JP7089964B2 - Magnetic resonance imaging device - Google Patents

Description

The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus), and more particularly to a technique for measuring a diffusion-weighted image.

One of the images obtained by the MRI apparatus is a diffusion weighted image (DWI). Diffusion-weighted images are obtained by applying a gradient magnetic field pulse called MPG: Motion Probing Gradient to suppress freely diffused protons. Therefore, in the imaging of the diffusion-weighted image, the signal of the tissue such as a tumor whose diffusion is suppressed is acquired as a high signal.

In diffusion-enhanced imaging, the signal is reduced not only by the diffusion of protons but also by movements due to body movements such as respiratory movements and beats in the imaging region, and the image becomes dark. It was not suitable for the diagnosis of the test target. In diffusion-weighted imaging, quantitative analysis values such as the apparent diffusion coefficient (ADC) are also used for diagnosis, but the above-mentioned signal reduction also reduces the accuracy of the quantitative analysis values.

Therefore, as an imaging method for preventing deterioration of image quality due to respiratory movement, a method of imaging in synchronization with respiration (Patent Document 1) and a method of increasing the number of times of integrating signals from an inspection target to obtain a diffusion-weighted image (Patent Document 2). ) Has come to be used.

Japanese Unexamined Patent Publication No. 2007-029250 Japanese Unexamined Patent Publication No. 2005-253802

In the imaging methods of Patent Documents 1 and 2 described above, when diffusion-weighted imaging is performed in a region such as the abdomen (particularly the left lobe of the liver) affected by the pulsation, an image in which the signal is reduced due to the influence of the pulsation is visualized. It is not possible to make a precise diagnosis.

There is also a method of performing imaging in synchronization with both the respiratory movement and the pulsation, but in this method, the signal is signaled at the timing when both the signal acquisition timing synchronized with the respiratory movement and the signal acquisition timing synchronized with the pulsation overlap. It takes a long time to take an image and the image efficiency is poor.

Further, there is also a method of acquiring a signal in a beating region by applying a rephase type MPG. This method prolongs the echo time (TE), but this method is also unfavorable because the prolongation of TE leads to signal degradation. Further, when comparing signals acquired with various b values (multi-b), it is preferable to keep parameters such as MPG application time constant, but this is also difficult with a rephase type MPG.

An object of the present invention is to obtain a diffusion-weighted image in which the imaging time is minimized and the accuracy of quantitative values is improved without limitation on imaging conditions.

In order to achieve the above object, the magnetic resonance imaging apparatus of the present invention has an imaging unit that repeatedly measures a nuclear magnetic resonance signal by varying the intensity of MPG pulses, and a nuclear magnetic resonance acquired by each measurement performed by the imaging unit. It is equipped with an image creation unit that creates an image for each different MPG pulse using a resonance signal, and the image creation unit is used to create an image of the nuclear magnetic resonance signals that are measured for each image capture with different MPG pulse intensities. An unnecessary signal determination unit for determining an unnecessary nuclear magnetic resonance signal is provided, and the image creation unit is characterized in that an image is created using the nuclear magnetic resonance signal excluding the unnecessary signal determined by the unnecessary signal determination unit. ..

According to the present invention, it is possible to obtain a diffusion-weighted image in which the imaging time is minimized and the accuracy of the quantitative value is improved without limitation on the imaging conditions.

The block diagram which shows the whole structure of the MRI apparatus of this invention. A basic diffusion-weighted sequence generated by an MRI machine. The block diagram which shows the structure of the control part provided with the MRI apparatus of Embodiment 1. FIG. Positioning UI example for setting the area of interest. A sequence of pre-measurements generated in Embodiment 1. The flowchart which shows the imaging method which carries out the MRI apparatus of Embodiment 1. An example of a UI that determines a timing for excluding a signal in order to set the imaging conditions of the first embodiment. The block diagram which shows the structure of the control part provided in the MRI apparatus of Embodiment 2. The flowchart which shows the imaging method which carries out the MRI apparatus of Embodiment 2. The flowchart which shows the imaging method which carries out the MRI apparatus of Embodiment 3. The flowchart which shows the imaging method which carries out the MRI apparatus of Embodiment 4. A UI example of displaying the result and changing the threshold value when the threshold value is applied by the MRI apparatus of the fourth embodiment.

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

FIG. 1 is a block diagram showing an overall configuration of the MRI apparatus 100 of the present embodiment.
The MRI apparatus 100 uses an imaging unit 114 that repeatedly measures a nuclear magnetic resonance signal with different MPG pulse intensities and a nuclear magnetic resonance signal acquired in each measurement performed by the imaging unit 114 for each different MPG pulse. Is provided with an image creating unit 120 for creating an image. The image creation unit 120 includes an unnecessary signal determination unit 111C for determining a nuclear magnetic resonance signal that is unnecessary for image creation among the measured nuclear magnetic resonance signals for each imaging with different MPG pulse intensities. The image creation unit 120 creates an image using the nuclear magnetic resonance signal excluding the unnecessary signal determined by the unnecessary signal determination unit 111C.

The imaging unit 114 images the inspection target of the subject 101. The imaging unit 114 includes a magnet 102 that generates a static magnetic field around the subject 101, a gradient magnetic field coil 103 that generates a gradient magnetic field in this region, and an RF coil 104 that applies a high frequency magnetic field to the subject 101. The RF probe 105 for detecting the MR signal generated by the subject 101, the signal detection unit 106, the gradient magnetic field power supply 109, and the RF transmission unit 110 are provided.

The image creation unit 120 includes a signal processing unit 107, a storage device 115, and an input unit 113 that receives instructions from the display unit 108 and the operator as a user interface (UI) for communicating with the operator. .. The display unit 108 may be a touch panel or the like integrally configured with the input unit 113. Further, the image creation unit 120 includes a control unit 111 that controls these operations.

The gradient magnetic field coil 103 is composed of gradient magnetic field coils in three directions of X, Y, and Z, and generates a gradient magnetic field in response to a signal from the gradient magnetic field power supply 109. The RF coil 104 generates a high frequency magnetic field in response to the signal of the RF transmitter 110. The signal received by the RF probe 105 is detected by the signal detection unit 106, signal-processed by the signal processing unit 107, converted into an image signal by calculation, arithmetic processing is performed on the captured image by the control unit 111, and the image is displayed. It is displayed by the unit 108.

The gradient magnetic field power supply 109, the RF transmission unit 110, and the signal detection unit 106 are controlled by the control unit 111, and the control time chart is generally called a pulse sequence. The imaging conditions necessary for generating the pulse sequence are input from the input unit 113 and confirmed by the display unit 108.

Further, the control unit 111 has a reception unit 111A that receives instructions such as the position and size of the region of interest by the operator operating the UI, and a pulse executed by the image pickup unit 114 based on the change instruction received by the reception unit 111A. A change instruction unit 111B for changing the sequence and an unnecessary signal determination unit 111C are provided.

In the present embodiment, a computer provided with a CPU and a memory realizes the function of the control unit 111. The calculation and control programs may be stored in the storage device 115 in advance, or may be taken in from the outside and uploaded by the CPU for execution. It should be noted that some of the functions of the arithmetic unit can also be realized by hardware such as ASIC (Application Specific Integrated Circuit) and FPGA (Field Programmable Gate Array).

The MRI apparatus 100 acquires a diffusion-weighted image to be inspected, and the internal memory of the control unit 111 or the storage apparatus 115 stores, for example, a diffusion-weighted sequence as shown in FIG. The imaging unit 114 executes this diffusion-weighted sequence under specific conditions. The horizontal axis in the figure is the time axis, the RF axis is the application of RF pulse, Gs is the gradient magnetic field in the slice direction, Gp is the gradient magnetic field in the phase encoding direction, Gr is the gradient magnetic field in the read (readout) direction, and Echo. Represents the generation of an echo signal. The imaging conditions required for generating the pulse sequence are input by the operator through the input unit 113 and can be confirmed by the display unit 108.

This diffusion-weighted sequence consists of an excited portion 201 for exciting only protons in a specific region, a read-out portion 202 for the generated signal, and an MPG pulse 203 for suppressing the signal of the protons moving before data acquisition. Will be done. Specifically, first, an RF pulse 201A having a flip angle of 90 ° is irradiated to excite a spin at a specific position determined by a slice selective gradient magnetic field (Gs) applied at the same time. Then, the first MPG pulse 203A is applied. In this figure, the MPG pulse is applied to a plurality of axes, but it may be applied to a single axis. Subsequently, a 180 ° RF pulse 201B that inverts the phase of the spin is irradiated. Then, a second MPG pulse 203B having the same application amount as the MPG pulse 203A and having the opposite polarity is applied. Then, a gradient magnetic field pulse in the slice direction and a phase-encoded gradient magnetic field pulse are applied to acquire a signal. With such a pulse sequence, a diffusion-weighted image can be acquired.

In the following embodiment, a spin echo (SE) type echo-planar imaging (DW-SE-EPI) sequence will be described as an example of this measurement for acquiring a diffusion-weighted image, but an excitation method and a readout method will be used. Is not limited to this.

Hereinafter, among the signals generated by applying the MPG pulse to the inspection target, the deterioration of the signal generated due to the pulsation of the inspection target is determined, and the reduced signal (unnecessary signal) unnecessary for image creation is removed. Then, a specific embodiment of the control function for creating a diffusion-weighted image will be described.

<Embodiment 1>
The MRI apparatus of Embodiment 1 will be described with reference to FIG. FIG. 3 is a block diagram showing a configuration of a control unit included in the MRI apparatus of the first embodiment.

The MRI apparatus 100 of the first embodiment performs pre-measurement prior to the main measurement of acquiring a diffusion-weighted image in order to determine an unnecessary signal, and how much delay time (Delay) from the pulsation (R wave) in the pre-measurement is performed. ) Determines whether an unnecessary signal is generated, and in this measurement, the signal is measured at a timing other than the delay time when it is determined that the unnecessary signal is generated.

As shown in FIG. 3, the unnecessary signal determination unit 111C of this example calculates the delay from the R wave in which the unnecessary signal is detected and the signal determination unit 111D that determines the unnecessary signal from the signal caused by the MPG pulse. It includes a timing calculation unit 111E and a signal removal instruction unit 111F that instructs the image pickup unit 114 to perform the main measurement at a timing other than the delay in which the calculated unnecessary signal is generated. Further, the control unit 111 is connected to a pulsation detection sensor 101B that detects the pulsation of the subject 101, such as an electrocardiographic electrode or a pulse wave sensor.

Subsequently, the imaging method using the MRI apparatus of the first embodiment will be described with reference to FIGS. 1, 3 to 7. FIG. 4 is an example of a positioning UI for setting a region of interest, FIG. 5 is a sequence of pre-measurement generated by the MRI apparatus of the first embodiment, and FIG. 6 is a flowchart showing an imaging method implemented by the MRI apparatus of the first embodiment. FIG. 7 is an example of a UI that determines a timing for excluding a signal in order to set the imaging conditions of the first embodiment. Here, a case where the MRI apparatus 100 targets the liver as an examination target and selectively visualizes a diffusion-weighted image of the liver and its surroundings will be described.

[Step S601]
The operator attaches the pulsation detection sensor 101B to the subject 101, and installs the subject 101 in the gantry of the MRI apparatus 100.

[Step S602]
The operator inputs and sets basic imaging conditions such as repetition time (TR), TE, positioning and the number of integrations of acquired signals from the input unit 113, sets them, and presses the START button to perform pre-measurement (imaging). To start.

[Step S603]
In step S603, the imaging unit 114 performs pre-measurement. The unnecessary signal determination unit 111C determines the delay time (Delay) for not acquiring a signal for each region (slice position) to be inspected by pre-measurement (details will be described in steps S603-1 to S603-3 below). ..

[Step S603-1]
The MRI apparatus 100 displays a two-dimensional image of the abdomen obtained in step S602 from the preset imaging conditions as a UI on the display unit 108, for example, as shown in FIG. The abdominal image, the boundary lines 301, 303 of the region of interest 300, and the like are displayed on the display unit 108.

While looking at this image, the operator uses UI such as the display unit 108 and the input unit 113 to set the position, angle, and size of the two-dimensional area (attention area) 300 of interest in the displayed image in the slice direction. Change for each area of. The slice direction may be set individually for each slice, or it may be divided into three parts, that is, the upper part, the middle part, and the lower part of the liver.

For example, when the operator drags and drops the position of the boundary line 301 with the input unit 113 such as a mouse to change the position, the reception unit 111A receives the change instruction and instructs the change instruction unit 111B. Based on this instruction, the change instruction unit 111B changes the size 302 of the attention area 300 to be displayed on the UI. Further, when the operator drags and drops the position of the boundary line 303 by the input unit 113 to change the position, the reception unit 111A and the change instruction unit 111B operate in the same manner as when the position of the boundary line 301 is changed, and the UI The size 304 of the area of interest 300 to be displayed changes. Further, when the operator drags and drops the angle setting unit 305 by the input unit 113, the angle of the attention area 300 changes. This makes it possible to change the position, size, and angle of the region of interest 300. Then, the change instruction unit 111B instructs the image pickup unit 114 of the changed conditions of the attention region 300.

This figure shows a state in which the operator is set to put the liver into the region of interest 300 by inputting from the input unit 113 while looking at the display unit 108. Note that step S603-1 may be performed in step S602 together with other imaging conditions.

[Step S603-2]
Next, the MRI apparatus 100 acquires the nuclear magnetic resonance signal in the region of interest 300 set in step S603-1.

Specifically, when the setting of the attention area 300 is completed, the operator presses the START icon (not shown) displayed on the positioning UI of the display unit 108 by the input unit 113. Then, the image pickup unit 114 generates a pulse sequence as shown in FIG. 5 according to the image pickup conditions received from the change instruction unit 111B. The image pickup unit 114 applies a two-dimensional excitation type pulse 401 so as to selectively excite the region of interest 300. The pulse 401 is executed from an RF pulse 401A composed of a plurality of pulse trains, a crusher gradient magnetic field pulse 402, and a gradient magnetic field pulse 403 whose amplitude oscillates. The region to which the pulse 401 is applied is suppressed.

The strength of the crusher gradient magnetic field pulse 402 is determined from the size of the region of interest 300 set in the UI shown in FIG. 4 in the slice direction, and the intensity of the blip gradient magnetic field 403 is determined from the angle and size set by moving the boundary line 301. .. By such a pulse sequence, a diffusion-weighted image of the liver in the region of interest 300 and its surroundings is visualized.

After applying the pulse 401, the image pickup unit 114 applies two MPG pulses 405A and 405B. Between the MPG pulse 405A and the MPG pulse 405B, a high frequency magnetic field pulse 406 called a 180 ° RF pulse that inverts the phase of the spin is applied. As a result, it is possible to acquire a signal for one echo with the phase encoding cut.

The image pickup unit 114 performs such signal acquisition with a plurality of Delays having different signal acquisition timings from the R wave 404 received from the pulsation detection sensor 101B. This is similarly repeated for each of the number of slices set in step S602 or the location set in step S603-1 to acquire a signal with a plurality of delays. Although the pulse 401 is a two-dimensional selective excitation type pulse here, the pulse 401 may be a normal slice selective excitation similar to that in FIG. 2, and presaturation outside the region sandwiched by the boundary line 301. The region of interest 300 set in FIG. 4 may be selectively excited by suppressing with a pulse. Which region is excited and suppressed may be internally held by the system or may be set by the operator.

[Step S603-3]
The unnecessary signal determination unit 111C refers to the R wave of the subject 101 received from the pulsation detection sensor 101B, and determines the unnecessary signal in the signal acquired in step S603-2 and the delay in which the unnecessary signal is generated. For Delay in which unnecessary signals are generated, the signal data acquired in step S603-2 is Fourier transformed by the unnecessary signal determination unit 111C to extract the inside of the region of interest 300, and the average signal strength of the extracted region 300 of interest is plotted in the Delay direction. It is determined by comparing.

Specifically, as shown in FIG. 7, the signal determination unit 111D determines an unnecessary signal to be excluded from a plurality of signals acquired by changing the delay time from the R wave received by the pulsation detection sensor 101B. do.

As a criterion for determining an unnecessary signal, for example, a signal threshold value with respect to the maximum value of the signal in the Delay direction is set. The threshold value may be a value internally held by the system, or may be a value stored in the storage unit 115 after the reception unit 111A accepts the value input in advance by the operator in step S602 or the like. .. Further, even if the relationship between the average signal strength to be compared and Delay is plotted as shown in FIG. 7 and displayed on the display unit 108 to clearly indicate to the operator, the operator determines the exclusion target from the specified result. good. This figure shows a case where the maximum value of the signal strength in the Delay direction is used as a reference (100%), and the average signal value that is equal to or less than the default value (80%) from the reference is judged to be an unnecessary signal. When the bar 307 is displayed on the display unit 108 in this way, the threshold value may be changed by the UI, such as by dragging and dropping the bar 307 and moving it up and down by the operator.

When the signal determination unit 111D determines the unnecessary signal, the timing calculation unit 111E calculates the delay when the signal value is equal to or less than the threshold value (the unnecessary signal is generated). Then, the signal removal instruction unit 111F stores the delay in which the unnecessary signal is generated in the storage device 115 as an exclusion target, and at the timing excluding the delay, the image pickup unit 114 so as to perform the main measurement of acquiring the signal for image creation. To instruct.

[Step S604]
The MRI apparatus 100 starts diffusion-weighted imaging (main measurement) by the diffusion-weighted sequence. During image pickup, the image pickup unit 114 acquires a signal at a timing other than Delay in which an unnecessary signal stored in the storage unit 115 is generated.

[Step S605]
Subsequently, the MRI apparatus 100 reconstructs the image and displays it on the display unit 108 when the signal acquisition is completed in step S604. Specifically, first, the RF probe 105 receives the generated signal, and the signal detection unit 106 detects this signal. This signal is signal-processed by the signal processing unit 107 and converted into an image signal by an image reconstruction operation such as a Fourier transform. Further, after the image processing unit 113 calculates an image signal or the like, the drawn image is displayed on the display unit 108.

As described above, in the diffusion-weighted image imaging method of this example, it is possible to acquire a diffusion-weighted image that does not include an unnecessary signal by not acquiring data at the timing of Delay with an unnecessary signal from the R wave. As a result, in this imaging method, a diffusion-weighted image can be drawn without being affected by the signal decrease due to the pulsation. Further, in this method, it is possible to obtain a diffusion-weighted image in which the imaging time is minimized and the accuracy of the quantitative value is improved without any limitation on the imaging conditions such as TE and b values. Further, in this method, since the exclusion criterion is set by the delay from the R wave, the imaging efficiency is improved as compared with the conventional method of performing imaging in synchronization with both respiratory movement and pulsation.

A two-dimensional image of the entire abdomen may be drawn, but by narrowing down the area of interest to the liver and its surroundings as described above, the brightly displayed part in the image is the tumor in the liver. The accuracy of diagnosis is improved because it is not necessary to judge whether the tissue is abdominal tissue (spleen, etc.) that is displayed brightly under normal conditions.

Further, since the susceptibility to the influence of pulsation differs depending on the part even in the same organ, it is preferable to further divide the region of interest into a plurality of slices and calculate the delay in which an unnecessary signal is generated for each slice. Specifically, for example, in the right lobe of liver and the left lobe of liver, the left lobe of liver located directly under the heart is more susceptible to the influence of beating, so the liver is divided into the right lobe of liver and the left lobe of liver. By acquiring the image of the liver, the number of unnecessary signals generated can be reduced and the imaging efficiency can be improved.

<Embodiment 2>
Hereinafter, the image pickup method of the MRI apparatus of the second embodiment will be described with reference to FIGS. 8 to 9 and different from the first embodiment. FIG. 8 is a configuration example of the control unit 111 included in the MRI apparatus of the second embodiment, and FIG. 9 is a flowchart of an imaging method implemented by the MRI apparatus of the second embodiment.

In this embodiment, the main measurement is performed even in the delay in which the unnecessary signal is generated calculated from the pre-measurement, but the unnecessary signal is excluded after the main measurement is completed, and the excluded unnecessary signal portion is excluded at the time when it is not excluded. The feature is that it is supplemented by a signal.

As shown in FIG. 8, the control unit 111 in the MRI apparatus 100 of the present embodiment is based on the control unit 111 described in the first embodiment, and instead of the signal removal instruction unit 111F, unnecessary signals are excluded after the main measurement. It is provided with an unnecessary signal removing unit 111G.

Subsequently, an imaging method using the MRI apparatus of the second embodiment will be described. In this method, in contrast to the imaging method using the MRI apparatus of the first embodiment, in step S603-3, the echo acquired in step S603-2 is Fourier transformed only in either the phase encoding direction or the readout direction to perform a Fourier transform to the region of interest. The following steps are different from the point of extracting the inside of 300. Since the other methods are the same as the imaging method using the MRI apparatus of the first embodiment, the description thereof will be omitted.

[Step S704]
In this method, step S704 is performed instead of step S604. Also in this method, the delay from the R wave in which the unnecessary signal is generated is determined in the pre-measurement, as described with reference to FIG. 7 of the first embodiment. In step S704, as shown in FIG. 9, the MRI apparatus 100 starts the main measurement by the diffusion-weighted sequence and acquires all the data including the unnecessary signal. During image pickup, the unnecessary signal determination unit 111C stores the delay at the time of each signal acquisition in the database of the storage device 115 as well as the data acquisition.

[Step S705]
After acquiring all the data, the unnecessary signal removing unit 111G excludes the unnecessary signals in the Delay determined in step S603-3 from all the acquired signals, and reconstructs the image. The criteria for exclusion are as described in step S603. The timing for excluding unnecessary signals is not limited to after all the data are acquired, and the unnecessary signals may be removed at a certain point during data measurement. In that case, it is preferable that the measurement is temporarily suspended and unnecessary signals are removed.

[Step S706]
Although this step is optional, the display unit 108 may display the reconstructed image and let the operator decide whether to reacquire the excluded echo signal and compensate for it. By reacquiring and compensating for the excluded echo signal, the data is fully integrated, and it is possible to suppress the deterioration of image quality due to the decrease in signal-noise ratio (SNR). .. When the operator determines that the image quality is insufficient, the unnecessary signal removing unit 111G re-acquires and compensates the data excluded by the imaging unit 114 at the timing of being excluded from the exclusion target, and all the data is excluded from the exclusion target. Image is executed until.

The unnecessary signal removing unit 111G reconstructs the image at the stage when all the data can be acquired, and displays it on the display unit 108. Then, the storage device 115 stores the reconstructed image in the database.

In the present embodiment, since unnecessary signals are excluded after acquiring at least a certain amount of data at the time of the actual measurement, it is not necessary to determine whether or not to acquire the signals immediately after the R wave is detected. Therefore, in the present embodiment, there is a margin in the determination time as compared with the case of determining whether or not the signal can be acquired immediately after the R wave is detected, and a high-speed response of the system is not required. On the contrary, it is possible to suppress the delay caused by the processing for determining whether or not the signal is acquired immediately after the R wave is detected, so that the processing speed can be further increased.

<Embodiment 3>
Hereinafter, an imaging method of the MRI apparatus according to the third embodiment will be described with reference to FIG. In the third embodiment, based on the imaging method of the MRI apparatus of the second embodiment, the average signal strength in the lead-out direction is not compared in step S603 of the second embodiment described above, and an unnecessary signal is not required for each position value in the lead-out direction. The feature is to judge the presence or absence of.

[Step S603B]
The signal determination unit 111D generates a real space profile by Fourier transforming the acquired signal only in the read-out direction, and compares the signals between Delays for each position in the real space as in the second embodiment. In the generated real space profile, the area formed by the unnecessary signal (unnecessary area) has a lower signal value than the Delay in which the unnecessary signal is generated and the other Delays. Therefore, the signal determination unit 111D extracts the unnecessary area from the real space profile of the plurality of Delays by comparing the signals for the Delay and the area and extracting the Delay having a low signal value and the unnecessary area in the Delay at that time. can do. The unnecessary area and Delay determined by the signal determination unit 111D are stored in the database of the storage device 115.

[Step S705B]
After acquiring all the echoes in this measurement, the unnecessary signal removing unit 111G adds and averages the acquired signals in a state where the extracted unnecessary signals are excluded. Even if the unnecessary signal is excluded, the signals other than the unnecessary signal are added and averaged in the same area as the unnecessary area, so that the image can be sufficiently reconstructed.

As described above, in the imaging method according to this embodiment, the SNR of the pixel formed from the signal other than the unnecessary signal is guaranteed by extracting and excluding the unnecessary region from the real space profile, so that the SNR decrease is reduced to the unnecessary region. Can only be limited. Therefore, it is possible to suppress the deterioration of the image quality due to the deterioration of the SNR of the entire image.

<Embodiment 4>
Hereinafter, the imaging method of the MRI apparatus of the fourth embodiment will be described with reference to FIGS. 11 and 12. In the present embodiment, the unnecessary signal determination unit 111C determines the presence / absence of an unnecessary signal for each pixel of the image created by integrating the nuclear magnetic resonance signals without using the threshold value set in the pixel value. It is characterized by points. FIG. 11 is a flowchart of an imaging method carried out by the MRI apparatus of the fourth embodiment, and FIG. 12 is a UI example of displaying the result and changing the threshold value when the threshold value is applied by the MRI apparatus of the fourth embodiment.

The control unit 111 of the fourth embodiment does not include the signal determination unit 111D and the timing calculation unit 111E shown in FIG. 8, and as shown in FIG. 11, the unnecessary signal removal unit 111G does not include the signal determination unit 111D and the timing calculation unit 111E. Signals are compared in the integration direction, and signals with pixel values that are equal to or less than a predetermined threshold are excluded. Diffusion-weighted imaging of the trunk is generally performed by multiple integrations, and the time when unnecessary signals are generated is shorter than the R-R interval of the heartbeat. Therefore, by comparing the pixel data at the same position in the integration direction, the pixel data Can be determined whether is an exclusion target.

[Step S802]
The operator inputs and sets basic conditions such as TR, TE, positioning, and setting of the number of times of signal integration from the input unit 113, and then starts imaging. Since statistical processing is performed in the integration direction, the number of integrations is limited to 2 or more. The number of integrations is not limited to the input by the operator, and may be a value internally held by the system. Further, at this stage, the operator may determine a threshold value (for example, a ratio to the maximum value of the signal) as a reference for excluding the signal by comparing with the integration direction. By setting a high threshold value, the number of exclusion targets increases, so the SNR decreases, but the accuracy of analysis values and the like can be improved. On the contrary, if the threshold value is set low, the accuracy of the analysis value etc. will decrease, but the exclusion target will decrease, so the SNR will improve. Further, the storage unit 115 may hold a value corresponding to the imaging region such as the abdomen and the head as the threshold value.

[Step S603-1]
In this embodiment, the implementation of this step is optional. When the operator specifies the region of interest in step S802, the processing time required for reconstruction is reduced by limiting the pixels for comparing the signal values in the integration direction to the set region of interest in step S805, which will be described later. Can be shortened. If this step is omitted, statistical processing is performed for all pixels, so that the operation can be simplified by eliminating the trouble of setting the attention area by the operator.

[Step S804]
When the conditions are set, the imaging unit 114 starts the main measurement of diffusion weighting by the diffusion weighting sequence. At this time, the image pickup unit 114 acquires all the signals under the conditions specified by the operator in step S802, and acquires a plurality of images. In the present embodiment, since the pre-measurement is not performed, the processing time for the pre-measurement can be shortened. The storage unit 115 holds a plurality of images before addition created from all the acquired signals.

[Step S805]
After acquiring the signals of all echoes, the unnecessary signal removing unit 111G compares the signals in the integration direction for each pixel position of the plurality of images, excludes the data below the threshold value, and presents the images by addition averaging. As the pixel to be compared, only the set area is targeted when the area of interest is set in step S603-1, and all the pixels are targeted when the area of interest is not set.

[Step S806]
When the operator determines that the presented image has an acceptable image quality, the OK button is pressed, and the image calculated with the set threshold value is saved in the database. When the operator determines that the presented image is not of acceptable image quality, the unnecessary signal removal unit 111G reacquires the excluded data, reconstructs the image, and displays the image again on the display unit 108 for operation. You may let a person judge.

The threshold value may be changed by the operator by the UI as shown in FIG. 12, and the display unit 108 may present an image according to the changed threshold value at any time. Specifically, when the initial setting of the threshold value is set to the median value of the signal, the result of addition averaging excluding the signal having the median value or less is presented to the operator on the display unit 108. When the operator drags and drops the arrow 307B displayed on the UI to move it up and down, the reception unit 111A accepts the change of the threshold value. The reception unit 111A instructs the unnecessary signal removal unit 111G of the changed threshold value, and causes the display unit 108 to present the image added and averaged by the changed threshold value at any time. When the operator determines that the image quality is acceptable when the threshold value is changed, the operator presses the OK button, and the image calculated with the set threshold value is saved in the database. When the operator determines that changing the threshold value is not sufficient, the operator presses the Continue button to reacquire the excluded data, reconstruct the image, and display the image again on the display unit 108. The operator decides.

According to this embodiment, in order to determine the decrease of the signal and remove the decreased signal (unnecessary signal) that is unnecessary for image creation, an electrocardiographic electrode or a pulsation detection sensor such as a pulse wave sensor is installed. It is not necessary to acquire the electrocardiographic waveform of this pulsation detection sensor, and it is possible to create a highly accurate diffusion-enhanced image in which the influence of pulsation and the like is reduced.

101 ... subject, 102 ... magnet, 103 ... gradient magnetic field coil, 104 ... RF coil, 105 ... RF probe, 106 ... signal detection unit, 107 ... signal processing unit , 108 ... Display unit, 109 ... Inclined magnetic field power supply, 110 ... RF transmission unit, 111 ... Control unit, 111C ... Unnecessary signal determination unit, 114 ... Imaging unit, 120 ...・ Image creation department

Claims (13)

An imaging unit that repeatedly measures nuclear magnetic resonance signals with different MPG pulse intensities,
An image creation unit that creates an image for each different MPG pulse using the nuclear magnetic resonance signal acquired in each measurement performed by the imaging unit is provided.
The image creating unit includes an unnecessary signal determination unit for determining a nuclear magnetic resonance signal that is unnecessary for image creation among the measured nuclear magnetic resonance signals for each imaging with different MPG pulse intensities, and the unnecessary signal . The determination unit determines the timing at which the signal drops based on the pre-measurement information, determines the signal measured at that timing as an unnecessary signal, and determines.
The image creating unit is a magnetic resonance imaging apparatus characterized in that an image is created using a nuclear magnetic resonance signal excluding unnecessary signals determined by the unnecessary signal determination unit. The magnetic resonance imaging apparatus according to claim 1.
The image creating unit is a magnetic resonance imaging apparatus characterized in that an image is created using a nuclear magnetic resonance signal excluding the unnecessary signal generated during the acquisition time of the unnecessary signal. The magnetic resonance imaging apparatus according to claim 2.
The unnecessary signal determination unit is a magnetic resonance imaging apparatus characterized in that the acquisition time is determined based on the delay time from the R wave collected from the inspection target by the imaging unit. The magnetic resonance imaging apparatus according to claim 3.
The unnecessary signal determination unit is a magnetic resonance imaging apparatus characterized in that the acquisition time is determined for each slice. The magnetic resonance imaging apparatus according to claim 4.
The unnecessary signal determination unit is a magnetic resonance imaging apparatus characterized in that the acquisition time of an unnecessary signal is determined for each region of interest set in the imaging region. The magnetic resonance imaging apparatus according to any one of claims 2 to 5.
The imaging unit is a magnetic resonance imaging device that measures the nuclear magnetic resonance signal except for the acquisition time determined by the unnecessary signal determination unit. The magnetic resonance imaging apparatus according to any one of claims 2 to 5.
The imaging unit continuously measures the nuclear magnetic resonance signal.
The image creating unit is characterized in that an image is created by excluding the nuclear magnetic resonance signal measured at the acquisition time determined by the unnecessary signal determination unit from the continuously measured nuclear magnetic resonance signals. Magnetic resonance imaging device. The magnetic resonance imaging apparatus according to any one of claims 2 to 7.
The unnecessary signal determination unit is a magnetic resonance imaging apparatus characterized in that the unnecessary signal is determined by comparing a threshold value set for the signal value of the nuclear magnetic resonance signal with the signal value of the nuclear magnetic resonance signal. The magnetic resonance imaging apparatus according to claim 8.
A magnetic resonance imaging device further comprising a reception unit that receives the setting of the threshold value from an operator. The magnetic resonance imaging apparatus according to claim 7.
The unnecessary signal determination unit is a magnetic resonance imaging apparatus characterized in that a real space profile is generated from the continuously measured nuclear magnetic resonance signals and an unnecessary region formed by the unnecessary signals is determined. The magnetic resonance imaging apparatus according to claim 1.
The unnecessary signal determination unit is a magnetic resonance imaging apparatus characterized in that the presence or absence of the unnecessary signal is determined using a threshold value set for each pixel of an image created by integrating the nuclear magnetic resonance signals. The magnetic resonance imaging apparatus according to claim 11.
A magnetic resonance imaging device further comprising a reception unit that receives the setting of the threshold value from an operator. The magnetic resonance imaging apparatus according to claim 12.
The image creating unit is a magnetic resonance imaging apparatus characterized in that the image is created at any time based on the change content of the threshold value received by the receiving unit.

Images