the value of the minimum Out-of-Phase time τ acquired in step 402 are Based on this, a corrected TE is calculated. The details of the calculation of the corrected TE are as described above.

  In step 404, the correction echo time setting unit 303 notifies the imaging parameter setting unit 301 of the correction TE calculated in step 403, and the input TE that is input and displayed in the imaging parameter setting GUI of the display unit 118. Replace with a modified TE. Then, the imaging parameter setting unit 301 sets the notified modified TE instead of the input TE as the echo time (TE) of the pulse sequence.

  In addition, the measurement timing setting unit 304 uses the set correction TE to set the Out-of-Phase time and In-Phase for measuring the Out-of-Phase echo signal based on Equation (6). The In-Phase time for measuring the echo signal is obtained and notified to the imaging parameter setting unit 301.

  Then, the imaging parameter setting unit 301 sets the imaging parameters of the GrE sequence so that echo signals are measured at the Out-of-Phase time and the In-Phase time, respectively.

  In step 405, the imaging parameter setting unit 301 determines whether or not the operator has corrected the echo time (TE) replaced with the correction TE again. If the operator does not correct the echo time (TE) again (No), the replaced correction TE is directly set as the echo time (TE) of the pulse sequence, and the process proceeds to step 406. If the operator corrects the echo time (TE) again (Yes), the process proceeds to step 403 using the corrected input echo time as the input TE.

In step 406, the measurement control unit 111 executes the water / fat separation sequence based on the value of the imaging parameter set in step 401, including the echo time (TE) replaced with the correction TE in step 404, The arithmetic processing unit 114 obtains a water image and a fat image based on the measured echo signal.
The above is the outline of the processing flow of the first embodiment.

  As described above, the MRI apparatus and echo time setting method of the first embodiment are closest to the input TE input by the operator based on a predetermined calculation formula in water / fat separation measurement based on the Dixon method in the MRI apparatus. The corrected TE is obtained, and the obtained corrected TE is set as the echo time (TE) of the pulse sequence. As a result, the operator can input the echo time (TE) of the pulse sequence to obtain the desired contrast, and easily obtain a water / fat separation image by the same calculation as the conventional water / fat separation calculation. be able to.

<< Example 2 >>
Next, a second embodiment of the MRI apparatus and the echo time setting method of the present invention will be described. In the above-described first embodiment, the nearest corrected TE is obtained for the input TE input by the operator based on a predetermined calculation formula. However, in the second embodiment, the adjacent Out-of-Phase time and In-Phase time are calculated. And the intermediate value (average value), and the nearest intermediate value is selected for the input TE input by the operator, and the selected intermediate value is used as the correction TE for the echo time (TE) of the pulse sequence. Set.

<Outline of Echo Time Setting Method of Example 2>
First, an outline of the echo time setting method according to the second embodiment will be described.

  As described above, the Out-of-Phase time and In-Phase time are values that are uniquely determined once the static magnetic field strength is determined, and the Out-of-Phase time τ determined by Equation (5) is used as the unit. Since -of-Phase and In-Phase appear alternately, multiple combinations of adjacent Out-of-Phase time and In-Phase time and their intermediate value (average value) are calculated in advance. . When the operator inputs the echo time (TE) of the pulse sequence for obtaining a desired contrast as the input TE, the adjacent Out-of-Phase time and In-Phase time calculated in advance and their time An intermediate value closest to the input TE is selected from among a plurality of sets of intermediate values (average values), and is set as a corrected TE. Then, the echo time (TE) value of the pulse sequence is replaced with the corrected TE value from the input TE value.

The value of the combination of adjacent Out-of-Phase time and In-Phase time and their intermediate value (average value) is k (k is a natural number)
Out-of-Phase time [k] = (2k−1) τ
In-Phase time [k] = 2kτ
Intermediate value [k] = (2k−1 / 2) τ (6)
It becomes. For example, when the static magnetic field strength is 1.5T, the k-th set values are as follows.

(Out-of-Phase time, In-Phase time, intermediate value) [1] = (2.24, 4.48, 3.36)
(Out-of-Phase time, In-Phase time, intermediate value) [2] = (6.72, 8.96, 7.84)
(Out-of-Phase time, In-Phase time, intermediate value) [3] = (11.20, 13.44, 12.32)
In addition, when the static magnetic field strength is 3.0T,
(Out-of-Phase time, In-Phase time, intermediate value) [1] = (1.12, 2.24, 1.68)
(Out-of-Phase time, In-Phase time, intermediate value) [2] = (3.36, 4.48, 3.92)
(Out-of-Phase time, In-Phase time, intermediate value) [3] = (5.60, 6.72, 6.16)
It becomes. These calculated values for each set are stored in the internal storage unit 115. Then, an intermediate value [k] closest to the input TE input by the operator as the echo time (TE) of the pulse sequence is selected, and the selected intermediate value [k] is set as the corrected TE.

<Each function and processing flow of Example 2>
The configuration of each function of the arithmetic processing unit 114 for realizing the MRI apparatus and the echo time setting method of the second embodiment is the same as that of the first embodiment, but the processing content of the echo time candidate calculating unit 302 is the same as that described above. Different from Example 1. Further, the processing flow performed in cooperation by the functional units of the second embodiment is partly different from the processing flow of the first embodiment shown in FIG. 4 and is the flowchart shown in FIG. That is, in the second embodiment, the process of step 502 is performed instead of the process of step 402, and the process of step 503 is performed instead of the process of step 403. Similar to the first embodiment, this processing flow is stored in advance in the internal storage unit 115 as a program, and is executed by the arithmetic processing unit 114 reading the program from the internal storage unit 115 and executing it. Hereinafter, the processing contents of steps 502 and 503 will be described in detail, and the description of the same processing steps as those described in FIG. 4 will be omitted.

  In step 502, the echo time candidate calculation unit 302, from the internal storage unit 115, sets the adjacent Out-of-Phase time and In-Phase time and their intermediate value (average value) [k] as described above. Values, especially intermediate values [k] for each set are read. Instead of storing each set of values in the internal storage unit 115, the value of each set may be obtained by calculation based on equation (6) each time.

In step 503, the echo time candidate calculation unit 302 compares the input TE input in step 401 or the input TE corrected in step 405 with the value of the intermediate value [k] read in step 502, and the most input The intermediate value [k] close to TE is selected, and the selected intermediate value [k] is set as the corrected TE.
The above is the outline of the processing flow of the second embodiment.

  As described above, the MRI apparatus and echo time setting method of the second embodiment, in the water / fat separation measurement in the MRI apparatus, the adjacent Out-of-Phase time and In-Phase time and their intermediate values (average) The intermediate value nearest to the input TE input by the operator is selected from a plurality of sets of (value), and the selected intermediate value is set as the correction TE to the echo time (TE) of the pal sequence. As a result, in addition to the effects described in the first embodiment, the corrected TE can be calculated more easily.

<Echo time (TE) setting GUI example>
Next, an example of an echo time (TE) setting GUI that can be commonly applied to the first and second embodiments will be described.

  FIG. 6 (a) is a first example of a GUI for setting an echo time (TE) of a pulse sequence. In the first example, an echo time (TE) 601 that is an imaging parameter is a region 602 where the value is input as an input TE, a down button 603 that decreases the value of the input TE to the next optimal value, and And an up button 604 to be increased.

  The value displayed in the area 602 is the modified TE set in the first embodiment or the second embodiment. In this state, when the down button 603 is pressed once, the value of the echo time (TE) and the value displayed in the area 602 are reduced to the next optimum value. Alternatively, when the up button 604 is pressed once, the value of the echo time (TE) and the value displayed in the area 602 increase to the next optimum value.

  Specifically, in accordance with the pressing of the down button 603 or the up button 604, in the case of Example 1, the corrected TE is calculated by setting the value of [x] ± 1 to [x] in Equation (4). Then, the value of the echo time (TE) and the value of the area 602 are replaced with the calculated correction TE. In the case of the second embodiment, the value of the echo time (TE) and the value of the region 602 are replaced with k as k ± 1 and the value of the intermediate value [k + 1] or the intermediate value [k-1] as the corrected TE. It is done.

  FIG. 6B is a second example of an echo time (TE) setting GUI. In the second example, an echo time (TE) 601 that is an imaging parameter is a region 602 where the value is input as an input TE, and a left button 605 that decreases the value of the input TE to the next optimal value. , A right button 606 for increasing, and a slider bar 607 for increasing / decreasing.

  The value displayed in the area 602 is the modified TE set in the first embodiment or the second embodiment. When the left button 605 or the slider bar 607 is moved to the left in this state, the value of the echo time (TE) and the value displayed in the area 602 are reduced to the next optimum value. Alternatively, when the right button 606 or the slider bar 607 is moved to the right, the value of the echo time (TE) and the value displayed in the area 602 are increased to the next optimum value. The specific process of increasing or decreasing the value is the same as in the case of FIG. 6 (a) described above.

  The above is the description of each embodiment according to the present invention. In each of the above-described embodiments, the case of the water signal and the fat signal has been described as an example. However, the present invention is limited to the water signal and the fat signal. In other words, the present invention can be applied in the same way to obtain an image in which a plurality of tissues having different nuclear magnetic resonance frequencies are mixed and separate them. In that case, σ may be set based on the difference in nuclear magnetic resonance frequency of the nuclide of interest.

  101 subject, 102 static magnetic field generating magnet, 103 gradient magnetic field coil, 104 transmitting RF coil, 105 RF receiving coil, 106 bed, 107 signal processing unit, 108 overall control unit, 109 gradient magnetic field power source, 110 RF transmitting unit, 111 measurement Control unit, 113 memory, 114 arithmetic processing unit (CPU), 115 internal storage unit, 116 network IF, 117 external storage unit, 118 display / operation unit

Claims (6)

An input unit for receiving an input of an echo time of a pulse sequence by an operator;
From a subject comprising a first tissue having a first nuclear magnetic resonance frequency and a second tissue having a second nuclear magnetic resonance frequency, the phase of the signal from the first tissue and the first The out-of-phase time at which the difference from the phase of the signal from the second tissue becomes π-out-of-phase, the phase of the signal from the first tissue, and the phase of the signal from the second tissue A measurement control unit that executes a pulse sequence for measuring an echo signal of each In-Phase time that becomes an In-Phase with a difference from zero,
Using the echo signal measured at the Out-of-Phase time and the echo signal measured at the In-Phase time, the first tissue is the main image, and the second tissue is the main. An arithmetic processing unit for acquiring an image;
With
The arithmetic processing unit is an intermediate value between the Out-of-Phase time and the In-Phase time based on the input echo time by the operator, and is closest to the input echo time among a plurality of intermediate values. An intermediate value is obtained as a corrected echo time, and the corrected echo time is set as an echo time of the pulse sequence. The magnetic resonance imaging apparatus according to claim 1.
The arithmetic processing unit includes an out-of-phase time for measuring an out-of-phase echo signal and an in-phase time for measuring an in-phase echo signal based on the modified echo time. And
The measurement control unit controls the measurement of an out-of-phase echo signal in an out-of-phase time, and controls the measurement of an in-phase echo signal in an in-phase time, respectively. apparatus. The magnetic resonance imaging apparatus according to claim 1 or 2,
The magnetic resonance imaging apparatus, wherein the arithmetic processing unit obtains the corrected echo time using a predetermined calculation formula. The magnetic resonance imaging apparatus according to claim 1.
A storage unit for storing a plurality of combinations of the Out-of-Phase time, the In-Phase time, and their intermediate values;
The arithmetic processing unit selects an intermediate value closest to the input echo time as a corrected echo time from a plurality of sets of intermediate values stored in the storage unit, and the corrected echo time is selected as the echo time of the pulse sequence. A magnetic resonance imaging apparatus characterized by being set as follows. The magnetic resonance imaging apparatus according to claim 4.
The arithmetic processing unit uses the same set of Out-of-Phase time and In-Phase time as the intermediate value selected as the modified echo time, and each of the Out-of-Phase for measuring an Out-of-Phase echo signal. A magnetic resonance imaging apparatus, wherein the phase is set as a Phase time and an In-Phase time for measuring an In-Phase echo signal. From a subject comprising a first tissue having a first nuclear magnetic resonance frequency and a second tissue having a second nuclear magnetic resonance frequency, the phase of the signal from the first tissue and the first The out-of-phase time at which the difference from the phase of the signal from the second tissue becomes π-out-of-phase, the phase of the signal from the first tissue, and the phase of the signal from the second tissue The echo signal is measured at the In-Phase time when the difference between the In-Phase is zero and the echo signal is measured at the Out-of-Phase time, and the echo is measured at the In-Phase time. An echo time setting method in a magnetic resonance imaging apparatus for acquiring a main image of the first tissue and a main image of the second tissue using a signal,
Receiving an input of an echo time of a pulse sequence by an operator;
Based on the input echo time input by the operator, an intermediate value between the Out-of-Phase time and the In-Phase time, and an intermediate value closest to the input echo time among a plurality of intermediate values Determining a corrected echo time, and setting the corrected echo time as the echo time of the pulse sequence;
An echo time setting method characterized by comprising:

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